webui: advanced configure using a yang tree

Navigating interfaces now work, and the tree follows the accordion style
like the rest of the UI.

Also, some updates to the curated pages: online help, lists of leafrefs
instead of hard-coded list options.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/webui/go.mod

@@ -1,3 +1,17 @@
 module github.com/kernelkit/webui
 
-go 1.22
+go 1.22.0
+
+toolchain go1.22.2
+
+require (
+	github.com/google/go-cmp v0.7.0 // indirect
+	github.com/openconfig/goyang v1.6.3 // indirect
+	github.com/pborman/getopt v1.1.0 // indirect
+)
+
+// Local fork of goyang with YANG 1.1 fixes:
+//   - Uses.Augment: *Augment → []*Augment (multiple augments per uses)
+//   - Value: add Reference field (when { reference "..."; })
+//   - Input/Output: add Must field (must statements in rpc input/output)
+replace github.com/openconfig/goyang => ./internal/goyang

src/webui/go.sum

@@ -0,0 +1,6 @@
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/openconfig/goyang v1.6.3 h1:9nWXBwd6b4+nZr8ni7O4zUXVhrVMXCLFz8os5YWFuo4=
+github.com/openconfig/goyang v1.6.3/go.mod h1:5WolITjek1NF8yrNERyVZ7jqjOClJTpO8p/+OwmETM4=
+github.com/pborman/getopt v1.1.0 h1:eJ3aFZroQqq0bWmraivjQNt6Dmm5M0h2JcDW38/Azb0=
+github.com/pborman/getopt v1.1.0/go.mod h1:FxXoW1Re00sQG/+KIkuSqRL/LwQgSkv7uyac+STFsbk=

src/webui/internal/auth/login.go

@@ -3,6 +3,7 @@
 package auth
 
 import (
+	"context"
 	"errors"
 	"html/template"
 	"log"
@@ -20,6 +21,11 @@ type LoginHandler struct {
 	Store    *SessionStore
 	RC       *restconf.Client
 	Template *template.Template
+	// OnLogin is called after every successful login with a context that
+	// carries the authenticated user's credentials.  It is invoked in the
+	// foreground, so implementations should start their own goroutines for
+	// slow work.  May be nil.
+	OnLogin func(ctx context.Context)
 }
 
 type loginData struct {
@@ -60,13 +66,20 @@ func (h *LoginHandler) DoLogin(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Probe optional features once at login and bake into the session.
+	// Build an authenticated context for post-login work.
 	ctx := restconf.ContextWithCredentials(r.Context(), restconf.Credentials{
 		Username: username,
 		Password: password,
 	})
+
+	// Probe optional features once at login and bake into the session.
 	caps := handlers.DetectCapabilities(ctx, h.RC)
 
+	// Trigger any post-login hooks (e.g. schema sync) with full credentials.
+	if h.OnLogin != nil {
+		h.OnLogin(ctx)
+	}
+
 	token, csrfToken, err := h.Store.Create(username, password, caps.Features())
 	if err != nil {
 		log.Printf("session create error: %v", err)

src/webui/internal/goyang/.github/dependabot.yml

@@ -0,0 +1,15 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "gomod" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: "/" # Location of package manifests
+    schedule:
+      interval: "weekly"

src/webui/internal/goyang/.github/linters/.golangci.yml

@@ -0,0 +1,53 @@
+---
+#########################
+#########################
+## Golang Linter rules ##
+#########################
+#########################
+
+# configure golangci-lint
+# see https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml
+run:
+  timeout: 10m
+issues:
+  exclude-rules:
+    - path: _test\.go
+      linters:
+        - dupl
+        - gosec
+        - goconst
+  new: true
+linters:
+  enable:
+    - gosec
+    - unconvert
+    - goconst
+    - goimports
+    - gofmt
+    - gocritic
+    - govet
+    - revive
+    - staticcheck
+    - unconvert
+    - unparam
+    - unused
+    - wastedassign
+    - whitespace
+linters-settings:
+  errcheck:
+    # report about assignment of errors to blank identifier: `num, _ := strconv.Atoi(numStr)`;
+    # default is false: such cases aren't reported by default.
+    check-blank: true
+  govet:
+    # report about shadowed variables
+    check-shadowing: false
+  maligned:
+    # print struct with more effective memory layout or not, false by default
+    suggest-new: true
+  gocritic:
+    disabled-checks:
+      - singleCaseSwitch
+      - appendAssign
+  revive:
+    ignore-generated-header: true
+    severity: warning

src/webui/internal/goyang/.github/linters/.yaml-lint.yml

@@ -0,0 +1,59 @@
+---
+###########################################
+# These are the rules used for            #
+# linting all the yaml files in the stack #
+# NOTE:                                   #
+# You can disable line with:              #
+# # yamllint disable-line                 #
+###########################################
+rules:
+  braces:
+    level: warning
+    min-spaces-inside: 0
+    max-spaces-inside: 0
+    min-spaces-inside-empty: 1
+    max-spaces-inside-empty: 5
+  brackets:
+    level: warning
+    min-spaces-inside: 0
+    max-spaces-inside: 0
+    min-spaces-inside-empty: 1
+    max-spaces-inside-empty: 5
+  colons:
+    level: warning
+    max-spaces-before: 0
+    max-spaces-after: 1
+  commas:
+    level: warning
+    max-spaces-before: 0
+    min-spaces-after: 1
+    max-spaces-after: 1
+  comments: disable
+  comments-indentation: disable
+  document-end: disable
+  document-start:
+    level: warning
+    present: true
+  empty-lines:
+    level: warning
+    max: 2
+    max-start: 0
+    max-end: 0
+  hyphens:
+    level: warning
+    max-spaces-after: 1
+  indentation:
+    level: warning
+    spaces: consistent
+    indent-sequences: true
+    check-multi-line-strings: false
+  key-duplicates: enable
+  line-length:
+    level: warning
+    max: 120
+    allow-non-breakable-words: true
+    allow-non-breakable-inline-mappings: true
+  new-line-at-end-of-file: disable
+  new-lines:
+    type: unix
+  trailing-spaces: disable

src/webui/internal/goyang/.github/workflows/go.yml

@@ -0,0 +1,15 @@
+name: Go
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+  schedule:
+    - cron: "0 0 * * *"
+
+jobs:
+  go:
+    uses: openconfig/common-ci/.github/workflows/go.yml@125b6b58286d116b216e45c33cb859f547965d61
+
+  linter:
+    uses: openconfig/common-ci/.github/workflows/linter.yml@125b6b58286d116b216e45c33cb859f547965d61

src/webui/internal/goyang/.gitignore

@@ -0,0 +1 @@
+tags

src/webui/internal/goyang/AUTHORS

@@ -0,0 +1,9 @@
+# This is the official list of goyang authors for copyright purposes.
+# This file is distinct from the CONTRIBUTORS files.
+# See the latter for an explanation.
+
+# Names should be added to this file as:
+# Name or Organization <email address>
+# The email address is not required for organizations.
+
+Google Inc.

src/webui/internal/goyang/CONTRIBUTING

@@ -0,0 +1,25 @@
+Want to contribute? Great! First, read this page (including the small print at the end).
+
+### Before you contribute
+Before we can use your code, you must sign the
+[Google Individual Contributor License Agreement](https://developers.google.com/open-source/cla/individual?csw=1)
+(CLA), which you can do online. The CLA is necessary mainly because you own the
+copyright to your changes, even after your contribution becomes part of our
+codebase, so we need your permission to use and distribute your code. We also
+need to be sure of various other things—for instance that you'll tell us if you
+know that your code infringes on other people's patents. You don't have to sign
+the CLA until after you've submitted your code for review and a member has
+approved it, but you must do it before we can put your code into our codebase.
+Before you start working on a larger contribution, you should get in touch with
+us first through the issue tracker with your idea so that we can help out and
+possibly guide you. Coordinating up front makes it much easier to avoid
+frustration later on.
+
+### Code reviews
+All submissions, including submissions by project members, require review. We
+use Github pull requests for this purpose.
+
+### The small print
+Contributions made by corporations are covered by a different agreement than
+the one above, the
+[Software Grant and Corporate Contributor License Agreement](https://cla.developers.google.com/about/google-corporate).

src/webui/internal/goyang/CONTRIBUTORS

@@ -0,0 +1,15 @@
+# People who have agreed to one of the CLAs and can contribute patches.
+# The AUTHORS file lists the copyright holders; this file
+# lists people.  For example, Google employees are listed here
+# but not in AUTHORS, because Google holds the copyright.
+#
+# https://developers.google.com/open-source/cla/individual
+# https://developers.google.com/open-source/cla/corporate
+#
+# Names should be added to this file as:
+#     Name <email address>
+
+Paul Borman <borman@google.com>
+Andrew Fort <afort@arista.com>
+Rob Shakir <robjs@google.com>
+Sean Condon <sean@opennetworking.org>

src/webui/internal/goyang/Copyright

@@ -0,0 +1,14 @@
+// Copyright 2015 Google Inc.
+// 
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//     http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+

src/webui/internal/goyang/LICENSE

@@ -0,0 +1,202 @@
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
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+      any Contribution intentionally submitted for inclusion in the Work
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+       http://www.apache.org/licenses/LICENSE-2.0
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+

src/webui/internal/goyang/README.md

@@ -0,0 +1,54 @@
+![Go](https://github.com/openconfig/goyang/workflows/Go/badge.svg?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/openconfig/goyang/badge.svg?branch=master)](https://coveralls.io/github/openconfig/goyang?branch=master)
+
+Current support for `goyang` is for the [latest 3 Go releases](https://golang.org/project/#release).
+
+# goyang
+YANG parser and compiler for Go programs.
+
+The yang package (pkg/yang) is used to convert a YANG schema into either an
+in memory abstract syntax trees (ast) or more fully resolved, in memory, "Entry"
+trees.  An Entry tree consists only of Entry structures and has had
+augmentation, imports, and includes all applied.
+
+goyang is a sample program that uses the yang (pkg/yang) package.
+
+goyang uses the yang package to create an in-memory tree representation of
+schemas defined in YANG and then dumps out the contents in several forms.
+The forms include:
+
+*  tree - a simple tree representation
+*  types - list understood types extracted from the schema
+
+The yang package, and the goyang program, are not complete and are a work in
+progress.
+
+For more complex output types, such as Go structs, and protobuf messages
+please use the [openconfig/ygot](https://github.com/openconfig/ygot) package,
+which uses this package as its backend.
+
+### Getting started
+
+To build goyang, ensure you have go language tools installed
+(available at [golang.org](https://golang.org/dl)) and that the `GOPATH`
+environment variable is set to your Go workspace.
+
+1. `go get github.com/openconfig/goyang`
+    * This will download goyang code and dependencies into the src
+subdirectory in your workspace.
+
+2. `cd <workspace>/src/github.com/openconfig/goyang`
+
+3. `go build`
+
+   * This will build the goyang binary and place it in the bin
+subdirectory in your workspace.
+
+### Contributing to goyang
+
+goyang is still a work-in-progress and we welcome contributions.  Please see
+the `CONTRIBUTING` file for information about how to contribute to the codebase.
+
+### Disclaimer
+
+This is not an official Google product.

src/webui/internal/goyang/go.mod

@@ -0,0 +1,12 @@
+module github.com/openconfig/goyang
+
+go 1.22.0
+
+toolchain go1.24.1
+
+require (
+	github.com/google/go-cmp v0.7.0
+	github.com/kylelemons/godebug v1.1.0
+	github.com/openconfig/gnmi v0.14.1
+	github.com/pborman/getopt v1.1.0
+)

src/webui/internal/goyang/go.sum

@@ -0,0 +1,8 @@
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
+github.com/openconfig/gnmi v0.14.1 h1:qKMuFvhIRR2/xxCOsStPQ25aKpbMDdWr3kI+nP9bhMs=
+github.com/openconfig/gnmi v0.14.1/go.mod h1:whr6zVq9PCU8mV1D0K9v7Ajd3+swoN6Yam9n8OH3eT0=
+github.com/pborman/getopt v1.1.0 h1:eJ3aFZroQqq0bWmraivjQNt6Dmm5M0h2JcDW38/Azb0=
+github.com/pborman/getopt v1.1.0/go.mod h1:FxXoW1Re00sQG/+KIkuSqRL/LwQgSkv7uyac+STFsbk=

src/webui/internal/goyang/pkg/indent/indent.go

@@ -0,0 +1,112 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package indent indents lines of text.
+package indent
+
+import (
+	"bytes"
+	"io"
+	"strings"
+)
+
+// String returns s with each line in s prefixed by indent.
+func String(indent, s string) string {
+	if indent == "" || s == "" {
+		return s
+	}
+	lines := strings.SplitAfter(s, "\n")
+	if len(lines[len(lines)-1]) == 0 {
+		lines = lines[:len(lines)-1]
+	}
+	return strings.Join(append([]string{""}, lines...), indent)
+}
+
+// Bytes returns b with each line in b prefixed by indent.
+func Bytes(indent, b []byte) []byte {
+	if len(indent) == 0 || len(b) == 0 {
+		return b
+	}
+	lines := bytes.SplitAfter(b, []byte{'\n'})
+	if len(lines[len(lines)-1]) == 0 {
+		lines = lines[:len(lines)-1]
+	}
+	return bytes.Join(append([][]byte{{}}, lines...), indent)
+}
+
+// NewWriter returns an io.Writer that prefixes the lines written to it with
+// indent and then writes them to w.  The writer returns the number of bytes
+// written to the underlying Writer.
+func NewWriter(w io.Writer, indent string) io.Writer {
+	if indent == "" {
+		return w
+	}
+	return &iw{
+		w:      w,
+		prefix: []byte(indent),
+	}
+}
+
+type iw struct {
+	w       io.Writer
+	prefix  []byte
+	partial bool // true if next line's indent already written
+}
+
+// Write implements io.Writer.
+func (w *iw) Write(buf []byte) (int, error) {
+	if len(buf) == 0 {
+		return 0, nil
+	}
+	lines := bytes.SplitAfter(buf, []byte{'\n'})
+	if len(lines[len(lines)-1]) == 0 {
+		lines = lines[:len(lines)-1]
+	}
+	if !w.partial {
+		lines = append([][]byte{{}}, lines...)
+	}
+	joined := bytes.Join(lines, w.prefix)
+	w.partial = joined[len(joined)-1] != '\n'
+
+	n, err := w.w.Write(joined)
+	if err != nil {
+		return actualWrittenSize(n, len(w.prefix), lines), err
+	}
+
+	return len(buf), nil
+}
+
+func actualWrittenSize(underlay, prefix int, lines [][]byte) int {
+	actual := 0
+	remain := underlay
+	for _, line := range lines {
+		if len(line) == 0 {
+			continue
+		}
+
+		addition := remain - prefix
+		if addition <= 0 {
+			return actual
+		}
+
+		if addition <= len(line) {
+			return actual + addition
+		}
+
+		actual += len(line)
+		remain -= prefix + len(line)
+	}
+
+	return actual
+}

src/webui/internal/goyang/pkg/indent/indent_test.go

@@ -0,0 +1,146 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package indent
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+var tests = []struct {
+	prefix, in, out string
+}{
+	{
+		"", "", "",
+	}, {
+		"--", "", "",
+	}, {
+		"", "x\nx", "x\nx",
+	}, {
+		"--", "x", "--x",
+	}, {
+		"--", "\n", "--\n",
+	}, {
+		"--", "\n\n", "--\n--\n",
+	}, {
+		"--", "x\n", "--x\n",
+	}, {
+		"--", "\nx", "--\n--x",
+	}, {
+		"--", "two\nlines\n", "--two\n--lines\n",
+	}, {
+		"--", "\nempty\nfirst\n", "--\n--empty\n--first\n",
+	}, {
+		"--", "empty\nlast\n\n", "--empty\n--last\n--\n",
+	}, {
+		"--", "empty\n\nmiddle\n", "--empty\n--\n--middle\n",
+	},
+}
+
+func TestIndent(t *testing.T) {
+	for x, tt := range tests {
+		out := String(tt.prefix, tt.in)
+		if out != tt.out {
+			t.Errorf("#%d: got %q, want %q", x, out, tt.out)
+		}
+		bout := string(Bytes([]byte(tt.prefix), []byte(tt.in)))
+		if bout != out {
+			t.Errorf("#%d: Bytes got %q\n String got %q", x, bout, out)
+		}
+	}
+}
+
+func TestWriter(t *testing.T) {
+Test:
+	for x, tt := range tests {
+		for size := 1; size < 64; size <<= 1 {
+			var b bytes.Buffer
+			w := NewWriter(&b, tt.prefix)
+			data := []byte(tt.in)
+			for len(data) > size {
+				if _, err := w.Write(data[:size]); err != nil {
+					t.Errorf("#%d: %v", x, err)
+					continue Test
+				}
+				data = data[size:]
+			}
+			if _, err := w.Write(data); err != nil {
+				t.Errorf("#%d/%d: %v", x, size, err)
+				continue Test
+			}
+
+			out := b.String()
+			if out != tt.out {
+				t.Errorf("#%d/%d: got %q, want %q", x, size, out, tt.out)
+			}
+		}
+	}
+}
+
+func TestWrittenSize(t *testing.T) {
+	for x, tt := range tests {
+		var b bytes.Buffer
+		w := NewWriter(&b, tt.prefix)
+		data := []byte(tt.in)
+		if n, _ := w.Write(data); n != len(data) {
+			t.Errorf("#%d: got %d, want %d", x, n, len(data))
+		}
+	}
+}
+
+func TestWrittenSizeWithError(t *testing.T) {
+	table := []struct {
+		prefix   string
+		input    string
+		underlay int
+		expected int
+	}{
+		{"--", "two\nlines\n", 0, 0},
+		{"--", "two\nlines\n", 1, 0},   // -
+		{"--", "two\nlines\n", 2, 0},   // -
+		{"--", "two\nlines\n", 3, 1},   // t
+		{"--", "two\nlines\n", 4, 2},   // w
+		{"--", "two\nlines\n", 5, 3},   // o
+		{"--", "two\nlines\n", 6, 4},   // \n
+		{"--", "two\nlines\n", 7, 4},   // -
+		{"--", "two\nlines\n", 8, 4},   // -
+		{"--", "two\nlines\n", 9, 5},   // l
+		{"--", "two\nlines\n", 10, 6},  // i
+		{"--", "two\nlines\n", 11, 7},  // n
+		{"--", "two\nlines\n", 12, 8},  // e
+		{"--", "two\nlines\n", 13, 9},  // s
+		{"--", "two\nlines\n", 14, 10}, // \n
+		{"--", "two\nlines\n", 15, 10}, // -
+		{"--", "two\nlines\n", 16, 10}, // -
+	}
+
+	for _, d := range table {
+		uw := errorWriter{d.underlay}
+		w := NewWriter(uw, d.prefix)
+		data := []byte(d.input)
+		if n, _ := w.Write(data); n != d.expected {
+			t.Errorf("underlay: %d, got %d, want %d, err: ", d.underlay, n, d.expected)
+		}
+	}
+}
+
+type errorWriter struct {
+	ret int
+}
+
+func (w errorWriter) Write(buf []byte) (int, error) {
+	return w.ret, errors.New("error")
+}

src/webui/internal/goyang/pkg/yang/ast.go

@@ -0,0 +1,461 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This file implements BuildAST() and its associated helper structs and
+// functions for constructing an AST of Nodes from a Statement tree. This
+// function also populates all typedefs into a type cache.
+//
+// The initTypes function generates the helper struct and functions that
+// recursively fill in the various Node structures defined in yang.go.
+// BuildAST() then uses those functions to convert raw parsed Statements into
+// an AST.
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+func init() {
+	// Initialize the global variables `typeMap` and `nameMap`.
+	// By doing this, we are making the assumption that all modules will be
+	// parsed according to the type hierarchy rooted at `meta`, and thus
+	// all input YANG modules will be parsed in this manner.
+	initTypes(reflect.TypeOf(&meta{}))
+}
+
+// A yangStatement contains all information needed to build a particular
+// type of statement into an AST node.
+type yangStatement struct {
+	// funcs is the map of YANG field names to the function that populates
+	// the statement into the AST node.
+	funcs map[string]func(*Statement, reflect.Value, reflect.Value, *typeDictionary) error
+	// required is a list of fields that must be present in the statement.
+	required []string
+	// sRequired maps a statement name to a list of required sub-field
+	// names. The statement name can be an alias of the primary field type.
+	//    e.g. If a field is required by statement type foo, then only foo
+	//    should have the field. If bar is an alias of foo, it must not
+	//    have this field.
+	sRequired map[string][]string
+	// addext is the function to handle possible extensions.
+	addext func(*Statement, reflect.Value, reflect.Value) error
+}
+
+// newYangStatement creates a new yangStatement.
+func newYangStatement() *yangStatement {
+	return &yangStatement{
+		funcs:     make(map[string]func(*Statement, reflect.Value, reflect.Value, *typeDictionary) error),
+		sRequired: make(map[string][]string),
+	}
+}
+
+var (
+	// The following maps are built up at init time.
+	// typeMap provides a lookup from a Node type to the corresponding
+	// yangStatement.
+	typeMap = map[reflect.Type]*yangStatement{}
+	// nameMap provides a lookup from a keyword string to the corresponding
+	// concrete type implementing the Node interface (see yang.go).
+	nameMap = map[string]reflect.Type{}
+
+	// The following are helper types used by the implementation.
+	statementType = reflect.TypeOf(&Statement{})
+	nilValue      = reflect.ValueOf(nil)
+	// nodeType is the reflect.Type of the Node interface.
+	nodeType = reflect.TypeOf((*Node)(nil)).Elem()
+)
+
+// meta is a collection of top-level statements.  There is no actual
+// statement named "meta".  All other statements are a sub-statement of one
+// of the meta statements.
+type meta struct {
+	Module []*Module `yang:"module"`
+}
+
+// aliases is a map of "aliased" names, that is, two types of statements
+// that parse (nearly) the same.
+// NOTE: This only works for root-level aliasing for now, which is good enough
+// for module/submodule. This is because yangStatement.funcs doesn't store the
+// handler function for aliased fields, and sRequired also may only store the
+// correct values when processing a root-level statement due to aliasing. These
+// issues would need to be fixed in order to support aliasing for non-top-level
+// statements.
+var aliases = map[string]string{
+	"submodule": "module",
+}
+
+// buildASTWithTypeDict creates an AST for the input statement, and returns its
+// root node. It also takes as input a type dictionary into which any
+// encountered typedefs within the statement are cached.
+func buildASTWithTypeDict(stmt *Statement, types *typeDictionary) (Node, error) {
+	v, err := build(stmt, nilValue, types)
+	if err != nil {
+		return nil, err
+	}
+	return v.Interface().(Node), nil
+}
+
+// build builds and returns an AST from the statement stmt and with parent node
+// parent. It also takes as input a type dictionary types into which any
+// encountered typedefs within the statement are cached. The type of value
+// returned depends on the keyword in stmt (see yang.go). It returns an error
+// if it cannot build the statement into its corresponding Node type.
+func build(stmt *Statement, parent reflect.Value, types *typeDictionary) (v reflect.Value, err error) {
+	defer func() {
+		// If we are returning a real Node then call addTypedefs
+		// if the node possibly contains typedefs.
+		// Cache these in the typedef cache for look-ups.
+		if err != nil || v == nilValue {
+			return
+		}
+		if t, ok := v.Interface().(Typedefer); ok {
+			types.addTypedefs(t)
+		}
+	}()
+	keyword := stmt.Keyword
+	if k, ok := aliases[stmt.Keyword]; ok {
+		keyword = k
+	}
+	t := nameMap[keyword]
+	y := typeMap[t]
+	// Keep track of which substatements are present in the statement.
+	found := map[string]bool{}
+
+	// Get the struct type we are pointing to.
+	t = t.Elem()
+	// v is a pointer to the instantiated structure we are building.
+	v = reflect.New(t)
+
+	// Handle special cases that are not actually substatements:
+
+	if fn := y.funcs["Name"]; fn != nil {
+		// Name uses stmt directly.
+		if err := fn(stmt, v, parent, types); err != nil {
+			return nilValue, err
+		}
+	}
+	if fn := y.funcs["Statement"]; fn != nil {
+		// Statement uses stmt directly.
+		if err := fn(stmt, v, parent, types); err != nil {
+			return nilValue, err
+		}
+	}
+	if fn := y.funcs["Parent"]; fn != nil {
+		// parent is the parent node, which is nilValue (reflect.ValueOf(nil)) if there is none.
+		// parent.IsValid will return false when parent is a nil interface
+		// parent.IsValid will true if parent references a concrete type
+		// (even if it is nil).
+		if parent.IsValid() {
+			if err := fn(stmt, v, parent, types); err != nil {
+				return nilValue, err
+			}
+		}
+	}
+
+	// Now handle the substatements
+
+	for _, ss := range stmt.statements {
+		found[ss.Keyword] = true
+		fn := y.funcs[ss.Keyword]
+		switch {
+		case fn != nil:
+			// Normal case, the keyword is known.
+			if err := fn(ss, v, parent, types); err != nil {
+				return nilValue, err
+			}
+		case len(strings.Split(ss.Keyword, ":")) == 2:
+			// Keyword is not known but it has a prefix so it might
+			// be an extension.
+			if y.addext == nil {
+				return nilValue, fmt.Errorf("%s: no extension function", ss.Location())
+			}
+			y.addext(ss, v, parent)
+		default:
+			return nilValue, fmt.Errorf("%s: unknown %s field: %s", ss.Location(), stmt.Keyword, ss.Keyword)
+		}
+	}
+
+	// Make sure all of our required field are there.
+	for _, r := range y.required {
+		if !found[r] {
+			return nilValue, fmt.Errorf("%s: missing required %s field: %s", stmt.Location(), stmt.Keyword, r)
+		}
+	}
+
+	// Make sure required fields based on our keyword are there (module vs submodule)
+	for _, r := range y.sRequired[stmt.Keyword] {
+		if !found[r] {
+			return nilValue, fmt.Errorf("%s: missing required %s field: %s", stmt.Location(), stmt.Keyword, r)
+		}
+	}
+
+	// Make sure we don't have any field set that is required by a different keyword.
+	for n, or := range y.sRequired {
+		if n == stmt.Keyword {
+			continue
+		}
+		for _, r := range or {
+			if found[r] {
+				return nilValue, fmt.Errorf("%s: unknown %s field: %s", stmt.Location(), stmt.Keyword, r)
+			}
+		}
+	}
+	return v, nil
+}
+
+// initTypes creates the functions necessary to build a Statement into the
+// given the type "at" based on its possible substatements. at must implement
+// Node, with its concrete type being a pointer to a struct defined in yang.go.
+//
+// This function also builds up the functions to populate the input type
+// dictionary types with any encountered typedefs within the statement.
+//
+// For each field of the struct with a yang tag (e.g., `yang:"command"`), a
+// function is created with "command" as its unique ID.  The complete map of
+// builder functions for at is then added to the typeMap map with at as the
+// key. The idea is to call these builder functions for each substatement
+// encountered.
+//
+// The functions have the form:
+//
+//	func fn(ss *Statement, v, p reflect.Value, types *typeDictionary) error
+//
+// Given stmt as a Statement of type at, ss is a substatement of stmt (in a few
+// exceptional cases, ss is the Statement itself).  v must have the same type
+// as at and is the structure being filled in.  p is the parent Node, or nil.
+// types is the type dictionary cache of the current set of modules being parsed,
+// which is used for looking up typedefs.  p is only used to set the Parent
+// field of a Node.  For example, given the following structure and variables:
+//
+//	type Include struct {
+//		Name         string       `yang:"Name"`
+//		Source       *Statement   `yang:"Statement"`
+//		Parent       Node         `yang:"Parent"`
+//		Extensions   []*Statement `yang:"Ext"`
+//		RevisionDate *Value       `yang:"revision-date"`
+//	}
+//
+//	var inc = &Include{}
+//	var vInc = reflect.ValueOf(inc)
+//	var tInc = reflect.TypeOf(inc)
+//
+// Functions are created for each fields and named Name, Statement, Parent, Ext,
+// and revision-date.
+//
+// The function built for RevisionDate will be called for any substatement,
+// ds, of stmt that has the keyword "revision-date" along with the value of
+// vInc and its parent:
+//
+//	typeMap[tInc]["revision-date"](ss, vInc, parent, types)
+//
+// Normal fields are all processed this same way.
+//
+// The other 4 fields are special.  In the case of Name, Statement, and Parent,
+// the function is passed stmt, rather than ss, as these fields are not filled in
+// by substatements.
+//
+// The Name command must set its field to the Statement's argument.  The
+// Statement command must set its field to the Statement itself.  The
+// Parent command must set its field with the Node of its parent (the
+// parent parameter).
+//
+// The Ext command is unique and must decode into a []*Statement.  This is a
+// slice of all statements that use unknown keywords with a prefix (in a valid
+// .yang file these should be the extensions).
+//
+// The Field can have attributes delimited by a ','.  The only
+// supported attributes are:
+//
+//	nomerge:       Do not merge this field
+//	required:      This field must be populated
+//	required=KIND: This field must be populated if the keyword is KIND
+//	               otherwise this field must not be present.
+//	               (This is to support merging Module and SubModule).
+//
+// If at contains substructures, initTypes recurses on the substructures.
+func initTypes(at reflect.Type) {
+	if at.Kind() != reflect.Ptr || at.Elem().Kind() != reflect.Struct {
+		panic(fmt.Sprintf("interface not a struct pointer, is %v", at))
+	}
+	if typeMap[at] != nil {
+		return // we already defined this type
+	}
+
+	y := newYangStatement()
+	typeMap[at] = y
+	t := at.Elem()
+	for i := 0; i != t.NumField(); i++ {
+		i := i
+		f := t.Field(i)
+		yang := f.Tag.Get("yang")
+		if yang == "" {
+			continue
+		}
+		parts := strings.Split(yang, ",")
+		name := parts[0]
+		if a, ok := aliases[name]; ok {
+			name = a
+		}
+
+		const reqe = "required="
+		for _, p := range parts[1:] {
+			switch {
+			case p == "nomerge":
+			case p == "required":
+				y.required = append(y.required, name)
+			case strings.HasPrefix(p, reqe):
+				p = p[len(reqe):]
+				y.sRequired[p] = append(y.sRequired[p], name)
+			default:
+				panic(f.Name + ": unknown tag: " + p)
+			}
+		}
+
+		// Ext means this is where we squirrel away extensions
+		if name == "Ext" {
+			// stmt is the extension to put into v at for field f.
+			y.addext = func(stmt *Statement, v, _ reflect.Value) error {
+				if v.Type() != at {
+					panic(fmt.Sprintf("given type %s, need type %s", v.Type(), at))
+				}
+				fv := v.Elem().Field(i)
+				fv.Set(reflect.Append(fv, reflect.ValueOf(stmt)))
+				return nil
+			}
+			continue
+		}
+
+		// descend runs initType on dt if it has not already done so.
+		descend := func(name string, dt reflect.Type) {
+			switch nameMap[name] {
+			case nil:
+				nameMap[name] = dt
+				initTypes(dt) // Make sure that structure type is included
+			case dt:
+			default:
+				panic("redeclared type " + name)
+			}
+		}
+
+		// Create a function, fn, that will build the field from a
+		// Statement.  These functions are used when actually making
+		// an AST from a Statement Tree.
+		var fn func(*Statement, reflect.Value, reflect.Value, *typeDictionary) error
+
+		// The field can be a pointer, a slice or a string
+		switch f.Type.Kind() {
+		default:
+			panic(fmt.Sprintf("invalid type: %v", f.Type.Kind()))
+
+		case reflect.Interface:
+			// The only case of this should be the "Parent" field.
+			if name != "Parent" {
+				panic(fmt.Sprintf("interface field is %s, not Parent", name))
+			}
+			fn = func(stmt *Statement, v, p reflect.Value, types *typeDictionary) error {
+				if !p.Type().Implements(nodeType) {
+					panic(fmt.Sprintf("invalid interface: %v", f.Type.Kind()))
+				}
+				v.Elem().Field(i).Set(p)
+				return nil
+			}
+		case reflect.String:
+			// The only case of this should be the "Name" field
+			if name != "Name" {
+				panic(fmt.Sprintf("string field is %s, not Name", name))
+			}
+			fn = func(stmt *Statement, v, _ reflect.Value, types *typeDictionary) error {
+				if v.Type() != at {
+					panic(fmt.Sprintf("got type %v, want %v", v.Type(), at))
+				}
+				fv := v.Elem().Field(i)
+				if fv.String() != "" {
+					return errors.New(stmt.Keyword + ": already set")
+				}
+
+				v.Elem().Field(i).SetString(stmt.Argument)
+				return nil
+			}
+
+		case reflect.Ptr:
+			if f.Type == statementType {
+				// The only case of this should be the
+				// "Statement" field
+				if name != "Statement" {
+					panic(fmt.Sprintf("string field is %s, not Statement", name))
+				}
+				fn = func(stmt *Statement, v, _ reflect.Value, types *typeDictionary) error {
+					if v.Type() != at {
+						panic(fmt.Sprintf("got type %v, want %v", v.Type(), at))
+					}
+					v.Elem().Field(i).Set(reflect.ValueOf(stmt))
+					return nil
+				}
+				break
+			}
+
+			// Make sure our field type is also setup.
+			descend(name, f.Type)
+
+			fn = func(stmt *Statement, v, p reflect.Value, types *typeDictionary) error {
+				if v.Type() != at {
+					panic(fmt.Sprintf("given type %s, need type %s", v.Type(), at))
+				}
+				fv := v.Elem().Field(i)
+				if !fv.IsNil() {
+					return errors.New(stmt.Keyword + ": already set")
+				}
+
+				// Use build to build the value for this field.
+				sv, err := build(stmt, v, types)
+				if err != nil {
+					return err
+				}
+				v.Elem().Field(i).Set(sv)
+				return nil
+			}
+
+		case reflect.Slice:
+			// A slice at this point is always a slice of
+			// substructures.  We may see the same keyword multiple
+			// times, each time we see it we just append to the
+			// slice.
+			st := f.Type.Elem()
+			switch st.Kind() {
+			default:
+				panic(fmt.Sprintf("invalid type: %v", st.Kind()))
+			case reflect.Ptr:
+				descend(name, st)
+				fn = func(stmt *Statement, v, p reflect.Value, types *typeDictionary) error {
+					if v.Type() != at {
+						panic(fmt.Sprintf("given type %s, need type %s", v.Type(), at))
+					}
+					sv, err := build(stmt, v, types)
+					if err != nil {
+						return err
+					}
+
+					fv := v.Elem().Field(i)
+					fv.Set(reflect.Append(fv, sv))
+					return nil
+				}
+			}
+		}
+		y.funcs[name] = fn
+	}
+}

src/webui/internal/goyang/pkg/yang/ast_test.go

@@ -0,0 +1,538 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+type MainNode struct {
+	Name       string       `yang:"Name,nomerge"`
+	Source     *Statement   `yang:"Statement,nomerge"`
+	Parent     Node         `yang:"Parent,nomerge"`
+	Extensions []*Statement `yang:"Ext"`
+
+	Field      *Value     `yang:"field"`
+	Slice      []*Value   `yang:"slice"`
+	ChildNode  *SubNode   `yang:"child_node"`
+	ChildSlice []*SubNode `yang:"child_slice"`
+	ReqNode    *ReqNode   `yang:"req_node"`
+	MainField  *Value     `yang:"main_field,required=main_node"`
+	AltField   *Value     `yang:"alt_field,required=alt_node"`
+}
+
+func (m *MainNode) Kind() string {
+	if m.AltField != nil {
+		return "alt_node"
+	}
+	return "main_node"
+}
+
+func (m *MainNode) ParentNode() Node      { return m.Parent }
+func (m *MainNode) NName() string         { return m.Name }
+func (m *MainNode) Statement() *Statement { return m.Source }
+func (m *MainNode) Exts() []*Statement    { return m.Extensions }
+
+func (m *MainNode) checkEqual(n Node) string {
+	o, ok := n.(*MainNode)
+	if !ok {
+		return fmt.Sprintf("expected *MainNode, got %T", n)
+	}
+	if m.Name != o.Name {
+		return fmt.Sprintf("got name %s, want %s", o.Name, m.Name)
+	}
+	if s := m.Source.checkEqual(o.Source); s != "" {
+		return s
+	}
+	if (m.Field == nil) != (o.Field == nil) {
+		if m.Field == nil {
+			return "unexpected field entry"
+		}
+		return "missing expected field entry"
+	}
+	if m.Field != nil {
+		if m.Field.Name != o.Field.Name {
+			return fmt.Sprintf("got field of %s, want %s", o.Field.Name, m.Field.Name)
+		}
+	}
+	if len(m.Slice) != len(o.Slice) {
+		return fmt.Sprintf("got slice of %d, want slice of %d", len(o.Slice), len(m.Slice))
+	}
+	for x, s1 := range m.Slice {
+		s2 := o.Slice[x]
+		if s1.Name != s2.Name {
+			return fmt.Sprintf("slice[%d] got %s, want %s", x, s2.Name, s1.Name)
+		}
+	}
+	if (m.ChildNode == nil) != (o.ChildNode == nil) {
+		if m.ChildNode == nil {
+			return "unexpected child_node entry"
+		}
+		return "missing expected child_node entry"
+	}
+	if m.ChildNode != nil {
+		if s := m.ChildNode.checkEqual(o.ChildNode); s != "" {
+			return fmt.Sprintf("child_node: %s", s)
+		}
+	}
+	if len(m.ChildSlice) != len(o.ChildSlice) {
+		return fmt.Sprintf("got child_slice of %d, want slice of %d", len(o.ChildSlice), len(m.ChildSlice))
+	}
+	for x, s1 := range m.ChildSlice {
+		s2 := o.ChildSlice[x]
+		if s := s1.checkEqual(s2); s != "" {
+			return fmt.Sprintf("child_slice[%d]: %s", x, s)
+		}
+	}
+	if (m.ReqNode == nil) != (o.ReqNode == nil) {
+		if m.ReqNode == nil {
+			return "unexpected req_node entry"
+		}
+		return "missing expected req_node entry"
+	}
+	if m.ReqNode != nil {
+		if s := m.ReqNode.checkEqual(o.ReqNode); s != "" {
+			return fmt.Sprintf("req_node: %s", s)
+		}
+	}
+	if (m.AltField == nil) != (o.AltField == nil) {
+		if m.AltField == nil {
+			return "unexpected alt_field entry"
+		}
+		return "missing expected alt_field entry"
+	}
+	if m.AltField != nil {
+		if m.AltField.Name != o.AltField.Name {
+			return fmt.Sprintf("got alt_field of %s, want %s", o.AltField.Name, m.AltField.Name)
+		}
+	}
+	return ""
+}
+
+type SubNode struct {
+	Name       string       `yang:"Name,nomerge"`
+	Source     *Statement   `yang:"Statement,nomerge"`
+	Parent     Node         `yang:"Parent,nomerge"`
+	Extensions []*Statement `yang:"Ext"`
+
+	SubField *Value `yang:"sub_field"`
+}
+
+func (SubNode) Kind() string             { return "sub_node" }
+func (s *SubNode) ParentNode() Node      { return s.Parent }
+func (s *SubNode) NName() string         { return s.Name }
+func (s *SubNode) Statement() *Statement { return s.Source }
+func (s *SubNode) Exts() []*Statement    { return s.Extensions }
+
+func (s *SubNode) checkEqual(o *SubNode) string {
+	if s.Name != o.Name {
+		return fmt.Sprintf("got name %s, want %s", o.Name, s.Name)
+	}
+	if s := s.Source.checkEqual(o.Source); s != "" {
+		return s
+	}
+	if (s.SubField == nil) != (o.SubField == nil) {
+		if s.SubField == nil {
+			return "unexpected sub_field entry"
+		}
+		return "missing expected sub_field entry"
+	}
+	if s.SubField != nil {
+		if s.SubField.Name != o.SubField.Name {
+			return fmt.Sprintf("got sub_field of %s, want %s", o.SubField.Name, s.SubField.Name)
+		}
+	}
+	return ""
+}
+
+type ReqNode struct {
+	Name   string     `yang:"Name,nomerge"`
+	Source *Statement `yang:"Statement,nomerge"`
+	Parent Node       `yang:"Parent,nomerge"`
+
+	ReqField    *Value `yang:"req_field,required"`
+	AltReqField *Value `yang:"alt_req_field,required=alt_req_node"`
+	Field       *Value `yang:"field"`
+}
+
+func (s *ReqNode) Kind() string {
+	return "req_node"
+}
+func (s *ReqNode) ParentNode() Node      { return s.Parent }
+func (s *ReqNode) NName() string         { return s.Name }
+func (s *ReqNode) Statement() *Statement { return s.Source }
+func (m *ReqNode) Exts() []*Statement    { return nil }
+
+func (s *ReqNode) checkEqual(o *ReqNode) string {
+	if s.Name != o.Name {
+		return fmt.Sprintf("got name %s, want %s", o.Name, s.Name)
+	}
+	if s := s.Source.checkEqual(o.Source); s != "" {
+		return s
+	}
+	if (s.ReqField == nil) != (o.ReqField == nil) {
+		if s.ReqField == nil {
+			return "unexpected req_field entry"
+		}
+		return "missing expected req_field entry"
+	}
+	if s.ReqField != nil {
+		if s.ReqField.Name != o.ReqField.Name {
+			return fmt.Sprintf("got req_field of %s, want %s", o.ReqField.Name, s.ReqField.Name)
+		}
+	}
+	if (s.AltReqField == nil) != (o.AltReqField == nil) {
+		if s.AltReqField == nil {
+			return "unexpected alt_req_field entry"
+		}
+		return "missing expected alt_req_field entry"
+	}
+	if s.AltReqField != nil {
+		if s.AltReqField.Name != o.AltReqField.Name {
+			return fmt.Sprintf("got alt_req_field of %s, want %s", o.AltReqField.Name, s.AltReqField.Name)
+		}
+	}
+	return ""
+}
+
+func (s *Statement) checkEqual(o *Statement) string {
+	if (s == nil) != (o == nil) {
+		var b bytes.Buffer
+		if s == nil {
+			o.Write(&b, "")
+			return fmt.Sprintf("unexpected Statement entry\n%s", &b)
+		}
+		s.Write(&b, "")
+		return fmt.Sprintf("missing expected Statement entry\n%s", &b)
+	}
+	if s == nil {
+		return ""
+	}
+	var b1, b2 bytes.Buffer
+	s.Write(&b1, "")
+	o.Write(&b2, "")
+	ss := b1.String()
+	os := b2.String()
+	if ss != os {
+		return fmt.Sprintf("got statement:\n%swant:\n%s", os, ss)
+	}
+	return ""
+}
+
+func TestAST(t *testing.T) {
+	// Teach the AST parser about our testing nodes
+	type meta struct {
+		MainNode []*MainNode `yang:"main_node"`
+	}
+
+	old_aliases := aliases
+	aliases = map[string]string{
+		"alt_node": "main_node",
+	}
+
+	for _, tt := range []struct {
+		line int
+		in   string
+		out  *MainNode
+		err  string
+	}{
+		{
+			line: line(),
+			in: `
+main_node the_node {
+	// This test is testing to make sure unknown statements, that
+	// might be extensions, are properly put in the Extensions slice.
+	// When an extension is used, it must be of the form "prefix:name".
+	// See https://tools.ietf.org/html/rfc6020#section-7.17
+	ex:ext1 value1;
+	ex:ext2 value2;
+	main_field foo;
+}
+`,
+			out: &MainNode{
+				Source: SA("main_node", "the_node",
+					SA("ex:ext1", "value1"),
+					SA("ex:ext2", "value2"),
+					SA("main_field", "foo")),
+				Name: "the_node",
+				Extensions: []*Statement{
+					SA("ex:ext1", "value1"),
+					SA("ex:ext2", "value2"),
+				},
+				MainField: &Value{
+					Name: "foo",
+				},
+			},
+		},
+		{
+			line: line(),
+			in: `
+main_node the_node {
+	// This test tests fields, slices, and sub-statements.
+	field field_value;
+	slice sl1;
+	slice sl2;
+	child_node the_child {
+		sub_field val1;
+	}
+	child_slice element1 {
+		sub_field el1;
+	}
+	child_slice element2 {
+		sub_field el2;
+	}
+	main_field foo;
+}`,
+			out: &MainNode{
+				Source: SA("main_node", "the_node",
+					SA("field", "field_value"),
+					SA("slice", "sl1"),
+					SA("slice", "sl2"),
+					SA("child_node", "the_child",
+						SA("sub_field", "val1")),
+					SA("child_slice", "element1",
+						SA("sub_field", "el1")),
+					SA("child_slice", "element2",
+						SA("sub_field", "el2")),
+					SA("main_field", "foo"),
+				),
+				Name: "the_node",
+				Field: &Value{
+					Name: "field_value",
+				},
+				Slice: []*Value{
+					{
+						Name: "sl1",
+					},
+					{
+						Name: "sl2",
+					},
+				},
+				ChildNode: &SubNode{
+					Source: SA("child_node", "the_child",
+						SA("sub_field", "val1")),
+					Name: "the_child",
+					SubField: &Value{
+						Name: "val1",
+					},
+				},
+				ChildSlice: []*SubNode{
+					{
+						Source: SA("child_slice", "element1",
+							SA("sub_field", "el1")),
+						Name: "element1",
+						SubField: &Value{
+							Name: "el1",
+						},
+					},
+					{
+						Source: SA("child_slice", "element2",
+							SA("sub_field", "el2")),
+						Name: "element2",
+						SubField: &Value{
+							Name: "el2",
+						},
+					},
+				},
+				MainField: &Value{
+					Name: "foo",
+				},
+			},
+		},
+		{
+			line: line(),
+			in: `
+// This test tests for the presence of a required field.
+// main_node requires the field named "main_field".
+main_node the_node {
+	main_field value1 {
+	}
+}
+`,
+			out: &MainNode{
+				Source: SA("main_node", "the_node",
+					SA("main_field", "value1"),
+				),
+				Name: "the_node",
+				MainField: &Value{
+					Name: "value1",
+				},
+			},
+		},
+		{
+			line: line(),
+			in: `
+// This test tests for the presence of a required= field.
+// alt_node requires the field named "alt_field".
+alt_node the_node {
+	alt_field value2 {
+	}
+}
+`,
+			out: &MainNode{
+				Source: SA("alt_node", "the_node",
+					SA("alt_field", "value2"),
+				),
+				Name: "the_node",
+				AltField: &Value{
+					Name: "value2",
+				},
+			},
+		},
+		{
+			line: line(),
+			in: `
+main_node the_node {
+	// This test tests that extensions are rejected when the node is not
+	// supposed to contain them.
+	req_node value1 {
+		req_field foo {
+		}
+		ex:ext1 value1;
+		ex:ext2 value2;
+	}
+}
+`,
+			err: `ast.yang:8:3: no extension function`,
+		},
+		{
+			line: line(),
+			in: `
+main_node the_node {
+	// This test tests for the presence of a required field.
+	// req_node requires the field named "req_field".
+	req_node value1 {
+		req_field foo {
+		}
+	}
+	main_field foo;
+}
+`,
+			out: &MainNode{
+				Source: SA("main_node", "the_node",
+					SA("req_node", "value1",
+						SA("req_field", "foo")),
+					SA("main_field", "foo"),
+				),
+				Name: "the_node",
+				ReqNode: &ReqNode{
+					Source: SA("req_node", "value1",
+						SA("req_field", "foo")),
+					Name: "value1",
+					ReqField: &Value{
+						Name: "foo",
+					},
+				},
+				MainField: &Value{
+					Name: "foo",
+				},
+			},
+		},
+		{
+			line: line(),
+			in: `
+main_node the_node {
+	// This test tests that the absence of a required field fails.
+	// req_node requires the field named "req_field".
+	req_node value1 {
+	}
+	main_field foo;
+}
+`,
+			err: `ast.yang:5:2: missing required req_node field: req_field`,
+		},
+		{
+			line: line(),
+			in: `
+main_node the_node {
+	// This test tests that the absence of a required field.
+	// main_node requires the field named "main_field".
+	req_node value1 {
+		req_field foo {
+		}
+	}
+}
+`,
+			err: `ast.yang:2:1: missing required main_node field: main_field`,
+		},
+		{
+			line: line(),
+			in: `
+// This test tests that the alt_field, specified with
+// required=alt_node, causes the AST construction to error when a
+// main_node contains it.
+main_node the_node {
+	main_field foo;
+	alt_field foo;
+}
+`,
+			err: `ast.yang:5:1: unknown main_node field: alt_field`,
+		},
+		{
+			line: line(),
+			in: `
+// This test tests that required=alt_node enforces that
+// alt_node must contain it.
+alt_node the_node {
+	main_field foo;
+	alt_field foo;
+}
+`,
+			err: `ast.yang:4:1: unknown alt_node field: main_field`,
+		},
+		{
+			line: line(),
+			in: `
+// This test tests that required=alt_node enforces that
+// alt_node must contain it.
+alt_node the_node {
+}
+`,
+			err: `ast.yang:4:1: missing required alt_node field: alt_field`,
+		},
+	} {
+		ss, err := Parse(tt.in, "ast.yang")
+		if err != nil {
+			t.Errorf("%d: %v", tt.line, err)
+			continue
+		}
+		if len(ss) != 1 {
+			t.Errorf("%d: got %d results, want 1", tt.line, len(ss))
+			continue
+		}
+
+		typeDict := newTypeDictionary()
+		initTypes(reflect.TypeOf(&meta{}))
+
+		ast, err := buildASTWithTypeDict(ss[0], typeDict)
+		switch {
+		case err == nil && tt.err == "":
+			if s := tt.out.checkEqual(ast); s != "" {
+				t.Errorf("%d: %s", tt.line, s)
+			}
+		case err == nil:
+			t.Errorf("%d: did not get expected error %s", tt.line, tt.err)
+		case tt.err == "":
+			t.Errorf("%d: %v", tt.line, err)
+		case err.Error() != tt.err:
+			t.Errorf("%d: got error %v, want %s", tt.line, err, tt.err)
+		}
+	}
+
+	aliases = old_aliases
+}

src/webui/internal/goyang/pkg/yang/bgp_test.go

@@ -0,0 +1,571 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"reflect"
+	"testing"
+)
+
+// TestBGP simply makes sure we are able to parse a version of Anees's
+// BGP model.  We don't actually attempt to validate we got the right
+// AST.  ast_test.go will test smaller peices to make sure the basics
+// of BuildAST produce expected results.
+func TestBGP(t *testing.T) {
+	ss, err := Parse(bgp, "bgp.yang")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(ss) != 1 {
+		t.Fatalf("got %d results, want 1", len(ss))
+	}
+	typeDict := newTypeDictionary()
+	initTypes(reflect.TypeOf(&meta{}))
+	if _, err := buildASTWithTypeDict(ss[0], typeDict); err != nil {
+		t.Fatal(err)
+	}
+}
+
+var bgp = `
+module google-bgp {
+
+  yang-version "1";
+
+  // namespace
+  namespace "http://google.com/yang/google-bgp-protocol-cfg";
+
+  prefix "gbgp";
+
+  // import some basic types -- no other dependency on
+  // in-progress models in draft status
+  import ietf-inet-types { prefix inet; }
+
+
+  // meta
+  organization "Google, Inc.";
+
+  contact
+    "Google, Inc.
+    1600 Amphitheatre Way
+    Mountain View, CA  94043";
+
+  description
+    "This module describes a YANG model for BGP protocol
+    configuration.It is a limited subset of all of the configuration
+    parameters available in the variety of vendor implementations,
+    hence it is expected that it would be augmented with vendor-
+    specific configuration data as needed.Additional modules or
+    submodules to handle other aspects of BGP configuration,
+    including policy, VRFs, and additional address families are also 
+    expected.";
+
+  revision "2014-07-07" {
+    description
+      "Initial revision";
+    reference "TBD";
+  }
+
+
+  identity afi-type {
+    description
+      "base identity type for BGP address family identifiers (AFI)";
+    reference "IETF RFC 4760";
+  }
+
+  identity safi-type {
+    description
+      "base identity type for BGP subsequent address family
+      identifiers (SAFI)";
+    reference "IETF RFC 4760";
+  }
+
+  identity ipv4-afi {
+    base afi-type;
+    description
+      "IPv4 AF identifier";
+  }
+
+  identity ipv6-afi {
+    base afi-type;
+    description
+      "IPv6 AF identifier";
+  }
+
+  identity unicast-safi {
+    base safi-type;
+    description
+      "unicast SAFI identifier";
+  }
+
+  identity labeled-unicast-safi {
+    base safi-type;
+    description
+      "labeled unicast SAFI identifier";
+    reference "RFC 3107 - Carrying Label Information in BGP-4";
+  }
+
+
+  typedef peer-group-type {
+    type enumeration {
+      enum INTERNAL {
+        description "internal (iBGP) peer";
+      }
+      enum EXTERNAL {
+        description "external (eBGP) peer";
+      }
+    }
+    description
+      "labels a peer as explicitly internal or external";
+  }
+
+
+  typedef remove-private-as-option {
+    type enumeration {
+      enum ALL {
+        description "remove all private ASes in the path";
+      }
+      enum REPLACE {
+        description "replace private ASes with local AS";
+      }
+    }
+    description
+      "set of options for configuring how private AS path numbers
+      are removed from advertisements";
+  }
+
+  typedef percentage {
+    type uint8 {
+      range "0..100";
+    }
+    description
+      "Integer indicating a percentage value";
+  }
+
+  typedef rr-cluster-id-type {
+    type union {
+      type uint32;
+      type inet:ipv4-address;
+    }
+    description
+      "union type for route reflector cluster ids:
+      option 1: 4-byte number
+      option 2: IP address";
+  }
+
+  grouping bgp-common-configuration {
+    description "Common configuration across neighbors, groups,
+    etc.";
+
+    leaf description {
+      type string;
+      description
+        "A textual description of the peer or group";
+    }
+    container use-multiple-paths {
+      description
+        "Configuration of BGP multipath to enable load sharing across
+        multiple paths to peers.";
+      leaf allow-multiple-as {
+        type boolean;
+        default "false";
+        description
+          "Allow multipath to use paths from different neighboring
+          ASes.  The default is to only consider multiple paths from
+          the same neighboring AS.";
+      }
+      leaf maximum-paths {
+        type uint32;
+        default 1;
+        description
+          "Maximum number of parallel paths to consider when using
+          BGP multipath.  The default is to use a single path.";
+        reference "draft-ietf-idr-add-paths-09.txt";
+      }
+    }
+
+  }
+
+  grouping bgp-group-common-configuration {
+    description "Configuration items that are applied at the peer
+    group level";
+  }
+
+  grouping bgp-group-neighbor-common-configuration {
+    description "Configuration options for peer and group context";
+
+    leaf auth-password {
+      type string;
+      description
+        "Configures an authentication password for use with
+        neighboring devices.";
+    }
+
+    container timers {
+      description "Configuration of various BGP timers";
+
+      leaf hold-time {
+        type decimal64 {
+          fraction-digits 2;
+        }
+        default 90;
+        // hold-time should typically be set to 3x the
+        // keepalive-interval -- create a constraint for this?
+        description
+          "Time interval in seconds that a BGP session will be
+          considered active in the absence of keepalive or other
+          messages from the peer";
+        reference
+          "RFC 1771 - A Border Gateway Protocol 4";
+      }
+
+      leaf keepalive-interval {
+        type decimal64 {
+          fraction-digits 2;
+        }
+        default 30;
+        description
+          "Time interval in seconds between transmission of keepalive
+          messages to the neighbor.  Typically set to 1/3 the 
+          hold-time.";
+      }
+
+      leaf advertisement-interval {
+        type decimal64 {
+          fraction-digits 2;
+        }
+        default 30;
+        description
+          "Mininum time interval in seconds between transmission 
+          of BGP updates to neighbors";
+        reference
+          "RFC 1771 - A Border Gateway Protocol 4";
+      }
+
+      leaf connect-retry {
+        type decimal64 {
+          fraction-digits 2;
+        }
+        default 30;
+        description
+          "Time interval in seconds between attempts to establish a
+          session with the peer.";
+      }
+    }
+
+    container ebgp-multihop {
+      description
+        "Configure multihop BGP for peers that are not directly
+        connected";
+
+      leaf multihop-ttl {
+        type uint8;
+        default 1;
+        description
+          "Time-to-live for multihop BGP sessions.  The default
+          value of 1 is for directly connected peers (i.e.,
+          multihop disabled";
+
+      }
+
+    }
+
+    container route-reflector {
+      description
+        "Configure the local router as a route-reflector
+        server";
+      leaf route-reflector-clusterid {
+        type rr-cluster-id-type;
+        description
+          "route-reflector cluster id to use when local router is
+          configured as a route reflector.  Commonly set at the group
+          level, but allows a different cluster
+          id to be set for each neighbor.";
+      }
+
+      leaf route-reflector-client {
+        type boolean;
+        default "false";
+        description
+          "configure the neighbor as a route reflector client";
+      }
+    }
+
+    leaf remove-private-as {
+      // could also make this a container with a flag to enable
+      // remove-private and separate option.  here, option implies 
+      // remove-private is enabled.
+      type remove-private-as-option;
+      description
+        "Remove private AS numbers from updates sent to peers";
+    }
+
+
+    container bgp-logging-options {
+      description
+        "Configure various tracing/logging options for BGP peers
+        or groups.  Expected that additional vendor-specific log
+        options would augment this container";
+
+      leaf log-neighbor-state-changes {
+        type boolean;
+        default "true";
+        description
+          "Configure logging of peer state changes.  Default is
+          to enable logging of peer state changes.";
+      }
+    }
+
+    container transport-options {
+      description
+        "Transport protocol options for BGP sessions";
+
+        leaf tcp-mss {
+          type uint16;
+          description
+            "Sets the max segment size for BGP TCP sessions";
+        }
+
+        leaf passive-mode {
+          type boolean;
+          description
+            "Wait for peers to issue requests to open a BGP session,
+            rather than initiating sessions from the local router";
+        }
+    }
+
+    leaf local-address {
+      type inet:ip-address;
+      description
+        "Set the local IP (either IPv4 or IPv6) address to use for
+        the session when sending BGP update messages";
+    }
+
+    leaf route-flap-damping {
+      type boolean;
+      description
+        "Enable route flap damping";
+    }
+  }
+
+  grouping bgp-address-family-common-configuration {
+    description "Configuration options per address family context";
+
+    list address-family {
+
+      key "afi-name";
+      description
+        "Per address-family configuration, uniquely identified by AF
+        name"; 
+      leaf afi-name {
+        type identityref {
+          base "afi-type";
+        }
+        description
+          "Address family names are drawn from the afi-type base
+          identity, which has specific address family types as
+          derived identities";
+      }
+
+      list subsequent-address-family {
+
+        key "safi-name";
+        description
+          "Per subsequent address family configuration, under a
+          specific address family";
+
+        leaf safi-name {
+          // do we need to specify which SAFIs are possible within
+          // each AF? with the current set  of AF/SAFI, all are
+          /// applicable
+          type identityref {
+            base "safi-type";
+          }
+          description
+            "Within each address family, subsequent address family
+            names are drawn from the subsequent-address-family base
+            identity";
+        } 
+   
+
+        container prefix-limit {
+          description
+          "Configure the maximum number of prefixes that will be
+          accepted from a peer";
+
+          leaf max-prefixes {
+            type uint32;
+            description
+              "Maximum number of prefixes that will be accepted from
+              the neighbor";
+          }
+
+          leaf shutdown-threshold-pct {
+            type percentage;
+            description
+              "Threshold on number of prefixes that can be received
+              from a neighbor before generation of warning messages
+              or log entries.  Expressed as a percentage of
+              max-prefixes.";
+          }
+
+          leaf restart-timer {
+            type decimal64 {
+              fraction-digits 2;
+            }
+            units "seconds";
+            description
+              "Time interval in seconds after which the BGP session
+              is reestablished after being torn down due to exceeding
+              the max-prefixes limit.";
+          }
+        }
+       }
+    }
+  }
+
+
+
+  container bgp {
+    description "Top-level configuration data for the BGP router";
+
+    container global {
+      description
+        "Top-level bgp protocol options applied across peer-groups,
+        neighbors, and address families";
+
+      leaf as {
+        type inet:as-number;
+        mandatory "true";
+        description
+          "Local autonomous system number of the router.  Uses 
+          the as-number type defined in RFC 6991";
+      }
+      leaf router-id {
+        type inet:ipv4-address;
+        description
+          "Router id of the router, expressed as an
+          IPv4 address";
+          // there is a typedef for this in draft module ietf-routing
+          // but it does not use an appropriate type
+      }
+      container route-selection-options {
+        description
+          "Set of configuration options that govern best
+          path selection";
+        leaf always-compare-med {
+          type boolean;
+          default "false";
+          description
+            "Compare multi-exit discriminator (MED) value from 
+            different ASes when selecting the best route.  The
+            default behavior is to only compare MEDs for paths
+            received from the same AS.";
+        }
+        leaf ignore-as-path {
+          type boolean;
+          default "false";
+          description
+            "Ignore the AS path length when selecting the best path.
+            The default is to use the AS path length and prefer paths
+            with shorter length.";
+        }
+        leaf external-compare-router-id {
+          type boolean;
+          default "true";
+          description
+            "When comparing similar routes received from external
+            BGP peers, use the router-id as a criterion to select 
+            the active path.  The default is to use the router-id to
+            select among similar routes.";
+        }
+        leaf advertise-inactive-routes {
+          type boolean;
+          default "false";
+          description
+            "Advertise inactive routes to external peers.  The
+            default is to only advertise active routes.";
+        }
+      }
+      container default-route-distance {
+        description
+          "Administrative distance (or preference) assigned to
+          routes received from different sources
+          (external, internal, and local.)";
+        leaf external-route-distance {
+          type uint8 {
+            range "1..255";
+          }
+          description
+            "Administrative distance for routes learned from external
+            BGP (eBGP)";
+        }
+        leaf internal-route-distance {
+          type uint8 {
+            range "1..255";
+          }
+          description
+            "Administrative distance for routes learned from internal
+            BGP (iBGP)";
+
+        }
+      }
+    }
+
+    uses bgp-address-family-common-configuration;
+
+    list peer-group {
+      key "group-name";
+      description
+        "List of peer-groups, uniquely identified by the peer group
+        names";
+      leaf group-name {
+        type string;
+        description "Name of the peer group";
+      }
+      leaf group-type {
+        type peer-group-type;
+        description
+          "Explicitly designate the peer group as internal (iBGP)
+          or external (eBGP)";
+      }
+      uses bgp-common-configuration;
+      uses bgp-address-family-common-configuration;
+      uses bgp-group-neighbor-common-configuration;
+    }
+
+    list neighbor {
+      key "neighbor-address";
+      description
+        "List of BGP peers, uniquely identified by neighbor address";
+      leaf neighbor-address {
+        type inet:ip-address;
+        description
+          "Address of the BGP peer, either IPv4 or IPv6";
+      }
+
+      leaf peer-as {
+        type inet:as-number;
+        mandatory "true";
+        description
+          "AS number of the peer";
+
+      }
+      uses bgp-common-configuration;
+      uses bgp-address-family-common-configuration;
+      uses bgp-group-neighbor-common-configuration;
+    }
+
+  }
+}`

src/webui/internal/goyang/pkg/yang/camelcase.go

@@ -0,0 +1,94 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+var knownWords = map[string]string{
+	"Ietf": "IETF",
+}
+
+// Is c an ASCII lower-case letter?
+func isASCIILower(c byte) bool {
+	return 'a' <= c && c <= 'z'
+}
+
+// Is c an ASCII digit?
+func isASCIIDigit(c byte) bool {
+	return '0' <= c && c <= '9'
+}
+
+// CamelCase returns a CamelCased name for a YANG identifier.
+// Currently this supports the output being used for a Go or proto identifier.
+// Dash and dot are first converted to underscore, and then any underscores
+// before a lower-case letter are removed, and the letter converted to
+// upper-case. Any input characters not part of the YANG identifier
+// specification (https://tools.ietf.org/html/rfc7950#section-6.2) are treated
+// as lower-case characters.
+// The first letter is always upper-case in order to be an exported name in Go.
+// There is a remote possibility of this rewrite causing a name collision, but
+// it's so remote we're prepared to pretend it's nonexistent - since the C++
+// generator lowercases names, it's extremely unlikely to have two fields with
+// different capitalizations. In short, _my_field-name_2 becomes XMyFieldName_2.
+func CamelCase(s string) string {
+	if s == "" {
+		return ""
+	}
+
+	fix := func(c byte) byte {
+		if c == '-' || c == '.' {
+			return '_'
+		}
+		return c
+	}
+
+	t := make([]byte, 0, 32)
+	i := 0
+	if fix(s[0]) == '_' {
+		// Need a capital letter; drop the '_'.
+		t = append(t, 'X')
+		i++
+	}
+
+	// Invariant: if the next letter is lower case, it must be converted
+	// to upper case.
+	// That is, we process a word at a time, where words are marked by _ or
+	// upper case letter. Digits are treated as words.
+	for ; i < len(s); i++ {
+		c := fix(s[i])
+		if c == '_' && i+1 < len(s) && isASCIILower(s[i+1]) {
+			continue // Skip the underscore in s.
+		}
+		if isASCIIDigit(c) {
+			t = append(t, c)
+			continue
+		}
+		// Assume we have a letter now - if not, it's a bogus identifier.
+		// The next word is a sequence of characters that must start upper case.
+		if isASCIILower(c) {
+			c ^= ' ' // Make it a capital letter.
+		}
+		start := len(t)
+		t = append(t, c) // Guaranteed not lower case.
+		// Accept lower case sequence that follows.
+		for i+1 < len(s) && isASCIILower(s[i+1]) {
+			i++
+			t = append(t, s[i])
+		}
+		// If the word turns out to be a special word, then use that instead.
+		if kn := knownWords[string(t[start:])]; kn != "" {
+			t = append(t[:start], []byte(kn)...)
+		}
+	}
+	return string(t)
+}

src/webui/internal/goyang/pkg/yang/camelcase_test.go

@@ -0,0 +1,53 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"testing"
+)
+
+func TestCamelCase(t *testing.T) {
+	tests := []struct {
+		in, want string
+	}{
+		{"one", "One"},
+		{"one_two", "OneTwo"},
+		{"__one__two__three__four", "XOne_Two_Three_Four"},
+		{"one.two.three", "OneTwoThree"},
+		{"one.two.three.", "OneTwoThree_"},
+		{"_my_field_name_2", "XMyFieldName_2"},
+		{"Something_Capped", "Something_Capped"},
+		{"_Foo-bar", "XFooBar"},
+		{"my_Name", "My_Name"},
+		{"OneTwo", "OneTwo"},
+		{"_", "X"},
+		{"_a_", "XA_"},
+		{"ietf-interface", "IETFInterface"},
+		{"ietf-interface-1", "IETFInterface_1"},
+		{"out-unicast.pkts", "OutUnicastPkts"},
+		// Invalid input conversion behaviours:
+		{"one/two", "One/two"},
+		{"/one/two", "/one/two"},
+		{"one:two", "One:two"},
+		{"::one::two", "::one::two"},
+		{"one|two", "One|two"},
+		{"one||two", "One||two"},
+	}
+	for _, tc := range tests {
+		if got := CamelCase(tc.in); got != tc.want {
+			t.Errorf("CamelCase(%q) = %q, want %q", tc.in, got, tc.want)
+		}
+	}
+}

src/webui/internal/goyang/pkg/yang/doc.go

@@ -0,0 +1,48 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package yang is used to parse .yang files (see RFC 6020).
+//
+// A generic yang statements takes one of the forms:
+//
+//	keyword [argument] ;
+//	keyword [argument] { [statement [...]] }
+//
+// At the lowest level, package yang returns a simple tree of statements via the
+// Parse function.  The Parse function makes no attempt to determine the
+// validity of the source, other than checking for generic syntax errors.
+//
+// At it's simplest, the GetModule function is used.  The GetModule function
+// searches the current directory, and any directory added to the Path variable,
+// for a matching .yang source file by appending .yang to the name of the
+// module:
+//
+//	// Get the tree for the module module-name by looking for the source
+//	// file named module-name.yang.
+//	e, errs := yang.GetModule("module-name" [, optional sources...])
+//	if len(errs) > 0 {
+//		for _, err := range errs {
+//			fmt.Fprintln(os.Stderr, err)
+//		}
+//		os.Exit(1)
+//	}
+//
+//	// e is the Entry tree for "module-name"
+//
+// More complicated uses cases should use NewModules and then some combination
+// of Modules.GetModule, Modules.Read, Modules.Parse, and Modules.GetErrors.
+//
+// The GetErrors method is mandatory, however, both yang.GetModule and
+// Modules.GetModule automatically call Modules.GetErrors.
+package yang

src/webui/internal/goyang/pkg/yang/file.go

@@ -0,0 +1,167 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+)
+
+var (
+	// revisionDateSuffixRegex matches on the revision-date portion of a YANG
+	// file's name.
+	revisionDateSuffixRegex = regexp.MustCompile(`^@\d{4}-\d{2}-\d{2}\.yang$`)
+)
+
+// PathsWithModules returns all paths under and including the
+// root containing files with a ".yang" extension, as well as
+// any error encountered
+func PathsWithModules(root string) (paths []string, err error) {
+	pm := map[string]bool{}
+	filepath.Walk(root, func(p string, info os.FileInfo, e error) error {
+		err = e
+		if err == nil {
+			if info == nil {
+				return nil
+			}
+			if !info.IsDir() && strings.HasSuffix(p, ".yang") {
+				dir := filepath.Dir(p)
+				if !pm[dir] {
+					pm[dir] = true
+					paths = append(paths, dir)
+				}
+			}
+			return nil
+		}
+		return err
+	})
+	return
+}
+
+// AddPath adds the directories specified in p, a colon separated list
+// of directory names, to Path, if they are not already in Path. Using
+// multiple arguments is also supported.
+func (ms *Modules) AddPath(paths ...string) {
+	for _, path := range paths {
+		for _, p := range strings.Split(path, ":") {
+			if !ms.pathMap[p] {
+				ms.pathMap[p] = true
+				ms.Path = append(ms.Path, p)
+			}
+		}
+	}
+}
+
+// readFile makes testing of findFile easier.
+var readFile = ioutil.ReadFile
+
+// scanDir makes testing of findFile easier.
+var scanDir = findInDir
+
+// findFile returns the name and contents of the .yang file associated with
+// name, or an error.  If name is a module name rather than a file name (it does
+// not have a .yang extension and there is no / in name), .yang is appended to
+// the the name.  The directory that the .yang file is found in is added to Path
+// if not already in Path. If a file is not found by exact match, directories
+// are scanned for "name@revision-date.yang" files, the latest (sorted by
+// YYYY-MM-DD revision-date) of these will be selected.
+//
+// If a path has the form dir/... then dir and all direct or indirect
+// subdirectories of dir are searched.
+//
+// The current directory (.) is always checked first, no matter the value of
+// Path.
+func (ms *Modules) findFile(name string) (string, string, error) {
+	slash := strings.Index(name, "/")
+	if slash < 0 && !strings.HasSuffix(name, ".yang") {
+		name += ".yang"
+		if best := scanDir(".", name, false); best != "" {
+			// we found a matching candidate in the local directory
+			name = best
+		}
+	}
+
+	switch data, err := readFile(name); true {
+	case err == nil:
+		ms.AddPath(filepath.Dir(name))
+		return name, string(data), nil
+	case slash >= 0:
+		// If there are any /'s in the name then don't search Path.
+		return "", "", fmt.Errorf("no such file: %s", name)
+	}
+
+	for _, dir := range ms.Path {
+		var n string
+		if filepath.Base(dir) == "..." {
+			n = scanDir(filepath.Dir(dir), name, true)
+		} else {
+			n = scanDir(dir, name, false)
+		}
+		if n == "" {
+			continue
+		}
+		if data, err := readFile(n); err == nil {
+			return n, string(data), nil
+		}
+	}
+	return "", "", fmt.Errorf("no such file: %s", name)
+}
+
+// findInDir looks for a file named name in dir or any of its subdirectories if
+// recurse is true. if recurse is false, scan only the directory dir.
+// If no matching file is found, an empty string is returned.
+//
+// The file SHOULD have the following name, per
+// https://tools.ietf.org/html/rfc7950#section-5.2:
+// module-or-submodule-name ['@' revision-date] '.yang'
+// where revision-date = 4DIGIT "-" 2DIGIT "-" 2DIGIT
+//
+// If a perfect name match is found, then that file's path is returned.
+// Else if file(s) with otherwise matching names but which contain a
+// revision-date pattern exactly matching the above are found, then path of the
+// one with the latest date is returned.
+func findInDir(dir, name string, recurse bool) string {
+	fis, err := ioutil.ReadDir(dir)
+	if err != nil {
+		return ""
+	}
+
+	var revisions []string
+	mname := strings.TrimSuffix(name, ".yang")
+	for _, fi := range fis {
+		switch {
+		case !fi.IsDir():
+			if fn := fi.Name(); fn == name {
+				return filepath.Join(dir, name)
+			} else if strings.HasPrefix(fn, mname) && revisionDateSuffixRegex.MatchString(strings.TrimPrefix(fn, mname)) {
+				revisions = append(revisions, fn)
+			}
+		case recurse:
+			if n := findInDir(filepath.Join(dir, fi.Name()), name, recurse); n != "" {
+				return n
+			}
+		}
+	}
+	if len(revisions) == 0 {
+		return ""
+	}
+	sort.Strings(revisions)
+	return filepath.Join(dir, revisions[len(revisions)-1])
+}

src/webui/internal/goyang/pkg/yang/file_test.go

@@ -0,0 +1,166 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"errors"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func TestFindFile(t *testing.T) {
+	sep := string(os.PathSeparator)
+
+	for _, tt := range []struct {
+		name  string
+		path  []string
+		check []string
+	}{
+		{
+			name:  "one",
+			check: []string{"one.yang"},
+		},
+		{
+			name:  "./two",
+			check: []string{"./two"},
+		},
+		{
+			name:  "three.yang",
+			check: []string{"three.yang"},
+		},
+		{
+			name:  "four",
+			path:  []string{"dir1", "dir2"},
+			check: []string{"four.yang", "dir1" + sep + "four.yang", "dir2" + sep + "four.yang"},
+		},
+	} {
+		var checked []string
+		ms := NewModules()
+		ms.Path = tt.path
+		readFile = func(path string) ([]byte, error) {
+			checked = append(checked, path)
+			return nil, errors.New("no such file")
+		}
+		scanDir = func(dir, name string, recurse bool) string {
+			return filepath.Join(dir, name)
+		}
+		if _, _, err := ms.findFile(tt.name); err == nil {
+			t.Errorf("%s unexpectedly succeeded", tt.name)
+			continue
+		}
+		if !reflect.DeepEqual(tt.check, checked) {
+			t.Errorf("%s: got %v, want %v", tt.name, checked, tt.check)
+		}
+	}
+}
+
+func TestScanForPathsAndAddModules(t *testing.T) {
+	// disable any readFile mock setup by other tests
+	readFile = ioutil.ReadFile
+
+	// Scan the directory tree for YANG modules
+	paths, err := PathsWithModules("../../testdata")
+	if err != nil {
+		t.Fatal(err)
+	}
+	// we should have seen two directories being testdata and
+	// testdata/subdir.
+	if len(paths) != 2 {
+		t.Errorf("got %d paths imported, want 2", len(paths))
+	}
+	ms := NewModules()
+	// add the paths found in the scan to the module path
+	ms.AddPath(paths...)
+
+	// confirm we can load the four modules that exist in
+	// the two paths we scanned.
+	modules := []string{"aug", "base", "other", "subdir1"}
+	for _, name := range modules {
+		if _, err := ms.GetModule(name); err != nil {
+			t.Errorf("getting %s: %v", name, err)
+		}
+	}
+
+	// however, a sub module is not a valid argument to GetModule.
+	if _, err := ms.GetModule("sub"); err == nil {
+		t.Error("want an error when loading 'sub', got nil")
+	}
+
+}
+
+func TestFindInDir(t *testing.T) {
+	testDir := "testdata/find-file-test"
+
+	tests := []struct {
+		desc      string
+		inDir     string
+		inName    string
+		inRecurse bool
+		want      string
+	}{{
+		desc:      "file not found",
+		inDir:     testDir,
+		inName:    "green.yang",
+		inRecurse: true,
+		want:      "",
+	}, {
+		desc:      "input directory does not exist",
+		inDir:     filepath.Join(testDir, "dne"),
+		inName:    "red.yang",
+		inRecurse: true,
+		want:      "",
+	}, {
+		desc:      "exact match",
+		inDir:     testDir,
+		inName:    "blue.yang",
+		inRecurse: false,
+		want:      filepath.Join(testDir, "blue.yang"),
+	}, {
+		desc:      "exact match, recursive",
+		inDir:     testDir,
+		inName:    "blue.yang",
+		inRecurse: true,
+		want:      filepath.Join(testDir, "blue.yang"),
+	}, {
+		desc:      "exact match with non-standard name",
+		inDir:     testDir,
+		inName:    "non-standard.name",
+		inRecurse: false,
+		want:      filepath.Join(testDir, "non-standard.name"),
+	}, {
+		desc:      "revision match without recursion, and ignoring invalid revision",
+		inDir:     testDir,
+		inName:    "red.yang",
+		inRecurse: false,
+		want:      filepath.Join(testDir, "red@2010-10-10.yang"),
+	}, {
+		desc:      "revision match with recursion",
+		inDir:     testDir,
+		inName:    "red.yang",
+		inRecurse: true,
+		want:      filepath.Join(testDir, "dir", "dirdir", "red@2022-02-22.yang"),
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			if got, want := findInDir(tt.inDir, tt.inName, tt.inRecurse), tt.want; got != want {
+				t.Errorf("got: %q, want: %q", got, want)
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yang/find.go

@@ -0,0 +1,96 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This file has functions that search the AST for specified nodes.
+
+import (
+	"reflect"
+	"strings"
+)
+
+// localPrefix returns the local prefix used by the containing (sub)module to
+// refer to its own module.
+func localPrefix(n Node) string {
+	return RootNode(n).GetPrefix()
+}
+
+// trimLocalPrefix trims the current module's prefix from the given name. If the
+// name is not prefixed with the local module's prefix or is unprefixed
+// entirely, then the same string is returned unchanged.
+func trimLocalPrefix(n Node, name string) string {
+	pfx := localPrefix(n)
+	if pfx != "" {
+		pfx += ":"
+	}
+	return strings.TrimPrefix(name, pfx)
+}
+
+// FindGrouping finds the grouping named name according to YANG namespace rules
+// using the input node as the initial context node. The seen parameter
+// provides a list of the modules previously seen by FindGrouping during
+// traversal. If the named grouping cannot be found, nil is returned.
+//
+// FindGrouping works by recursively looking through the context node's parent
+// nodes for grouping fields, or in included or imported submodules/modules for
+// externally-defined groupings. Note that any prefix in the name must match
+// the module prefix of its import statement in the context node's module.
+func FindGrouping(n Node, name string, seen map[string]bool) *Grouping {
+	name = trimLocalPrefix(n, name)
+	for n != nil {
+		// Grab the Grouping field of the underlying structure.  n is
+		// always a pointer to a structure,
+		e := reflect.ValueOf(n).Elem()
+		v := e.FieldByName("Grouping")
+		if v.IsValid() {
+			for _, g := range v.Interface().([]*Grouping) {
+				if g.Name == name {
+					return g
+				}
+			}
+		}
+		v = e.FieldByName("Import")
+		if v.IsValid() {
+			for _, i := range v.Interface().([]*Import) {
+				// If the prefix matches the import statement,
+				// then search for the trimmed name in that module.
+				pname := strings.TrimPrefix(name, i.Prefix.Name+":")
+				if pname == name {
+					continue
+				}
+				if g := FindGrouping(i.Module, pname, seen); g != nil {
+					return g
+				}
+			}
+		}
+		v = e.FieldByName("Include")
+		if v.IsValid() {
+			for _, i := range v.Interface().([]*Include) {
+				if seen[i.Module.Name] {
+					// Prevent infinite loops in the case that we have already looked at
+					// this submodule. This occurs where submodules have include statements
+					// in them, or there is a circular dependency.
+					continue
+				}
+				seen[i.Module.Name] = true
+				if g := FindGrouping(i.Module, name, seen); g != nil {
+					return g
+				}
+			}
+		}
+		n = n.ParentNode()
+	}
+	return nil
+}

src/webui/internal/goyang/pkg/yang/find_test.go

@@ -0,0 +1,358 @@
+package yang
+
+import (
+	"testing"
+)
+
+func TestFindGrouping(t *testing.T) {
+	tests := []struct {
+		desc              string
+		inMods            map[string]string
+		inNode            func(*Modules) (Node, error)
+		inName            string
+		wantGroupNodePath string
+		// wantCannotFound indicates that the grouping cannot be found.
+		wantCannotFound bool
+	}{{
+		desc: "grouping within module",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } }
+
+					container c { leaf b { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "c")
+		},
+		inName:            "g",
+		wantGroupNodePath: "/dev/g",
+	}, {
+		desc: "nested grouping within module",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { grouping gg { leaf a { type string; } } uses gg; }
+
+					container c { leaf b { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "g")
+		},
+		inName:            "gg",
+		wantGroupNodePath: "/dev/g/gg",
+	}, {
+		desc: "grouping that uses another grouping both within the same module",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping gg { leaf a { type string; } }
+
+					grouping g { uses gg; }
+
+					container c { leaf b { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "g")
+		},
+		inName:            "gg",
+		wantGroupNodePath: "/dev/gg",
+	}, {
+		desc: "grouping in included submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					container c { leaf b { type string; } }
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "c")
+		},
+		inName:            "g",
+		wantGroupNodePath: "/sys/g",
+	}, {
+		desc: "grouping in indirectly-included submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container c { leaf b { type string; } }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+					include sysdb;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sysdb": `
+				submodule sysdb {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "c")
+		},
+		inName:            "g",
+		wantGroupNodePath: "/sysdb/g",
+	}, {
+		desc: "grouping in indirectly-included submodule with node in submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+					include sysdb;
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container c { leaf b { type string; } }
+				}`,
+			"sysdb": `
+				submodule sysdb {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.SubModules["sys"], "c")
+		},
+		inName:            "g",
+		wantGroupNodePath: "/sysdb/g",
+	}, {
+		desc: "grouping in submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					import sysdb { prefix "s"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container c { leaf b { type string; } uses s:g; }
+				}`,
+			"sysdb": `
+				module sysdb {
+					prefix sd;
+					namespace "urn:sd";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "c")
+		},
+		inName:            "s:g",
+		wantGroupNodePath: "/sysdb/g",
+	}, {
+		desc: "grouping that uses another grouping both in different modules",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					import dev2 { prefix "de2"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container c { leaf l { type string; } uses de2:g; }
+				}`,
+			"dev2": `
+				module dev2 {
+					prefix d2;
+					namespace "urn:d2";
+					import dev3 { prefix "de3"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } uses de3:gg; }
+				}`,
+			"dev3": `
+				module dev3 {
+					prefix d3;
+					namespace "urn:d3";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping gg { leaf b { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev2"], "g")
+		},
+		inName:            "de3:gg",
+		wantGroupNodePath: "/dev3/gg",
+	}, {
+		desc: "grouping that uses another grouping both in different modules but prefix is wrong",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					import dev2 { prefix "de2"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container c { leaf l { type string; } uses de2:g; }
+				}`,
+			"dev2": `
+				module dev2 {
+					prefix d2;
+					namespace "urn:d2";
+					import dev3 { prefix "de3"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } uses de3:gg; }
+				}`,
+			"dev3": `
+				module dev3 {
+					prefix dev3;
+					namespace "urn:dev3";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping gg { leaf b { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev2"], "g")
+		},
+		inName:          "d3:gg",
+		wantCannotFound: true,
+	}, {
+		desc: "grouping that uses another grouping both in different modules but uses wrong context node",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					import dev2 { prefix "de2"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container c { leaf l { type string; } uses de2:g; }
+				}`,
+			"dev2": `
+				module dev2 {
+					prefix d2;
+					namespace "urn:d2";
+					import dev3 { prefix "dev3"; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping g { leaf a { type string; } uses dev3:gg; }
+				}`,
+			"dev3": `
+				module dev3 {
+					prefix dev3;
+					namespace "urn:dev3";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					grouping gg { leaf b { type string; } }
+				}`,
+		},
+		inNode: func(ms *Modules) (Node, error) {
+			return FindNode(ms.Modules["dev"], "c")
+		},
+		inName:          "dev3:gg",
+		wantCannotFound: true,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ms := NewModules()
+
+			for n, m := range tt.inMods {
+				if err := ms.Parse(m, n); err != nil {
+					t.Fatalf("cannot parse module %s, err: %v", n, err)
+				}
+			}
+
+			if errs := ms.Process(); errs != nil {
+				t.Fatalf("cannot process modules: %v", errs)
+			}
+
+			seen := map[string]bool{}
+			node, err := tt.inNode(ms)
+			if err != nil {
+				t.Fatalf("cannot find input node: %v", err)
+			}
+			g := FindGrouping(node, tt.inName, seen)
+			if got, want := g == nil, tt.wantCannotFound; got != want {
+				t.Fatalf("got grouping: %v, wantCannotFound: %v", got, want)
+			}
+			if tt.wantCannotFound {
+				return
+			}
+			if got, want := NodePath(g), tt.wantGroupNodePath; got != want {
+				t.Errorf("found grouping path doesn't match expected, got: %s, want: %s", got, want)
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yang/identity.go

@@ -0,0 +1,192 @@
+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"fmt"
+	"sort"
+	"sync"
+)
+
+// This file implements data structures and functions that relate to the
+// identity type.
+
+// identityDictionary stores a set of identities across all parsed Modules that
+// have been resolved to be identified by their module and name.
+type identityDictionary struct {
+	mu sync.Mutex
+	// dict is a global cache of identities keyed by
+	// modulename:identityname, where modulename is the full name of the
+	// module to which the identity belongs. If the identity were defined
+	// in a submodule, then the parent module name is used instead.
+	dict map[string]resolvedIdentity
+}
+
+// resolvedIdentity is an Identity that has been disambiguated.
+type resolvedIdentity struct {
+	Module   *Module
+	Identity *Identity
+}
+
+// isEmpty determines whether the resolvedIdentity struct value is populated.
+func (r resolvedIdentity) isEmpty() bool {
+	return r.Module == nil && r.Identity == nil
+}
+
+// newResolvedIdentity creates a resolved identity from an identity and its
+// associated module, and returns the prefixed name (Prefix:IdentityName)
+// along with the resolved identity.
+func newResolvedIdentity(m *Module, i *Identity) (string, *resolvedIdentity) {
+	r := &resolvedIdentity{
+		Module:   m,
+		Identity: i,
+	}
+	return i.modulePrefixedName(), r
+}
+
+func appendIfNotIn(ids []*Identity, chk *Identity) []*Identity {
+	for _, id := range ids {
+		if id == chk {
+			return ids
+		}
+	}
+	return append(ids, chk)
+}
+
+// addChildren adds identity r and all of its children to ids
+// deterministically.
+func addChildren(r *Identity, ids []*Identity) []*Identity {
+	ids = appendIfNotIn(ids, r)
+
+	// Iterate through the values of r.
+	for _, ch := range r.Values {
+		ids = addChildren(ch, ids)
+	}
+	return ids
+}
+
+// findIdentityBase returns the resolved identity that is corresponds to the
+// baseStr string in the context of the module/submodule mod.
+func (mod *Module) findIdentityBase(baseStr string) (*resolvedIdentity, []error) {
+	var base resolvedIdentity
+	var ok bool
+	var errs []error
+
+	basePrefix, baseName := getPrefix(baseStr)
+	rootPrefix := mod.GetPrefix()
+	source := Source(mod)
+	typeDict := mod.Modules.typeDict
+
+	switch basePrefix {
+	case "", rootPrefix:
+		// This is a local identity which is defined within the current
+		// module
+		keyName := fmt.Sprintf("%s:%s", module(mod).Name, baseName)
+		base, ok = typeDict.identities.dict[keyName]
+		if !ok {
+			errs = append(errs, fmt.Errorf("%s: can't resolve the local base %s as %s", source, baseStr, keyName))
+		}
+	default:
+		// This is an identity which is defined within another module
+		extmod := FindModuleByPrefix(mod, basePrefix)
+		if extmod == nil {
+			errs = append(errs,
+				fmt.Errorf("%s: can't find external module with prefix %s", source, basePrefix))
+			break
+		}
+		// The identity we are looking for is modulename:basename.
+		if id, ok := typeDict.identities.dict[fmt.Sprintf("%s:%s", module(extmod).Name, baseName)]; ok {
+			base = id
+			break
+		}
+
+		// Error if we did not find the identity that had the name specified in
+		// the module it was expected to be in.
+		if base.isEmpty() {
+			errs = append(errs, fmt.Errorf("%s: can't resolve remote base %s", source, baseStr))
+		}
+	}
+	return &base, errs
+}
+
+func (ms *Modules) resolveIdentities() []error {
+	defer ms.typeDict.identities.mu.Unlock()
+	ms.typeDict.identities.mu.Lock()
+
+	var errs []error
+
+	// Across all modules, read the identity values that have been extracted
+	// from them, and compile them into a "fully resolved" map that means that
+	// we can look them up based on the 'real' prefix of the module and the
+	// name of the identity.
+	for _, mod := range ms.Modules {
+		for _, i := range mod.Identities() {
+			keyName, r := newResolvedIdentity(mod, i)
+			ms.typeDict.identities.dict[keyName] = *r
+		}
+
+		// Hoist up all identities in our included submodules.
+		// We could just do a range on ms.SubModules, but that
+		// might process a submodule that no module included.
+		for _, in := range mod.Include {
+			if in.Module == nil {
+				continue
+			}
+			for _, i := range in.Module.Identities() {
+				keyName, r := newResolvedIdentity(in.Module, i)
+				ms.typeDict.identities.dict[keyName] = *r
+			}
+		}
+	}
+
+	// Now, we want to create for all identities a view of all of their children.
+	// A child identity here means an inherited identity.
+	//
+	// We start by finding the direct children of all identities using the
+	// 'base' statement.
+	for _, i := range ms.typeDict.identities.dict {
+		if i.Identity.Base != nil {
+			// This identity inherits from one or more other identities.
+
+			root := RootNode(i.Identity)
+			for _, b := range i.Identity.Base {
+				base, baseErr := root.findIdentityBase(b.asString())
+
+				if baseErr != nil {
+					errs = append(errs, baseErr...)
+					continue
+				}
+
+				// Build up a list of direct children of this identity.
+				base.Identity.Values = append(base.Identity.Values, i.Identity)
+			}
+		}
+	}
+
+	// Now, we can find all transitive identities by recursively populating
+	// the children of each identity.
+	for _, i := range ms.typeDict.identities.dict {
+		newValues := []*Identity{}
+		for _, j := range i.Identity.Values {
+			newValues = addChildren(j, newValues)
+		}
+		sort.SliceStable(newValues, func(j, k int) bool {
+			return newValues[j].Name < newValues[k].Name
+		})
+		i.Identity.Values = newValues
+	}
+
+	return errs
+}

src/webui/internal/goyang/pkg/yang/identity_test.go

@@ -0,0 +1,802 @@
+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/openconfig/gnmi/errdiff"
+)
+
+// inputModule is a mock input YANG module.
+type inputModule struct {
+	name    string // The filename of the YANG module.
+	content string // The contents of the YANG module.
+}
+
+type idrefOut struct {
+	module string   // The module that the identityref is within.
+	name   string   // The name of the identityref.
+	values []string // Names of the identities that the identityref relates to.
+}
+
+// identityOut is the output for a particular identity within the test case.
+type identityOut struct {
+	module    string   // The module that the identity is within.
+	name      string   // The name of the identity.
+	baseNames []string // The base(s) of the identity as string(s).
+	values    []string // The string names of derived identities.
+}
+
+// identityTestCase is a test case for a module which contains identities.
+type identityTestCase struct {
+	name          string
+	in            []inputModule // The set of input modules for the test
+	identities    []identityOut // Slice of the identity values expected
+	idrefs        []idrefOut    // Slice of identityref results expected
+	wantErrSubstr string        // wanErrSubstr is a substring of the wanted error.
+}
+
+// getBaseNamesFrom is a utility function for getting the base name(s) of an identity
+func getBaseNamesFrom(i *Identity) []string {
+	baseNames := []string{}
+	for _, base := range i.Base {
+		baseNames = append(baseNames, base.Name)
+	}
+	return baseNames
+}
+
+// Test cases for basic identity extraction.
+var basicTestCases = []identityTestCase{
+	{
+		name: "basic-test-case-1: Check identity is found in module.",
+		in: []inputModule{
+			{
+				name: "idtest-one",
+				content: `
+					module idtest-one {
+					  namespace "urn:idone";
+					  prefix "idone";
+
+					  identity TEST_ID;
+					}
+				`},
+		},
+		identities: []identityOut{
+			{module: "idtest-one", name: "TEST_ID"},
+		},
+	},
+	{
+		name: "basic-test-case-2: Check identity with base is found in module.",
+		in: []inputModule{
+			{
+				name: "idtest-two",
+				content: `
+					module idtest-two {
+					  namespace "urn:idtwo";
+					  prefix "idone";
+
+					  identity TEST_ID;
+					  identity TEST_ID_TWO;
+					  identity TEST_CHILD {
+					    base TEST_ID;
+					  }
+					}
+				`},
+		},
+		identities: []identityOut{
+			{module: "idtest-two", name: "TEST_ID"},
+			{module: "idtest-two", name: "TEST_ID_TWO"},
+			{module: "idtest-two", name: "TEST_CHILD", baseNames: []string{"TEST_ID"}},
+		},
+	},
+	{
+		name: "basic-test-case-3: Check identity with multiple bases.",
+		in: []inputModule{
+			{
+				name: "idtest-three",
+				content: `
+					module idtest-three {
+					  namespace "urn:idthree";
+					  prefix "idthree";
+
+					  identity BASE_ONE;
+					  identity BASE_TWO;
+					  identity TEST_CHILD_WITH_MULTIPLE_BASES {
+						base BASE_ONE;
+						base BASE_TWO;
+					  }
+					}
+				`},
+		},
+		identities: []identityOut{
+			{module: "idtest-three", name: "BASE_ONE"},
+			{module: "idtest-three", name: "BASE_TWO"},
+			{module: "idtest-three", name: "TEST_CHILD_WITH_MULTIPLE_BASES", baseNames: []string{"BASE_ONE", "BASE_TWO"}},
+		},
+	},
+	{
+		name: "basic-test-case-4: Check identity base is found from submodule.",
+		in: []inputModule{
+			{
+				name: "idtest-one",
+				content: `
+					module idtest-one {
+					  namespace "urn:idone";
+					  prefix "idone";
+
+					  include "idtest-one-sub";
+
+					  identity TEST_ID_DERIVED {
+					    base TEST_ID;
+					  }
+					}
+				`},
+			{
+				name: "idtest-one-sub",
+				content: `
+					submodule idtest-one-sub {
+					  belongs-to idtest-one {
+					    prefix "idone";
+					  }
+
+					  identity TEST_ID;
+					}
+				`},
+		},
+		identities: []identityOut{
+			{module: "idtest-one", name: "TEST_ID"},
+			{module: "idtest-one", name: "TEST_ID_DERIVED", baseNames: []string{"TEST_ID"}},
+		},
+	},
+	{
+		name: "basic-test-case-5: Check identity base is found from module.",
+		in: []inputModule{
+			{
+				name: "idtest-one",
+				content: `
+					module idtest-one {
+					  namespace "urn:idone";
+					  prefix "idone";
+
+					  include "idtest-one-sub";
+
+					  identity TEST_ID;
+					}
+				`},
+			{
+				name: "idtest-one-sub",
+				content: `
+					submodule idtest-one-sub {
+					  belongs-to idtest-one {
+					    prefix "idone";
+					  }
+
+					  identity TEST_ID_DERIVED {
+					    base TEST_ID;
+					  }
+					}
+				`},
+		},
+		identities: []identityOut{
+			{module: "idtest-one", name: "TEST_ID_DERIVED", baseNames: []string{"TEST_ID"}},
+			{module: "idtest-one", name: "TEST_ID"},
+		},
+	},
+}
+
+// Test the ability to extract identities from a module with the correct base
+// statements.
+func TestIdentityExtract(t *testing.T) {
+	for _, tt := range basicTestCases {
+		ms := NewModules()
+		for _, mod := range tt.in {
+			_ = ms.Parse(mod.content, mod.name)
+		}
+
+		for _, ti := range tt.identities {
+			_, err := ms.GetModule(ti.module)
+
+			if err != nil {
+				t.Errorf("Could not parse module : %s", ti.module)
+				continue
+			}
+
+			foundIdentity := false
+			var thisID *Identity
+			for _, ri := range ms.typeDict.identities.dict {
+				moduleName := module(ri.Module).Name
+				if ri.Identity.Name == ti.name && moduleName == ti.module {
+					foundIdentity = true
+					thisID = ri.Identity
+					break
+				}
+			}
+
+			if !foundIdentity {
+				t.Errorf("Could not find identity %s in module %s, identity dict:\n%+v", ti.name, ti.module, ms.typeDict.identities.dict)
+				continue
+			}
+
+			actualBaseNames := getBaseNamesFrom(thisID)
+			if len(ti.baseNames) > 0 {
+				if diff := cmp.Diff(actualBaseNames, ti.baseNames); diff != "" {
+					t.Errorf("(-got, +want):\n%s", diff)
+				}
+			} else {
+				if thisID.Base != nil {
+					t.Errorf("Identity %s had unexpected base(s) %s", thisID.Name,
+						actualBaseNames)
+				}
+			}
+		}
+	}
+}
+
+// Test cases for validating that identities can be resolved correctly.
+var treeTestCases = []identityTestCase{
+	{
+		name: "tree-test-case-0: Validate identity resolution across submodules",
+		in: []inputModule{
+			{
+				name: "base.yang",
+				content: `
+				  module base {
+				    namespace "urn:base";
+				    prefix "base";
+
+				    include side;
+
+				    identity REMOTE_BASE;
+				  }
+				`},
+			{
+				name: "remote.yang",
+				content: `
+				  submodule side {
+				    belongs-to base {
+				      prefix "r";
+				    }
+
+				    identity LOCAL_REMOTE_BASE {
+				      base r:REMOTE_BASE;
+				    }
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{
+				module: "base",
+				name:   "REMOTE_BASE",
+				values: []string{"LOCAL_REMOTE_BASE"},
+			},
+		},
+	},
+	{
+		name: "tree-test-case-1: Validate identity resolution across modules",
+		in: []inputModule{
+			{
+				name: "base.yang",
+				content: `
+				  module base {
+				    namespace "urn:base";
+				    prefix "base";
+
+				    import remote { prefix "r"; }
+				    import remote2 { prefix "r2"; }
+
+				    identity LOCAL_REMOTE_BASE {
+				      base r:REMOTE_BASE;
+				    }
+
+				    identity LOCAL_REMOTE_BASE2 {
+				      base r2:REMOTE_BASE2;
+				    }
+				  }
+				`},
+			{
+				name: "remote.yang",
+				content: `
+				  module remote {
+				    namespace "urn:remote";
+				    prefix "r";
+
+				    identity REMOTE_BASE;
+				  }
+				`},
+			{
+				name: "remote2.yang",
+				content: `
+				  module remote2 {
+				    namespace "urn:remote2";
+				    prefix "remote";
+
+				    identity REMOTE_BASE2;
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{
+				module: "remote",
+				name:   "REMOTE_BASE",
+				values: []string{"LOCAL_REMOTE_BASE"},
+			},
+			{
+				module: "remote2",
+				name:   "REMOTE_BASE2",
+				values: []string{"LOCAL_REMOTE_BASE2"},
+			},
+			{
+				module:    "base",
+				name:      "LOCAL_REMOTE_BASE",
+				baseNames: []string{"r:REMOTE_BASE"},
+			},
+			{
+				module:    "base",
+				name:      "LOCAL_REMOTE_BASE2",
+				baseNames: []string{"r2:REMOTE_BASE2"},
+			},
+		},
+	},
+	{
+		name: "tree-test-case-2: Multi-level inheritance validation.",
+		in: []inputModule{
+			{
+				name: "base.yang",
+				content: `
+				  module base {
+				    namespace "urn:base";
+				    prefix "base";
+
+				    identity GREATGRANDFATHER;
+						identity GRANDFATHER {
+							base "GREATGRANDFATHER";
+						}
+						identity FATHER {
+							base "GRANDFATHER";
+						}
+						identity SON {
+							base "FATHER";
+						}
+						identity UNCLE {
+							base "GRANDFATHER";
+						}
+						identity BROTHER {
+							base "FATHER";
+						}
+						identity GREATUNCLE {
+							base "GREATGRANDFATHER";
+						}
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{
+				module: "base",
+				name:   "GREATGRANDFATHER",
+				values: []string{
+					"BROTHER", // Order is alphabetical
+					"FATHER",
+					"GRANDFATHER",
+					"GREATUNCLE",
+					"SON",
+					"UNCLE",
+				},
+			},
+			{
+				module:    "base",
+				name:      "GRANDFATHER",
+				baseNames: []string{"GREATGRANDFATHER"},
+				values:    []string{"BROTHER", "FATHER", "SON", "UNCLE"},
+			},
+			{
+				module:    "base",
+				name:      "GREATUNCLE",
+				baseNames: []string{"GREATGRANDFATHER"},
+			},
+			{
+				module:    "base",
+				name:      "FATHER",
+				baseNames: []string{"GRANDFATHER"},
+				values:    []string{"BROTHER", "SON"},
+			},
+			{
+				module:    "base",
+				name:      "UNCLE",
+				baseNames: []string{"GRANDFATHER"},
+			},
+			{
+				module:    "base",
+				name:      "BROTHER",
+				baseNames: []string{"FATHER"},
+			},
+		},
+	},
+	{
+		name: "tree-test-case-3",
+		in: []inputModule{
+			{
+				name: "base.yang",
+				content: `
+				  module base {
+				    namespace "urn:base";
+				    prefix "base";
+
+						identity BASE;
+						identity NOTBASE {
+							base BASE;
+						}
+
+						leaf idref {
+							type identityref {
+								base "BASE";
+							}
+						}
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{
+				module: "base",
+				name:   "BASE",
+				values: []string{"NOTBASE"},
+			},
+			{
+				module:    "base",
+				name:      "NOTBASE",
+				baseNames: []string{"BASE"},
+			},
+		},
+		idrefs: []idrefOut{
+			{
+				module: "base",
+				name:   "idref",
+				values: []string{"NOTBASE"},
+			},
+		},
+	},
+	{
+		name: "tree-test-case-4",
+		in: []inputModule{
+			{
+				name: "base.yang",
+				content: `
+				  module base4 {
+				    namespace "urn:base";
+				    prefix "base4";
+
+						identity BASE4;
+						identity CHILD4 {
+							base BASE4;
+						}
+
+						typedef t {
+							type identityref {
+								base BASE4;
+							}
+						}
+
+						leaf tref {
+							type t;
+						}
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{
+				module: "base4",
+				name:   "BASE4",
+				values: []string{"CHILD4"},
+			},
+			{
+				module:    "base4",
+				name:      "CHILD4",
+				baseNames: []string{"BASE4"},
+			},
+		},
+		idrefs: []idrefOut{
+			{
+				module: "base4",
+				name:   "tref",
+				values: []string{"CHILD4"},
+			},
+		},
+	},
+	{
+		name: "tree-test-case-5",
+		in: []inputModule{
+			{
+				name: "base.yang",
+				content: `
+					module base5 {
+						namespace "urn:base";
+						prefix "base5";
+
+						identity BASE5A;
+						identity BASE5B;
+
+						identity FIVE_ONE {
+							base BASE5A;
+						}
+
+						identity FIVE_TWO {
+							base BASE5B;
+						}
+
+						leaf union {
+							type union {
+								type identityref {
+									base BASE5A;
+								}
+								type identityref {
+									base BASE5B;
+								}
+							}
+						}
+					}`},
+		},
+		identities: []identityOut{
+			{
+				module: "base5",
+				name:   "BASE5A",
+				values: []string{"FIVE_ONE"},
+			},
+			{
+				module: "base5",
+				name:   "BASE5B",
+				values: []string{"FIVE_TWO"},
+			},
+		},
+		idrefs: []idrefOut{
+			{
+				module: "base5",
+				name:   "union",
+				values: []string{"FIVE_ONE", "FIVE_TWO"},
+			},
+		},
+	},
+	{
+		name: "identity's base can't be found",
+		in: []inputModule{
+			{
+				name: "idtest",
+				content: `
+					module idtest{
+					  namespace "urn:idtwo";
+					  prefix "idone";
+
+					  identity TEST_ID_TWO;
+					  identity TEST_CHILD {
+					    base TEST_ID;
+					  }
+					}
+				`},
+		},
+		identities: []identityOut{
+			{module: "idtest", name: "TEST_ID2"},
+		},
+		wantErrSubstr: "can't resolve the local base",
+	},
+	{
+		name: "identity's base can't be found in remote",
+		in: []inputModule{
+			{
+				name: "remote.yang",
+				content: `
+				  module remote {
+				    namespace "urn:remote";
+				    prefix "remote";
+
+				    identity REMOTE_BASE_ESCAPE;
+				  }
+				`},
+			{
+				name: "base.yang",
+				content: `
+				  module base {
+				    namespace "urn:base";
+				    prefix "base";
+
+				    import remote { prefix "r"; }
+
+				    identity LOCAL_REMOTE_BASE {
+				      base r:REMOTE_BASE;
+				    }
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{module: "base", name: "LOCAL_REMOTE_BASE"},
+		},
+		wantErrSubstr: "can't resolve remote base",
+	},
+	{
+		name: "identity's base's module can't be found",
+		in: []inputModule{
+			{
+				name: "remote.yang",
+				content: `
+				  module remote {
+				    namespace "urn:remote";
+				    prefix "remote";
+
+				    identity REMOTE_BASE;
+				  }
+				`},
+			{
+				name: "base.yang",
+				content: `
+				  module base {
+				    namespace "urn:base";
+				    prefix "base";
+
+				    import remote { prefix "r"; }
+
+				    identity LOCAL_REMOTE_BASE {
+				      base roe:REMOTE_BASE;
+				    }
+				  }
+				`},
+		},
+		identities: []identityOut{
+			{module: "base", name: "LOCAL_REMOTE_BASE"},
+		},
+		wantErrSubstr: "can't find external module",
+	},
+}
+
+// TestIdentityTree - check inheritance of identities from local and remote
+// sources. The Values of an Identity correspond to the values that are
+// referenced by that identity, which need to be inherited.
+func TestIdentityTree(t *testing.T) {
+	for _, tt := range treeTestCases {
+		t.Run(tt.name, func(t *testing.T) {
+			ms := NewModules()
+
+			for _, mod := range tt.in {
+				_ = ms.Parse(mod.content, mod.name)
+			}
+
+			errs := ms.Process()
+
+			var err error
+			switch len(errs) {
+			case 1:
+				err = errs[0]
+				if diff := errdiff.Substring(err, tt.wantErrSubstr); diff != "" {
+					t.Fatalf("%s", diff)
+				}
+				return
+			case 0:
+				if diff := errdiff.Substring(err, tt.wantErrSubstr); diff != "" {
+					t.Fatalf("%s", diff)
+				}
+			default:
+				t.Fatalf("got multiple errors: %v", errs)
+			}
+
+			// Walk through the identities that are defined in the test case output
+			// and validate that they exist, and their base and values are as expected.
+			for _, chkID := range tt.identities {
+				m, errs := ms.GetModule(chkID.module)
+				if errs != nil {
+					t.Errorf("Couldn't find expected module: %v", errs)
+					continue
+				}
+
+				var foundID *Identity
+				for _, i := range m.Identities {
+					if i.Name == chkID.name {
+						foundID = i
+						break
+					}
+				}
+
+				if foundID == nil {
+					t.Errorf("Couldn't find identity %s in module %s", chkID.name,
+						chkID.module)
+					continue
+				}
+
+				if len(chkID.baseNames) > 0 {
+					actualBaseNames := getBaseNamesFrom(foundID)
+					if diff := cmp.Diff(actualBaseNames, chkID.baseNames); diff != "" {
+						t.Errorf("(-got, +want):\n%s", diff)
+					}
+				}
+
+				valueMap := make(map[string]bool)
+
+				for i, val := range chkID.values {
+					valueMap[val] = false
+					// Check that IsDefined returns the right result
+					if !foundID.IsDefined(val) {
+						t.Errorf("Couldn't find defined value %s  for %s", val, chkID.name)
+					}
+
+					// Check that the values are sorted in a consistent order
+					if foundID.Values[i].Name != val {
+						t.Errorf("Invalid order for value #%d. Expecting %s Got %s", i, foundID.Values[i].Name, val)
+					}
+					// Check that GetValue returns the right Identity
+					idval := foundID.GetValue(val)
+					if idval == nil {
+						t.Errorf("Couldn't GetValue(%s) for %s", val, chkID.name)
+					}
+				}
+
+				// Ensure that IsDefined does not return false positives
+				if foundID.IsDefined("DoesNotExist") {
+					t.Errorf("Non-existent value IsDefined for %s", foundID.Name)
+				}
+
+				if foundID.GetValue("DoesNotExist") != nil {
+					t.Errorf("Non-existent value GetValue not nil for %s", foundID.Name)
+				}
+
+				for _, chkv := range foundID.Values {
+					_, ok := valueMap[chkv.Name]
+					if !ok {
+						t.Errorf("Found unexpected value %s for %s", chkv.Name, chkID.name)
+						continue
+					}
+					valueMap[chkv.Name] = true
+				}
+
+				for k, v := range valueMap {
+					if v == false {
+						t.Errorf("Could not find identity %s for %s", k, chkID.name)
+					}
+				}
+			}
+
+			for _, idr := range tt.idrefs {
+				m, errs := ms.GetModule(idr.module)
+				if errs != nil {
+					t.Errorf("Couldn't find expected module %s: %v", idr.module, errs)
+					continue
+				}
+
+				if _, ok := m.Dir[idr.name]; !ok {
+					t.Errorf("Could not find expected identity, got: nil, want: %v", idr.name)
+					continue
+				}
+
+				identity := m.Dir[idr.name]
+				var vals []*Identity
+				switch len(identity.Type.Type) {
+				case 0:
+					vals = identity.Type.IdentityBase.Values
+				default:
+					for _, b := range identity.Type.Type {
+						if b.IdentityBase != nil {
+							vals = append(vals, b.IdentityBase.Values...)
+						}
+					}
+				}
+
+				var valNames []string
+				for _, v := range vals {
+					valNames = append(valNames, v.Name)
+				}
+
+				if diff := cmp.Diff(idr.values, valNames); diff != "" {
+					t.Errorf("Identity %s did not have expected values, (-got, +want):\n%s", idr.name, diff)
+				}
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yang/lex.go

@@ -0,0 +1,522 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This file implements the lexical tokenization of yang.  The lexer returns
+// a series of tokens with one of the following codes:
+//
+//    tError       // an error was encountered
+//    tEOF         // end-of-file
+//    tString      // A de-quoted string (e.g., "\"bob\"" becomes "bob")
+//    tUnquoted    // An un-quoted string
+//    '{'
+//    ';'
+//    '}'
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"runtime"
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	eof       = 0x7fffffff // end of file, also an invalid rune
+	maxErrors = 8
+	tooMany   = "too many errors...\n"
+)
+
+// stateFn represents a state in the lexer as a function, returning the next
+// state the lexer should move to.
+type stateFn func(*lexer) stateFn
+
+// A lexer holds the internal state of the lexer.
+type lexer struct {
+	errout io.Writer // destination for errors, defaults to os.Stderr
+	errcnt int       // number of errors encountered
+
+	file  string // name of file we are processing
+	input string // contents of the file
+	start int    // start position in input of unconsumed data.
+	pos   int    // current position in the input.
+	line  int    // the current line number (1's based)
+	col   int    // the current column number (0 based, add 1 before displaying)
+
+	debug     bool        // set to true to include internal debugging
+	inPattern bool        // set when parsing the argument to a pattern
+	items     chan *token // channel of scanned items.
+	tcol      int         // column with tabs expanded (for multi-line strings)
+	scol      int         // starting col of current token
+	sline     int         // starting line of current token
+	state     stateFn     // current state of the lexer
+	width     int         // width of last rune read from input.
+}
+
+// A code is a token code.  Single character tokens (i.e., punctuation)
+// are represented by their unicode code point.
+type code int
+
+const (
+	tEOF      = code(-1 - iota) // Reached end of file
+	tError                      // An error
+	tString                     // A dequoted string
+	tUnquoted                   // A non-quoted string
+)
+
+// String returns c as a string.
+func (c code) String() string {
+	switch c {
+	case tError:
+		return "Error"
+	case tString:
+		return "String"
+	case tUnquoted:
+		return "Unquoted"
+	}
+	if c < 0 || c > '~' {
+		return fmt.Sprintf("%d", c)
+	}
+	return fmt.Sprintf("'%c'", c)
+}
+
+// A token represents one lexical unit read from the input.
+// Line and Col are both 1's based.
+type token struct {
+	code code
+	Text string // the actual text of the token
+	File string // the source file the token is from
+	Line int    // the source line number the token is from
+	Col  int    // the source column number the token is from (8 space tabs)
+}
+
+// Code returns the code of t.  If t is nil, tEOF is returned.
+func (t *token) Code() code {
+	if t == nil {
+		return tEOF
+	}
+	return t.code
+}
+
+// String returns the location, code, and text of t as a string.
+func (t *token) String() string {
+	var s []string
+	if t.File != "" {
+		s = append(s, t.File+":")
+	}
+	if t.Line != 0 {
+		s = append(s, fmt.Sprintf("%d:%d:", t.Line, t.Col))
+	}
+	if t.Text == "" {
+		s = append(s, fmt.Sprintf(" %v", t.code))
+	} else {
+		s = append(s, " ", t.Text)
+	}
+	return strings.Join(s, "")
+}
+
+// A note on writing to errout.  Errors should always be written to errout
+// in a single Write call.  The test code makes this assumption for testing
+// expected errors.
+
+// newLexer returns a new lexer, importing into it the provided input and path.
+// The provided path should indicate where the source originated.
+func newLexer(input, path string) *lexer {
+	// Force input to be newline terminated.
+	if len(input) > 0 && input[len(input)-1] != '\n' {
+		input += "\n"
+	}
+	return &lexer{
+		file:   path,
+		input:  input,
+		line:   1, // humans start with 1
+		items:  make(chan *token, maxErrors),
+		state:  lexGround,
+		errout: os.Stderr,
+	}
+}
+
+// NextToken returns the next token from the input, returning nil on EOF.
+func (l *lexer) NextToken() *token {
+	for {
+		select {
+		case item := <-l.items:
+			return item
+		default:
+			if l.state == nil {
+				return nil
+			}
+			if l.debug {
+				name := runtime.FuncForPC(reflect.ValueOf(l.state).Pointer()).Name()
+				name = name[strings.LastIndex(name, ".")+1:]
+				name = strings.TrimPrefix(name, "lex")
+				input := l.input[l.pos:]
+				if len(input) > 8 {
+					input = input[:8] + "..."
+				}
+				fmt.Fprintf(os.Stderr, "%d:%d: state %s %q\n", l.line, l.col+1, name, input)
+			}
+			l.state = l.state(l)
+		}
+	}
+}
+
+// emit emits the currently parsed token marked with code c using emitText.
+func (l *lexer) emit(c code) {
+	l.emitText(c, l.input[l.start:l.pos])
+}
+
+// emitText emits text as a token marked with c.
+// All input up to the current cursor (pos) is consumed.
+func (l *lexer) emitText(c code, text string) {
+	if l.debug {
+		fmt.Fprintf(os.Stderr, "%v: %q\n", c, text)
+	}
+	select {
+	case l.items <- &token{
+		code: c,
+		Text: text,
+		File: l.file,
+		Line: l.sline,
+		Col:  l.scol + 1,
+	}:
+	default:
+	}
+	l.consume()
+}
+
+// consume consumes all input to the current cursor.
+func (l *lexer) consume() {
+	l.start = l.pos
+}
+
+// backup steps back one rune.  It can be called only immediately after a call
+// of next.  Backing up over a tab will set tcol to the last position of the
+// tab, not where the tab started.  This is okay as when we call next again it
+// will move tcol back to where it was before backup was called.
+func (l *lexer) backup() {
+	l.pos -= l.width
+	if l.width > 0 {
+		l.col--
+		l.tcol--
+		if l.col < 0 {
+			// We must have backuped up over a newline.
+			// Don't bother to figure out the column number
+			// as the next call to next will reset it to 0.
+			l.line--
+			l.col = 0
+			l.tcol = 0
+		}
+	}
+}
+
+// peek returns but does not move past the next rune in the input.  backup
+// is not supported over peeked characters.
+func (l *lexer) peek() rune {
+	rune := l.next()
+	l.backup()
+	return rune
+}
+
+// next returns the next rune in the input.  If next encounters the end of input
+// then it will return eof.
+func (l *lexer) next() (rune rune) {
+	if l.pos >= len(l.input) {
+		l.width = 0
+		return eof
+	}
+	// l.width is what limits more than a single backup.
+	rune, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += l.width
+	switch rune {
+	case '\n':
+		l.line++
+		l.col = 0
+		l.tcol = 0
+	case '\t':
+		l.tcol = (l.tcol + 8) & ^7
+		l.col++ // should this be l.width?
+	default:
+		l.tcol++
+		l.col++ // should this be l.width?
+	}
+	return rune
+}
+
+// acceptRun moves the cursor forward up to, but not including, the first rune
+// not found in the valid set.  It returns true if any runes were accepted.
+func (l *lexer) acceptRun(valid string) bool {
+	ret := false
+	for strings.ContainsRune(valid, l.next()) {
+		ret = true
+	}
+	l.backup()
+	return ret
+}
+
+// skipTo moves the cursor up to, but not including, s.
+// Returns whether s was found in the remaining input.
+func (l *lexer) skipTo(s string) bool {
+	if x := strings.Index(l.input[l.pos:], s); x >= 0 {
+		l.updateCursor(x)
+		return true
+	}
+	return false
+}
+
+// updateCursor moves the cursor forward n bytes.  updateCursor does not
+// correctly handle tabs.  This is okay as it is only used by skipTo, and skipTo
+// is never used to skip to an initial " (which is the only time that tcol is
+// necessary, as per YANG's multi-line quoted string requirement).
+func (l *lexer) updateCursor(n int) {
+	s := l.input[l.pos : l.pos+n]
+	l.pos += n
+	// we could get away without updating width at all because backup is
+	// only promised to work after a call to next.
+	l.width = n
+
+	if c := strings.Count(s, "\n"); c > 0 {
+		l.line += c
+		l.col = 0
+	}
+	l.col += utf8.RuneCountInString(s[strings.LastIndex(s, "\n")+1:])
+}
+
+// Errorf writes an error on l.errout and increments the error count.
+// If too many errors (8) are encountered then lexing will stop and
+// eof is returned as the next token.
+func (l *lexer) Errorf(f string, v ...interface{}) {
+	buf := &bytes.Buffer{}
+
+	if l.debug {
+		// For internal debugging, print the file and line number
+		// of the call to Errorf
+		_, name, line, _ := runtime.Caller(1)
+
+		fmt.Fprintf(buf, "%s:%d: ", name, line)
+	}
+	fmt.Fprintf(buf, "%s:%d:%d: ", l.file, l.line, l.col+1)
+	fmt.Fprintf(buf, f, v...)
+	b := buf.Bytes()
+	if b[len(b)-1] != '\n' {
+		buf.Write([]byte{'\n'})
+	}
+	l.emit(tError)
+	l.adderror(buf.Bytes())
+}
+
+func (l *lexer) ErrorfAt(line, col int, f string, v ...interface{}) {
+	oline, ocol := l.line, l.col
+	defer func() {
+		l.line, l.col = oline, ocol
+	}()
+	l.line, l.col = line, col
+	l.Errorf(f, v...)
+}
+
+// adderror writes out the error string err and increases the error count.
+// If more than maxErrors are encountered, a "too many errors" message is
+// displayed and processing stops (by clearing the input).
+func (l *lexer) adderror(err []byte) {
+	if l.errcnt == maxErrors {
+		l.pos = 0
+		l.start = 0
+		l.input = ""
+		l.errout.Write([]byte(tooMany))
+		l.errcnt++
+		return
+	} else if l.errcnt == maxErrors+1 {
+		return
+	}
+	l.errout.Write(err)
+	l.errcnt++
+}
+
+// Below are all the states
+
+// lexGround is the state when the lexer is not in the middle of a token.  The
+// ground state is left once the start of a token is found.  Pure comment lines
+// leave the lexer in the ground state.
+func lexGround(l *lexer) stateFn {
+	l.acceptRun(" \t\r\n") // Skip leading spaces
+	l.consume()
+	l.sline = l.line
+	l.scol = l.col
+
+	switch c := l.peek(); c {
+	case eof:
+		return nil
+	case ';', '{', '}':
+		l.next()
+		l.emit(code(c))
+		return lexGround
+	case '\'':
+		l.next()
+		l.consume() // Toss the leading '
+		if !l.skipTo("'") {
+			l.ErrorfAt(l.line, l.col-1, `missing closing '`)
+			return nil
+		}
+		l.emit(tString)
+		l.next() // Either EOF or the matching '
+		return lexGround
+	case '"':
+		l.next()
+		return lexQString
+	case '/':
+		l.next()
+		switch l.peek() {
+		case '/':
+			// Start of a // comment
+			if !l.skipTo("\n") {
+				// Here "\n" should always be found, since we force all
+				// input to be "\n" terminated.
+				l.ErrorfAt(l.line, l.col-1, `lexer internal error: all lines should be newline-terminated.`)
+				return nil
+			}
+			return lexGround
+		case '*':
+			// Start of a /* comment
+			if !l.skipTo("*/") {
+				l.ErrorfAt(l.line, l.col-1, `missing closing */`)
+				return nil
+			}
+			// Now actually skip the */
+			l.next()
+			l.next()
+			return lexGround
+		default:
+			return lexUnquoted
+		}
+	case '+':
+		l.next()
+		switch l.peek() {
+		case '"', '\'':
+			l.emit(tUnquoted)
+			return lexGround
+		default:
+			return lexUnquoted
+		}
+	default:
+		return lexUnquoted
+	}
+}
+
+// From the YANG standard:
+//
+//   If the double-quoted string contains a line break followed by space
+//   or tab characters that are used to indent the text according to the
+//   layout in the YANG file, this leading whitespace is stripped from the
+//   string, up to and including the column of the double quote character,
+//   or to the first non-whitespace character, whichever occurs first.  In
+//   this process, a tab character is treated as 8 space characters.
+//
+//   If the double-quoted string contains space or tab characters before a
+//   line break, this trailing whitespace is stripped from the string.
+
+// lexQString handles double quoted strings, see the above text on how they
+// work.  The leading " has already been parsed.
+func lexQString(l *lexer) stateFn {
+	indent := l.tcol // the column our text starts on
+	over := true     // set to false when we are not past the indent
+
+	// Keep track of where the starting quote was
+	line, col := l.line, l.col-1
+
+	var text []byte
+	for {
+		// l.next can return non-8bit unicode code points.
+		// c cannot be treated as only a single byte.
+		switch c := l.next(); c {
+		case eof:
+			l.ErrorfAt(line, col, `missing closing "`)
+			return nil
+		case '"':
+			l.emitText(tString, string(text))
+
+			return lexGround
+		case '\n':
+		Loop:
+			// Trim trailing white space from the line.
+			for i := len(text); i > 0; {
+				i--
+				switch text[i] {
+				case ' ', '\t':
+					text = text[:i]
+				default:
+					break Loop
+				}
+			}
+			text = append(text, []byte(string(c))...)
+			over = false
+		case ' ', '\t':
+			// Ignore leading white space up to our indent.
+			if !over && l.tcol <= indent {
+				break
+			}
+			over = true
+			text = append(text, []byte(string(c))...)
+		case '\\':
+			switch c = l.next(); c {
+			case 'n':
+				c = '\n'
+			case 't':
+				c = '\t'
+			case '"':
+			case '\\':
+			default:
+				// Strings are use both in descriptions and
+				// in patterns.  In strings only \n, \t, \"
+				// and \\ are defined.  In patterns the \
+				// can either mean to escape the character
+				// (e..g., \{) or to be part of of a special
+				// sequence such as \S.
+				if !l.inPattern {
+					l.ErrorfAt(l.line, l.col-2, `invalid escape sequence: \`+string(c))
+				}
+				text = append(text, '\\')
+			}
+			fallthrough
+		default:
+			over = true
+			text = append(text, []byte(string(c))...)
+		}
+	}
+}
+
+// lexUnquoted reads one identifier/number/un-quoted-string/...
+//
+// From https://tools.ietf.org/html/rfc7950#section-6.1.3:
+// An unquoted string is any sequence of characters that does not
+// contain any space, tab, carriage return, or line feed characters, a
+// single or double quote character, a semicolon (";"), braces ("{" or
+// "}"), or comment sequences ("//", "/*", or "*/").
+func lexUnquoted(l *lexer) stateFn {
+	for {
+		switch c := l.peek(); c {
+		// TODO: Support detection of comment immediately following an
+		// unquoted string, likely through supporting two peeks instead
+		// of just one.
+		case ' ', '\r', '\n', '\t', ';', '"', '\'', '{', '}', eof:
+			l.emit(tUnquoted)
+			return lexGround
+		default:
+			l.next()
+		}
+	}
+}

src/webui/internal/goyang/pkg/yang/lex_test.go

@@ -0,0 +1,309 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"bytes"
+	"runtime"
+	"testing"
+)
+
+// line returns the line number from which it was called.
+// Used to mark where test entries are in the source.
+func line() int {
+	_, _, line, _ := runtime.Caller(1)
+	return line
+
+}
+
+// Equal returns true if t and tt are equal (have the same code and text),
+// false if not.
+func (t *token) Equal(tt *token) bool {
+	return t.code == tt.code && t.Text == tt.Text
+}
+
+// T Creates a new token from the provided code and string.
+func T(c code, text string) *token { return &token{code: c, Text: text} }
+
+func TestLex(t *testing.T) {
+Tests:
+	for _, tt := range []struct {
+		line   int
+		in     string
+		tokens []*token
+	}{
+		{line(), "", nil},
+		{line(), "bob", []*token{
+			T(tUnquoted, "bob"),
+		}},
+		{line(), "bob //bob", []*token{
+			T(tUnquoted, "bob"),
+		}},
+		{line(), "/the/path", []*token{
+			T(tUnquoted, "/the/path"),
+		}},
+		{line(), "+the/path", []*token{
+			T(tUnquoted, "+the/path"),
+		}},
+		{line(), "+the+path", []*token{
+			T(tUnquoted, "+the+path"),
+		}},
+		{line(), "+ the/path", []*token{
+			T(tUnquoted, "+"),
+			T(tUnquoted, "the/path"),
+		}},
+		{line(), "{bob}", []*token{
+			T('{', "{"),
+			T(tUnquoted, "bob"),
+			T('}', "}"),
+		}},
+		{line(), "bob;fred", []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), "\t bob\t; fred ", []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), `
+	bob;
+	fred
+`, []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), `
+	// This is a comment
+	bob;
+	fred
+`, []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), `
+	/* This is a comment */
+	bob;
+	fred
+`, []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), `
+	/*
+	 * This is a comment
+	 */
+	bob;
+	fred
+`, []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), `
+	bob; // This is bob
+	fred // This is fred
+`, []*token{
+			T(tUnquoted, "bob"),
+			T(';', ";"),
+			T(tUnquoted, "fred"),
+		}},
+		{line(), `
+pattern '[a-zA-Z0-9!#$%&'+"'"+'*+/=?^_` + "`" + `{|}~-]+';
+`, []*token{
+			T(tUnquoted, "pattern"),
+			T(tString, "[a-zA-Z0-9!#$%&"),
+			T(tUnquoted, "+"),
+			T(tString, "'"),
+			T(tUnquoted, "+"),
+			T(tString, "*+/=?^_`{|}~-]+"),
+			T(';', ";"),
+		}},
+		{line(), `
+// tab indent both lines
+	"Broken
+	line"
+`, []*token{
+			T(tString, "Broken\nline"),
+		}},
+		{line(), `
+// tab indent both lines, trailing spaces and tabs
+	"Broken
+	 line"
+`, []*token{
+			T(tString, "Broken\nline"),
+		}},
+		{line(), `
+// tab indent first line, spaces and tab second line
+	"Broken
+    	 line"
+`, []*token{
+			T(tString, "Broken\nline"),
+		}},
+		{line(), `
+// tab indent first line, spaces second linfe
+	"Broken
+         line"
+`, []*token{
+			T(tString, "Broken\nline"),
+		}},
+		{line(), `
+// extra space in second line
+	"Broken
+          space"
+`, []*token{
+			T(tString, "Broken\n space"),
+		}},
+		{line(), `
+// spaces first line, tab on second
+       "Broken
+	space"
+`, []*token{
+			T(tString, "Broken\nspace"),
+		}},
+		{line(), `
+// Odd indenting
+   "Broken
+  space"
+`, []*token{
+			T(tString, "Broken\nspace"),
+		}},
+		{line(), `
+// Odd indenting
+   "Broken  \t
+  space with trailing space"
+`, []*token{
+			T(tString, "Broken\nspace with trailing space"),
+		}},
+	} {
+		l := newLexer(tt.in, "")
+		// l.debug = true
+		for i := 0; ; i++ {
+			token := l.NextToken()
+			if token == nil {
+				if len(tt.tokens) != i {
+					t.Errorf("%d: got %d tokens, want %d", tt.line, i, len(tt.tokens))
+				}
+				continue Tests
+			}
+			if len(tt.tokens) > i && !token.Equal(tt.tokens[i]) {
+				t.Errorf("%d, %d: got (%v, %q) want (%v, %q)", tt.line, i, token.code, token.Text, tt.tokens[i].code, tt.tokens[i].Text)
+			}
+		}
+	}
+}
+
+func TestLexErrors(t *testing.T) {
+	for _, tt := range []struct {
+		line   int
+		in     string
+		errcnt int
+		errs   string
+	}{
+		{line(),
+			`1: "no closing quote`,
+			1,
+			`test.yang:1:4: missing closing "
+`,
+		},
+		{line(),
+			`1: on another line
+2: there is "no closing quote\"`,
+			1,
+			`test.yang:2:13: missing closing "
+`,
+		},
+		{line(),
+			`1:
+2: "Mares eat oats,"
+3: "And does eat oats,"
+4: "But little lambs eat ivy,"
+5: "and if I were a little lamb,"
+6: "I'ld eat ivy too.
+5: So saith the sage.`,
+			1,
+			`test.yang:6:4: missing closing "
+`,
+		},
+		{line(),
+			`1:
+2: "Quoted string"
+3: "Missing quote
+4: "Another quoted string"
+`,
+			1,
+			`test.yang:4:26: missing closing "
+`,
+		},
+		{line(),
+			`1:
+2: 'Quoted string'
+3: 'Missing quote
+4: 'Another quoted string'
+`,
+			1,
+			`test.yang:4:26: missing closing '
+`,
+		},
+		{line(),
+			`1: "Quoted string\"
+2: Missing end-quote\q`,
+			2,
+			`test.yang:2:21: invalid escape sequence: \q
+test.yang:1:4: missing closing "
+`,
+		},
+		{line(),
+			`/* This is a comment
+without an ending.
+`,
+			1,
+			`test.yang:1:1: missing closing */
+`,
+		},
+		{line(),
+			// Two errors too many.
+			`yang-version 1.1;description "\/\/\/\/\/\/\/\/\/\/";`,
+			9,
+			`test.yang:1:31: invalid escape sequence: \/
+test.yang:1:33: invalid escape sequence: \/
+test.yang:1:35: invalid escape sequence: \/
+test.yang:1:37: invalid escape sequence: \/
+test.yang:1:39: invalid escape sequence: \/
+test.yang:1:41: invalid escape sequence: \/
+test.yang:1:43: invalid escape sequence: \/
+test.yang:1:45: invalid escape sequence: \/
+` + tooMany,
+		},
+	} {
+		l := newLexer(tt.in, "test.yang")
+		errbuf := &bytes.Buffer{}
+		l.errout = errbuf
+		for l.NextToken() != nil {
+
+		}
+		if l.errcnt != tt.errcnt {
+			t.Errorf("%d: got %d errors, want %v", tt.line, l.errcnt, tt.errcnt)
+		}
+		errs := errbuf.String()
+		if errs != tt.errs {
+			t.Errorf("%d: got errors:\n%s\nwant:\n%s", tt.line, errs, tt.errs)
+		}
+	}
+}

src/webui/internal/goyang/pkg/yang/marshal_test.go

@@ -0,0 +1,832 @@
+// Copyright 2017 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/kylelemons/godebug/pretty"
+)
+
+func TestMarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		in      *Entry
+		want    string
+		wantErr bool
+	}{{
+		name: "simple leaf entry",
+		in: &Entry{
+			Name: "leaf",
+			Node: &Leaf{
+				Name: "leaf",
+			},
+			Description: "This is a fake leaf.",
+			Default:     []string{"default-leaf-value"},
+			Errors:      []error{fmt.Errorf("error one")},
+			Kind:        LeafEntry,
+			Config:      TSTrue,
+			Prefix: &Value{
+				Name: "ModulePrefix",
+				Source: &Statement{
+					Keyword:     "prefix",
+					Argument:    "ModulePrefix",
+					HasArgument: true,
+				},
+			},
+			Type: &YangType{
+				Name:    "string",
+				Kind:    Ystring,
+				Default: "string-value",
+			},
+			Annotation: map[string]interface{}{
+				"fish": struct{ Side string }{"chips"},
+			},
+		},
+		want: `{
+  "Name": "leaf",
+  "Description": "This is a fake leaf.",
+  "Default": [
+    "default-leaf-value"
+  ],
+  "Kind": 0,
+  "Config": 1,
+  "Prefix": {
+    "Name": "ModulePrefix",
+    "Source": {
+      "Keyword": "prefix",
+      "HasArgument": true,
+      "Argument": "ModulePrefix"
+    }
+  },
+  "Type": {
+    "Name": "string",
+    "Kind": 18,
+    "Default": "string-value"
+  },
+  "Annotation": {
+    "fish": {
+      "Side": "chips"
+    }
+  }
+}`,
+	}, {
+		name: "simple container entry with parent",
+		in: &Entry{
+			Name: "container",
+			Node: &Container{
+				Name: "container",
+			},
+			Kind:   DirectoryEntry,
+			Config: TSFalse,
+			Prefix: &Value{
+				Name: "ModulePrefix",
+				Source: &Statement{
+					Keyword:     "prefix",
+					Argument:    "ModulePrefix",
+					HasArgument: true,
+				},
+			},
+			Dir: map[string]*Entry{
+				"child": {
+					Name: "leaf",
+					Node: &Leaf{
+						Name: "leaf",
+					},
+					Kind:   LeafEntry,
+					Config: TSUnset,
+					Prefix: &Value{
+						Name: "ModulePrefix",
+						Source: &Statement{
+							Keyword:     "prefix",
+							Argument:    "ModulePrefix",
+							HasArgument: true,
+						},
+					},
+					Type: &YangType{
+						Name: "union",
+						Type: []*YangType{{
+							Name:    "string",
+							Pattern: []string{"^a.*$"},
+							Kind:    Ystring,
+							Length: YangRange{{
+								Min: FromInt(10),
+								Max: FromInt(20),
+							}},
+						}},
+					},
+				},
+			},
+			Augments: []*Entry{{
+				Name: "augment",
+				Node: &Leaf{
+					Name: "leaf",
+				},
+				Kind:   LeafEntry,
+				Config: TSFalse,
+				Prefix: &Value{
+					Name: "ModulePrefix",
+					Source: &Statement{
+						Keyword:     "prefix",
+						Argument:    "ModulePrefix",
+						HasArgument: true,
+					},
+				},
+			}},
+			Augmented: []*Entry{{
+				Name: "augmented",
+				Node: &Leaf{
+					Name: "leaf",
+				},
+				Kind:   LeafEntry,
+				Config: TSTrue,
+				Prefix: &Value{
+					Name: "ModulePrefix",
+					Source: &Statement{
+						Keyword:     "prefix",
+						Argument:    "ModulePrefix",
+						HasArgument: true,
+					},
+				},
+			}},
+			Uses: []*UsesStmt{{
+				Uses: &Uses{
+					Name: "grouping",
+				},
+				Grouping: &Entry{
+					Name: "grouping",
+					Node: &Grouping{
+						Name: "grouping",
+						Leaf: []*Leaf{{
+							Name: "groupingLeaf",
+						}},
+					},
+					Config: TSFalse,
+					Prefix: &Value{
+						Name: "ModulePrefix",
+						Source: &Statement{
+							Keyword:     "prefix",
+							Argument:    "ModulePrefix",
+							HasArgument: true,
+						},
+					},
+				},
+			}},
+		},
+		want: `{
+  "Name": "container",
+  "Kind": 1,
+  "Config": 2,
+  "Prefix": {
+    "Name": "ModulePrefix",
+    "Source": {
+      "Keyword": "prefix",
+      "HasArgument": true,
+      "Argument": "ModulePrefix"
+    }
+  },
+  "Dir": {
+    "child": {
+      "Name": "leaf",
+      "Kind": 0,
+      "Config": 0,
+      "Prefix": {
+        "Name": "ModulePrefix",
+        "Source": {
+          "Keyword": "prefix",
+          "HasArgument": true,
+          "Argument": "ModulePrefix"
+        }
+      },
+      "Type": {
+        "Name": "union",
+        "Kind": 0,
+        "Type": [
+          {
+            "Name": "string",
+            "Kind": 18,
+            "Length": [
+              {
+                "Min": {
+                  "Value": 10,
+                  "FractionDigits": 0,
+                  "Negative": false
+                },
+                "Max": {
+                  "Value": 20,
+                  "FractionDigits": 0,
+                  "Negative": false
+                }
+              }
+            ],
+            "Pattern": [
+              "^a.*$"
+            ]
+          }
+        ]
+      }
+    }
+  },
+  "Augments": [
+    {
+      "Name": "augment",
+      "Kind": 0,
+      "Config": 2,
+      "Prefix": {
+        "Name": "ModulePrefix",
+        "Source": {
+          "Keyword": "prefix",
+          "HasArgument": true,
+          "Argument": "ModulePrefix"
+        }
+      }
+    }
+  ],
+  "Augmented": [
+    {
+      "Name": "augmented",
+      "Kind": 0,
+      "Config": 1,
+      "Prefix": {
+        "Name": "ModulePrefix",
+        "Source": {
+          "Keyword": "prefix",
+          "HasArgument": true,
+          "Argument": "ModulePrefix"
+        }
+      }
+    }
+  ],
+  "Uses": [
+    {
+      "Uses": {
+        "Name": "grouping"
+      },
+      "Grouping": {
+        "Name": "grouping",
+        "Kind": 0,
+        "Config": 2,
+        "Prefix": {
+          "Name": "ModulePrefix",
+          "Source": {
+            "Keyword": "prefix",
+            "HasArgument": true,
+            "Argument": "ModulePrefix"
+          }
+        }
+      }
+    }
+  ]
+}`,
+	}, {
+		name: "Entry with list and leaflist",
+		in: &Entry{
+			Name:   "list",
+			Kind:   DirectoryEntry,
+			Config: TSUnset,
+			Dir: map[string]*Entry{
+				"leaf": {
+					Name: "string",
+					Kind: LeafEntry,
+				},
+				"leaf-list": {
+					Name: "leaf-list",
+					ListAttr: &ListAttr{
+						MaxElements: 18446744073709551615,
+						MinElements: 0,
+					},
+				},
+			},
+			ListAttr: &ListAttr{
+				MaxElements: 42,
+				MinElements: 48,
+			},
+			Identities: []*Identity{{
+				Name: "ID_ONE",
+			}},
+			Exts: []*Statement{{
+				Keyword:     "some-extension:ext",
+				Argument:    "ext-value",
+				HasArgument: true,
+			}},
+		},
+		want: `{
+  "Name": "list",
+  "Kind": 1,
+  "Config": 0,
+  "Dir": {
+    "leaf": {
+      "Name": "string",
+      "Kind": 0,
+      "Config": 0
+    },
+    "leaf-list": {
+      "Name": "leaf-list",
+      "Kind": 0,
+      "Config": 0,
+      "ListAttr": {
+        "MinElements": 0,
+        "MaxElements": 18446744073709551615,
+        "OrderedBy": null,
+        "OrderedByUser": false
+      }
+    }
+  },
+  "Exts": [
+    {
+      "Keyword": "some-extension:ext",
+      "HasArgument": true,
+      "Argument": "ext-value"
+    }
+  ],
+  "ListAttr": {
+    "MinElements": 48,
+    "MaxElements": 42,
+    "OrderedBy": null,
+    "OrderedByUser": false
+  },
+  "Identities": [
+    {
+      "Name": "ID_ONE"
+    }
+  ]
+}`,
+	}}
+
+	for _, tt := range tests {
+		got, err := json.MarshalIndent(tt.in, "", "  ")
+		if err != nil {
+			if !tt.wantErr {
+				t.Errorf("%s: json.MarshalIndent(%v, ...): got unexpected error: %v", tt.name, tt.in, err)
+			}
+			continue
+		}
+
+		if diff := pretty.Compare(string(got), tt.want); diff != "" {
+			t.Errorf("%s: jsonMarshalIndent(%v, ...): did not get expected JSON, diff(-got,+want):\n%s", tt.name, tt.in, diff)
+		}
+	}
+}
+
+func TestParseAndMarshal(t *testing.T) {
+	tests := []struct {
+		name string
+		in   []inputModule
+		want map[string]string
+	}{{
+		name: "simple single module",
+		in: []inputModule{{
+			name: "test.yang",
+			content: `module test {
+											prefix "t";
+											namespace "urn:t";
+
+											typedef foobar {
+												type string {
+													length "10";
+												}
+											}
+
+											identity "BASE";
+											identity "DERIVED" { base "BASE"; }
+
+											container test {
+												list a {
+													key "k";
+													min-elements 10;
+													max-elements "unbounded";
+													leaf k { type string; }
+
+													leaf bar {
+														type foobar;
+													}
+												}
+
+												leaf d {
+													type decimal64 {
+														fraction-digits 8;
+													}
+												}
+
+												leaf-list zip {
+													type string;
+												}
+
+												leaf-list zip2 {
+													max-elements 1000;
+													type string;
+												}
+
+												leaf x {
+													type union {
+														type string;
+														type identityref {
+															base "BASE";
+														}
+													}
+												}
+											}
+										}`,
+		}},
+		want: map[string]string{
+			"test": `{
+  "Name": "test",
+  "Kind": 1,
+  "Config": 0,
+  "Prefix": {
+    "Name": "t",
+    "Source": {
+      "Keyword": "prefix",
+      "HasArgument": true,
+      "Argument": "t"
+    }
+  },
+  "Dir": {
+    "test": {
+      "Name": "test",
+      "Kind": 1,
+      "Config": 0,
+      "Prefix": {
+        "Name": "t",
+        "Source": {
+          "Keyword": "prefix",
+          "HasArgument": true,
+          "Argument": "t"
+        }
+      },
+      "Dir": {
+        "a": {
+          "Name": "a",
+          "Kind": 1,
+          "Config": 0,
+          "Prefix": {
+            "Name": "t",
+            "Source": {
+              "Keyword": "prefix",
+              "HasArgument": true,
+              "Argument": "t"
+            }
+          },
+          "Dir": {
+            "bar": {
+              "Name": "bar",
+              "Kind": 0,
+              "Config": 0,
+              "Prefix": {
+                "Name": "t",
+                "Source": {
+                  "Keyword": "prefix",
+                  "HasArgument": true,
+                  "Argument": "t"
+                }
+              },
+              "Type": {
+                "Name": "foobar",
+                "Kind": 18,
+                "Length": [
+                  {
+                    "Min": {
+                      "Value": 10,
+                      "FractionDigits": 0,
+                      "Negative": false
+                    },
+                    "Max": {
+                      "Value": 10,
+                      "FractionDigits": 0,
+                      "Negative": false
+                    }
+                  }
+                ]
+              }
+            },
+            "k": {
+              "Name": "k",
+              "Kind": 0,
+              "Config": 0,
+              "Prefix": {
+                "Name": "t",
+                "Source": {
+                  "Keyword": "prefix",
+                  "HasArgument": true,
+                  "Argument": "t"
+                }
+              },
+              "Type": {
+                "Name": "string",
+                "Kind": 18
+              }
+            }
+          },
+          "Key": "k",
+          "ListAttr": {
+            "MinElements": 10,
+            "MaxElements": 18446744073709551615,
+            "OrderedBy": null,
+            "OrderedByUser": false
+          }
+        },
+        "d": {
+          "Name": "d",
+          "Kind": 0,
+          "Config": 0,
+          "Prefix": {
+            "Name": "t",
+            "Source": {
+              "Keyword": "prefix",
+              "HasArgument": true,
+              "Argument": "t"
+            }
+          },
+          "Type": {
+            "Name": "decimal64",
+            "Kind": 12,
+            "FractionDigits": 8,
+            "Range": [
+              {
+                "Min": {
+                  "Value": 9223372036854775808,
+                  "FractionDigits": 8,
+                  "Negative": true
+                },
+                "Max": {
+                  "Value": 9223372036854775807,
+                  "FractionDigits": 8,
+                  "Negative": false
+                }
+              }
+            ]
+          }
+        },
+        "x": {
+          "Name": "x",
+          "Kind": 0,
+          "Config": 0,
+          "Prefix": {
+            "Name": "t",
+            "Source": {
+              "Keyword": "prefix",
+              "HasArgument": true,
+              "Argument": "t"
+            }
+          },
+          "Type": {
+            "Name": "union",
+            "Kind": 19,
+            "Type": [
+              {
+                "Name": "string",
+                "Kind": 18
+              },
+              {
+                "Name": "identityref",
+                "Kind": 15,
+                "IdentityBase": {
+                  "Name": "BASE",
+                  "Values": [
+                    {
+                      "Name": "DERIVED"
+                    }
+                  ]
+                }
+              }
+            ]
+          }
+        },
+        "zip": {
+          "Name": "zip",
+          "Kind": 0,
+          "Config": 0,
+          "Prefix": {
+            "Name": "t",
+            "Source": {
+              "Keyword": "prefix",
+              "HasArgument": true,
+              "Argument": "t"
+            }
+          },
+          "Type": {
+            "Name": "string",
+            "Kind": 18
+          },
+          "ListAttr": {
+            "MinElements": 0,
+            "MaxElements": 18446744073709551615,
+            "OrderedBy": null,
+            "OrderedByUser": false
+          }
+        },
+        "zip2": {
+          "Name": "zip2",
+          "Kind": 0,
+          "Config": 0,
+          "Prefix": {
+            "Name": "t",
+            "Source": {
+              "Keyword": "prefix",
+              "HasArgument": true,
+              "Argument": "t"
+            }
+          },
+          "Type": {
+            "Name": "string",
+            "Kind": 18
+          },
+          "ListAttr": {
+            "MinElements": 0,
+            "MaxElements": 1000,
+            "OrderedBy": null,
+            "OrderedByUser": false
+          }
+        }
+      }
+    }
+  },
+  "Identities": [
+    {
+      "Name": "BASE",
+      "Values": [
+        {
+          "Name": "DERIVED"
+        }
+      ]
+    },
+    {
+      "Name": "DERIVED"
+    }
+  ],
+  "extra-unstable": {
+    "namespace": [
+      {
+        "Name": "urn:t",
+        "Source": {
+          "Keyword": "namespace",
+          "HasArgument": true,
+          "Argument": "urn:t"
+        }
+      }
+    ]
+  }
+}`,
+		},
+	}, {
+		name: "multiple modules with extension",
+		in: []inputModule{{
+			name: "ext.yang",
+			content: `module ext {
+										prefix "e";
+										namespace "urn:e";
+
+										extension foobar {
+											argument "baz";
+										}
+									}`,
+		}, {
+			name: "test.yang",
+			content: `module test {
+											prefix "t";
+											namespace "urn:t";
+
+											import ext { prefix ext; }
+
+											leaf t {
+												type string;
+												ext:foobar "marked";
+											}
+										}`,
+		}},
+		want: map[string]string{
+			"test": `{
+  "Name": "test",
+  "Kind": 1,
+  "Config": 0,
+  "Prefix": {
+    "Name": "t",
+    "Source": {
+      "Keyword": "prefix",
+      "HasArgument": true,
+      "Argument": "t"
+    }
+  },
+  "Dir": {
+    "t": {
+      "Name": "t",
+      "Kind": 0,
+      "Config": 0,
+      "Prefix": {
+        "Name": "t",
+        "Source": {
+          "Keyword": "prefix",
+          "HasArgument": true,
+          "Argument": "t"
+        }
+      },
+      "Type": {
+        "Name": "string",
+        "Kind": 18
+      },
+      "Exts": [
+        {
+          "Keyword": "ext:foobar",
+          "HasArgument": true,
+          "Argument": "marked"
+        }
+      ]
+    }
+  },
+  "extra-unstable": {
+    "namespace": [
+      {
+        "Name": "urn:t",
+        "Source": {
+          "Keyword": "namespace",
+          "HasArgument": true,
+          "Argument": "urn:t"
+        }
+      }
+    ]
+  }
+}`,
+			"ext": `{
+  "Name": "ext",
+  "Kind": 1,
+  "Config": 0,
+  "Prefix": {
+    "Name": "e",
+    "Source": {
+      "Keyword": "prefix",
+      "HasArgument": true,
+      "Argument": "e"
+    }
+  },
+  "extra-unstable": {
+    "extension": [
+      {
+        "Name": "foobar",
+        "Argument": {
+          "Name": "baz"
+        }
+      }
+    ],
+    "namespace": [
+      {
+        "Name": "urn:e",
+        "Source": {
+          "Keyword": "namespace",
+          "HasArgument": true,
+          "Argument": "urn:e"
+        }
+      }
+    ]
+  }
+}`,
+		},
+	}}
+
+	for _, tt := range tests {
+		ms := NewModules()
+
+		for _, mod := range tt.in {
+			if err := ms.Parse(mod.content, mod.name); err != nil {
+				t.Errorf("%s: ms.Parse(..., %v): parsing error with module: %v", tt.name, mod.name, err)
+				continue
+			}
+
+			if errs := ms.Process(); len(errs) != 0 {
+				t.Errorf("%s: ms.Process(): could not parse modules: %v", tt.name, errs)
+				continue
+			}
+
+			entries := make(map[string]*Entry)
+			for _, m := range ms.Modules {
+				if _, ok := entries[m.Name]; !ok {
+					entries[m.Name] = ToEntry(m)
+
+					got, err := json.MarshalIndent(entries[m.Name], "", "  ")
+					if err != nil {
+						t.Errorf("%s: json.MarshalIndent(...): got unexpected error: %v", tt.name, err)
+						continue
+					}
+
+					if diff := cmp.Diff(string(got), tt.want[m.Name]); diff != "" {
+						t.Errorf("%s: json.MarshalIndent(...): did not get expected JSON, diff(-got,+want):\n%s", tt.name, diff)
+					}
+				}
+			}
+		}
+	}
+}

src/webui/internal/goyang/pkg/yang/modules.go

@@ -0,0 +1,466 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This file implements the Modules type.  This includes the processing of
+// include and import statements, which must be done prior to turning the
+// module into an Entry tree.
+
+import (
+	"fmt"
+	"sync"
+)
+
+// Modules contains information about all the top level modules and
+// submodules that are read into it via its Read method.
+type Modules struct {
+	Modules      map[string]*Module // All "module" nodes
+	SubModules   map[string]*Module // All "submodule" nodes
+	includes     map[*Module]bool   // Modules we have already done include on
+	nsMu         sync.Mutex         // nsMu protects the byNS map.
+	byNS         map[string]*Module // Cache of namespace lookup
+	typeDict     *typeDictionary    // Cache for type definitions.
+	entryCacheMu sync.RWMutex       // entryCacheMu protects the entryCache map.
+	// entryCache is used to prevent unnecessary recursion into previously
+	// converted nodes. To access the map, use the get/set/ClearEntryCache()
+	// thread-safe functions.
+	entryCache map[Node]*Entry
+	// mergedSubmodule is used to prevent re-parsing a submodule that has already
+	// been merged into a particular entity when circular dependencies are being
+	// ignored. The keys of the map are a string that is formed by concatenating
+	// the name of the including (sub)module and the included submodule.
+	mergedSubmodule map[string]bool
+	// ParseOptions sets the options for the current YANG module parsing. It can be
+	// directly set by the caller to influence how goyang will behave in the presence
+	// of certain exceptional cases.
+	ParseOptions Options
+	// Path is the list of directories to look for .yang files in.
+	Path []string
+	// pathMap is used to prevent adding dups in Path.
+	pathMap map[string]bool
+}
+
+// NewModules returns a newly created and initialized Modules.
+func NewModules() *Modules {
+	ms := &Modules{
+		Modules:         map[string]*Module{},
+		SubModules:      map[string]*Module{},
+		includes:        map[*Module]bool{},
+		byNS:            map[string]*Module{},
+		typeDict:        newTypeDictionary(),
+		mergedSubmodule: map[string]bool{},
+		entryCache:      map[Node]*Entry{},
+		pathMap:         map[string]bool{},
+	}
+	return ms
+}
+
+// Read reads the named yang module into ms.  The name can be the name of an
+// actual .yang file or a module/submodule name (the base name of a .yang file,
+// e.g., foo.yang is named foo).  An error is returned if the file is not
+// found or there was an error parsing the file.
+func (ms *Modules) Read(name string) error {
+	name, data, err := ms.findFile(name)
+	if err != nil {
+		return err
+	}
+	return ms.Parse(data, name)
+}
+
+// Parse parses data as YANG source and adds it to ms.  The name should reflect
+// the source of data.
+// Note: If an error is returned, valid modules might still have been added to
+// the Modules cache.
+func (ms *Modules) Parse(data, name string) error {
+	ss, err := Parse(data, name)
+	if err != nil {
+		return err
+	}
+	for _, s := range ss {
+		n, err := buildASTWithTypeDict(s, ms.typeDict)
+		if err != nil {
+			return err
+		}
+		if err := ms.add(n); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// GetModule returns the Entry of the module named by name.  GetModule will
+// search for and read the file named name + ".yang" if it cannot satisfy the
+// request from what it has currently read.
+//
+// GetModule is a convenience function for calling Read and Process, and
+// then looking up the module name.  It is safe to call Read and Process prior
+// to calling GetModule.
+func (ms *Modules) GetModule(name string) (*Entry, []error) {
+	if ms.Modules[name] == nil {
+		if err := ms.Read(name); err != nil {
+			return nil, []error{err}
+		}
+		if ms.Modules[name] == nil {
+			return nil, []error{fmt.Errorf("module not found: %s", name)}
+		}
+	}
+	// Make sure that the modules have all been processed and have no
+	// errors.
+	if errs := ms.Process(); len(errs) != 0 {
+		return nil, errs
+	}
+	return ToEntry(ms.Modules[name]), nil
+}
+
+// GetModule optionally reads in a set of YANG source files, named by sources,
+// and then returns the Entry for the module named module.  If sources is
+// missing, or the named module is not yet known, GetModule searches for name
+// with the suffix ".yang".  GetModule either returns an Entry or returns
+// one or more errors.
+//
+// GetModule is a convenience function for calling NewModules, Read, and Process,
+// and then looking up the module name.
+func GetModule(name string, sources ...string) (*Entry, []error) {
+	var errs []error
+	ms := NewModules()
+	for _, source := range sources {
+		if err := ms.Read(source); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	if len(errs) > 0 {
+		return nil, errs
+	}
+	return ms.GetModule(name)
+}
+
+// add adds Node n to ms.  n must be assignable to *Module (i.e., it is a
+// "module" or "submodule").  An error is returned if n is a duplicate of
+// a name already added, or n is not assignable to *Module.
+func (ms *Modules) add(n Node) error {
+	var m map[string]*Module
+
+	name := n.NName()
+	kind := n.Kind()
+	switch kind {
+	case "module":
+		m = ms.Modules
+	case "submodule":
+		m = ms.SubModules
+	default:
+		return fmt.Errorf("not a module or submodule: %s is of type %s", name, kind)
+	}
+
+	mod := n.(*Module)
+	fullName := mod.FullName()
+	mod.Modules = ms
+
+	if o := m[fullName]; o != nil {
+		return fmt.Errorf("duplicate %s %s at %s and %s", kind, fullName, Source(o), Source(n))
+	}
+	m[fullName] = mod
+	if fullName == name {
+		return nil
+	}
+
+	// Add us to the map if:
+	// name has not been added before
+	// fullname is a more recent version of the entry.
+	if o := m[name]; o == nil || o.FullName() < fullName {
+		m[name] = mod
+	}
+	return nil
+}
+
+// FindModule returns the Module/Submodule specified by n, which must be a
+// *Include or *Import.  If n is a *Include then a submodule is returned.  If n
+// is a *Import then a module is returned.
+func (ms *Modules) FindModule(n Node) *Module {
+	name := n.NName()
+	rev := name
+	var m map[string]*Module
+
+	switch i := n.(type) {
+	case *Include:
+		m = ms.SubModules
+		if i.RevisionDate != nil {
+			rev = name + "@" + i.RevisionDate.Name
+		}
+		// TODO(borman): we should check the BelongsTo field below?
+	case *Import:
+		m = ms.Modules
+		if i.RevisionDate != nil {
+			rev = name + "@" + i.RevisionDate.Name
+		}
+	default:
+		return nil
+	}
+	if n := m[rev]; n != nil {
+		return n
+	}
+	if n := m[name]; n != nil {
+		return n
+	}
+
+	// Try to read first a module by revision
+	if err := ms.Read(rev); err != nil {
+		// if failed, try to read a module by its bare name
+		if err := ms.Read(name); err != nil {
+			return nil
+		}
+	}
+	if n := m[rev]; n != nil {
+		return n
+	}
+	return m[name]
+}
+
+// FindModuleByNamespace either returns the Module specified by the namespace
+// or returns an error.
+func (ms *Modules) FindModuleByNamespace(ns string) (*Module, error) {
+	// Protect the byNS map from concurrent accesses
+	ms.nsMu.Lock()
+	defer ms.nsMu.Unlock()
+
+	if m, ok := ms.byNS[ns]; ok {
+		return m, nil
+	}
+	var found *Module
+	for _, m := range ms.Modules {
+		if m.Namespace.Name == ns {
+			switch {
+			case m == found:
+			case found != nil:
+				return nil, fmt.Errorf("namespace %s matches two or more modules (%s, %s)",
+					ns, found.Name, m.Name)
+			default:
+				found = m
+			}
+		}
+	}
+	if found == nil {
+		return nil, fmt.Errorf("%q: no such namespace", ns)
+	}
+	// Don't cache negative results because new modules could be added.
+	ms.byNS[ns] = found
+	return found, nil
+}
+
+// process satisfies all include and import statements and verifies that all
+// link ref paths reference a known node.  If an import or include references
+// a [sub]module that is not already known, Process will search for a .yang
+// file that contains it, returning an error if not found.  An error is also
+// returned if there is an unknown link ref path or other parsing errors.
+//
+// Process must be called once all the source modules have been read in and
+// prior to converting Node tree into an Entry tree.
+func (ms *Modules) process() []error {
+	var mods []*Module
+	var errs []error
+
+	// Collect the list of modules we know about now so when we range
+	// below we don't pick up new modules.  We assume the user tells
+	// us explicitly which modules they are interested in.
+	for _, m := range ms.Modules {
+		mods = append(mods, m)
+	}
+	for _, m := range mods {
+		if err := ms.include(m); err != nil {
+			errs = append(errs, err)
+		}
+	}
+
+	// Resolve identities before resolving typedefs, otherwise when we resolve a
+	// typedef that has an identityref within it, then the identity dictionary
+	// has not yet been built.
+	errs = append(errs, ms.resolveIdentities()...)
+	// Append any errors found trying to resolve typedefs
+	errs = append(errs, ms.typeDict.resolveTypedefs()...)
+
+	return errs
+}
+
+// Process processes all the modules and submodules that have been read into
+// ms.  While processing, if an include or import is found for which there
+// is no matching module, Process attempts to locate the source file (using
+// Path) and automatically load them.  If a file cannot be found then an
+// error is returned.  When looking for a source file, Process searches for a
+// file using the module's or submodule's name with ".yang" appended.  After
+// searching the current directory, the directories in Path are searched.
+//
+// Process builds Entry trees for each modules and submodules in ms.  These
+// trees are accessed using the ToEntry function.  Process does augmentation
+// on Entry trees once all the modules and submodules in ms have been built.
+// Following augmentation, Process inserts implied case statements.  I.e.,
+//
+//	choice interface-type {
+//	    container ethernet { ... }
+//	}
+//
+// has a case statement inserted to become:
+//
+//	choice interface-type {
+//	    case ethernet {
+//	        container ethernet { ... }
+//	    }
+//	}
+//
+// Process may return multiple errors if multiple errors were encountered
+// while processing.  Even though multiple errors may be returned, this does
+// not mean these are all the errors.  Process will terminate processing early
+// based on the type and location of the error.
+func (ms *Modules) Process() []error {
+	// Reset globals that may remain stale if multiple Process() calls are
+	// made by the same caller.
+	ms.mergedSubmodule = map[string]bool{}
+	ms.ClearEntryCache()
+
+	errs := ms.process()
+	if len(errs) > 0 {
+		return errorSort(errs)
+	}
+
+	for _, m := range ms.Modules {
+		errs = append(errs, ToEntry(m).GetErrors()...)
+	}
+	for _, m := range ms.SubModules {
+		errs = append(errs, ToEntry(m).GetErrors()...)
+	}
+
+	if len(errs) > 0 {
+		return errorSort(errs)
+	}
+
+	// Now handle all the augments.  We don't have a good way to know
+	// what order to process them in, so repeat until no progress is made
+
+	mods := make([]*Module, 0, len(ms.Modules)+len(ms.SubModules))
+	for _, m := range ms.Modules {
+		mods = append(mods, m)
+	}
+	for _, m := range ms.SubModules {
+		mods = append(mods, m)
+	}
+	for len(mods) > 0 {
+		var processed int
+		for i := 0; i < len(mods); {
+			m := mods[i]
+			p, s := ToEntry(m).Augment(false)
+			processed += p
+			if s == 0 {
+				mods[i] = mods[len(mods)-1]
+				mods = mods[:len(mods)-1]
+				continue
+			}
+			i++
+		}
+		if processed == 0 {
+			break
+		}
+	}
+
+	// Now fix up all the choice statements to add in the missing case
+	// statements.
+	for _, m := range ms.Modules {
+		ToEntry(m).FixChoice()
+	}
+	for _, m := range ms.SubModules {
+		ToEntry(m).FixChoice()
+	}
+
+	// Go through any modules that have remaining augments and collect
+	// the errors.
+	for _, m := range mods {
+		ToEntry(m).Augment(true)
+		errs = append(errs, ToEntry(m).GetErrors()...)
+	}
+
+	// The deviation statement is only valid under a module or submodule,
+	// which allows us to avoid having to process it within ToEntry, and
+	// rather we can just walk all modules and submodules *after* entries
+	// are resolved. This means we do not need to concern ourselves that
+	// an entry does not exist.
+	dvP := map[string]bool{} // cache the modules we've handled since we have both modname and modname@revision-date
+	for _, devmods := range []map[string]*Module{ms.Modules, ms.SubModules} {
+		for _, m := range devmods {
+			e := ToEntry(m)
+			if !dvP[e.Name] {
+				errs = append(errs, e.ApplyDeviate(ms.ParseOptions.DeviateOptions)...)
+				dvP[e.Name] = true
+			}
+		}
+	}
+
+	return errorSort(errs)
+}
+
+// include resolves all the include and import statements for m.  It returns
+// an error if m, or recursively, any of the modules it includes or imports,
+// reference a module that cannot be found.
+func (ms *Modules) include(m *Module) error {
+	if ms.includes[m] {
+		return nil
+	}
+	ms.includes[m] = true
+
+	// First process any includes in this module.
+	for _, i := range m.Include {
+		im := ms.FindModule(i)
+		if im == nil {
+			return fmt.Errorf("no such submodule: %s", i.Name)
+		}
+		// Process the include statements in our included module.
+		if err := ms.include(im); err != nil {
+			return err
+		}
+		i.Module = im
+	}
+
+	// Next process any imports in this module.  Imports are used
+	// when searching.
+	for _, i := range m.Import {
+		im := ms.FindModule(i)
+		if im == nil {
+			return fmt.Errorf("no such module: %s", i.Name)
+		}
+		// Process the include statements in our included module.
+		if err := ms.include(im); err != nil {
+			return err
+		}
+
+		i.Module = im
+	}
+	return nil
+}
+
+func (ms *Modules) getEntryCache(n Node) *Entry {
+	ms.entryCacheMu.RLock()
+	defer ms.entryCacheMu.RUnlock()
+	return ms.entryCache[n]
+}
+
+func (ms *Modules) setEntryCache(n Node, e *Entry) {
+	ms.entryCacheMu.Lock()
+	defer ms.entryCacheMu.Unlock()
+	ms.entryCache[n] = e
+}
+
+// ClearEntryCache clears the entryCache containing previously converted nodes
+// used by the ToEntry function.
+func (ms *Modules) ClearEntryCache() {
+	ms.entryCacheMu.Lock()
+	defer ms.entryCacheMu.Unlock()
+	ms.entryCache = map[Node]*Entry{}
+}

src/webui/internal/goyang/pkg/yang/modules_test.go

@@ -0,0 +1,414 @@
+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/openconfig/gnmi/errdiff"
+)
+
+var testdataFindModulesText = map[string]string{
+	"foo":         `module foo { prefix "foo"; namespace "urn:foo"; }`,
+	"bar":         `module bar { prefix "bar"; namespace "urn:bar"; }`,
+	"baz":         `module baz { prefix "baz"; namespace "urn:baz"; }`,
+	"dup-pre-one": `module dup-pre-one { prefix duplicate; namespace urn:duplicate:one; }`,
+	"dup-pre-two": `module dup-pre-two { prefix duplicate; namespace urn:duplicate:two; }`,
+	"dup-ns-one":  `module dup-ns-one { prefix ns-one; namespace urn:duplicate; }`,
+	"dup-ns-two":  `module dup-ns-two { prefix ns-two; namespace urn:duplicate; }`,
+}
+
+func TestDupModule(t *testing.T) {
+	tests := []struct {
+		desc      string
+		inModules map[string]string
+		wantErr   bool
+	}{{
+		desc: "two modules with the same name",
+		inModules: map[string]string{
+			"foo": `module foo { prefix "foo"; namespace "urn:foo"; }`,
+			"bar": `module foo { prefix "foo"; namespace "urn:foo"; }`,
+		},
+		wantErr: true,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ms := NewModules()
+			var err error
+			for name, modtext := range tt.inModules {
+				if err = ms.Parse(modtext, name+".yang"); err != nil {
+					break
+				}
+			}
+			if gotErr := err != nil; gotErr != tt.wantErr {
+				t.Fatalf("wantErr: %v, got error: %v", tt.wantErr, err)
+			}
+		})
+	}
+}
+
+func testModulesForTestdataModulesText(t *testing.T) *Modules {
+	ms := NewModules()
+	for name, modtext := range testdataFindModulesText {
+		if err := ms.Parse(modtext, name+".yang"); err != nil {
+			t.Fatalf("error importing testdataFindModulesText[%q]: %v", name, err)
+		}
+	}
+	if errs := ms.Process(); errs != nil {
+		for _, err := range errs {
+			t.Errorf("error: %v", err)
+		}
+		t.Fatalf("fatal error(s) calling Process()")
+	}
+	return ms
+}
+
+func testModulesFindByCommonHandler(t *testing.T, i int, got, want *Module, wantError string, err error) {
+	if err != nil {
+		if wantError != "" {
+			if !strings.Contains(err.Error(), wantError) {
+				t.Errorf("[%d] want error containing %q, got %q",
+					i, wantError, err.Error())
+			}
+		} else {
+			t.Errorf("[%d] unexpected error: %v", i, err)
+		}
+	} else if wantError != "" {
+		t.Errorf("[%d] want error containing %q, got nil", i, wantError)
+	} else if want != got {
+		t.Errorf("[%d] want module %#v, got %#v", i, want, got)
+	}
+}
+
+func TestModulesFindByNamespace(t *testing.T) {
+	ms := testModulesForTestdataModulesText(t)
+
+	for i, tc := range []struct {
+		namespace string
+		want      *Module
+		wantError string
+	}{
+		{
+			namespace: "does-not-exist",
+			wantError: `"does-not-exist": no such namespace`,
+		},
+		{
+			namespace: "urn:foo",
+			want:      ms.Modules["foo"],
+		},
+		{
+			namespace: "urn:bar",
+			want:      ms.Modules["bar"],
+		},
+		{
+			namespace: "urn:baz",
+			want:      ms.Modules["baz"],
+		},
+		{
+			namespace: "urn:duplicate",
+			wantError: "namespace urn:duplicate matches two or more modules (dup-ns-",
+		},
+	} {
+		got, err := ms.FindModuleByNamespace(tc.namespace)
+		testModulesFindByCommonHandler(t, i, got, tc.want, tc.wantError, err)
+	}
+}
+
+func TestModuleLinkage(t *testing.T) {
+	tests := []struct {
+		desc          string
+		inMods        map[string]string
+		wantErrSubstr string
+	}{{
+		desc: "invalid import",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					import sys { prefix sys; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					deviation /sys:sys/sys:hostname {
+						deviate not-supported;
+					}
+				}`,
+		},
+		wantErrSubstr: "no such module",
+	}, {
+		desc: "valid include",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+		},
+	}, {
+		desc: "invalid include",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sysdb": `
+				submodule sysdb {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+		},
+		wantErrSubstr: "no such submodule",
+	}, {
+		desc: "valid include in submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+					include sysdb;
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+			"sysdb": `
+				submodule sysdb {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sysdb { leaf hostname { type string; } }
+				}`,
+		},
+	}, {
+		desc: "invalid include in submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+					include sysdb;
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+			"syyysdb": `
+				submodule syyysdb {
+					belongs-to dev {
+						prefix "d";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sysdb { leaf hostname { type string; } }
+				}`,
+		},
+		wantErrSubstr: "no such submodule",
+	}, {
+		desc: "valid import in submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+					import sysdb {
+						prefix "sd";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+			"sysdb": `
+				module sysdb {
+					prefix sd;
+					namespace "urn:sd";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sysdb { leaf hostname { type string; } }
+				}`,
+		},
+	}, {
+		desc: "invalid import in submodule",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					include sys;
+
+					revision 01-01-01 { description "the start of time"; }
+				}`,
+			"sys": `
+				submodule sys {
+					belongs-to dev {
+						prefix "d";
+					}
+					import sysdb {
+						prefix "sd";
+					}
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+			"syyysdb": `
+				module syyysdb {
+					prefix sd;
+					namespace "urn:sd";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sysdb { leaf hostname { type string; } }
+				}`,
+		},
+		wantErrSubstr: "no such module",
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ms := NewModules()
+
+			for n, m := range tt.inMods {
+				if err := ms.Parse(m, n); err != nil {
+					t.Fatalf("cannot parse module %s, err: %v", n, err)
+				}
+			}
+
+			errs := ms.Process()
+			var err error
+			switch len(errs) {
+			case 1:
+				err = errs[0]
+				fallthrough
+			case 0:
+				if diff := errdiff.Substring(err, tt.wantErrSubstr); diff != "" {
+					t.Fatalf("%s", diff)
+				}
+			default:
+				t.Fatalf("got multiple errors: %v", errs)
+			}
+		})
+	}
+}
+
+func TestModulesTotalProcess(t *testing.T) {
+	tests := []struct {
+		desc    string
+		inMods  map[string]string
+		wantErr bool
+	}{{
+		desc: "import with deviation",
+		inMods: map[string]string{
+			"dev": `
+				module dev {
+					prefix d;
+					namespace "urn:d";
+					import sys { prefix sys; }
+
+					revision 01-01-01 { description "the start of time"; }
+
+					deviation /sys:sys/sys:hostname {
+						deviate not-supported;
+					}
+				}`,
+			"sys": `
+				module sys {
+					prefix s;
+					namespace "urn:s";
+
+					revision 01-01-01 { description "the start of time"; }
+
+					container sys { leaf hostname { type string; } }
+				}`,
+		},
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ms := NewModules()
+
+			for n, m := range tt.inMods {
+				if err := ms.Parse(m, n); err != nil {
+					t.Fatalf("cannot parse module %s, err: %v", n, err)
+				}
+			}
+
+			errs := ms.Process()
+			switch {
+			case len(errs) == 0 && tt.wantErr:
+				t.Fatalf("did not get expected errors, got: %v, wantErr: %v", errs, tt.wantErr)
+			case len(errs) != 0 && !tt.wantErr:
+				t.Fatalf("got unexpected errors, got: %v, wantErr: %v", errs, tt.wantErr)
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yang/node.go

@@ -0,0 +1,388 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"reflect"
+	"strings"
+
+	"github.com/openconfig/goyang/pkg/indent"
+)
+
+// A Node contains a yang statement and all attributes and sub-statements.
+// Only pointers to structures should implement Node.
+type Node interface {
+	// Kind returns the kind of yang statement (the keyword).
+	Kind() string
+	// NName returns the node's name (the argument)
+	NName() string
+	// Statement returns the original Statement of this Node.
+	Statement() *Statement
+	// ParentNode returns the parent of this Node, or nil if the
+	// Node has no parent.
+	ParentNode() Node
+	// Exts returns the list of extension statements found.
+	Exts() []*Statement
+}
+
+// A Typedefer is a Node that defines typedefs.
+type Typedefer interface {
+	Node
+	Typedefs() []*Typedef
+}
+
+// An ErrorNode is a node that only contains an error.
+type ErrorNode struct {
+	Parent Node `yang:"Parent,nomerge"`
+
+	Error error
+}
+
+func (ErrorNode) Kind() string             { return "error" }
+func (s *ErrorNode) ParentNode() Node      { return s.Parent }
+func (s *ErrorNode) NName() string         { return "error" }
+func (s *ErrorNode) Statement() *Statement { return &Statement{} }
+func (s *ErrorNode) Exts() []*Statement    { return nil }
+
+// isRPCNode is a terrible hack to return back that a path points into
+// an RPC and we should ignore it.
+var isRPCNode = &ErrorNode{Error: errors.New("rpc is unsupported")}
+
+// Source returns the location of the source where n was defined.
+func Source(n Node) string {
+	if n != nil && n.Statement() != nil {
+		return n.Statement().Location()
+	}
+	return "unknown"
+}
+
+// getPrefix returns the prefix and base name of s.  If s has no prefix
+// then the returned prefix is "".
+func getPrefix(s string) (string, string) {
+	f := strings.SplitN(s, ":", 2)
+	if len(f) == 1 {
+		return "", s
+	}
+	return f[0], f[1]
+}
+
+// Prefix notes for types:
+//
+// If there is prefix, look in nodes ancestors.
+//
+// If prefix matches the module's prefix statement, look in nodes ancestors.
+//
+// If prefix matches the submodule's belongs-t statement, look in nodes
+// ancestors.
+//
+// Finally, look in the module imported with prefix.
+
+// FindModuleByPrefix finds the module or submodule with the provided prefix
+// relative to where n was defined.  If the prefix cannot be resolved then nil
+// is returned.
+func FindModuleByPrefix(n Node, prefix string) *Module {
+	if n == nil {
+		return nil
+	}
+	mod := RootNode(n)
+
+	if prefix == "" || prefix == mod.GetPrefix() {
+		return mod
+	}
+
+	for _, i := range mod.Import {
+		if prefix == i.Prefix.Name {
+			return mod.Modules.FindModule(i)
+		}
+	}
+	return nil
+}
+
+// MatchingExtensions returns the subset of the given node's extensions
+// that match the given module and identifier.
+func MatchingExtensions(n Node, module, identifier string) ([]*Statement, error) {
+	return matchingExtensions(n, n.Exts(), module, identifier)
+}
+
+// MatchingEntryExtensions returns the subset of the given entry's extensions
+// that match the given module and identifier.
+func MatchingEntryExtensions(e *Entry, module, identifier string) ([]*Statement, error) {
+	return matchingExtensions(e.Node, e.Exts, module, identifier)
+}
+
+// matchingEntryExtensions returns the subset of the given node's extensions
+// that match the given module and identifier.
+func matchingExtensions(n Node, exts []*Statement, module, identifier string) ([]*Statement, error) {
+	var matchingExtensions []*Statement
+	for _, ext := range exts {
+		names := strings.SplitN(ext.Keyword, ":", 2)
+		mod := FindModuleByPrefix(n, names[0])
+		if mod == nil {
+			return nil, fmt.Errorf("matchingExtensions: module prefix %q not found", names[0])
+		}
+		if len(names) == 2 && names[1] == identifier && mod.Name == module {
+			matchingExtensions = append(matchingExtensions, ext)
+		}
+	}
+	return matchingExtensions, nil
+}
+
+// RootNode returns the submodule or module that n was defined in.
+func RootNode(n Node) *Module {
+	for ; n.ParentNode() != nil; n = n.ParentNode() {
+	}
+	if mod, ok := n.(*Module); ok {
+		return mod
+	}
+	return nil
+}
+
+// module returns the Module to which n belongs. If n resides in a submodule,
+// the belonging module will be returned.
+// If n is nil or a module could not be find, nil is returned.
+func module(n Node) *Module {
+	m := RootNode(n)
+	if m.Kind() == "submodule" {
+		m = m.Modules.Modules[m.BelongsTo.Name]
+	}
+	return m
+}
+
+// NodePath returns the full path of the node from the module name.
+func NodePath(n Node) string {
+	var path string
+	for n != nil {
+		path = "/" + n.NName() + path
+		n = n.ParentNode()
+	}
+	return path
+}
+
+// FindNode finds the node referenced by path relative to n.  If path does not
+// reference a node then nil is returned (i.e. path not found).  The path looks
+// similar to an XPath but currently has no wildcarding.  For example:
+// "/if:interfaces/if:interface" and "../config".
+func FindNode(n Node, path string) (Node, error) {
+	if path == "" {
+		return n, nil
+	}
+	// / is not a valid path, it needs a module name
+	if path == "/" {
+		return nil, fmt.Errorf("invalid path %q", path)
+	}
+	// Paths do not end in /'s
+	if path[len(path)-1] == '/' {
+		return nil, fmt.Errorf("invalid path %q", path)
+	}
+
+	parts := strings.Split(path, "/")
+
+	// An absolute path has a leading component of "".
+	// We need to discover which module they are part of
+	// based on our imports.
+	if parts[0] == "" {
+		parts = parts[1:]
+
+		// TODO(borman): merge this with FindModuleByPrefix?
+		// The base is always a module
+		mod := RootNode(n)
+		n = mod
+		prefix, _ := getPrefix(parts[0])
+		if mod.Kind() == "submodule" {
+			m := mod.Modules.Modules[mod.BelongsTo.Name]
+			if m == nil {
+				return nil, fmt.Errorf("%s: unknown module %s", m.Name, mod.BelongsTo.Name)
+			}
+			if prefix == "" || prefix == mod.BelongsTo.Prefix.Name {
+				goto processing
+			}
+			mod = m
+		}
+
+		if prefix == "" || prefix == mod.Prefix.Name {
+			goto processing
+		}
+
+		for _, i := range mod.Import {
+			if prefix == i.Prefix.Name {
+				n = i.Module
+				goto processing
+			}
+		}
+		// We didn't find a matching prefix.
+		return nil, fmt.Errorf("unknown prefix: %q", prefix)
+	processing:
+		// At this point, n should be pointing to the Module node
+		// of module we are rooted in
+	}
+
+	for _, part := range parts {
+		// If we encounter an RPC node in our search then we
+		// return the magic isRPCNode Node which just contains
+		// an error that it is an RPC node.  isRPCNode is a singleton
+		// and can be checked against.
+		if n.Kind() == "rpc" {
+			return isRPCNode, nil
+		}
+		if part == ".." {
+		Loop:
+			for {
+				n = n.ParentNode()
+				if n == nil {
+					return nil, fmt.Errorf(".. with no parent")
+				}
+				// choice, leaf, and case nodes
+				// are "invisible" when doing ".."
+				// up the tree.
+				switch n.Kind() {
+				case "choice", "leaf", "case":
+				default:
+					break Loop
+				}
+			}
+			continue
+		}
+		// For now just strip off any prefix
+		// TODO(borman): fix this
+		_, spart := getPrefix(part)
+		n = ChildNode(n, spart)
+		if n == nil {
+			return nil, fmt.Errorf("%s: no such element", part)
+		}
+	}
+	return n, nil
+}
+
+// ChildNode finds n's child node named name.  It returns nil if the node
+// could not be found.  ChildNode looks at every direct Node pointer in
+// n as well as every node in all slices of Node pointers.  Names must
+// be non-ambiguous, otherwise ChildNode has a non-deterministic result.
+func ChildNode(n Node, name string) Node {
+	v := reflect.ValueOf(n).Elem()
+	t := v.Type()
+	nf := t.NumField()
+
+Loop:
+	for i := 0; i < nf; i++ {
+		ft := t.Field(i)
+		yang := ft.Tag.Get("yang")
+		if yang == "" {
+			continue
+		}
+		parts := strings.Split(yang, ",")
+		for _, p := range parts[1:] {
+			if p == "nomerge" {
+				continue Loop
+			}
+		}
+
+		f := v.Field(i)
+		if !f.IsValid() || f.IsNil() {
+			continue
+		}
+
+		check := func(n Node) Node {
+			if n.NName() == name {
+				return n
+			}
+			return nil
+		}
+		if parts[0] == "uses" {
+			check = func(n Node) Node {
+				uname := n.NName()
+				// unrooted uses are rooted at root
+				if !strings.HasPrefix(uname, "/") {
+					uname = "/" + uname
+				}
+				if n, _ = FindNode(n, uname); n != nil {
+					return ChildNode(n, name)
+				}
+				return nil
+			}
+		}
+
+		switch ft.Type.Kind() {
+		case reflect.Ptr:
+			if n = check(f.Interface().(Node)); n != nil {
+				return n
+			}
+		case reflect.Slice:
+			sl := f.Len()
+			for i := 0; i < sl; i++ {
+				n = f.Index(i).Interface().(Node)
+				if n = check(n); n != nil {
+					return n
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// PrintNode prints node n to w, recursively.
+// TODO(borman): display more information
+func PrintNode(w io.Writer, n Node) {
+	v := reflect.ValueOf(n).Elem()
+	t := v.Type()
+	nf := t.NumField()
+	fmt.Fprintf(w, "%s [%s]\n", n.NName(), n.Kind())
+Loop:
+	for i := 0; i < nf; i++ {
+		ft := t.Field(i)
+		yang := ft.Tag.Get("yang")
+		if yang == "" {
+			continue
+		}
+		parts := strings.Split(yang, ",")
+		for _, p := range parts[1:] {
+			if p == "nomerge" {
+				continue Loop
+			}
+		}
+
+		// Skip uppercase elements.
+		if parts[0][0] >= 'A' && parts[0][0] <= 'Z' {
+			continue
+		}
+
+		f := v.Field(i)
+		if !f.IsValid() || f.IsNil() {
+			continue
+		}
+
+		switch ft.Type.Kind() {
+		case reflect.Ptr:
+			n = f.Interface().(Node)
+			if v, ok := n.(*Value); ok {
+				fmt.Fprintf(w, "%s = %s\n", ft.Name, v.Name)
+			} else {
+				PrintNode(indent.NewWriter(w, "    "), n)
+			}
+		case reflect.Slice:
+			sl := f.Len()
+			for i := 0; i < sl; i++ {
+				n = f.Index(i).Interface().(Node)
+				if v, ok := n.(*Value); ok {
+					fmt.Fprintf(w, "%s[%d] = %s\n", ft.Name, i, v.Name)
+				} else {
+					PrintNode(indent.NewWriter(w, "    "), n)
+				}
+			}
+		}
+	}
+}

src/webui/internal/goyang/pkg/yang/node_test.go

@@ -0,0 +1,622 @@
+// Copyright 2019 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/openconfig/gnmi/errdiff"
+)
+
+func TestNodePath(t *testing.T) {
+	tests := []struct {
+		desc string
+		in   Node
+		want string
+	}{{
+		desc: "basic",
+		in: &Leaf{
+			Name: "bar",
+			Parent: &Container{
+				Name: "c",
+				Parent: &List{
+					Name: "b",
+					Parent: &Module{
+						Name: "foo",
+					},
+				},
+			},
+		},
+		want: "/foo/b/c/bar",
+	}, {
+		desc: "nil input node",
+		in:   nil,
+		want: "",
+	}, {
+		desc: "single node",
+		in: &Module{
+			Name: "foo",
+		},
+		want: "/foo",
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			if diff := cmp.Diff(NodePath(tt.in), tt.want); diff != "" {
+				t.Errorf("(-got, +want):\n%s", diff)
+			}
+		})
+	}
+}
+
+// TestNode provides a framework for processing tests that can check particular
+// nodes being added to the grammar. It can be used to ensure that particular
+// statement combinations are supported, especially where they are opaque to
+// the YANG library.
+func TestNode(t *testing.T) {
+	tests := []struct {
+		desc          string
+		inFn          func(*Modules) (Node, error)
+		inModules     map[string]string
+		wantNode      func(Node) error
+		wantErrSubstr string
+	}{{
+		desc: "import reference statement",
+		inFn: func(ms *Modules) (Node, error) {
+
+			const module = "test"
+			m, ok := ms.Modules[module]
+			if !ok {
+				return nil, fmt.Errorf("can't find module %q", module)
+			}
+
+			if len(m.Import) == 0 {
+				return nil, fmt.Errorf("node %v is missing imports", m)
+			}
+
+			return m.Import[0], nil
+		},
+		inModules: map[string]string{
+			"test": `
+				module test {
+					prefix "t";
+					namespace "urn:t";
+
+					import foo {
+						prefix "f";
+						reference "bar";
+					}
+				}
+			`,
+			"foo": `
+				module foo {
+					prefix "f";
+					namespace "urn:f";
+				}
+			`,
+		},
+		wantNode: func(n Node) error {
+			is, ok := n.(*Import)
+			if !ok {
+				return fmt.Errorf("got node: %v, want type: import", n)
+			}
+
+			switch {
+			case is.Reference == nil:
+				return errors.New("did not get expected reference, got: nil, want: *yang.Statement")
+			case is.Reference.Statement().Argument != "bar":
+				return fmt.Errorf("did not get expected reference, got: %v, want: 'bar'", is.Reference.Statement())
+			}
+
+			return nil
+		},
+	}, {
+		desc: "get submodule from prefix in submodule",
+		inFn: func(ms *Modules) (Node, error) {
+
+			m, ok := ms.SubModules["foo"]
+			if !ok {
+				return nil, fmt.Errorf("can't find submodule in %v", ms)
+			}
+
+			if m.BelongsTo == nil {
+				return nil, fmt.Errorf("node %v is missing belongs-to", m)
+			}
+
+			return m.BelongsTo, nil
+		},
+		inModules: map[string]string{
+			"test": `
+				module test {
+					prefix "t";
+					namespace "urn:t";
+
+					include foo {
+						revision-date 2008-01-01;
+					}
+				}
+			`,
+			"foo": `
+				submodule foo {
+					belongs-to test {
+					  prefix "t";
+					}
+				}
+			`,
+		},
+		wantNode: func(n Node) error {
+			is, ok := n.(*BelongsTo)
+			if !ok {
+				return fmt.Errorf("got node: %v, want type: belongs-to", n)
+			}
+
+			switch {
+			case is.Prefix == nil:
+				return errors.New("did not get expected reference, got: nil, want: *yang.Statement")
+			case is.Prefix.Statement().Argument != "t":
+				return fmt.Errorf("did not get expected reference, got: %v, want: 't'", is.Prefix.Statement())
+			}
+
+			m := FindModuleByPrefix(is, is.Prefix.Statement().Argument)
+			if m == nil {
+				return fmt.Errorf("can't find module from submodule's belongs-to prefix value")
+			}
+			if want := "foo"; m.Name != want {
+				return fmt.Errorf("module from submodule's belongs-to prefix value doesn't match, got %q, want %q", m.Name, want)
+			}
+
+			return nil
+		},
+	}, {
+		desc: "import statement from submodule",
+		inFn: func(ms *Modules) (Node, error) {
+
+			m, ok := ms.SubModules["foo"]
+			if !ok {
+				return nil, fmt.Errorf("can't find submodule in %v", ms)
+			}
+
+			if len(m.Import) == 0 {
+				return nil, fmt.Errorf("node %v is missing import statement", m)
+			}
+
+			return m.Import[0], nil
+		},
+		inModules: map[string]string{
+			"test": `
+				module test {
+					prefix "t";
+					namespace "urn:t";
+
+					include foo {
+						revision-date 2008-01-01;
+					}
+
+					typedef t {
+						type string;
+					}
+				}
+			`,
+			"foo": `
+				submodule foo {
+					belongs-to test {
+					  prefix "t";
+					}
+
+					import test2 {
+						prefix "t2";
+						description "test2 module";
+					}
+				}
+			`,
+			"test2": `
+				module test2 {
+					prefix "t2";
+					namespace "urn:t2";
+				}
+			`,
+		},
+		wantNode: func(n Node) error {
+			is, ok := n.(*Import)
+			if !ok {
+				return fmt.Errorf("got node: %v, want type: belongs-to", n)
+			}
+
+			switch {
+			case is.Prefix == nil:
+				return errors.New("did not get expected reference, got: nil, want: *yang.Statement")
+			case is.Prefix.Statement().Argument != "t2":
+				return fmt.Errorf("did not get expected reference, got: %v, want: 't'", is.Prefix.Statement())
+			}
+
+			m := FindModuleByPrefix(is, is.Prefix.Statement().Argument)
+			if m == nil {
+				return fmt.Errorf("can't find module from submodule's import prefix value")
+			}
+			if want := "test2"; m.Name != want {
+				return fmt.Errorf("module from submodule's import prefix value doesn't match, got %q, want %q", m.Name, want)
+			}
+
+			return nil
+		},
+	}, {
+		desc: "import description statement",
+		inFn: func(ms *Modules) (Node, error) {
+
+			const module = "test"
+			m, ok := ms.Modules[module]
+			if !ok {
+				return nil, fmt.Errorf("can't find module %q", module)
+			}
+
+			if len(m.Import) == 0 {
+				return nil, fmt.Errorf("node %v is missing imports", m)
+			}
+
+			return m.Import[0], nil
+		},
+		inModules: map[string]string{
+			"test": `
+				module test {
+					prefix "t";
+					namespace "urn:t";
+
+					import foo {
+						prefix "f";
+						description "foo module";
+					}
+				}
+			`,
+			"foo": `
+				module foo {
+					prefix "f";
+					namespace "urn:f";
+				}
+			`,
+		},
+		wantNode: func(n Node) error {
+			is, ok := n.(*Import)
+			if !ok {
+				return fmt.Errorf("got node: %v, want type: import", n)
+			}
+
+			switch {
+			case is.Description == nil:
+				return errors.New("did not get expected reference, got: nil, want: *yang.Statement")
+			case is.Description.Statement().Argument != "foo module":
+				return fmt.Errorf("did not get expected reference, got: '%v', want: 'foo module'", is.Description.Statement().Argument)
+			}
+
+			return nil
+		},
+	}, {
+		desc: "Test matchingExtensions",
+		inFn: func(ms *Modules) (Node, error) {
+
+			module := "test"
+			m, ok := ms.Modules[module]
+			if !ok {
+				return nil, fmt.Errorf("can't find module %q", module)
+			}
+
+			if len(m.Leaf) == 0 {
+				return nil, fmt.Errorf("node %v is missing imports", m)
+			}
+
+			module = "foo"
+			if _, ok := ms.Modules[module]; !ok {
+				return nil, fmt.Errorf("can't find module %q", module)
+			}
+
+			return m.Leaf[0].Type, nil
+		},
+		inModules: map[string]string{
+			"test": `
+				module test {
+					prefix "t";
+					namespace "urn:t";
+
+					import foo {
+						prefix "f";
+						description "foo module";
+					}
+
+					import foo2 {
+						prefix "f2";
+						description "foo2 module";
+					}
+
+					leaf test-leaf {
+						type string {
+							pattern 'alpha';
+							// Test different modules and different ext names.
+							f:bar 'boo';
+							f2:bar 'boo2';
+
+							f:bar 'coo';
+							f2:bar 'coo2';
+
+							f:far 'doo';
+							f2:far 'doo2';
+
+							f:bar 'foo';
+							f2:bar 'foo2';
+
+							f:far 'goo';
+							f2:far 'goo2';
+						}
+					}
+				}
+			`,
+			"foo": `
+				module foo {
+					prefix "f";
+					namespace "urn:f";
+
+					extension bar {
+						argument "baz";
+					}
+
+					extension far {
+						argument "baz";
+					}
+				}
+			`,
+			"foo2": `
+				module foo2 {
+					prefix "f2";
+					namespace "urn:f2";
+
+					extension bar {
+						argument "baz";
+					}
+
+					extension far {
+						argument "baz";
+					}
+				}
+			`,
+		},
+		wantNode: func(n Node) error {
+			n, ok := n.(*Type)
+			if !ok {
+				return fmt.Errorf("got node: %v, want type: Leaf", n)
+			}
+
+			var bars []string
+			matches, err := matchingExtensions(n, n.Exts(), "foo", "bar")
+			if err != nil {
+				return err
+			}
+			for _, ext := range matches {
+				bars = append(bars, ext.Argument)
+			}
+
+			if diff := cmp.Diff(bars, []string{"boo", "coo", "foo"}); diff != "" {
+				return fmt.Errorf("matchingExtensions (-got, +want):\n%s", diff)
+			}
+
+			return nil
+		},
+	}, {
+		desc: "Test matchingExtensions when module is not found",
+		inFn: func(ms *Modules) (Node, error) {
+
+			module := "test"
+			m, ok := ms.Modules[module]
+			if !ok {
+				return nil, fmt.Errorf("can't find module %q", module)
+			}
+
+			if len(m.Leaf) == 0 {
+				return nil, fmt.Errorf("node %v is missing imports", m)
+			}
+
+			module = "foo"
+			if _, ok := ms.Modules[module]; !ok {
+				return nil, fmt.Errorf("can't find module %q", module)
+			}
+
+			return m.Leaf[0].Type, nil
+		},
+		inModules: map[string]string{
+			"test": `
+				module test {
+					prefix "t";
+					namespace "urn:t";
+
+					import foo {
+						prefix "f";
+						description "foo module";
+					}
+
+					leaf test-leaf {
+						type string {
+							pattern 'alpha';
+							not-found:bar 'foo';
+						}
+					}
+				}
+			`,
+			"foo": `
+				module foo {
+					prefix "f";
+					namespace "urn:f";
+
+					extension bar {
+						argument "baz";
+					}
+
+					extension far {
+						argument "baz";
+					}
+				}
+			`,
+		},
+		wantNode: func(n Node) error {
+			n, ok := n.(*Type)
+			if !ok {
+				return fmt.Errorf("got node: %v, want type: Leaf", n)
+			}
+
+			var bars []string
+			matches, err := matchingExtensions(n, n.Exts(), "foo", "bar")
+			if err != nil {
+				return err
+			}
+			for _, ext := range matches {
+				bars = append(bars, ext.Argument)
+			}
+
+			if diff := cmp.Diff(bars, []string{"boo", "coo", "foo"}); diff != "" {
+				return fmt.Errorf("matchingExtensions (-got, +want):\n%s", diff)
+			}
+
+			return nil
+		},
+		wantErrSubstr: `module prefix "not-found" not found`,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			ms := NewModules()
+
+			for n, m := range tt.inModules {
+				if err := ms.Parse(m, n); err != nil {
+					t.Errorf("error parsing module %s, got: %v, want: nil", n, err)
+				}
+			}
+
+			errs := ms.Process()
+			var err error
+			if len(errs) > 1 {
+				t.Fatalf("Got more than 1 error: %v", errs)
+			} else if len(errs) == 1 {
+				err = errs[0]
+			}
+			if diff := errdiff.Substring(err, tt.wantErrSubstr); diff != "" {
+				t.Errorf("Did not get expected error: %s", diff)
+			}
+			if err != nil {
+				return
+			}
+
+			node, err := tt.inFn(ms)
+			if err != nil {
+				t.Fatalf("cannot run in function, %v", err)
+			}
+
+			if err := tt.wantNode(node); err != nil {
+				t.Fatalf("failed check function, %v", err)
+			}
+		})
+	}
+}
+
+func TestModulesFindByPrefix(t *testing.T) {
+	// Some examples of where prefixes might be used are in the following
+	// YANG statements: extension, uses, augment, deviation, type, leafref.
+	// Not all are put into the test here, since the logic is the same for
+	// each.
+	modules := map[string]string{
+		"foo": `module foo { prefix "foo"; namespace "urn:foo"; include bar; leaf leafref { type leafref { path "../foo:leaf"; } } uses foo:lg; }`,
+		"bar": `submodule bar { belongs-to foo { prefix "bar"; } container c { uses bar:lg; } grouping lg { leaf leaf { type string; } } }`,
+		"baz": `module baz { prefix "foo"; namespace "urn:foo"; import foo { prefix f; } extension e; uses f:lg; foo:e; }`,
+	}
+
+	ms := NewModules()
+	for name, modtext := range modules {
+		if err := ms.Parse(modtext, name+".yang"); err != nil {
+			t.Fatalf("error parsing module %q: %v", name, err)
+		}
+	}
+	if errs := ms.Process(); errs != nil {
+		for _, err := range errs {
+			t.Errorf("error: %v", err)
+		}
+		t.Fatalf("fatal error(s) calling Process()")
+	}
+
+	for _, tt := range []struct {
+		desc   string
+		node   Node
+		prefix string
+		want   *Module
+	}{
+		{
+			desc:   "nil node",
+			node:   nil,
+			prefix: "does-not-exist",
+			want:   nil,
+		},
+		{
+			desc:   "module foo",
+			node:   ms.Modules["foo"],
+			prefix: "foo",
+			want:   ms.Modules["foo"],
+		},
+		{
+			desc:   "submodule bar",
+			node:   ms.SubModules["bar"],
+			prefix: "bar",
+			want:   ms.SubModules["bar"],
+		},
+		{
+			desc:   "module baz",
+			node:   ms.Modules["baz"],
+			prefix: "foo",
+			want:   ms.Modules["baz"],
+		},
+		{
+			desc:   "foo leafref",
+			node:   ms.Modules["foo"].Leaf[0].Type,
+			prefix: "foo",
+			want:   ms.Modules["foo"],
+		},
+		{
+			desc:   "foo uses",
+			node:   ms.Modules["foo"].Uses[0],
+			prefix: "foo",
+			want:   ms.Modules["foo"],
+		},
+		{
+			desc:   "bar uses",
+			node:   ms.SubModules["bar"].Container[0].Uses[0],
+			prefix: "bar",
+			want:   ms.SubModules["bar"],
+		},
+		{
+			desc:   "baz uses",
+			node:   ms.Modules["baz"].Uses[0],
+			prefix: "f",
+			want:   ms.Modules["foo"],
+		},
+		{
+			desc:   "baz extension",
+			node:   ms.Modules["baz"],
+			prefix: "foo",
+			want:   ms.Modules["baz"],
+		},
+	} {
+		t.Run(tt.desc, func(t *testing.T) {
+			if got := FindModuleByPrefix(tt.node, tt.prefix); got != tt.want {
+				t.Errorf("got: %v, want: %v", got, tt.want)
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yang/options.go

@@ -0,0 +1,59 @@
+// Copyright 2017 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// Options defines the options that should be used when parsing YANG modules,
+// including specific overrides for potentially problematic YANG constructs.
+type Options struct {
+	// IgnoreSubmoduleCircularDependencies specifies whether circular dependencies
+	// between submodules. Setting this value to true will ensure that this
+	// package will explicitly ignore the case where a submodule will include
+	// itself through a circular reference.
+	IgnoreSubmoduleCircularDependencies bool
+	// StoreUses controls whether the Uses field of each YANG entry should be
+	// populated. Setting this value to true will cause each Entry which is
+	// generated within the schema to store the logical grouping from which it
+	// is derived.
+	StoreUses bool
+	// DeviateOptions contains options for how deviations are handled.
+	DeviateOptions DeviateOptions
+}
+
+// DeviateOptions contains options for how deviations are handled.
+type DeviateOptions struct {
+	// IgnoreDeviateNotSupported indicates to the parser to retain nodes
+	// that are marked with "deviate not-supported". An example use case is
+	// where the user wants to interact with different targets that have
+	// different support for a leaf without having to use a second instance
+	// of an AST.
+	IgnoreDeviateNotSupported bool
+}
+
+// IsDeviateOpt ensures that DeviateOptions satisfies the DeviateOpt interface.
+func (DeviateOptions) IsDeviateOpt() {}
+
+// DeviateOpt is an interface that can be used in function arguments.
+type DeviateOpt interface {
+	IsDeviateOpt()
+}
+
+func hasIgnoreDeviateNotSupported(opts []DeviateOpt) bool {
+	for _, o := range opts {
+		if opt, ok := o.(DeviateOptions); ok {
+			return opt.IgnoreDeviateNotSupported
+		}
+	}
+	return false
+}

src/webui/internal/goyang/pkg/yang/parse.go

@@ -0,0 +1,338 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This file implements Parse, which  parses the input as generic YANG and
+// returns a slice of base Statements (which in turn may contain more
+// Statements, i.e., a slice of Statement trees.)
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// a parser is used to parse the contents of a single .yang file.
+type parser struct {
+	lex    *lexer
+	errout *bytes.Buffer
+	tokens []*token // stack of pushed tokens (for backing up)
+
+	// Depth of statements in nested braces
+	statementDepth int
+
+	// hitBrace is returned when we encounter a '}'.  The statement location
+	// is updated with the location of the '}'.  The brace may be legitimate
+	// but only the caller will know if it is.  That is, the brace may be
+	// closing our parent or may be an error (we didn't expect it).
+	// hitBrace is updated with the file, line, and column of the brace's
+	// location.
+	hitBrace *Statement
+}
+
+// Statement is a generic YANG statement that may have sub-statements.
+// It implements the Node interface.
+//
+// Within the parser, it represents a non-terminal token.
+// From https://tools.ietf.org/html/rfc7950#section-6.3:
+// statement = keyword [argument] (";" / "{" *statement "}")
+// The argument is a string.
+type Statement struct {
+	Keyword     string
+	HasArgument bool
+	Argument    string
+	statements  []*Statement
+
+	file string
+	line int // 1's based line number
+	col  int // 1's based column number
+}
+
+func (s *Statement) NName() string         { return s.Argument }
+func (s *Statement) Kind() string          { return s.Keyword }
+func (s *Statement) Statement() *Statement { return s }
+func (s *Statement) ParentNode() Node      { return nil }
+func (s *Statement) Exts() []*Statement    { return nil }
+
+// Arg returns the optional argument to s.  It returns false if s has no
+// argument.
+func (s *Statement) Arg() (string, bool) { return s.Argument, s.HasArgument }
+
+// SubStatements returns a slice of Statements found in s.
+func (s *Statement) SubStatements() []*Statement { return s.statements }
+
+// Location returns the location in the source where s was defined.
+func (s *Statement) Location() string {
+	switch {
+	case s.file == "" && s.line == 0:
+		return "unknown"
+	case s.file == "":
+		return fmt.Sprintf("line %d:%d", s.line, s.col)
+	case s.line == 0:
+		return s.file
+	default:
+		return fmt.Sprintf("%s:%d:%d", s.file, s.line, s.col)
+	}
+}
+
+// Write writes the tree in s to w, each line indented by ident.  Children
+// nodes are indented further by a tab.  Typically indent is "" at the top
+// level.  Write is intended to display the contents of Statement, but
+// not necessarily reproduce the input of Statement.
+func (s *Statement) Write(w io.Writer, indent string) error {
+	if s.Keyword == "" {
+		// We are just a collection of statements at the top level.
+		for _, s := range s.statements {
+			if err := s.Write(w, indent); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+
+	parts := []string{fmt.Sprintf("%s%s", indent, s.Keyword)}
+	if s.HasArgument {
+		args := strings.Split(s.Argument, "\n")
+		if len(args) == 1 {
+			parts = append(parts, fmt.Sprintf(" %q", s.Argument))
+		} else {
+			parts = append(parts, ` "`, args[0], "\n")
+			i := fmt.Sprintf("%*s", len(s.Keyword)+1, "")
+			for x, p := range args[1:] {
+				s := fmt.Sprintf("%q", p)
+				s = s[1 : len(s)-1]
+				parts = append(parts, indent, " ", i, s)
+				if x == len(args[1:])-1 {
+					// last part just needs the closing "
+					parts = append(parts, `"`)
+				} else {
+					parts = append(parts, "\n")
+				}
+			}
+		}
+	}
+
+	if len(s.statements) == 0 {
+		_, err := fmt.Fprintf(w, "%s;\n", strings.Join(parts, ""))
+		return err
+	}
+	if _, err := fmt.Fprintf(w, "%s {\n", strings.Join(parts, "")); err != nil {
+		return err
+	}
+	for _, s := range s.statements {
+		if err := s.Write(w, indent+"\t"); err != nil {
+			return err
+		}
+	}
+	if _, err := fmt.Fprintf(w, "%s}\n", indent); err != nil {
+		return err
+	}
+	return nil
+}
+
+// ignoreMe is an error recovery token used by the parser in order
+// to continue processing for other errors in the file.
+var ignoreMe = &Statement{}
+
+// Parse parses the input as generic YANG and returns the statements parsed.
+// The path parameter should be the source name where input was read from (e.g.,
+// the file name the input was read from).  If one more more errors are
+// encountered, nil and an error are returned.  The error's text includes all
+// errors encountered.
+func Parse(input, path string) ([]*Statement, error) {
+	var statements []*Statement
+	p := &parser{
+		lex:      newLexer(input, path),
+		errout:   &bytes.Buffer{},
+		hitBrace: &Statement{},
+	}
+	p.lex.errout = p.errout
+Loop:
+	for {
+		switch ns := p.nextStatement(); ns {
+		case nil:
+			break Loop
+		case p.hitBrace:
+			fmt.Fprintf(p.errout, "%s:%d:%d: unexpected %c\n", ns.file, ns.line, ns.col, '}')
+		default:
+			statements = append(statements, ns)
+		}
+	}
+
+	p.checkStatementDepthIsZero()
+
+	if p.errout.Len() == 0 {
+		return statements, nil
+	}
+	return nil, errors.New(strings.TrimSpace(p.errout.String()))
+}
+
+// push pushes tokens t back on the input stream so they will be the next
+// tokens returned by next.  The tokens list is a LIFO so the final token
+// listed to push will be the next token returned.
+func (p *parser) push(t ...*token) {
+	p.tokens = append(p.tokens, t...)
+}
+
+// pop returns the last token pushed, or nil if the token stack is empty.
+func (p *parser) pop() *token {
+	if n := len(p.tokens); n > 0 {
+		n--
+		defer func() { p.tokens = p.tokens[:n] }()
+		return p.tokens[n]
+	}
+	return nil
+}
+
+// next returns the next token from the lexer. If the next token is a
+// concatenated string, it returns the concatenated string as the token.
+func (p *parser) next() *token {
+	if t := p.pop(); t != nil {
+		return t
+	}
+	// next returns the next unprocessed lexer token.
+	next := func() *token {
+		for {
+			if t := p.lex.NextToken(); t.Code() != tError {
+				return t
+			}
+		}
+	}
+	t := next()
+	if t.Code() != tString {
+		return t
+	}
+	// Process string concatenation (both single and double quote).
+	// See https://tools.ietf.org/html/rfc7950#section-6.1.3.1
+	// The lexer trimmed the quotes already.
+	for {
+		nt := next()
+		switch nt.Code() {
+		case tEOF:
+			return t
+		case tUnquoted:
+			if nt.Text != "+" {
+				p.push(nt)
+				return t
+			}
+		default:
+			p.push(nt)
+			return t
+		}
+		// Invariant: nt is a + sign.
+		nnt := next()
+		switch nnt.Code() {
+		case tEOF:
+			p.push(nt)
+			return t
+		case tString:
+			// Accumulate the concatenation.
+			t.Text += nnt.Text
+		default:
+			p.push(nnt, nt)
+			return t
+		}
+	}
+}
+
+// nextStatement returns the next statement in the input, which may in turn
+// recurse to read sub statements.
+// nil is returned when EOF has been reached, or is reached halfway through
+// parsing the next statement (with associated syntax errors printed to
+// errout).
+func (p *parser) nextStatement() *Statement {
+	t := p.next()
+	switch t.Code() {
+	case tEOF:
+		return nil
+	case '}':
+		p.statementDepth -= 1
+		p.hitBrace.file = t.File
+		p.hitBrace.line = t.Line
+		p.hitBrace.col = t.Col
+		return p.hitBrace
+	case tUnquoted:
+	default:
+		fmt.Fprintf(p.errout, "%v: keyword token not an unquoted string\n", t)
+		return ignoreMe
+	}
+	// Invariant: t represents a keyword token.
+
+	s := &Statement{
+		Keyword: t.Text,
+		file:    t.File,
+		line:    t.Line,
+		col:     t.Col,
+	}
+
+	// The keyword "pattern" must be treated specially. When
+	// parsing the argument for "pattern", escape sequences
+	// must be expanded differently.
+	p.lex.inPattern = t.Text == "pattern"
+	t = p.next()
+	p.lex.inPattern = false
+	switch t.Code() {
+	case tString, tUnquoted:
+		s.HasArgument = true
+		s.Argument = t.Text
+		t = p.next()
+	}
+
+	switch t.Code() {
+	case tEOF:
+		fmt.Fprintf(p.errout, "%s: unexpected EOF\n", s.file)
+		return nil
+	case ';':
+		return s
+	case '{':
+		p.statementDepth += 1
+		for {
+			switch ns := p.nextStatement(); ns {
+			case nil:
+				// Signal EOF reached.
+				return nil
+			case p.hitBrace:
+				return s
+			default:
+				s.statements = append(s.statements, ns)
+			}
+		}
+	default:
+		fmt.Fprintf(p.errout, "%v: syntax error, expected ';' or '{'\n", t)
+		return ignoreMe
+	}
+}
+
+// checkStatementDepthIsZero checks that we aren't missing closing
+// braces. Note: the parser will error out for the case where we
+// start with an unmatched close brace, i.e. depth < 0
+//
+// This test should only be done if there are no other errors as
+// we may exit early due to those errors -- and therefore there *might*
+// not really be a mismatched brace issue.
+func (p *parser) checkStatementDepthIsZero() {
+	if p.errout.Len() > 0 || p.statementDepth == 0 {
+		return
+	}
+
+	plural := ""
+	if p.statementDepth > 1 {
+		plural = "s"
+	}
+	fmt.Fprintf(p.errout, "%s:%d:%d: missing %d closing brace%s\n",
+		p.lex.file, p.lex.line, p.lex.col, p.statementDepth, plural)
+}

src/webui/internal/goyang/pkg/yang/parse_test.go

@@ -0,0 +1,539 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"bytes"
+	"testing"
+)
+
+func (s1 *Statement) equal(s2 *Statement) bool {
+	if s1.Keyword != s2.Keyword ||
+		s1.HasArgument != s2.HasArgument ||
+		s1.Argument != s2.Argument ||
+		len(s1.statements) != len(s2.statements) {
+		return false
+	}
+
+	for x, ss := range s1.statements {
+		if !ss.equal(s2.statements[x]) {
+			return false
+		}
+	}
+	return true
+}
+
+// SA returns a statement with an argument and optional substatements.
+func SA(k, a string, ss ...*Statement) *Statement {
+	return &Statement{
+		Keyword:     k,
+		Argument:    a,
+		HasArgument: true,
+		statements:  ss,
+	}
+}
+
+// S returns a statement with no argument and optional substatements.
+func S(k string, ss ...*Statement) *Statement {
+	return &Statement{
+		Keyword:    k,
+		statements: ss,
+	}
+}
+
+func TestParse(t *testing.T) {
+	for _, tt := range []struct {
+		line int
+		in   string
+		out  []*Statement
+		err  string
+	}{
+		{line: line()},
+		{line: line(), in: `
+foo;
+`,
+			out: []*Statement{
+				S("foo"),
+			},
+		},
+		{line: line(), in: `
+foo {}
+`,
+			out: []*Statement{
+				S("foo"),
+			},
+		},
+		{line: line(), in: `
+foo "";
+`,
+			out: []*Statement{
+				SA("foo", ""),
+			},
+		},
+		{line: line(), in: `
+foo bar;
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+			},
+		},
+		{line: line(), in: `
+foo "bar";
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+			},
+		},
+		{line: line(), in: `
+foo "\\ \S \n";
+`,
+			err: `test.yang:2:9: invalid escape sequence: \S`,
+		},
+		{line: line(), in: `
+pattern "\\ \S \n";
+`,
+			out: []*Statement{
+				SA("pattern", `\ \S 
+`),
+			},
+		},
+		{line: line(), in: `
+foo '\\ \S \n';
+`,
+			out: []*Statement{
+				SA("foo", `\\ \S \n`),
+			},
+		},
+		{line: line(), in: `
+pattern '\\ \S \n';
+`,
+			out: []*Statement{
+				SA("pattern", `\\ \S \n`),
+			},
+		},
+		{line: line(), in: `
+foo "bar" + "baz";
+`,
+			out: []*Statement{
+				SA("foo", "barbaz"),
+			},
+		},
+		{line: line(), in: `
+foo "bar" + "+" + "baz";
+`,
+			out: []*Statement{
+				SA("foo", "bar+baz"),
+			},
+		},
+		{line: line(), in: `
+foo "bar"
+`,
+			err: `test.yang: unexpected EOF`,
+		},
+		{line: line(), in: `
+foo "bar" + "baz"
+`,
+			err: `test.yang: unexpected EOF`,
+		},
+		{line: line(), in: `
+foo "bar" baz;
+`,
+			err: `test.yang:2:11: baz: syntax error, expected ';' or '{'
+test.yang:2:14: ;: keyword token not an unquoted string`,
+		},
+		{line: line(), in: `
+foo "bar" + baz;
+`,
+			err: `test.yang:2:11: +: syntax error, expected ';' or '{'`,
+		},
+		{line: line(), in: `
+foo "bar" +
+`,
+			err: `test.yang:2:11: +: syntax error, expected ';' or '{'`,
+		},
+		{line: line(), in: `
+foo "bar";
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+			},
+		},
+		{line: line(), in: `
+foo "bar" {}
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+			},
+		},
+		{line: line(), in: `
+foo 'bar' + 'baz';
+`,
+			out: []*Statement{
+				SA("foo", "barbaz"),
+			},
+		},
+		{line: line(), in: `
+foo 'bar' + '+' + 'baz';
+`,
+			out: []*Statement{
+				SA("foo", "bar+baz"),
+			},
+		},
+		{line: line(), in: `
+foo 'bar'
+`,
+			err: `test.yang: unexpected EOF`,
+		},
+		{line: line(), in: `
+foo 'bar' + 'baz'
+`,
+			err: `test.yang: unexpected EOF`,
+		},
+		{line: line(), in: `
+foo 'bar' baz;
+`,
+			err: `test.yang:2:11: baz: syntax error, expected ';' or '{'
+test.yang:2:14: ;: keyword token not an unquoted string`,
+		},
+		{line: line(), in: `
+foo 'bar' + baz;
+`,
+			err: `test.yang:2:11: +: syntax error, expected ';' or '{'`,
+		},
+		{line: line(), in: `
+foo 'bar' +
+`,
+			err: `test.yang:2:11: +: syntax error, expected ';' or '{'`,
+		},
+		{line: line(), in: `
+foo 'bar';
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+			},
+		},
+		{line: line(), in: `
+foo 'bar' {}
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+			},
+		},
+		{line: line(), in: `
+foo bar;
+red black;
+`,
+			out: []*Statement{
+				SA("foo", "bar"),
+				SA("red", "black"),
+			},
+		},
+		{line: line(), in: `
+foo {
+   key value;
+}
+`,
+			out: []*Statement{
+				S("foo",
+					SA("key", "value"),
+				),
+			},
+		},
+		{line: line(), in: `
+foo {
+   key value;
+}
+`,
+			out: []*Statement{
+				S("foo",
+					SA("key", "value"),
+				),
+			},
+		},
+		{line: line(), in: `
+foo {
+   key "value1     value2
+
+	 value3";
+}
+`,
+			out: []*Statement{
+				S("foo",
+					SA("key", "value1     value2\n\n value3"),
+				),
+			},
+		},
+		{line: line(), in: `
+foo {
+   key value;
+   key2;
+}
+`,
+			out: []*Statement{
+				S("foo",
+					SA("key", "value"),
+					S("key2"),
+				),
+			},
+		},
+		{line: line(), in: `
+foo1 {
+   key value1;
+}
+foo2 {
+   key value2;
+}
+foo3 value3;
+`,
+			out: []*Statement{
+				S("foo1",
+					SA("key", "value1"),
+				),
+				S("foo2",
+					SA("key", "value2"),
+				),
+				SA("foo3", "value3"),
+			},
+		},
+		{line: line(), in: `
+foo1 {
+    key value1;
+    foo2 {
+        key value2;
+    }
+}
+`,
+			out: []*Statement{
+				S("foo1",
+					SA("key", "value1"),
+					S("foo2",
+						SA("key", "value2"),
+					),
+				),
+			},
+		},
+		{line: line(), in: `
+foo1 {
+    key value1;
+    foo2 {
+      pattern '[a-zA-Z0-9!#$%&'+"'"+'*+/=?^_` + "`" + `{|}~-]+'
+            + '(\.[a-zA-Z0-9!#$%&'+"'"+'*+/=?^_` + "`" + `{|}~-]+)*'
+            + '@'
+            + '[a-zA-Z0-9!#$%&'+"'"+'*+/=?^_` + "`" + `{|}~-]+'
+            + '(\.[a-zA-Z0-9!#$%&'+"'"+'*+/=?^_` + "`" + `{|}~-]+)*';
+    }
+}
+`,
+			out: []*Statement{
+				S("foo1",
+					SA("key", "value1"),
+					S("foo2",
+						SA("pattern", "[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+(\\.[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+)*@[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+(\\.[a-zA-Z0-9!#$%&'*+/=?^_`{|}~-]+)*"),
+					),
+				),
+			},
+		},
+		{line: line(), in: `
+ }
+`,
+			err: `test.yang:2:2: unexpected }`,
+		},
+		{line: line(), in: `
+id
+`,
+			err: `test.yang: unexpected EOF`,
+		},
+		{line: line(), in: `
+   {
+`,
+			err: `test.yang:2:4: {: keyword token not an unquoted string`,
+		},
+		{line: line(), in: `
+;
+`,
+			err: `test.yang:2:1: ;: keyword token not an unquoted string`,
+		},
+		{line: line(), in: `
+statement one two { }
+`,
+			err: `test.yang:2:15: two: syntax error, expected ';' or '{'
+test.yang:2:19: {: keyword token not an unquoted string
+test.yang:2:21: unexpected }`,
+		},
+		{line: line(), in: `
+    }
+foo {
+	key: "value";
+}
+`,
+			err: `test.yang:2:5: unexpected }`,
+		},
+		{line: line(), in: `
+{
+	something: "bad";
+}
+foo {
+	key: "\Value";
+	key2: "value2";
+	bar {
+		key3: "value\3;
+	}
+}`,
+			err: `test.yang:2:1: {: keyword token not an unquoted string
+test.yang:4:1: unexpected }
+test.yang:6:8: invalid escape sequence: \V
+test.yang:9:15: invalid escape sequence: \3
+test.yang:9:9: missing closing "
+test.yang: unexpected EOF`,
+		},
+		{line: line(), in: `
+module base {
+   container top-missing-close-brace {
+      leaf my-leaf {
+        type string;
+      }
+   }
+`,
+			err: "test.yang:8:0: missing 1 closing brace",
+		},
+		{line: line(), in: `
+module base {
+   container top-missing-close-brace {
+      leaf my-leaf {
+        type string;
+   }
+`,
+			err: "test.yang:7:0: missing 2 closing braces",
+		},
+	} {
+		s, err := Parse(tt.in, "test.yang")
+		if (s == nil) != (tt.out == nil) {
+			if s == nil {
+				t.Errorf("%d: did not get expected statements: %v", tt.line, tt.out)
+			} else {
+				t.Errorf("%d: get unexpected statements: %v", tt.line, s)
+			}
+		}
+		switch {
+		case err == nil && tt.err == "":
+		case tt.err == "":
+			t.Errorf("%d: unexpected error %v", tt.line, err)
+			continue
+		case err == nil:
+			t.Errorf("%d: did not get expected error %v", tt.line, tt.err)
+			continue
+		case err.Error() == tt.err:
+			continue
+		default:
+			t.Errorf("%d: got error:\n%s\nwant:\n%s", tt.line, err, tt.err)
+			continue
+		}
+		s1 := &Statement{statements: s}
+		s2 := &Statement{statements: tt.out}
+		if !s1.equal(s2) {
+			t.Errorf("%d: got:\n%v\nwant:\n%v", tt.line, s1, s2)
+		}
+	}
+}
+
+func TestWrite(t *testing.T) {
+Testing:
+	for _, tt := range []struct {
+		line int
+		in   string
+		out  string
+	}{
+		{line: line(),
+			in: `key arg { substatement; }`,
+			out: `key "arg" {
+	substatement;
+}
+`,
+		},
+		{line: line(),
+			in: `key { substatement { key arg; }}`,
+			out: `key {
+	substatement {
+		key "arg";
+	}
+}
+`,
+		},
+		{line: line(),
+			in: `
+module base {
+   namespace "urn:mod";
+   prefix "base";
+
+   typedef base-type { type int32; }
+
+   grouping base-group {
+     description
+       "The base-group is used to test the
+        'uses' statement below.  This description
+        is here to simply include a multi-line
+        string as an example of multi-line strings";
+     leaf base-group-leaf {
+       config false;
+       type string;
+     }
+   }
+   uses base-group;
+}
+`, out: `module "base" {
+	namespace "urn:mod";
+	prefix "base";
+	typedef "base-type" {
+		type "int32";
+	}
+	grouping "base-group" {
+		description "The base-group is used to test the
+		             'uses' statement below.  This description
+		             is here to simply include a multi-line
+		             string as an example of multi-line strings";
+		leaf "base-group-leaf" {
+			config "false";
+			type "string";
+		}
+	}
+	uses "base-group";
+}
+`,
+		},
+	} {
+		in := tt.in
+		// Run twice.  The first time we are parsing tt.in, the second
+		// time we are parsing the output from the first parsing.
+		for i := 0; i < 2; i++ {
+			s, err := Parse(in, "test.yang")
+			if err != nil {
+				t.Errorf("%d: unexpected error %v", tt.line, err)
+				continue Testing
+			}
+			if len(s) != 1 {
+				t.Errorf("%d: got %d statements, expected 1", tt.line, len(s))
+				continue Testing
+			}
+			var buf bytes.Buffer
+			s[0].Write(&buf, "")
+			out := buf.String()
+			if out != tt.out {
+				t.Errorf("%d: got:\n%swant:\n%s", tt.line, out, tt.out)
+				continue Testing
+			}
+			in = out
+		}
+	}
+}

src/webui/internal/goyang/pkg/yang/testdata/deviate-delete.yang

@@ -0,0 +1,89 @@
+module deviate {
+    prefix "d";
+    namespace "urn:d";
+
+    grouping substmts {
+        leaf config {
+            type string;
+            config true;
+        }
+        leaf default {
+            type string;
+            default "fish";
+        }
+        leaf mandatory {
+            type string;
+            mandatory false;
+        }
+        leaf-list max-elements {
+            type string;
+            max-elements 1000;
+        }
+        leaf-list min-elements {
+            type string;
+            min-elements 1000;
+        }
+        leaf-list max-and-min-elements {
+            type string;
+            max-elements 1024;
+            min-elements 1;
+        }
+        leaf type {
+            type string;
+        }
+        // TODO(robjs): unique for deviation
+        leaf units {
+            type uint16;
+            units "nanofish per millenium";
+        }
+    }
+
+    container target {
+        container delete {
+            uses substmts;
+        }
+    }
+
+    deviation /target/delete/config {
+        deviate delete {
+            config true;
+        }
+    }
+
+    deviation /target/delete/default {
+        deviate delete {
+            default "fish";
+        }
+    }
+
+    deviation /target/delete/mandatory {
+        deviate delete {
+            mandatory false;
+        }
+    }
+
+    deviation /target/delete/min-elements {
+        deviate delete {
+            min-elements 1000;
+        }
+    }
+
+    deviation /target/delete/max-elements {
+        deviate delete {
+            max-elements 1000;
+        }
+    }
+
+    deviation /target/delete/max-and-min-elements {
+        deviate delete {
+            max-elements 1024;
+            min-elements 1;
+        }
+    }
+
+    deviation /target/delete/units {
+        deviate delete {
+            units "nanofish per millenium";
+        }
+    }
+}

src/webui/internal/goyang/pkg/yang/testdata/deviate-notsupported.yang

@@ -0,0 +1,42 @@
+module deviate {
+    prefix "d";
+    namespace "urn:d";
+
+    grouping substmts {
+        container child {
+            leaf zzz { type string; }
+        }
+    }
+
+    container target {
+        uses substmts;
+    }
+
+    list target-list {
+        key "k";
+
+        leaf k { type string; }
+        uses substmts;
+    }
+
+    leaf a-leaf { type string; }
+    leaf a-leaflist { type string; }
+
+    leaf survivor { type string; }
+
+    deviation /target {
+        deviate not-supported;
+    }
+
+    deviation /target-list {
+        deviate not-supported;
+    }
+
+    deviation /a-leaf {
+        deviate not-supported;
+    }
+
+    deviation /a-leaflist {
+        deviate not-supported;
+    }
+}

src/webui/internal/goyang/pkg/yang/testdata/deviate-replace.yang

@@ -0,0 +1,106 @@
+module deviate {
+    prefix "d";
+    namespace "urn:d";
+
+    grouping substmts {
+        leaf config {
+            type string;
+            config true;
+        }
+        leaf default {
+            type string;
+            default "fish";
+        }
+        leaf-list default-list {
+            type string;
+            default "fish";
+            default "sticks";
+        }
+        leaf mandatory {
+            type string;
+            mandatory false;
+        }
+        leaf-list max-elements {
+            type string;
+            max-elements 1000;
+        }
+        leaf-list min-elements {
+            type string;
+            min-elements 1000;
+        }
+        leaf-list max-and-min-elements {
+            type string;
+            max-elements 1024;
+            min-elements 1;
+        }
+        leaf type {
+            type string;
+        }
+        // TODO(robjs): unique for deviation
+        leaf units {
+            type uint16;
+            units "nanofish per millenium";
+        }
+    }
+
+    container target {
+        container replace {
+            uses substmts;
+        }
+    }
+
+    deviation /target/replace/config {
+        deviate replace {
+            config false;
+        }
+    }
+
+    deviation /target/replace/default {
+        deviate replace {
+            default "a default value";
+        }
+    }
+
+    deviation /target/replace/default-list {
+        deviate replace {
+            default "nematodes";
+        }
+    }
+
+    deviation /target/replace/mandatory {
+        deviate replace {
+            mandatory true;
+        }
+    }
+
+    deviation /target/replace/min-elements {
+        deviate replace {
+            min-elements 42;
+        }
+    }
+
+    deviation /target/replace/max-elements {
+        deviate replace {
+            max-elements 42;
+        }
+    }
+
+    deviation /target/replace/max-and-min-elements {
+        deviate replace {
+            max-elements 42;
+            min-elements 42;
+        }
+    }
+
+    deviation /target/replace/type {
+        deviate replace {
+            type uint16;
+        }
+    }
+
+    deviation /target/replace/units {
+        deviate replace {
+            units "fish per second";
+        }
+    }
+}

src/webui/internal/goyang/pkg/yang/testdata/deviate.yang

@@ -0,0 +1,81 @@
+module deviate {
+    prefix "d";
+    namespace "urn:d";
+
+    typedef derived-string {
+      type string;
+      default "barnacles";
+    }
+
+    grouping substmts {
+        leaf config { type string; }
+        leaf default { type string; }
+        leaf default-typedef { type derived-string; }
+        leaf-list default-list { type string; default "foo"; default "bar"; }
+        leaf-list default-list-typedef-default { type derived-string; }
+        leaf mandatory { type string; }
+        leaf-list max-elements { type string; }
+        leaf-list min-elements { type string; }
+        leaf-list max-and-min-elements { type string; }
+        leaf type { type string; }
+        // TODO(robjs): unique requires a list target
+        leaf units { type uint16; }
+    }
+
+    container target {
+        container add {
+            uses substmts;
+        }
+    }
+
+    deviation /target/add/config {
+        deviate add {
+            config false;
+        }
+    }
+
+    deviation /target/add/default {
+        deviate add {
+            default "a default value";
+        }
+    }
+
+    deviation /target/add/default-list {
+        deviate add {
+            default "foo";
+            // TODO(wenovus): support multiple default statements for deviate.
+            //default "baz";
+        }
+    }
+
+    deviation /target/add/mandatory {
+        deviate add {
+            mandatory true;
+        }
+    }
+
+    deviation /target/add/min-elements {
+        deviate add {
+            min-elements 42;
+        }
+    }
+
+    deviation /target/add/max-elements {
+        deviate add {
+            max-elements 42;
+        }
+    }
+
+    deviation /target/add/max-and-min-elements {
+        deviate add {
+            max-elements 42;
+            min-elements 42;
+        }
+    }
+
+    deviation /target/add/units {
+        deviate add {
+            units "fish per second";
+        }
+    }
+}

src/webui/internal/goyang/pkg/yang/types.go

@@ -0,0 +1,425 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This file implements the functions relating to types and typedefs.
+
+import (
+	"errors"
+	"fmt"
+	"regexp/syntax"
+	"sync"
+)
+
+// A typeDictionary is a dictionary of all Typedefs defined in all Typedefers.
+// A map of Nodes is used rather than a map of Typedefers to simplify usage
+// when traversing up a Node tree.
+type typeDictionary struct {
+	mu   sync.Mutex
+	dict map[Node]map[string]*Typedef
+	// identities contains a dictionary of resolved identities.
+	identities identityDictionary
+}
+
+func newTypeDictionary() *typeDictionary {
+	return &typeDictionary{
+		dict:       map[Node]map[string]*Typedef{},
+		identities: identityDictionary{dict: map[string]resolvedIdentity{}},
+	}
+}
+
+// add adds an entry to the typeDictionary d.
+func (d *typeDictionary) add(n Node, name string, td *Typedef) {
+	defer d.mu.Unlock()
+	d.mu.Lock()
+	if d.dict[n] == nil {
+		d.dict[n] = map[string]*Typedef{}
+	}
+	d.dict[n][name] = td
+}
+
+// find returns the Typedef name define in node n, or nil.
+func (d *typeDictionary) find(n Node, name string) *Typedef {
+	defer d.mu.Unlock()
+	d.mu.Lock()
+	if d.dict[n] == nil {
+		return nil
+	}
+	return d.dict[n][name]
+}
+
+// findExternal finds the externally-defined typedef name in a module imported
+// by n's root with the specified prefix.
+func (d *typeDictionary) findExternal(n Node, prefix, name string) (*Typedef, error) {
+	root := FindModuleByPrefix(n, prefix)
+	if root == nil {
+		return nil, fmt.Errorf("%s: unknown prefix: %s for type %s", Source(n), prefix, name)
+	}
+	if td := d.find(root, name); td != nil {
+		return td, nil
+	}
+	if prefix != "" {
+		name = prefix + ":" + name
+	}
+	return nil, fmt.Errorf("%s: unknown type %s", Source(n), name)
+}
+
+// typedefs returns a slice of all typedefs in d.
+func (d *typeDictionary) typedefs() []*Typedef {
+	var tds []*Typedef
+	defer d.mu.Unlock()
+	d.mu.Lock()
+	for _, dict := range d.dict {
+		for _, td := range dict {
+			tds = append(tds, td)
+		}
+	}
+	return tds
+}
+
+// addTypedefs is called from BuildAST after each Typedefer is defined.  There
+// are no error conditions in this process as it is simply used to build up the
+// typedef dictionary.
+func (d *typeDictionary) addTypedefs(t Typedefer) {
+	for _, td := range t.Typedefs() {
+		d.add(t, td.Name, td)
+	}
+}
+
+// resolveTypedefs is called after all of modules and submodules have been read,
+// as well as their imports and includes.  It resolves all typedefs found in all
+// modules and submodules read in.
+func (d *typeDictionary) resolveTypedefs() []error {
+	var errs []error
+
+	// When resolve typedefs, we may need to look up other typedefs.
+	// We gather all typedefs into a slice so we don't deadlock on
+	// typeDict.
+	for _, td := range d.typedefs() {
+		errs = append(errs, td.resolve(d)...)
+	}
+	return errs
+}
+
+// resolve creates a YangType for t, if not already done.  Resolving t
+// requires resolving the Type that t is based on.
+func (t *Typedef) resolve(d *typeDictionary) []error {
+	// If we have no parent we are a base type and
+	// are already resolved.
+	if t.Parent == nil || t.YangType != nil {
+		return nil
+	}
+
+	if errs := t.Type.resolve(d); len(errs) != 0 {
+		return errs
+	}
+
+	// Make a copy of the YangType we are based on and then
+	// update it with local information.
+	y := *t.Type.YangType
+	y.Name = t.Name
+	y.Base = t.Type
+
+	if t.Units != nil {
+		y.Units = t.Units.Name
+	}
+	if t.Default != nil {
+		y.HasDefault = true
+		y.Default = t.Default.Name
+	}
+
+	if t.Type.IdentityBase != nil {
+		// We need to copy over the IdentityBase statement if the type has one
+		if idBase, err := RootNode(t).findIdentityBase(t.Type.IdentityBase.Name); err == nil {
+			y.IdentityBase = idBase.Identity
+		} else {
+			return []error{fmt.Errorf("could not resolve identity base for typedef: %s", t.Type.IdentityBase.Name)}
+		}
+	}
+
+	// If we changed something, we are the new root.
+	if y.Root == t.Type.YangType || !y.Equal(y.Root) {
+		y.Root = &y
+	}
+	t.YangType = &y
+	return nil
+}
+
+// resolve resolves Type t, as well as the underlying typedef for t.  If t
+// cannot be resolved then one or more errors are returned.
+func (t *Type) resolve(d *typeDictionary) (errs []error) {
+	if t.YangType != nil {
+		return nil
+	}
+
+	// If t.Name is a base type then td will not be nil, otherwise
+	// td will be nil and of type *Typedef.
+	td := BaseTypedefs[t.Name]
+
+	prefix, name := getPrefix(t.Name)
+	root := RootNode(t)
+	rootPrefix := root.GetPrefix()
+
+	source := "unknown"
+check:
+	switch {
+	case td != nil:
+		source = "builtin"
+		// This was a base type
+	case prefix == "" || rootPrefix == prefix:
+		source = "local"
+		// If we have no prefix, or the prefix is what we call our own
+		// root, then we look in our ancestors for a typedef of name.
+		for n := Node(t); n != nil; n = n.ParentNode() {
+			if td = d.find(n, name); td != nil {
+				break check
+			}
+		}
+		// We need to check our sub-modules as well
+		for _, in := range root.Include {
+			if td = d.find(in.Module, name); td != nil {
+				break check
+			}
+		}
+		var pname string
+		switch {
+		case prefix == "", prefix == root.Prefix.Name:
+			pname = root.Prefix.Name + ":" + t.Name
+		default:
+			pname = fmt.Sprintf("%s[%s]:%s", prefix, root.Prefix.Name, t.Name)
+		}
+
+		return []error{fmt.Errorf("%s: unknown type: %s", Source(t), pname)}
+
+	default:
+		source = "imported"
+		// prefix is not local to our module, so we have to go find
+		// what module it is part of and if it is defined at the top
+		// level of that module.
+		var err error
+		td, err = d.findExternal(t, prefix, name)
+		if err != nil {
+			return []error{err}
+		}
+	}
+	if errs := td.resolve(d); len(errs) > 0 {
+		return errs
+	}
+
+	// Make a copy of the typedef we are based on so we can
+	// augment it.
+	if td.YangType == nil {
+		return []error{fmt.Errorf("%s: no YangType defined for %s %s", Source(td), source, td.Name)}
+	}
+	y := *td.YangType
+
+	y.Base = td.Type
+	t.YangType = &y
+
+	if v := t.RequireInstance; v != nil {
+		b, err := v.asBool()
+		if err != nil {
+			errs = append(errs, err)
+		}
+		y.OptionalInstance = !b
+	}
+	if v := t.Path; v != nil {
+		y.Path = v.asString()
+	}
+	isDecimal64 := y.Kind == Ydecimal64 && (t.Name == "decimal64" || y.FractionDigits != 0)
+	switch {
+	case isDecimal64 && y.FractionDigits != 0:
+		if t.FractionDigits != nil {
+			return append(errs, fmt.Errorf("%s: overriding of fraction-digits not allowed", Source(t)))
+		}
+		// FractionDigits already set via type inheritance.
+	case isDecimal64:
+		// If we are directly of type decimal64 then we must specify
+		// fraction-digits in the range from 1-18.
+		i, err := t.FractionDigits.asRangeInt(1, 18)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("%s: %v", Source(t), err))
+		}
+		y.FractionDigits = int(i)
+		// We only know to how to populate Range after knowing the
+		// fractional digit value.
+		y.Range = YangRange{{
+			Number{Value: AbsMinInt64, Negative: true, FractionDigits: uint8(i)},
+			Number{Value: MaxInt64, FractionDigits: uint8(i)},
+		}}
+	case t.FractionDigits != nil:
+		errs = append(errs, fmt.Errorf("%s: fraction-digits only allowed for decimal64 values", Source(t)))
+	case y.Kind == Yidentityref:
+		if source != "builtin" {
+			// This is a typedef that refers to an identityref, so we want to simply
+			// maintain the base that the typedef resolution provided
+			break
+		}
+
+		if t.IdentityBase == nil {
+			errs = append(errs, fmt.Errorf("%s: an identityref must specify a base", Source(t)))
+			break
+		}
+
+		root := RootNode(t.Parent)
+		resolvedBase, baseErr := root.findIdentityBase(t.IdentityBase.Name)
+		if baseErr != nil {
+			errs = append(errs, baseErr...)
+			break
+		}
+
+		if resolvedBase.Identity == nil {
+			errs = append(errs, fmt.Errorf("%s: identity has a null base", t.IdentityBase.Name))
+			break
+		}
+		y.IdentityBase = resolvedBase.Identity
+	}
+
+	if t.Range != nil {
+		yr, err := y.Range.parseChildRanges(t.Range.Name, isDecimal64, uint8(y.FractionDigits))
+		switch {
+		case err != nil:
+			errs = append(errs, fmt.Errorf("%s: bad range: %v", Source(t.Range), err))
+		case yr.Equal(y.Range):
+		default:
+			y.Range = yr
+		}
+	}
+
+	if t.Length != nil {
+		parentRange := Uint64Range
+		if y.Length != nil {
+			parentRange = y.Length
+		}
+		yr, err := parentRange.parseChildRanges(t.Length.Name, false, 0)
+		switch {
+		case err != nil:
+			errs = append(errs, fmt.Errorf("%s: bad length: %v", Source(t.Length), err))
+		case yr.Equal(y.Length):
+		default:
+			for _, r := range yr {
+				if r.Min.Negative {
+					errs = append(errs, fmt.Errorf("%s: negative length: %v", Source(t.Length), yr))
+					break
+				}
+			}
+			y.Length = yr
+		}
+	}
+
+	set := func(e *EnumType, name string, value *Value) error {
+		if value == nil {
+			return e.SetNext(name)
+		}
+		n, err := ParseInt(value.Name)
+		if err != nil {
+			return err
+		}
+		i, err := n.Int()
+		if err != nil {
+			return err
+		}
+		return e.Set(name, i)
+	}
+
+	if len(t.Enum) > 0 {
+		enum := NewEnumType()
+		for _, e := range t.Enum {
+			if err := set(enum, e.Name, e.Value); err != nil {
+				errs = append(errs, fmt.Errorf("%s: %v", Source(e), err))
+			}
+		}
+		y.Enum = enum
+	}
+
+	if len(t.Bit) > 0 {
+		bit := NewBitfield()
+		for _, e := range t.Bit {
+			if err := set(bit, e.Name, e.Position); err != nil {
+				errs = append(errs, fmt.Errorf("%s: %v", Source(e), err))
+			}
+		}
+		y.Bit = bit
+	}
+
+	// Append any newly found patterns to the end of the list of patterns.
+	// Patterns are ANDed according to section 9.4.6.  If all the patterns
+	// declared by t were also declared by the type t is based on, then
+	// no patterns are added.
+	seenPatterns := map[string]bool{}
+	for _, p := range y.Pattern {
+		seenPatterns[p] = true
+	}
+	seenPOSIXPatterns := map[string]bool{}
+	for _, p := range y.POSIXPattern {
+		seenPOSIXPatterns[p] = true
+	}
+
+	// First parse out the pattern statements.
+	// These patterns are not checked because there is no support for W3C regexes by Go.
+	for _, pv := range t.Pattern {
+		if !seenPatterns[pv.Name] {
+			seenPatterns[pv.Name] = true
+			y.Pattern = append(y.Pattern, pv.Name)
+		}
+	}
+
+	// Then, parse out the posix-pattern statements, if they exist.
+	// A YANG module could make use of either or both, so we deal with each separately.
+	posixPatterns, err := MatchingExtensions(t, "openconfig-extensions", "posix-pattern")
+	if err != nil {
+		return []error{err}
+	}
+
+	checkPattern := func(n Node, p string, flags syntax.Flags) {
+		if _, err := syntax.Parse(p, flags); err != nil {
+			if re, ok := err.(*syntax.Error); ok {
+				// Error adds "error parsing regexp" to
+				// the error, re.Code is the real error.
+				err = errors.New(re.Code.String())
+			}
+			errs = append(errs, fmt.Errorf("%s: bad pattern: %v: %s", Source(n), err, p))
+		}
+	}
+	for _, ext := range posixPatterns {
+		checkPattern(ext, ext.Argument, syntax.POSIX)
+		if !seenPOSIXPatterns[ext.Argument] {
+			seenPOSIXPatterns[ext.Argument] = true
+			y.POSIXPattern = append(y.POSIXPattern, ext.Argument)
+		}
+	}
+
+	// I don't know of an easy way to use a type as a key to a map,
+	// so we have to check equality the hard way.
+looking:
+	for _, ut := range t.Type {
+		errs = append(errs, ut.resolve(d)...)
+		if ut.YangType != nil {
+			for _, yt := range y.Type {
+				if ut.YangType.Equal(yt) {
+					continue looking
+				}
+			}
+			y.Type = append(y.Type, ut.YangType)
+		}
+	}
+
+	// If we changed something, we are the new root.
+	if !y.Equal(y.Root) {
+		y.Root = &y
+	}
+
+	return errs
+}

src/webui/internal/goyang/pkg/yang/types_builtin.go

@@ -0,0 +1,700 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+// This module contains all the builtin types as well as types related
+// to types (such as ranges, enums, etc).
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// This file handles interpretation of types
+
+// These are the default ranges defined by the YANG standard.
+var (
+	Int8Range  = mustParseRangesInt("-128..127")
+	Int16Range = mustParseRangesInt("-32768..32767")
+	Int32Range = mustParseRangesInt("-2147483648..2147483647")
+	Int64Range = mustParseRangesInt("-9223372036854775808..9223372036854775807")
+
+	Uint8Range  = mustParseRangesInt("0..255")
+	Uint16Range = mustParseRangesInt("0..65535")
+	Uint32Range = mustParseRangesInt("0..4294967295")
+	Uint64Range = mustParseRangesInt("0..18446744073709551615")
+)
+
+const (
+	// MaxInt64 corresponds to the maximum value of a signed int64.
+	MaxInt64 = 1<<63 - 1
+	// MinInt64 corresponds to the maximum value of a signed int64.
+	MinInt64 = -1 << 63
+	// Min/MaxDecimal64 are the max/min decimal64 values.
+	MinDecimal64 float64 = -922337203685477580.8
+	MaxDecimal64 float64 = 922337203685477580.7
+	// AbsMinInt64 is the absolute value of MinInt64.
+	AbsMinInt64 = 1 << 63
+	// MaxEnum is the maximum value of an enumeration.
+	MaxEnum = 1<<31 - 1
+	// MinEnum is the minimum value of an enumeration.
+	MinEnum = -1 << 31
+	// MaxBitfieldSize is the maximum number of bits in a bitfield.
+	MaxBitfieldSize = 1 << 32
+	// MaxFractionDigits is the maximum number of fractional digits as per RFC6020 Section 9.3.4.
+	MaxFractionDigits uint8 = 18
+
+	space18 = "000000000000000000" // used for prepending 0's
+)
+
+// A Number is either an integer the range of [-(1<<64) - 1, (1<<64)-1], or a
+// YANG decimal conforming to https://tools.ietf.org/html/rfc6020#section-9.3.4.
+type Number struct {
+	// Absolute value of the number.
+	Value uint64
+	// Number of fractional digits.
+	// 0 means it's an integer. For decimal64 it falls within [1, 18].
+	FractionDigits uint8
+	// Negative indicates whether the number is negative.
+	Negative bool
+}
+
+// IsDecimal reports whether n is a decimal number.
+func (n Number) IsDecimal() bool {
+	return n.FractionDigits != 0
+}
+
+// String returns n as a string in decimal.
+func (n Number) String() string {
+	out := strconv.FormatUint(n.Value, 10)
+
+	if n.IsDecimal() {
+		if fd := int(n.FractionDigits); fd > 0 {
+			ofd := len(out) - fd
+			if ofd <= 0 {
+				// We want 0.1 not .1
+				out = space18[:-ofd+1] + out
+				ofd = 1
+			}
+			out = out[:ofd] + "." + out[ofd:]
+		}
+	}
+	if n.Negative {
+		out = "-" + out
+	}
+
+	return out
+}
+
+// Int returns n as an int64. It returns an error if n overflows an int64 or
+// the number is decimal.
+func (n Number) Int() (int64, error) {
+	if n.IsDecimal() {
+		return 0, errors.New("called Int() on decimal64 value")
+	}
+	if n.Negative {
+		return -int64(n.Value), nil
+	}
+	if n.Value <= MaxInt64 {
+		return int64(n.Value), nil
+	}
+	return 0, errors.New("signed integer overflow")
+}
+
+// addQuantum adds the smallest quantum to n without checking overflow.
+func (n Number) addQuantum(i uint64) Number {
+	switch n.Negative {
+	case true:
+		if n.Value <= i {
+			n.Value = i - n.Value
+			n.Negative = false
+		} else {
+			n.Value -= i
+		}
+	case false:
+		n.Value += i
+	}
+	return n
+}
+
+// Less returns true if n is less than m. Panics if n and m are a mix of integer
+// and decimal.
+func (n Number) Less(m Number) bool {
+	switch {
+	case n.Negative && !m.Negative:
+		return true
+	case !n.Negative && m.Negative:
+		return false
+	}
+
+	nt, mt := n.Trunc(), m.Trunc()
+	lt := nt < mt
+	if nt == mt {
+		nf, mf := n.frac(), m.frac()
+		if nf == mf {
+			return false
+		}
+		lt = nf < mf
+	}
+
+	if n.Negative {
+		return !lt
+	}
+	return lt
+}
+
+// Equal returns true if n is equal to m.
+func (n Number) Equal(m Number) bool {
+	return !n.Less(m) && !m.Less(n)
+}
+
+// Trunc returns the whole part of abs(n) as a signed integer.
+func (n Number) Trunc() uint64 {
+	nv := n.Value
+	e := pow10(n.FractionDigits)
+	return nv / e
+}
+
+// frac returns the fraction part with a precision of 18 fractional digits.
+// E.g. if n is 3.1 then n.frac() returns 100,000,000,000,000,000
+func (n Number) frac() uint64 {
+	frac := n.FractionDigits
+	i := n.Trunc() * pow10(frac)
+	return (n.Value - i) * pow10(uint8(18-frac))
+}
+
+// YRange is a single range of consecutive numbers, inclusive.
+type YRange struct {
+	Min Number
+	Max Number
+}
+
+// Valid returns false if r is not a valid range (min > max).
+func (r YRange) Valid() bool {
+	return !r.Max.Less(r.Min)
+}
+
+// String returns r as a string using YANG notation, either a simple
+// value if min == max or min..max.
+func (r YRange) String() string {
+	if r.Min.Equal(r.Max) {
+		return r.Min.String()
+	}
+	return r.Min.String() + ".." + r.Max.String()
+}
+
+// Equal compares whether two YRanges are equal.
+func (r YRange) Equal(s YRange) bool {
+	return r.Min.Equal(s.Min) && r.Max.Equal(s.Max)
+}
+
+// A YangRange is a set of non-overlapping ranges.
+type YangRange []YRange
+
+// String returns the ranges r using YANG notation.  Individual ranges
+// are separated by pipes (|).
+func (r YangRange) String() string {
+	s := make([]string, len(r))
+	for i, r := range r {
+		s[i] = r.String()
+	}
+	return strings.Join(s, "|")
+}
+
+func (r YangRange) Len() int      { return len(r) }
+func (r YangRange) Swap(i, j int) { r[i], r[j] = r[j], r[i] }
+func (r YangRange) Less(i, j int) bool {
+	switch {
+	case r[i].Min.Less(r[j].Min):
+		return true
+	case r[j].Min.Less(r[i].Min):
+		return false
+	default:
+		return r[i].Max.Less(r[j].Max)
+	}
+}
+
+// Validate returns an error if r has either an invalid range or has
+// overlapping ranges.
+// r is expected to be sorted use YangRange.Sort()
+func (r YangRange) Validate() error {
+	if !sort.IsSorted(r) {
+		return errors.New("range not sorted")
+	}
+	switch {
+	case len(r) == 0:
+		return nil
+	case !r[0].Valid():
+		return errors.New("invalid number")
+	}
+	p := r[0]
+
+	for _, n := range r[1:] {
+		if n.Min.Less(p.Max) {
+			return errors.New("overlapping ranges")
+		}
+	}
+	return nil
+}
+
+// Sort r. Must be called before Validate and coalesce if unsorted
+func (r YangRange) Sort() {
+	sort.Sort(r)
+}
+
+// Equal returns true if ranges r and q are identically equivalent.
+// TODO(borman): should we coalesce ranges in the comparison?
+func (r YangRange) Equal(q YangRange) bool {
+	if len(r) != len(q) {
+		return false
+	}
+	for i, r := range r {
+		if !r.Equal(q[i]) {
+			return false
+		}
+	}
+	return true
+}
+
+// Contains returns true if all possible values in s are also possible values
+// in r. An empty range is assumed to be min..max when it is the receiver
+// argument.
+func (r YangRange) Contains(s YangRange) bool {
+	if len(r) == 0 || len(s) == 0 {
+		return true
+	}
+
+	// Check if every range in s is subsumed under r.
+	// Both range lists should be in order and non-adjacent (coalesced).
+	ri := 0
+	for _, ss := range s {
+		for r[ri].Max.Less(ss.Min) {
+			ri++
+			if ri == len(r) {
+				return false
+			}
+		}
+		if ss.Min.Less(r[ri].Min) || r[ri].Max.Less(ss.Max) {
+			return false
+		}
+	}
+	return true
+}
+
+// FromInt creates a Number from an int64.
+func FromInt(i int64) Number {
+	if i < 0 {
+		return Number{Negative: true, Value: uint64(-i)}
+	}
+	return Number{Value: uint64(i)}
+}
+
+// FromUint creates a Number from a uint64.
+func FromUint(i uint64) Number {
+	return Number{Value: i}
+}
+
+// FromFloat creates a Number from a float64. Input values with absolute value
+// outside the boundaries specified for the decimal64 value specified in
+// RFC6020/RFC7950 are clamped down to the closest boundary value.
+func FromFloat(f float64) Number {
+	if f > MaxDecimal64 {
+		return Number{
+			Value:          FromInt(MaxInt64).Value,
+			FractionDigits: 1,
+		}
+	}
+	if f < MinDecimal64 {
+		return Number{
+			Negative:       true,
+			Value:          FromInt(MaxInt64).Value,
+			FractionDigits: 1,
+		}
+	}
+
+	// Per RFC7950/6020, fraction-digits must be at least 1.
+	fracDig := uint8(1)
+	f *= 10.0
+	for ; Frac(f) != 0.0 && fracDig <= MaxFractionDigits; fracDig++ {
+		f *= 10.0
+	}
+	negative := false
+	if f < 0 {
+		negative = true
+		f = -f
+	}
+	v := uint64(f)
+
+	return Number{Negative: negative, Value: v, FractionDigits: fracDig}
+}
+
+// ParseInt returns s as a Number with FractionDigits=0.
+// octal, or hexadecimal using the standard prefix notations (e.g., 0 and 0x)
+func ParseInt(s string) (Number, error) {
+	s = strings.TrimSpace(s)
+	var n Number
+	switch s {
+	case "":
+		return n, errors.New("converting empty string to number")
+	case "+", "-":
+		return n, errors.New("sign with no value")
+	}
+
+	ns := s
+	switch s[0] {
+	case '+':
+		ns = s[1:]
+	case '-':
+		n.Negative = true
+		ns = s[1:]
+	}
+
+	var err error
+	n.Value, err = strconv.ParseUint(ns, 0, 64)
+	return n, err
+}
+
+// ParseDecimal returns s as a Number with a non-zero FractionDigits.
+// octal, or hexadecimal using the standard prefix notations (e.g., 0 and 0x)
+func ParseDecimal(s string, fracDigRequired uint8) (n Number, err error) {
+	s = strings.TrimSpace(s)
+	switch s {
+	case "":
+		return n, errors.New("converting empty string to number")
+	case "+", "-":
+		return n, errors.New("sign with no value")
+	}
+
+	return decimalValueFromString(s, fracDigRequired)
+}
+
+// decimalValueFromString returns a decimal Number representation of numStr.
+// fracDigRequired is used to set the number of fractional digits, which must
+// be at least the greatest precision seen in numStr.
+// which must be between 1 and 18.
+// numStr must conform to Section 9.3.4.
+func decimalValueFromString(numStr string, fracDigRequired uint8) (n Number, err error) {
+	if fracDigRequired > MaxFractionDigits || fracDigRequired < 1 {
+		return n, fmt.Errorf("invalid number of fraction digits %d > max of %d, minimum 1", fracDigRequired, MaxFractionDigits)
+	}
+
+	s := numStr
+	dx := strings.Index(s, ".")
+	var fracDig uint8
+	if dx >= 0 {
+		fracDig = uint8(len(s) - 1 - dx)
+		// remove first decimal, if dx > 1, will fail ParseInt below
+		s = s[:dx] + s[dx+1:]
+	}
+
+	if fracDig > fracDigRequired {
+		return n, fmt.Errorf("%s has too much precision, expect <= %d fractional digits", s, fracDigRequired)
+	}
+
+	s += space18[:fracDigRequired-fracDig]
+
+	v, err := strconv.ParseInt(s, 10, 64)
+	if err != nil {
+		return n, fmt.Errorf("%s is not a valid decimal number: %s", numStr, err)
+	}
+
+	negative := false
+	if v < 0 {
+		negative = true
+		v = -v
+	}
+
+	return Number{Value: uint64(v), FractionDigits: fracDigRequired, Negative: negative}, nil
+}
+
+// ParseRangesInt parses s into a series of ranges. Each individual range is in s
+// is separated by the pipe character (|).  The min and max value of a range
+// are separated by "..".  An error is returned if the range is invalid. The
+// output range is sorted and coalesced.
+func ParseRangesInt(s string) (YangRange, error) {
+	return YangRange{}.parseChildRanges(s, false, 0)
+}
+
+// ParseRangesDecimal parses s into a series of ranges. Each individual range is in s
+// is separated by the pipe character (|).  The min and max value of a range
+// are separated by "..".  An error is returned if the range is invalid. The
+// output range is sorted and coalesced.
+func ParseRangesDecimal(s string, fracDigRequired uint8) (YangRange, error) {
+	return YangRange{}.parseChildRanges(s, true, fracDigRequired)
+}
+
+// parseChildRanges parses a child ranges statement 's' into a series of ranges
+// based on an already-parsed parent YangRange. Each individual range is in s
+// is separated by the pipe character (|). The min and max value of a range are
+// separated by "..". An error is returned if the child ranges are not
+// equally-limiting or more limiting than the parent range
+// (rfc7950#section-9.2.5). The output range is sorted and coalesced.
+// fracDigRequired is ignored when decimal=false.
+func (y YangRange) parseChildRanges(s string, decimal bool, fracDigRequired uint8) (YangRange, error) {
+	parseNumber := func(s string) (Number, error) {
+		switch {
+		case s == "max":
+			if len(y) == 0 {
+				return Number{}, errors.New("cannot resolve 'max' keyword using an empty YangRange parent object")
+			}
+			max := y[len(y)-1].Max
+			max.FractionDigits = fracDigRequired
+			return max, nil
+		case s == "min":
+			if len(y) == 0 {
+				return Number{}, errors.New("cannot resolve 'min' keyword using an empty YangRange parent object")
+			}
+			min := y[0].Min
+			min.FractionDigits = fracDigRequired
+			return min, nil
+		case decimal:
+			return ParseDecimal(s, fracDigRequired)
+		default:
+			return ParseInt(s)
+		}
+	}
+
+	parts := strings.Split(s, "|")
+	r := make(YangRange, len(parts))
+	for i, s := range parts {
+		parts := strings.Split(s, "..")
+		min, err := parseNumber(strings.TrimSpace(parts[0]))
+		if err != nil {
+			return nil, err
+		}
+		var max Number
+		switch len(parts) {
+		case 1:
+			max = min
+		case 2:
+			if max, err = parseNumber(strings.TrimSpace(parts[1])); err != nil {
+				return nil, err
+			}
+		default:
+			return nil, fmt.Errorf("too many '..' in %s", s)
+		}
+		if max.Less(min) {
+			return nil, fmt.Errorf("range boundaries out of order (%s less than %s): %s", max, min, s)
+		}
+		r[i] = YRange{min, max}
+	}
+	r.Sort()
+	r = coalesce(r)
+
+	if !y.Contains(r) {
+		return nil, fmt.Errorf("%v not within %v", s, y)
+	}
+
+	if err := r.Validate(); err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+// coalesce coalesces r into as few ranges as possible.  For example,
+// 1..5|6..10 would become 1..10.  r is assumed to be sorted.
+func coalesce(r YangRange) YangRange {
+	// coalesce the ranges if we have more than 1.
+	if len(r) < 2 {
+		return r
+	}
+	cr := make(YangRange, len(r))
+	i := 0
+	cr[i] = r[0]
+	for _, r1 := range r[1:] {
+		// r1.Min is always at least as large as cr[i].Min
+		// Cases are:
+		// r1 is contained in cr[i]
+		// r1 starts inside of cr[i]
+		// r1.Min cr[i].Max+1
+		// r1 is beyond cr[i]
+		if cr[i].Max.addQuantum(1).Less(r1.Min) {
+			// r1 starts after cr[i], this is a new range
+			i++
+			cr[i] = r1
+		} else if cr[i].Max.Less(r1.Max) {
+			cr[i].Max = r1.Max
+		}
+	}
+	return cr[:i+1]
+}
+
+func mustParseRangesInt(s string) YangRange {
+	r, err := ParseRangesInt(s)
+	if err != nil {
+		panic(err)
+	}
+	return r
+}
+
+func mustParseRangesDecimal(s string, fracDigRequired uint8) YangRange {
+	r, err := ParseRangesDecimal(s, fracDigRequired)
+	if err != nil {
+		panic(err)
+	}
+	return r
+}
+
+// Frac returns the fractional part of f.
+func Frac(f float64) float64 {
+	return f - math.Trunc(f)
+}
+
+// pow10 returns 10^e without checking for overflow.
+func pow10(e uint8) uint64 {
+	var out uint64 = 1
+	for i := uint8(0); i < e; i++ {
+		out *= 10
+	}
+	return out
+}
+
+// A EnumType represents a mapping of strings to integers.  It is used both
+// for enumerations as well as bitfields.
+type EnumType struct {
+	last     int64            // maximum value assigned thus far
+	min      int64            // minimum value allowed
+	max      int64            // maximum value allowed
+	unique   bool             // numeric values must be unique (enums)
+	ToString map[int64]string `json:",omitempty"` // map of enum entries by value (integer)
+	ToInt    map[string]int64 `json:",omitempty"` // map of enum entries by name (string)
+}
+
+// NewEnumType returns an initialized EnumType.
+func NewEnumType() *EnumType {
+	return &EnumType{
+		last:     -1, // +1 will start at 0
+		min:      MinEnum,
+		max:      MaxEnum,
+		unique:   true,
+		ToString: map[int64]string{},
+		ToInt:    map[string]int64{},
+	}
+}
+
+// NewBitfield returns an EnumType initialized as a bitfield.  Multiple string
+// values may map to the same numeric values.  Numeric values must be small
+// non-negative integers.
+func NewBitfield() *EnumType {
+	return &EnumType{
+		last:     -1, // +1 will start at 0
+		min:      0,
+		max:      MaxBitfieldSize - 1,
+		ToString: map[int64]string{},
+		ToInt:    map[string]int64{},
+	}
+}
+
+// Set sets name in e to the provided value.  Set returns an error if the value
+// is invalid, name is already signed, or when used as an enum rather than a
+// bitfield, the value has previousl been used.  When two different names are
+// assigned to the same value, the conversion from value to name will result in
+// the most recently assigned name.
+func (e *EnumType) Set(name string, value int64) error {
+	if _, ok := e.ToInt[name]; ok {
+		return fmt.Errorf("field %s already assigned", name)
+	}
+	if oname, ok := e.ToString[value]; e.unique && ok {
+		return fmt.Errorf("fields %s and %s conflict on value %d", name, oname, value)
+	}
+	if value < e.min {
+		return fmt.Errorf("value %d for %s too small (minimum is %d)", value, name, e.min)
+	}
+	if value > e.max {
+		return fmt.Errorf("value %d for %s too large (maximum is %d)", value, name, e.max)
+	}
+	e.ToString[value] = name
+	e.ToInt[name] = value
+	if value >= e.last {
+		e.last = value
+	}
+	return nil
+}
+
+// SetNext sets the name in e using the next possible value that is greater than
+// all previous values.
+func (e *EnumType) SetNext(name string) error {
+	if e.last == MaxEnum {
+		return fmt.Errorf("enum %q must specify a value since previous enum is the maximum value allowed", name)
+	}
+	return e.Set(name, e.last+1)
+}
+
+// Name returns the name in e associated with value.  The empty string is
+// returned if no name has been assigned to value.
+func (e *EnumType) Name(value int64) string { return e.ToString[value] }
+
+// Value returns the value associated with name in e associated.  0 is returned
+// if name is not in e, or if it is the first value in an unnumbered enum. Use
+// IsDefined to definitively confirm name is in e.
+func (e *EnumType) Value(name string) int64 { return e.ToInt[name] }
+
+// IsDefined returns true if name is defined in e, else false.
+func (e *EnumType) IsDefined(name string) bool {
+	_, defined := e.ToInt[name]
+	return defined
+}
+
+// Names returns the sorted list of enum string names.
+func (e *EnumType) Names() []string {
+	names := make([]string, len(e.ToInt))
+	i := 0
+	for name := range e.ToInt {
+		names[i] = name
+		i++
+	}
+	sort.Strings(names)
+	return names
+}
+
+type int64Slice []int64
+
+func (p int64Slice) Len() int           { return len(p) }
+func (p int64Slice) Less(i, j int) bool { return p[i] < p[j] }
+func (p int64Slice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
+// Values returns the sorted list of enum values.
+func (e *EnumType) Values() []int64 {
+	values := make([]int64, len(e.ToInt))
+	i := 0
+	for _, value := range e.ToInt {
+		values[i] = value
+		i++
+	}
+	sort.Sort(int64Slice(values))
+	return values
+}
+
+// NameMap returns a map of names to values.
+func (e *EnumType) NameMap() map[string]int64 {
+	m := make(map[string]int64, len(e.ToInt))
+	for name, value := range e.ToInt {
+		m[name] = value
+	}
+	return m
+}
+
+// ValueMap returns a map of values to names.
+func (e *EnumType) ValueMap() map[int64]string {
+	m := make(map[int64]string, len(e.ToString))
+	for name, value := range e.ToString {
+		m[name] = value
+	}
+	return m
+}

src/webui/internal/goyang/pkg/yang/types_builtin_test.go

@@ -0,0 +1,915 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/openconfig/gnmi/errdiff"
+)
+
+const (
+	maxUint64 uint64 = 18446744073709551615
+	maxUint32        = 0xFFFFFFFF
+	maxUint16        = 0xFFFF
+	maxUint8         = 0xFF
+	maxInt32         = 1<<31 - 1
+	minInt32         = -1 << 31
+	maxInt16         = 1<<15 - 1
+	minInt16         = -1 << 15
+	maxInt8          = 1<<7 - 1
+	minInt8          = -1 << 7
+)
+
+// R is a test helper for creating an int-based YRange.
+func R(a, b int64) YRange {
+	return YRange{FromInt(a), FromInt(b)}
+}
+
+// Rf is a test helper for creating a float-based YRange.
+func Rf(a, b int64, fracDig uint8) YRange {
+	n1 := Number{Value: uint64(a), FractionDigits: fracDig}
+	n2 := Number{Value: uint64(b), FractionDigits: fracDig}
+	if a < 0 {
+		n1.Value = uint64(-a)
+		n1.Negative = true
+	}
+	if b < 0 {
+		n2.Value = uint64(-b)
+		n2.Negative = true
+	}
+	return YRange{n1, n2}
+}
+
+func TestFromFloat(t *testing.T) {
+	tests := []struct {
+		desc string
+		in   float64
+		want Number
+	}{{
+		desc: "positive - no decimals",
+		in:   10.0,
+		want: Number{
+			Negative:       false,
+			Value:          10,
+			FractionDigits: 0,
+		},
+	}, {
+		desc: "positive - decimals",
+		in:   10.15,
+		want: Number{
+			Negative:       false,
+			Value:          1015,
+			FractionDigits: 2,
+		},
+	}, {
+		desc: "negative - no decimals",
+		in:   -10.0,
+		want: Number{
+			Negative:       true,
+			Value:          10,
+			FractionDigits: 0,
+		},
+	}, {
+		desc: "negative - decimals",
+		in:   -10.15,
+		want: Number{
+			Negative:       true,
+			Value:          1015,
+			FractionDigits: 2,
+		},
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			if got := FromFloat(tt.in); !cmp.Equal(got, tt.want) {
+				t.Fatalf("FromFloat(%v): did not get expected value, got: %+v, want: %+v", tt.in, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNumberInt(t *testing.T) {
+	tests := []struct {
+		desc    string
+		in      Number
+		want    int64
+		wantErr bool
+	}{{
+		desc: "zero",
+		in:   FromInt(0),
+		want: 0,
+	}, {
+		desc: "positive",
+		in:   FromInt(42),
+		want: 42,
+	}, {
+		desc: "negative",
+		in:   FromInt(-42),
+		want: -42,
+	}, {
+		desc:    "decimal",
+		in:      FromFloat(42),
+		wantErr: true,
+	}, {
+		desc:    "overflow",
+		in:      FromUint(maxUint64),
+		wantErr: true,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got, err := tt.in.Int()
+			if got != tt.want {
+				t.Errorf("got: %v, want: %v", got, tt.want)
+			}
+			if (err != nil) != tt.wantErr {
+				t.Errorf("gotErr: %v, wantErr: %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
+func TestRangeEqual(t *testing.T) {
+	tests := []struct {
+		desc        string
+		inBaseRange YangRange
+		inTestRange YangRange
+		want        bool
+	}{{
+		desc: "empty range equals empty range",
+		want: true,
+	}, {
+		desc:        "test range is default",
+		inBaseRange: YangRange{R(1, 2)}, want: false,
+	}, {
+		desc:        "base range is default",
+		inTestRange: YangRange{R(1, 2)}, want: false,
+	}, {
+		desc:        "equal ranges",
+		inBaseRange: YangRange{R(1, 2)},
+		inTestRange: YangRange{R(1, 2)},
+		want:        true,
+	}, {
+		desc:        "wider base range",
+		inBaseRange: YangRange{R(1, 3)},
+		inTestRange: YangRange{R(1, 2)},
+		want:        false,
+	}, {
+		desc:        "equal ranges with multiple subranges",
+		inBaseRange: YangRange{R(1, 2), R(4, 5)},
+		inTestRange: YangRange{R(1, 2), R(4, 5)},
+		want:        true,
+	}, {
+		desc:        "multiple subranges with one unequal",
+		inBaseRange: YangRange{R(1, 2), R(4, 6)},
+		inTestRange: YangRange{R(1, 2), R(4, 5)},
+		want:        false,
+	}, {
+		desc:        "extra subrange in base range",
+		inBaseRange: YangRange{R(1, 2)},
+		inTestRange: YangRange{R(1, 2), R(4, 5)},
+		want:        false,
+	}, {
+		desc:        "extra subrange in test range",
+		inBaseRange: YangRange{R(1, 2), R(4, 5)},
+		inTestRange: YangRange{R(1, 2)},
+		want:        false,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			if want := tt.inBaseRange.Equal(tt.inTestRange); want != tt.want {
+				t.Errorf("got %v, want %v", want, tt.want)
+			}
+		})
+	}
+}
+
+func TestRangeContains(t *testing.T) {
+	tests := []struct {
+		desc        string
+		inBaseRange YangRange
+		inTestRange YangRange
+		want        bool
+	}{{
+		desc: "empty range contained in empty range",
+		want: true,
+	}, {
+		desc:        "empty range contained in non-empty range",
+		inBaseRange: YangRange{R(1, 2)},
+		want:        true,
+	}, {
+		desc:        "non-empty range contained in empty range",
+		inTestRange: YangRange{R(1, 2)},
+		want:        true,
+	}, {
+		desc:        "equal ranges contain",
+		inBaseRange: YangRange{R(1, 2)},
+		inTestRange: YangRange{R(1, 2)},
+		want:        true,
+	}, {
+		desc:        "superset contains",
+		inBaseRange: YangRange{R(1, 5)},
+		inTestRange: YangRange{R(2, 3)},
+		want:        true,
+	}, {
+		desc:        "subset doesn't contain",
+		inBaseRange: YangRange{R(2, 3)},
+		inTestRange: YangRange{R(1, 5)},
+		want:        false,
+	}, {
+		desc:        "contain subranges",
+		inBaseRange: YangRange{R(1, 10)},
+		inTestRange: YangRange{R(1, 2), R(4, 5), R(7, 10)},
+		want:        true,
+	}, {
+		desc:        "subranges leaks out",
+		inBaseRange: YangRange{R(1, 10)},
+		inTestRange: YangRange{R(1, 2), R(7, 11)},
+		want:        false,
+	}, {
+		desc:        "subranges containing a subset",
+		inBaseRange: YangRange{R(1, 9), R(11, 19), R(21, 29)},
+		inTestRange: YangRange{R(23, 25)},
+		want:        true,
+	}, {
+		desc:        "subranges containing a single valued range",
+		inBaseRange: YangRange{R(1, 9), R(11, 19), R(21, 29)},
+		inTestRange: YangRange{R(23, 23)},
+		want:        true,
+	}, {
+		desc:        "subranges doesn't contain a single outside value",
+		inBaseRange: YangRange{R(1, 9), R(11, 19), R(21, 29)},
+		inTestRange: YangRange{R(20, 20)},
+		want:        false,
+	}, {
+		desc:        "smaller range doesn't contain min..max",
+		inBaseRange: YangRange{R(1, 10)},
+		inTestRange: YangRange{R(MinInt64, MaxInt64)},
+		want:        false,
+	}, {
+		desc:        "full range contains any",
+		inBaseRange: YangRange{R(MinInt64, MaxInt64)},
+		inTestRange: YangRange{R(1, 10)},
+		want:        true,
+	}, {
+		desc:        "smaller range doesn't contain min..a|b..max",
+		inBaseRange: YangRange{R(1024, 65535)},
+		inTestRange: YangRange{R(MinInt64, 4096), R(5120, MaxInt64)},
+		want:        false,
+	}, {
+		desc:        "ranges don't overlap with max word used",
+		inBaseRange: YangRange{R(1024, 65535)},
+		inTestRange: YangRange{R(-999999, 4096), R(5120, MaxInt64)},
+		want:        false,
+	}, {
+		desc:        "ranges don't overlap with min word used",
+		inBaseRange: YangRange{R(1024, 65535)},
+		inTestRange: YangRange{R(MinInt64, 4096), R(5120, 999999)},
+		want:        false,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			if got := tt.inBaseRange.Contains(tt.inTestRange); got != tt.want {
+				t.Errorf("got %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestParseRangesInt(t *testing.T) {
+	tests := []struct {
+		desc             string
+		inParentRange    YangRange
+		in               string
+		want             YangRange
+		wantErrSubstring string
+	}{{
+		desc: "small numbers, coalescing",
+		in:   "0|2..3|4..5",
+		want: YangRange{R(0, 0), R(2, 5)},
+	}, {
+		desc: "small numbers, out of order, coalescing",
+		in:   "4..5|0|2..3",
+		want: YangRange{R(0, 0), R(2, 5)},
+	}, {
+		desc:             "invalid input: too many ..s",
+		in:               "0|2..3|4..5..6",
+		wantErrSubstring: "too many '..' in 4..5..6",
+	}, {
+		desc:             "invalid input: range boundaries out of order",
+		in:               "0|2..3|5..4",
+		wantErrSubstring: "range boundaries out of order",
+	}, {
+		desc:          "range with min",
+		inParentRange: Int64Range,
+		in:            "min..0|2..3|4..5",
+		want:          YangRange{R(MinInt64, 0), R(2, 5)},
+	}, {
+		desc:             "range with min but without parent range",
+		in:               "min..0|2..3|4..5",
+		wantErrSubstring: "empty YangRange parent object",
+	}, {
+		desc:          "range with max",
+		inParentRange: Int32Range,
+		in:            "min..0|2..3|4..5|7..max",
+		want:          YangRange{R(minInt32, 0), R(2, 5), R(7, maxInt32)},
+	}, {
+		desc:          "coalescing from min to max for uint64",
+		inParentRange: Uint64Range,
+		in:            "min..0|1..max",
+		want:          YangRange{YRange{FromInt(0), FromUint(maxUint64)}},
+	}, {
+		desc:          "coalescing from min to max for uint32",
+		inParentRange: Uint32Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(0, maxUint32)},
+	}, {
+		desc:          "coalescing from min to max for uint16",
+		inParentRange: Uint16Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(0, maxUint16)},
+	}, {
+		desc:          "coalescing from min to max for uint8",
+		inParentRange: Uint8Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(0, maxUint8)},
+	}, {
+		desc:          "coalescing from min to max for int64",
+		inParentRange: Int64Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(MinInt64, MaxInt64)},
+	}, {
+		desc:          "coalescing from min to max for int32",
+		inParentRange: Int32Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(minInt32, maxInt32)},
+	}, {
+		desc:          "coalescing from min to max for int16",
+		inParentRange: Int16Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(minInt16, maxInt16)},
+	}, {
+		desc:          "coalescing from min to max for int8",
+		inParentRange: Int8Range,
+		in:            "min..0|1..max",
+		want:          YangRange{R(minInt8, maxInt8)},
+	}, {
+		desc:             "spelling error",
+		inParentRange:    Int64Range,
+		in:               "mean..0|1..max",
+		wantErrSubstring: "invalid syntax",
+	}, {
+		desc: "big numbers, coalescing",
+		in:   "0..69|4294967294|4294967295",
+		want: YangRange{R(0, 69), R(4294967294, 4294967295)},
+	}, {
+		desc: "no ranges",
+		in:   "250|500|1000",
+		want: YangRange{R(250, 250), R(500, 500), R(1000, 1000)},
+	}, {
+		desc: "no ranges unsorted",
+		in:   "1000|500|250",
+		want: YangRange{R(250, 250), R(500, 500), R(1000, 1000)},
+	}, {
+		desc: "negative numbers",
+		in:   "-31..-1|1..31",
+		want: YangRange{R(-31, -1), R(1, 31)},
+	}, {
+		desc: "spaces",
+		in:   "-22 | -15 | -7 | 0",
+		want: YangRange{R(-22, -22), R(-15, -15), R(-7, -7), R(0, 0)},
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got, err := tt.inParentRange.parseChildRanges(tt.in, false, 0)
+			if err != nil {
+				if diff := errdiff.Substring(err, tt.wantErrSubstring); diff != "" {
+					t.Fatalf("did not get expected error, %s", diff)
+				}
+				return
+			}
+
+			if diff := cmp.Diff(tt.want, got); diff != "" {
+				t.Errorf("parseChildRanges (-want, +got):\n%s", diff)
+			}
+
+			if tt.inParentRange == nil {
+				if got, err = ParseRangesInt(tt.in); err != nil {
+					t.Fatalf("ParseRangesInt: unexpected error: %v", err)
+				}
+				if diff := cmp.Diff(tt.want, got); diff != "" {
+					t.Errorf("ParseRangesInt (-want, +got):\n%s", diff)
+				}
+			}
+		})
+	}
+}
+
+func TestCoalesce(t *testing.T) {
+	for x, tt := range []struct {
+		in, out YangRange
+	}{
+		{},
+		{YangRange{R(1, 4)}, YangRange{R(1, 4)}},
+		{YangRange{R(1, 2), R(3, 4)}, YangRange{R(1, 4)}},
+		{YangRange{Rf(10, 25, 1), Rf(30, 40, 1)}, YangRange{Rf(10, 25, 1), Rf(30, 40, 1)}},
+		{YangRange{Rf(10, 29, 1), Rf(30, 40, 1)}, YangRange{Rf(10, 40, 1)}},
+		{YangRange{R(1, 2), R(2, 4)}, YangRange{R(1, 4)}},
+		{YangRange{R(1, 2), R(4, 5)}, YangRange{R(1, 2), R(4, 5)}},
+		{YangRange{R(1, 3), R(2, 5)}, YangRange{R(1, 5)}},
+		{YangRange{R(1, 10), R(2, 5)}, YangRange{R(1, 10)}},
+		{YangRange{R(1, 10), R(1, 2), R(4, 5), R(7, 8)}, YangRange{R(1, 10)}},
+		{YangRange{Rf(1, 10, 3), Rf(1, 2, 3), Rf(4, 5, 3), Rf(7, 8, 3)}, YangRange{Rf(1, 10, 3)}},
+	} {
+		out := coalesce(tt.in)
+		if !out.Equal(tt.out) {
+			t.Errorf("#%d: got %v, want %v", x, out, tt.out)
+		}
+	}
+}
+
+func TestYangRangeSort(t *testing.T) {
+	for x, tt := range []struct {
+		in, out YangRange
+	}{
+		{YangRange{}, YangRange{}},
+		{YangRange{R(1, 4), R(6, 10)}, YangRange{R(1, 4), R(6, 10)}},
+		{YangRange{R(6, 10), R(1, 4)}, YangRange{R(1, 4), R(6, 10)}},
+		{YangRange{Rf(10, 25, 1), Rf(30, 40, 1)}, YangRange{Rf(10, 25, 1), Rf(30, 40, 1)}},
+		{YangRange{Rf(30, 40, 1), Rf(10, 25, 1)}, YangRange{Rf(10, 25, 1), Rf(30, 40, 1)}},
+		{YangRange{R(1, 2)}, YangRange{R(1, 2)}},
+		{YangRange{R(1, 2), R(4, 5)}, YangRange{R(1, 2), R(4, 5)}},
+		{YangRange{R(1, 3), R(2, 5)}, YangRange{R(1, 3), R(2, 5)}},
+		{YangRange{R(1, 10), R(2, 5)}, YangRange{R(1, 10), R(2, 5)}},
+		{YangRange{R(1, 10), R(1, 2), R(4, 5), R(7, 8)}, YangRange{R(1, 2), R(1, 10), R(4, 5), R(7, 8)}},
+	} {
+		tt.in.Sort()
+		if !tt.in.Equal(tt.out) {
+			t.Errorf("#%d: got %v, want %v", x, tt.in, tt.out)
+		}
+	}
+}
+
+func TestParseRangesDecimal(t *testing.T) {
+	rangeMax := mustParseRangesDecimal("-922337203685477580.8..922337203685477580.7", 1)
+	rangeRestricted := mustParseRangesDecimal("-42..42|100", 5)
+
+	tests := []struct {
+		desc             string
+		inParentRange    YangRange
+		in               string
+		inFracDig        uint8
+		want             YangRange
+		wantErrSubstring string
+	}{{
+		desc:          "min..max fraction-digits 1",
+		inParentRange: rangeMax,
+		in:            "min..max",
+		inFracDig:     1,
+		want:          YangRange{Rf(MinInt64, MaxInt64, 1)},
+	}, {
+		desc:          "min..max fraction-digits 2",
+		inParentRange: rangeMax,
+		in:            "min..max",
+		inFracDig:     2,
+		want:          YangRange{Rf(MinInt64, MaxInt64, 2)},
+	}, {
+		desc:             "min..max no parent range",
+		in:               "min..max",
+		inFracDig:        2,
+		want:             YangRange{Rf(MinInt64, MaxInt64, 2)},
+		wantErrSubstring: "empty YangRange parent object",
+	}, {
+		desc:             "min..max on fragmented range",
+		inParentRange:    rangeRestricted,
+		in:               "min..max",
+		inFracDig:        5,
+		wantErrSubstring: "not within",
+	}, {
+		desc:          "small decimals",
+		inParentRange: rangeMax,
+		in:            "0.0|2.0..30.0|1.34..1.99",
+		inFracDig:     2,
+		want:          YangRange{Rf(0, 0, 2), Rf(134, 3000, 2)},
+	}, {
+		desc:          "small decimals on restricted range",
+		inParentRange: rangeRestricted,
+		in:            "0.0|2.0..30.0|1.34..1.99999",
+		inFracDig:     5,
+		want:          YangRange{Rf(0, 0, 5), Rf(134000, 3000000, 5)},
+	}, {
+		desc:          "small decimals with coalescing",
+		inParentRange: rangeMax,
+		in:            "0.0|2.0..30.0",
+		inFracDig:     1,
+		want:          YangRange{Rf(0, 0, 1), Rf(20, 300, 1)},
+	}, {
+		desc:             "fractional digit cannot be too high",
+		in:               "0.0|2.0..30.0",
+		inFracDig:        19,
+		wantErrSubstring: "invalid number of fraction digits",
+	}, {
+		desc:             "fractional digit cannot be 0",
+		in:               "0.0|2.0..30.0",
+		inFracDig:        0,
+		wantErrSubstring: "invalid number of fraction digits",
+	}, {
+		desc:      "big decimals",
+		in:        "0.0..69|4294967294.1234|4294967295.1234",
+		inFracDig: 4,
+		want:      YangRange{Rf(0, 690000, 4), Rf(42949672941234, 42949672941234, 4), Rf(42949672951234, 42949672951234, 4)},
+	}, {
+		desc:      "small decimals, out of order",
+		in:        "4.0..5.55|0|2.32..3.23",
+		inFracDig: 3,
+		want:      YangRange{Rf(0, 0, 3), Rf(2320, 3230, 3), Rf(4000, 5550, 3)},
+	}, {
+		desc:             "invalid input: too many ..s",
+		in:               "4.0..5.55..6.66|0|2.32..3.23",
+		inFracDig:        3,
+		wantErrSubstring: "too many '..'",
+	}, {
+		desc:             "invalid input: range boundaries out of order",
+		in:               "5..4.0|0|2.32..3.23",
+		inFracDig:        3,
+		wantErrSubstring: "range boundaries out of order",
+	}, {
+		desc:          "range with min",
+		inParentRange: rangeMax,
+		in:            "4.0..5.55|min..0|2.32..3.23",
+		inFracDig:     3,
+		want:          YangRange{Rf(MinInt64, 0, 3), Rf(2320, 3230, 3), Rf(4000, 5550, 3)},
+	}, {
+		desc:          "range with max",
+		inParentRange: rangeMax,
+		in:            "4.0..max|min..0|2.32..3.23",
+		inFracDig:     3,
+		want:          YangRange{Rf(MinInt64, 0, 3), Rf(2320, 3230, 3), Rf(4000, MaxInt64, 3)},
+	}, {
+		desc:          "coalescing from min to max",
+		inParentRange: rangeMax,
+		in:            "min..0.9|1..max",
+		inFracDig:     1,
+		want:          YangRange{Rf(MinInt64, MaxInt64, 1)},
+	}, {
+		desc:             "spelling error",
+		inParentRange:    rangeMax,
+		in:               "min..0.9|1..masks",
+		inFracDig:        1,
+		wantErrSubstring: "invalid syntax",
+	}, {
+		desc:      "no ranges",
+		in:        "250.55|500.0|1000",
+		inFracDig: 2,
+		want:      YangRange{Rf(25055, 25055, 2), Rf(50000, 50000, 2), Rf(100000, 100000, 2)},
+	}, {
+		desc:      "no ranges unsorted",
+		in:        "1000|500.0|250.55",
+		inFracDig: 2,
+		want:      YangRange{Rf(25055, 25055, 2), Rf(50000, 50000, 2), Rf(100000, 100000, 2)},
+	}, {
+		desc:      "negative decimals",
+		in:        "-31.2..-1.5|1.5..31.2",
+		inFracDig: 1,
+		want:      YangRange{Rf(-312, -15, 1), Rf(15, 312, 1)},
+	}, {
+		desc:      "spaces",
+		in:        "-22.5 | -15 | -7.5 | 0",
+		inFracDig: 1,
+		want:      YangRange{Rf(-225, -225, 1), Rf(-150, -150, 1), Rf(-75, -75, 1), Rf(0, 0, 1)},
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got, err := tt.inParentRange.parseChildRanges(tt.in, true, tt.inFracDig)
+			if err != nil {
+				if diff := errdiff.Substring(err, tt.wantErrSubstring); diff != "" {
+					t.Fatalf("did not get expected error, %s", diff)
+				}
+				return
+			}
+
+			if diff := cmp.Diff(tt.want, got); diff != "" {
+				t.Errorf("(-want, +got):\n%s", diff)
+			}
+
+			if tt.inParentRange == nil {
+				if got, err = ParseRangesDecimal(tt.in, tt.inFracDig); err != nil {
+					t.Fatalf("ParseRangesDecimal: unexpected error: %v", err)
+				}
+				if diff := cmp.Diff(tt.want, got); diff != "" {
+					t.Errorf("ParseRangesDecimal (-want, +got):\n%s", diff)
+				}
+			}
+		})
+	}
+}
+
+func TestAdd(t *testing.T) {
+	tests := []struct {
+		desc  string
+		inVal Number
+		inAdd uint64
+		want  Number
+	}{{
+		desc:  "add one to integer",
+		inVal: FromInt(1),
+		inAdd: 1,
+		want:  FromInt(2),
+	}, {
+		desc:  "add one to decimal64",
+		inVal: FromFloat(1.0),
+		inAdd: 1,
+		want:  FromFloat(1.1),
+	}, {
+		desc:  "negative int becomes positive",
+		inVal: FromInt(-2),
+		inAdd: 3,
+		want:  FromInt(1),
+	}, {
+		desc:  "negative int stays negative",
+		inVal: FromInt(-3),
+		inAdd: 1,
+		want:  FromInt(-2),
+	}, {
+		desc:  "negative decimal becomes positive",
+		inVal: FromFloat(-2),
+		inAdd: 35,
+		want:  FromFloat(1.5),
+	}, {
+		desc:  "negative decimal stays negative",
+		inVal: FromFloat(-42.22),
+		inAdd: 4122,
+		want:  FromFloat(-1.0),
+	}, {
+		desc:  "explicitly set fraction digits",
+		inVal: Number{Value: 10000, FractionDigits: 5},
+		inAdd: 1,
+		want:  Number{Value: 10001, FractionDigits: 5},
+	}, {
+		desc:  "explicitly set fraction digits - negative",
+		inVal: Number{Value: 0, FractionDigits: 3},
+		inAdd: 42,
+		want:  FromFloat(0.042),
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got := tt.inVal.addQuantum(tt.inAdd)
+			if !cmp.Equal(got, tt.want) {
+				t.Fatalf("did get expected result, got: %s, want: %s", got.String(), tt.want.String())
+			}
+		})
+	}
+}
+
+func TestParseInt(t *testing.T) {
+	tests := []struct {
+		desc             string
+		inStr            string
+		want             Number
+		wantErrSubstring string
+	}{{
+		desc:             "invalid string supplied",
+		inStr:            "fish",
+		wantErrSubstring: "valid syntax",
+	}, {
+		desc:  "negative int",
+		inStr: "-42",
+		want:  FromInt(-42),
+	}, {
+		desc:  "positive int",
+		inStr: "42",
+		want:  FromInt(42),
+	}, {
+		desc:  "positive int with plus sign",
+		inStr: "+42",
+		want:  FromInt(42),
+	}, {
+		desc:  "zero",
+		inStr: "0",
+		want:  FromInt(0),
+	}, {
+		desc:             "min",
+		inStr:            "min",
+		wantErrSubstring: "invalid syntax",
+	}, {
+		desc:             "max",
+		inStr:            "max",
+		wantErrSubstring: "invalid syntax",
+	}, {
+		desc:             "just a sign",
+		inStr:            "-",
+		wantErrSubstring: "sign with no value",
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got, err := ParseInt(tt.inStr)
+			if err != nil {
+				if diff := errdiff.Substring(err, tt.wantErrSubstring); diff != "" {
+					t.Fatalf("did not get expected error, %s", diff)
+				}
+				return
+			}
+
+			if !cmp.Equal(got, tt.want) {
+				t.Errorf("did not get expected Number, got: %s, want: %s", got, tt.want)
+			}
+
+			if got.IsDecimal() {
+				t.Errorf("Got decimal value instead of int: %v", got)
+			}
+		})
+	}
+}
+
+func TestParseDecimal(t *testing.T) {
+	tests := []struct {
+		desc                    string
+		inStr                   string
+		inFracDig               uint8
+		skipFractionDigitsCheck bool
+		want                    Number
+		wantErrSubstring        string
+	}{{
+		desc:             "too few fractional digits",
+		inStr:            "1.000",
+		inFracDig:        0,
+		wantErrSubstring: "invalid number of fraction digits",
+	}, {
+		desc:             "too many fraction digits",
+		inStr:            "1.000",
+		inFracDig:        24,
+		wantErrSubstring: "invalid number of fraction digits",
+	}, {
+		desc:             "more digits supplied",
+		inStr:            "1.14242",
+		inFracDig:        2,
+		wantErrSubstring: "has too much precision",
+	}, {
+		desc:      "single digit precision",
+		inStr:     "1.1",
+		inFracDig: 1,
+		want:      Number{Value: 11, FractionDigits: 1},
+	}, {
+		desc:                    "max precision",
+		inStr:                   "0.100000000000000000",
+		inFracDig:               18,
+		skipFractionDigitsCheck: true,
+		want:                    FromFloat(0.1),
+	}, {
+		desc:                    "max precision but not supplied",
+		inStr:                   "0.1",
+		inFracDig:               4,
+		skipFractionDigitsCheck: true,
+		want:                    FromFloat(0.1),
+	}, {
+		desc:             "invalid string supplied",
+		inStr:            "fish",
+		inFracDig:        17,
+		wantErrSubstring: "not a valid decimal number",
+	}, {
+		desc:      "negative number",
+		inStr:     "-42.0",
+		inFracDig: 1,
+		want:      FromFloat(-42),
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got, err := ParseDecimal(tt.inStr, tt.inFracDig)
+			if err != nil {
+				if diff := errdiff.Substring(err, tt.wantErrSubstring); diff != "" {
+					t.Fatalf("did not get expected error, %s", diff)
+				}
+				return
+			}
+
+			if !cmp.Equal(got, tt.want) {
+				t.Errorf("did not get expected Number, got: %s, want: %s", got, tt.want)
+			}
+
+			if !tt.skipFractionDigitsCheck {
+				if got, want := got.FractionDigits, tt.want.FractionDigits; got != want {
+					t.Errorf("fractional digits not equal, got: %d, want: %d", got, want)
+				}
+			}
+
+			if !got.IsDecimal() {
+				t.Errorf("Got non-decimal value: %v", got)
+			}
+		})
+	}
+}
+
+func TestNumberString(t *testing.T) {
+	tests := []struct {
+		desc string
+		in   Number
+		want string
+	}{{
+		desc: "min",
+		in:   FromInt(MinInt64),
+		want: "-9223372036854775808",
+	}, {
+		desc: "max",
+		in:   FromInt(MaxInt64),
+		want: "9223372036854775807",
+	}, {
+		desc: "integer",
+		in:   Number{Value: 1},
+		want: "1",
+	}, {
+		desc: "negative integer",
+		in:   Number{Value: 1, Negative: true},
+		want: "-1",
+	}, {
+		desc: "decimal, fractional digits = 1",
+		in:   Number{Value: 1, FractionDigits: 1},
+		want: "0.1",
+	}, {
+		desc: "decimal, fractional digits = 18",
+		in:   Number{Value: 123456789012345678, FractionDigits: 18},
+		want: "0.123456789012345678",
+	}, {
+		desc: "negative decimal",
+		in:   Number{Value: 100, FractionDigits: 2, Negative: true},
+		want: "-1.00",
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			if got := tt.in.String(); got != tt.want {
+				t.Fatalf("did not get expected number, got: %s, want: %s", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestEnumToJson(t *testing.T) {
+	tests := []struct {
+		desc    string
+		in      *EnumType
+		want    string
+		wantErr bool
+	}{{
+		"empty enum to JSON",
+		&EnumType{
+			last:     -1, // +1 will start at 0
+			min:      0,
+			max:      MaxBitfieldSize - 1,
+			ToString: map[int64]string{},
+			ToInt:    map[string]int64{},
+		},
+		`{}`,
+		false,
+	}, {
+		"2 value enum to JSON",
+		&EnumType{
+			last: 2,
+			min:  0,
+			max:  MaxBitfieldSize - 1,
+			ToString: map[int64]string{
+				1: "value1",
+				2: "value2",
+			},
+			ToInt: map[string]int64{
+				"value1": 1,
+				"value2": 2,
+			},
+		},
+		`{"ToString":{"1":"value1","2":"value2"},"ToInt":{"value1":1,"value2":2}}`,
+		false,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got, err := json.Marshal(tt.in)
+			if string(got) != tt.want {
+				t.Errorf("got: %v, want: %v", string(got), tt.want)
+			}
+			if (err != nil) != tt.wantErr {
+				t.Errorf("gotErr: %v, wantErr: %v", err, tt.wantErr)
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yang/yangtype.go

@@ -0,0 +1,330 @@
+// Copyright 2021 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"fmt"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+var (
+	// TypeKindFromName maps the string name used in a YANG file to the enumerated
+	// TypeKind used in this library.
+	TypeKindFromName = map[string]TypeKind{
+		"none":                Ynone,
+		"int8":                Yint8,
+		"int16":               Yint16,
+		"int32":               Yint32,
+		"int64":               Yint64,
+		"uint8":               Yuint8,
+		"uint16":              Yuint16,
+		"uint32":              Yuint32,
+		"uint64":              Yuint64,
+		"binary":              Ybinary,
+		"bits":                Ybits,
+		"boolean":             Ybool,
+		"decimal64":           Ydecimal64,
+		"empty":               Yempty,
+		"enumeration":         Yenum,
+		"identityref":         Yidentityref,
+		"instance-identifier": YinstanceIdentifier,
+		"leafref":             Yleafref,
+		"string":              Ystring,
+		"union":               Yunion,
+	}
+
+	// TypeKindToName maps the enumerated type used in this library to the string
+	// used in a YANG file.
+	TypeKindToName = map[TypeKind]string{
+		Ynone:               "none",
+		Yint8:               "int8",
+		Yint16:              "int16",
+		Yint32:              "int32",
+		Yint64:              "int64",
+		Yuint8:              "uint8",
+		Yuint16:             "uint16",
+		Yuint32:             "uint32",
+		Yuint64:             "uint64",
+		Ybinary:             "binary",
+		Ybits:               "bits",
+		Ybool:               "boolean",
+		Ydecimal64:          "decimal64",
+		Yempty:              "empty",
+		Yenum:               "enumeration",
+		Yidentityref:        "identityref",
+		YinstanceIdentifier: "instance-identifier",
+		Yleafref:            "leafref",
+		Ystring:             "string",
+		Yunion:              "union",
+	}
+
+	// BaseTypedefs is a map of all base types to the Typedef structure manufactured
+	// for the type.
+	BaseTypedefs = map[string]*Typedef{}
+
+	baseTypes = map[string]*YangType{
+		"int8": {
+			Name:  "int8",
+			Kind:  Yint8,
+			Range: Int8Range,
+		},
+		"int16": {
+			Name:  "int16",
+			Kind:  Yint16,
+			Range: Int16Range,
+		},
+		"int32": {
+			Name:  "int32",
+			Kind:  Yint32,
+			Range: Int32Range,
+		},
+		"int64": {
+			Name:  "int64",
+			Kind:  Yint64,
+			Range: Int64Range,
+		},
+		"uint8": {
+			Name:  "uint8",
+			Kind:  Yuint8,
+			Range: Uint8Range,
+		},
+		"uint16": {
+			Name:  "uint16",
+			Kind:  Yuint16,
+			Range: Uint16Range,
+		},
+		"uint32": {
+			Name:  "uint32",
+			Kind:  Yuint32,
+			Range: Uint32Range,
+		},
+		"uint64": {
+			Name:  "uint64",
+			Kind:  Yuint64,
+			Range: Uint64Range,
+		},
+
+		"decimal64": {
+			Name: "decimal64",
+			Kind: Ydecimal64,
+		},
+		"string": {
+			Name: "string",
+			Kind: Ystring,
+		},
+		"boolean": {
+			Name: "boolean",
+			Kind: Ybool,
+		},
+		"enumeration": {
+			Name: "enumeration",
+			Kind: Yenum,
+		},
+		"bits": {
+			Name: "bits",
+			Kind: Ybits,
+		},
+		"binary": {
+			Name: "binary",
+			Kind: Ybinary,
+		},
+		"leafref": {
+			Name: "leafref",
+			Kind: Yleafref,
+		},
+		"identityref": {
+			Name: "identityref",
+			Kind: Yidentityref,
+		},
+		"empty": {
+			Name: "empty",
+			Kind: Yempty,
+		},
+		"union": {
+			Name: "union",
+			Kind: Yunion,
+		},
+		"instance-identifier": {
+			Name: "instance-identifier",
+			Kind: YinstanceIdentifier,
+		},
+	}
+)
+
+// Install builtin types as know types
+func init() {
+	for k, v := range baseTypes {
+		// Base types are always their own root
+		v.Root = v
+		BaseTypedefs[k] = v.typedef()
+	}
+}
+
+// TypeKind is the enumeration of the base types available in YANG.  It
+// is analogous to reflect.Kind.
+type TypeKind uint
+
+func (k TypeKind) String() string {
+	if s := TypeKindToName[k]; s != "" {
+		return s
+	}
+	return fmt.Sprintf("unknown-type-%d", k)
+}
+
+const (
+	// Ynone represents the invalid (unset) type.
+	Ynone = TypeKind(iota)
+	// Yint8 is an int in the range [-128, 127].
+	Yint8
+	// Yint16 is an int in the range [-32768, 32767].
+	Yint16
+	// Yint32 is an int in the range [-2147483648, 2147483647].
+	Yint32
+	// Yint64 is an int in the range [-9223372036854775808, 9223372036854775807]
+	Yint64
+	// Yuint8 is an int in the range [0, 255]
+	Yuint8
+	// Yuint16 is an int in the range [0, 65535]
+	Yuint16
+	// Yuint32 is an int in the range [0, 4294967295]
+	Yuint32
+	// Yuint64 is an int in the range [0, 18446744073709551615]
+	Yuint64
+
+	// Ybinary stores arbitrary data.
+	Ybinary
+	// Ybits is a named set of bits or flags.
+	Ybits
+	// Ybool is true or false.
+	Ybool
+	// Ydecimal64 is a signed decimal number.
+	Ydecimal64
+	// Yempty has no associated value.
+	Yempty
+	// Yenum stores enumerated strings.
+	Yenum
+	// Yidentityref stores an extensible enumeration.
+	Yidentityref
+	// YinstanceIdentifier stores a reference to a data tree node.
+	YinstanceIdentifier
+	// Yleafref stores a reference to a leaf instance.
+	Yleafref
+	// Ystring is a human readable string.
+	Ystring
+	// Yunion is a choice of types.
+	Yunion
+)
+
+// A YangType is the internal representation of a type in YANG.  It may
+// refer to either a builtin type or type specified with typedef.  Not
+// all fields in YangType are used for all types.
+type YangType struct {
+	Name             string
+	Kind             TypeKind    // Ynone if not a base type
+	Base             *Type       `json:"-"`          // Base type for non-builtin types
+	IdentityBase     *Identity   `json:",omitempty"` // Base statement for a type using identityref
+	Root             *YangType   `json:"-"`          // root of this type that is the same
+	Bit              *EnumType   `json:",omitempty"` // bit position, "status" is lost
+	Enum             *EnumType   `json:",omitempty"` // enum name to value, "status" is lost
+	Units            string      `json:",omitempty"` // units to be used for this type
+	Default          string      `json:",omitempty"` // default value, if any
+	HasDefault       bool        `json:",omitempty"` // whether the type has a default.
+	FractionDigits   int         `json:",omitempty"` // decimal64 fixed point precision
+	Length           YangRange   `json:",omitempty"` // this should be processed by section 12
+	OptionalInstance bool        `json:",omitempty"` // !require-instances which defaults to true
+	Path             string      `json:",omitempty"` // the path in a leafref
+	Pattern          []string    `json:",omitempty"` // limiting XSD-TYPES expressions on strings
+	POSIXPattern     []string    `json:",omitempty"` // limiting POSIX ERE on strings (specified by openconfig-extensions:posix-pattern)
+	Range            YangRange   `json:",omitempty"` // range for integers
+	Type             []*YangType `json:",omitempty"` // for unions
+}
+
+// Equal returns true if y and t describe the same type.
+func (y *YangType) Equal(t *YangType) bool {
+	switch {
+	case y == t:
+		return true
+	case y == nil || t == nil:
+		return false
+	case
+		// Don't check the Name, it contains no information
+		y.Kind != t.Kind,
+		y.Units != t.Units,
+		y.Default != t.Default,
+		y.HasDefault != t.HasDefault,
+		y.FractionDigits != t.FractionDigits,
+		y.IdentityBase != t.IdentityBase,
+		len(y.Length) != len(t.Length),
+		!y.Length.Equal(t.Length),
+		y.OptionalInstance != t.OptionalInstance,
+		y.Path != t.Path,
+		!ssEqual(y.Pattern, t.Pattern),
+		!ssEqual(y.POSIXPattern, t.POSIXPattern),
+		len(y.Range) != len(t.Range),
+		!y.Range.Equal(t.Range),
+		!tsEqual(y.Type, t.Type),
+		!cmp.Equal(y.Enum, t.Enum, cmp.Comparer(func(t, u EnumType) bool {
+			return cmp.Equal(t.unique, u.unique) && cmp.Equal(t.ToInt, u.ToInt) && cmp.Equal(t.ToString, u.ToString)
+		})):
+
+		return false
+	}
+	// TODO(borman): Base, Bit
+	return true
+}
+
+// typedef returns a Typedef created from y for insertion into the BaseTypedefs
+// map.
+func (y *YangType) typedef() *Typedef {
+	return &Typedef{
+		Name:   y.Name,
+		Source: &Statement{},
+		Type: &Type{
+			Name:     y.Name,
+			Source:   &Statement{},
+			YangType: y,
+		},
+		YangType: y,
+	}
+}
+
+// ssEqual returns true if the two slices are equivalent.
+func ssEqual(s1, s2 []string) bool {
+	if len(s1) != len(s2) {
+		return false
+	}
+	for x, s := range s1 {
+		if s != s2[x] {
+			return false
+		}
+	}
+	return true
+}
+
+// tsEqual returns true if the two Type slices are identical.
+func tsEqual(t1, t2 []*YangType) bool {
+	if len(t1) != len(t2) {
+		return false
+	}
+	// For now we compare absolute pointers.
+	// This may be wrong.
+	for x, t := range t1 {
+		if !t.Equal(t2[x]) {
+			return false
+		}
+	}
+	return true
+}

src/webui/internal/goyang/pkg/yang/yangtype_test.go

@@ -0,0 +1,136 @@
+// Copyright 2021 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yang
+
+import (
+	"testing"
+)
+
+func TestYangTypeEqual(t *testing.T) {
+
+	tests := []struct {
+		name      string
+		inLeft    *YangType
+		inRight   *YangType
+		wantEqual bool
+	}{{
+		name:      "both-nil",
+		inLeft:    nil,
+		inRight:   nil,
+		wantEqual: true,
+	}, {
+		name: "one-nil",
+		inLeft: &YangType{
+			Kind:           Ydecimal64,
+			FractionDigits: 5,
+		},
+		inRight:   nil,
+		wantEqual: false,
+	}, {
+		name: "name-unequal",
+		inLeft: &YangType{
+			Name:           "foo",
+			Kind:           Ydecimal64,
+			FractionDigits: 5,
+		},
+		inRight: &YangType{
+			Name:           "bar",
+			Kind:           Ydecimal64,
+			FractionDigits: 5,
+		},
+		wantEqual: true,
+	}, {
+		name: "fraction-digits-unequal",
+		inLeft: &YangType{
+			Name:           "foo",
+			Kind:           Ydecimal64,
+			FractionDigits: 5,
+		},
+		inRight: &YangType{
+			Name:           "foo",
+			Kind:           Ydecimal64,
+			FractionDigits: 4,
+		},
+		wantEqual: false,
+	}, {
+		name: "types-unequal",
+		inLeft: &YangType{
+			Name:           "foo",
+			Kind:           Ydecimal64,
+			FractionDigits: 5,
+		},
+		inRight: &YangType{
+			Name: "foo",
+			Kind: Yint64,
+		},
+		wantEqual: false,
+	}, {
+		name: "defaults-equal",
+		inLeft: &YangType{
+			Name:       "foo",
+			Kind:       Ystring,
+			Default:    "bar",
+			HasDefault: true,
+		},
+		inRight: &YangType{
+			Name:       "foo",
+			Kind:       Ystring,
+			Default:    "bar",
+			HasDefault: true,
+		},
+		wantEqual: true,
+	}, {
+		name: "defaults-unequal",
+		inLeft: &YangType{
+			Name:       "foo",
+			Kind:       Ystring,
+			Default:    "bar",
+			HasDefault: true,
+		},
+		inRight: &YangType{
+			Name:       "foo",
+			Kind:       Ystring,
+			Default:    "baz",
+			HasDefault: true,
+		},
+		wantEqual: false,
+	}, {
+		name: "has-default-unequal",
+		inLeft: &YangType{
+			Name:    "foo",
+			Kind:    Ystring,
+			Default: "",
+		},
+		inRight: &YangType{
+			Name:       "foo",
+			Kind:       Ystring,
+			Default:    "",
+			HasDefault: true,
+		},
+		wantEqual: false,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if gotEqual := tt.inLeft.Equal(tt.inRight); gotEqual != tt.wantEqual {
+				t.Errorf("gotEqual: %v, wantEqual: %v", gotEqual, tt.wantEqual)
+			}
+			// Must be symmetric
+			if reverseEqual := tt.inRight.Equal(tt.inLeft); reverseEqual != tt.wantEqual {
+				t.Errorf("got reverseEqual: %v, wantEqual: %v", reverseEqual, tt.wantEqual)
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yangentry/build_yang.go

@@ -0,0 +1,78 @@
+// Copyright 2020 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package yangentry contains high-level helpers for using yang.Entry objects.
+package yangentry
+
+import (
+	"fmt"
+
+	"github.com/openconfig/goyang/pkg/yang"
+)
+
+// Parse takes a list of either module/submodule names or .yang file
+// paths, and a list of include paths. It runs the yang parser on the YANG
+// files by searching for them in the include paths or in the current
+// directory, returning a slice of yang.Entry pointers which represent the
+// parsed top level modules. It also returns a list of errors encountered while
+// parsing, if any.
+func Parse(yangfiles, path []string) (map[string]*yang.Entry, []error) {
+	return parse(yangfiles, path, yang.NewModules())
+}
+
+// ParseWithOptions takes a list of either module/submodule names or .yang file
+// paths, a list of include paths, and a set of parse options. It configures the
+// yang parser with the specified parse options and runs it on the YANG
+// files by searching for them in the include paths or in the current
+// directory, returning a slice of yang.Entry pointers which represent the
+// parsed top level modules. It also returns a list of errors encountered while
+// parsing, if any.
+func ParseWithOptions(yangfiles, path []string, parseOptions yang.Options) (map[string]*yang.Entry, []error) {
+	ms := yang.NewModules()
+	ms.ParseOptions = parseOptions
+
+	return parse(yangfiles, path, ms)
+}
+
+func parse(yangfiles, path []string, ms *yang.Modules) (map[string]*yang.Entry, []error) {
+	for _, p := range path {
+		ms.AddPath(fmt.Sprintf("%s/...", p))
+	}
+
+	var processErr []error
+	for _, name := range yangfiles {
+		if name == "" {
+			continue
+		}
+		if err := ms.Read(name); err != nil {
+			processErr = append(processErr, err)
+		}
+	}
+
+	if len(processErr) > 0 {
+		return nil, processErr
+	}
+
+	if errs := ms.Process(); len(errs) != 0 {
+		return nil, errs
+	}
+
+	entries := make(map[string]*yang.Entry)
+	for _, m := range ms.Modules {
+		e := yang.ToEntry(m)
+		entries[e.Name] = e
+	}
+
+	return entries, nil
+}

src/webui/internal/goyang/pkg/yangentry/build_yang_test.go

@@ -0,0 +1,129 @@
+// Copyright 2020 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package yangentry
+
+import (
+	"testing"
+
+	"github.com/openconfig/goyang/pkg/yang"
+)
+
+// TestParse tests the Parse function - which takes an input
+// set of modules and processes them using the goyang compiler into a set of
+// yang.Entry pointers.
+func TestParse(t *testing.T) {
+	tests := []struct {
+		name     string
+		inFiles  []string
+		inPath   []string
+		wantErr  bool
+		wantMods []string
+	}{{
+		name:     "simple valid module",
+		inFiles:  []string{"testdata/00-valid-module.yang"},
+		inPath:   []string{"testdata"},
+		wantMods: []string{"test-module"},
+	}, {
+		name:     "simple valid module without .yang extension",
+		inFiles:  []string{"00-valid-module"},
+		inPath:   []string{"testdata"},
+		wantMods: []string{"test-module"},
+	}, {
+		name:    "simple invalid module",
+		inFiles: []string{"testdata/01-invalid-module.yang"},
+		inPath:  []string{"testdata"},
+		wantErr: true,
+	}, {
+		name:     "valid import",
+		inFiles:  []string{"testdata/02-valid-import.yang"},
+		inPath:   []string{"testdata/subdir"},
+		wantMods: []string{"test-module"},
+	}, {
+		name:    "invalid import",
+		inFiles: []string{"testdata/03-invalid-import.yang"},
+		inPath:  []string{},
+		wantErr: true,
+	}, {
+		name:     "two modules",
+		inFiles:  []string{"testdata/04-valid-module-one.yang", "testdata/04-valid-module-two.yang"},
+		inPath:   []string{},
+		wantMods: []string{"module-one", "module-two"},
+	}, {
+		name:    "circular submodule dependency",
+		inFiles: []string{"testdata/05-circular-main.yang"},
+		inPath:  []string{"testdata/subdir"},
+		wantErr: true,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			entries, errs := Parse(tt.inFiles, tt.inPath)
+			if len(errs) != 0 && !tt.wantErr {
+				t.Fatalf("%s: unexpected error processing modules: %v", tt.name, errs)
+			}
+
+			for _, m := range tt.wantMods {
+				if _, ok := entries[m]; !ok {
+					t.Fatalf("%s: could not find module %s", tt.name, m)
+				}
+			}
+		})
+	}
+}
+
+// TestParseWithOptions tests the ParseWithOptions function - which takes an input
+// set of modules along with a set of parse options, and processes them using the goyang
+// compiler into a set of yang.Entry pointers.
+func TestParseWithOptions(t *testing.T) {
+	tests := []struct {
+		name         string
+		inFiles      []string
+		inPath       []string
+		parseOptions yang.Options
+		wantErr      bool
+		wantMods     []string
+	}{
+		{
+			name:         "circular submodule dependency with default options",
+			inFiles:      []string{"testdata/05-circular-main.yang"},
+			inPath:       []string{"testdata/subdir"},
+			parseOptions: yang.Options{},
+			wantErr:      true,
+		},
+		{
+			name:         "circular submodule dependency with IgnoreSubmoduleCircularDependencies",
+			inFiles:      []string{"testdata/05-circular-main.yang"},
+			inPath:       []string{"testdata/subdir"},
+			parseOptions: yang.Options{IgnoreSubmoduleCircularDependencies: true},
+			wantMods:     []string{"circular-main"},
+			wantErr:      false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			entries, errs := ParseWithOptions(tt.inFiles, tt.inPath, tt.parseOptions)
+			if len(errs) != 0 && !tt.wantErr {
+				t.Fatalf("%s: unexpected error processing modules: %v", tt.name, errs)
+			}
+
+			for _, m := range tt.wantMods {
+				if _, ok := entries[m]; !ok {
+					t.Fatalf("%s: could not find module %s", tt.name, m)
+				}
+			}
+		})
+	}
+}

src/webui/internal/goyang/pkg/yangentry/testdata/00-valid-module.yang

@@ -0,0 +1,6 @@
+module test-module {
+  prefix "t";
+  namespace "urn:t";
+
+  leaf valid-leaf { type string; }
+}

src/webui/internal/goyang/pkg/yangentry/testdata/01-invalid-module.yang

@@ -0,0 +1,6 @@
+module test-module {
+  prefix "t";
+  namespace "urn:t";
+
+  leaf invalid-leaf { }
+}

src/webui/internal/goyang/pkg/yangentry/testdata/02-valid-import.yang

@@ -0,0 +1,6 @@
+module test-module {
+  prefix "t";
+  namespace "urn:t";
+
+  import imported { prefix "i"; }
+}

src/webui/internal/goyang/pkg/yangentry/testdata/03-invalid-import.yang

@@ -0,0 +1,6 @@
+module test-module {
+  prefix "t";
+  namespace "urn:t";
+
+  import import-not-found { prefix "i"; }
+}

src/webui/internal/goyang/pkg/yangentry/testdata/04-valid-module-one.yang

@@ -0,0 +1,6 @@
+module module-one {
+  prefix "t";
+  namespace "urn:t";
+
+  leaf one { type int8; }
+}

src/webui/internal/goyang/pkg/yangentry/testdata/04-valid-module-two.yang

@@ -0,0 +1,6 @@
+module module-two {
+  prefix "t";
+  namespace "urn:t";
+
+  leaf two { type int8; }
+}

src/webui/internal/goyang/pkg/yangentry/testdata/05-circular-main.yang

@@ -0,0 +1,12 @@
+module circular-main {
+    yang-version "1.1";
+
+    namespace "urn:test:circular:main";
+
+    prefix "main";
+
+    include circular-sub-one;
+    include circular-sub-two;
+
+    revision "2025-02-15";
+}

src/webui/internal/goyang/pkg/yangentry/testdata/subdir/circular-sub-one.yang

@@ -0,0 +1,9 @@
+submodule circular-sub-one {
+    yang-version "1.1";
+
+    belongs-to circular-main { prefix "main"; }
+
+    include circular-sub-two;
+
+    revision "2025-02-15";
+}

src/webui/internal/goyang/pkg/yangentry/testdata/subdir/circular-sub-two.yang

@@ -0,0 +1,9 @@
+submodule circular-sub-two {
+    yang-version "1.1";
+
+    belongs-to circular-main { prefix "main"; }
+
+    include circular-sub-one;
+
+    revision "2025-02-15";
+}

src/webui/internal/goyang/pkg/yangentry/testdata/subdir/imported.yang

@@ -0,0 +1,5 @@
+module imported {
+  prefix "imported";
+  namespace "urn:i";
+  
+}

src/webui/internal/goyang/testdata/aug.yang

@@ -0,0 +1,28 @@
+module aug {
+  namespace "yang-sucks";
+  prefix "yang";
+  grouping bgp-neighbor_config {
+    leaf peer-as { type string; }
+  }
+  grouping bgp-neighbors {
+    list neighbor {
+      uses bgp-neighbor-group;
+    }
+  }
+  grouping bgp-neighbor-group {
+    container config {
+      uses bgp-neighbor_config;
+    }
+  }
+  grouping bgp-neighbor-peer-group_config {
+    leaf peer-group { type string; }
+  }
+  augment /bgp/neighbors/neighbor/config {
+    uses bgp-neighbor-peer-group_config;
+  }
+  container bgp {
+    container neighbors {
+      uses bgp-neighbors;
+    }
+  }
+}

src/webui/internal/goyang/testdata/base.yang

@@ -0,0 +1,93 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Base test yang module.
+module base {
+  namespace "urn:mod";
+  prefix "base";
+
+  include sub;
+  import other {
+    prefix bother;
+  }
+
+  // basic type tests
+  typedef base-type { type int32; }
+  leaf base-leaf1 { type base-type; }
+  leaf base-leaf2 { type base:base-type; }
+  leaf base-leaf3 { type bother:other-type; }
+  leaf base-leaf4 { type sub-type; }
+
+  grouping base-group {
+    description
+      "The base-group is used to test the 'uses' statement below.
+       This description is here to simply include a multi-line string
+       as an example of multi-line strings";
+    leaf base-group-leaf {
+      config false;
+      type string;
+    }
+  }
+
+  // test uses and leaf ref
+  container base-container-1 {
+    uses base-group;
+    uses bother:other-group;
+    uses base:sub-group;
+    choice base-choice {
+      case choice-a {
+          leaf base-choice-a1 { type string; }
+          leaf base-choice-a2 {
+            type leafref { path ../base-container-1-leaf; }
+          }
+      }
+      case choice-b {
+          leaf base-choice-b1 { type string; }
+          leaf base-choice-b2 {
+            type leafref { path ../../base-container-2/base-container-2a/base-container-2a-leaf; }
+          }
+      }
+    }
+    leaf base-container-1-leaf { type string; }
+  }
+
+  // container referenced by a leafref above
+  container base-container-2 {
+    container base-container-2a {
+      leaf base-container-2a-leaf { type string; }
+    }
+  }
+
+  // test basic augmenting
+  augment /base-container-1/base-choice/choice-a {
+     leaf base-choice-a3 { type string; }
+  }
+  augment /base-container-1/base-choice {
+     case choice-c {
+        leaf base-choice-c1 { type string; }
+     }
+  }
+
+  // simple extension test
+  extension base-ext {
+     argument base-arg;
+  }
+  container ext-container {
+     config false;
+     leaf ext-container-leaf { type string; }
+     base:base-ext "EXTENSION" {
+       leaf base-ext-leaf { type string; }
+     }
+  }
+}

src/webui/internal/goyang/testdata/other.yang

@@ -0,0 +1,30 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// imported by base.yang.
+module other {
+  namespace "uri:empty";
+  prefix "otherp";
+  typedef other-type { type string; }
+
+  // This container should not appear in base, even though this file is
+  // imported by base.  That is just the YANG is defined.
+  container other-container {
+    leaf other-container-leaf1 { type other-type; }
+    leaf other-container-leaf2 { type otherp:other-type; }
+  }
+  grouping other-group {
+    leaf other-group-leaf { type string; }
+  }
+}

src/webui/internal/goyang/testdata/sub.yang

@@ -0,0 +1,26 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// included by base.yang.
+submodule sub {
+  belongs-to base { prefix "sbase"; }
+  typedef sub-type { type sub-type2; }
+  typedef sub-type2 { type int8; }
+  container sub-container {
+    leaf sub-container-leaf { type sub-type; }
+  }
+  grouping sub-group {
+    leaf sub-group-leaf { type string; }
+  }
+}

src/webui/internal/goyang/testdata/subdir/subdir1.yang

@@ -0,0 +1,12 @@
+// A YANG module located in a subdirectory, to test the AddYANGPaths
+// helper function.
+
+module subdir1 {
+  yang-version "1";
+
+namespace "namespace:goes:here";
+  prefix "subdir1";
+
+  description
+    "This module is to be found by test cases.";
+}

src/webui/internal/goyang/tree.go

@@ -0,0 +1,112 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"sort"
+
+	"github.com/openconfig/goyang/pkg/indent"
+	"github.com/openconfig/goyang/pkg/yang"
+)
+
+func init() {
+	register(&formatter{
+		name: "tree",
+		f:    doTree,
+		help: "display in a tree format",
+	})
+}
+
+func doTree(w io.Writer, entries []*yang.Entry) {
+	for _, e := range entries {
+		Write(w, e)
+	}
+}
+
+// Write writes e, formatted, and all of its children, to w.
+func Write(w io.Writer, e *yang.Entry) {
+	if e.Description != "" {
+		fmt.Fprintln(w)
+		fmt.Fprintln(indent.NewWriter(w, "// "), e.Description)
+	}
+	if len(e.Exts) > 0 {
+		fmt.Fprintf(w, "extensions: {\n")
+		for _, ext := range e.Exts {
+			if n := ext.NName(); n != "" {
+				fmt.Fprintf(w, "  %s %s;\n", ext.Kind(), n)
+			} else {
+				fmt.Fprintf(w, "  %s;\n", ext.Kind())
+			}
+		}
+		fmt.Fprintln(w, "}")
+	}
+	switch {
+	case e.RPC != nil:
+		fmt.Fprintf(w, "RPC: ")
+	case e.ReadOnly():
+		fmt.Fprintf(w, "RO: ")
+	default:
+		fmt.Fprintf(w, "rw: ")
+	}
+	if e.Type != nil {
+		fmt.Fprintf(w, "%s ", getTypeName(e))
+	}
+	name := e.Name
+	if e.Prefix != nil {
+		name = e.Prefix.Name + ":" + name
+	}
+	switch {
+	case e.Dir == nil && e.ListAttr != nil:
+		fmt.Fprintf(w, "[]%s\n", name)
+		return
+	case e.Dir == nil:
+		fmt.Fprintf(w, "%s\n", name)
+		return
+	case e.ListAttr != nil:
+		fmt.Fprintf(w, "[%s]%s {\n", e.Key, name) //}
+	default:
+		fmt.Fprintf(w, "%s {\n", name) //}
+	}
+	if r := e.RPC; r != nil {
+		if r.Input != nil {
+			Write(indent.NewWriter(w, "  "), r.Input)
+		}
+		if r.Output != nil {
+			Write(indent.NewWriter(w, "  "), r.Output)
+		}
+	}
+	var names []string
+	for k := range e.Dir {
+		names = append(names, k)
+	}
+	sort.Strings(names)
+	for _, k := range names {
+		Write(indent.NewWriter(w, "  "), e.Dir[k])
+	}
+	// { to match the brace below to keep brace matching working
+	fmt.Fprintln(w, "}")
+}
+
+func getTypeName(e *yang.Entry) string {
+	if e == nil || e.Type == nil {
+		return ""
+	}
+	// Return our root's type name.
+	// This is should be the builtin type-name
+	// for this entry.
+	return e.Type.Root.Name
+}

src/webui/internal/goyang/types.go

@@ -0,0 +1,135 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/openconfig/goyang/pkg/indent"
+	"github.com/openconfig/goyang/pkg/yang"
+	"github.com/pborman/getopt"
+)
+
+var (
+	typesDebug   bool
+	typesVerbose bool
+)
+
+func init() {
+	flags := getopt.New()
+	register(&formatter{
+		name:  "types",
+		f:     doTypes,
+		help:  "display found types",
+		flags: flags,
+	})
+	flags.BoolVarLong(&typesDebug, "types_debug", 0, "display debug information")
+	flags.BoolVarLong(&typesVerbose, "types_verbose", 0, "include base information")
+}
+
+func doTypes(w io.Writer, entries []*yang.Entry) {
+	types := Types{}
+	for _, e := range entries {
+		types.AddEntry(e)
+	}
+
+	for t := range types {
+		printType(w, t, typesVerbose)
+	}
+	if typesDebug {
+		for _, e := range entries {
+			showall(w, e)
+		}
+	}
+}
+
+// Types keeps track of all the YangTypes defined.
+type Types map[*yang.YangType]struct{}
+
+// AddEntry adds all types defined in e and its descendants to t.
+func (t Types) AddEntry(e *yang.Entry) {
+	if e == nil {
+		return
+	}
+	if e.Type != nil {
+		t[e.Type.Root] = struct{}{}
+	}
+	for _, d := range e.Dir {
+		t.AddEntry(d)
+	}
+}
+
+// printType prints type t in a moderately human readable format to w.
+func printType(w io.Writer, t *yang.YangType, verbose bool) {
+	if verbose && t.Base != nil {
+		base := yang.Source(t.Base)
+		if base == "unknown" {
+			base = "unnamed type"
+		}
+		fmt.Fprintf(w, "%s: ", base)
+	}
+	fmt.Fprintf(w, "%s", t.Root.Name)
+	if t.Kind.String() != t.Root.Name {
+		fmt.Fprintf(w, "(%s)", t.Kind)
+	}
+	if t.Units != "" {
+		fmt.Fprintf(w, " units=%s", t.Units)
+	}
+	if t.Default != "" {
+		fmt.Fprintf(w, " default=%q", t.Default)
+	}
+	if t.FractionDigits != 0 {
+		fmt.Fprintf(w, " fraction-digits=%d", t.FractionDigits)
+	}
+	if len(t.Length) > 0 {
+		fmt.Fprintf(w, " length=%s", t.Length)
+	}
+	if t.Kind == yang.YinstanceIdentifier && !t.OptionalInstance {
+		fmt.Fprintf(w, " required")
+	}
+	if t.Kind == yang.Yleafref && t.Path != "" {
+		fmt.Fprintf(w, " path=%q", t.Path)
+	}
+	if len(t.Pattern) > 0 {
+		fmt.Fprintf(w, " pattern=%s", strings.Join(t.Pattern, "|"))
+	}
+	b := yang.BaseTypedefs[t.Kind.String()].YangType
+	if len(t.Range) > 0 && !t.Range.Equal(b.Range) {
+		fmt.Fprintf(w, " range=%s", t.Range)
+	}
+	if len(t.Type) > 0 {
+		fmt.Fprintf(w, "{\n")
+		for _, t := range t.Type {
+			printType(indent.NewWriter(w, "  "), t, verbose)
+		}
+		fmt.Fprintf(w, "}")
+	}
+	fmt.Fprintf(w, ";\n")
+}
+
+func showall(w io.Writer, e *yang.Entry) {
+	if e == nil {
+		return
+	}
+	if e.Type != nil {
+		fmt.Fprintf(w, "\n%s\n  ", e.Node.Statement().Location())
+		printType(w, e.Type.Root, false)
+	}
+	for _, d := range e.Dir {
+		showall(w, d)
+	}
+}

src/webui/internal/goyang/yang.go

@@ -0,0 +1,214 @@
+// Copyright 2015 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Program yang parses YANG files, displays errors, and possibly writes
+// something related to the input on output.
+//
+// Usage: yang [--path DIR] [--format FORMAT] [FORMAT OPTIONS] [MODULE] [FILE ...]
+//
+// If MODULE is specified (an argument that does not end in .yang), it is taken
+// as the name of the module to display.  Any FILEs specified are read, and the
+// tree for MODULE is displayed.  If MODULE was not defined in FILEs (or no
+// files were specified), then the file MODULES.yang is read as well.  An error
+// is displayed if no definition for MODULE was found.
+//
+// If MODULE is missing, then all base modules read from the FILEs are
+// displayed.  If there are no arguments then standard input is parsed.
+//
+// If DIR is specified, it is considered a comma separated list of paths
+// to append to the search directory.  If DIR appears as DIR/... then
+// DIR and all direct and indirect subdirectories are checked.
+//
+// FORMAT, which defaults to "tree", specifies the format of output to produce.
+// Use "goyang --help" for a list of available formats.
+//
+// FORMAT OPTIONS are flags that apply to a specific format.  They must follow
+// --format.
+//
+// THIS PROGRAM IS STILL JUST A DEVELOPMENT TOOL.
+package main
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"runtime/trace"
+	"sort"
+	"strings"
+
+	"github.com/openconfig/goyang/pkg/indent"
+	"github.com/openconfig/goyang/pkg/yang"
+	"github.com/pborman/getopt"
+)
+
+// Each format must register a formatter with register.  The function f will
+// be called once with the set of yang Entry trees generated.
+type formatter struct {
+	name  string
+	f     func(io.Writer, []*yang.Entry)
+	help  string
+	flags *getopt.Set
+}
+
+var formatters = map[string]*formatter{}
+
+func register(f *formatter) {
+	formatters[f.name] = f
+}
+
+// exitIfError writes errs to standard error and exits with an exit status of 1.
+// If errs is empty then exitIfError does nothing and simply returns.
+func exitIfError(errs []error) {
+	if len(errs) > 0 {
+		for _, err := range errs {
+			fmt.Fprintln(os.Stderr, err)
+		}
+		stop(1)
+	}
+}
+
+var stop = os.Exit
+
+func main() {
+	var format string
+	formats := make([]string, 0, len(formatters))
+	for k := range formatters {
+		formats = append(formats, k)
+	}
+	sort.Strings(formats)
+
+	var traceP string
+	var help bool
+	var paths []string
+	var ignoreSubmoduleCircularDependencies bool
+	getopt.ListVarLong(&paths, "path", 'p', "comma separated list of directories to add to search path", "DIR[,DIR...]")
+	getopt.StringVarLong(&format, "format", 'f', "format to display: "+strings.Join(formats, ", "), "FORMAT")
+	getopt.StringVarLong(&traceP, "trace", 't', "write trace into to TRACEFILE", "TRACEFILE")
+	getopt.BoolVarLong(&help, "help", 'h', "display help")
+	getopt.BoolVarLong(&ignoreSubmoduleCircularDependencies, "ignore-circdep", 'g', "ignore circular dependencies between submodules")
+	getopt.SetParameters("[FORMAT OPTIONS] [SOURCE] [...]")
+
+	if err := getopt.Getopt(func(o getopt.Option) bool {
+		if o.Name() == "--format" {
+			f, ok := formatters[format]
+			if !ok {
+				fmt.Fprintf(os.Stderr, "%s: invalid format.  Choices are %s\n", format, strings.Join(formats, ", "))
+				stop(1)
+			}
+			if f.flags != nil {
+				f.flags.VisitAll(func(o getopt.Option) {
+					getopt.AddOption(o)
+				})
+			}
+		}
+		return true
+	}); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		getopt.PrintUsage(os.Stderr)
+		os.Exit(1)
+	}
+
+	if traceP != "" {
+		fp, err := os.Create(traceP)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		trace.Start(fp)
+		stop = func(c int) { trace.Stop(); os.Exit(c) }
+		defer func() { trace.Stop() }()
+	}
+
+	if help {
+		getopt.CommandLine.PrintUsage(os.Stderr)
+		fmt.Fprintf(os.Stderr, `
+SOURCE may be a module name or a .yang file.
+
+Formats:
+`)
+		for _, fn := range formats {
+			f := formatters[fn]
+			fmt.Fprintf(os.Stderr, "    %s - %s\n", f.name, f.help)
+			if f.flags != nil {
+				f.flags.PrintOptions(indent.NewWriter(os.Stderr, "   "))
+			}
+			fmt.Fprintln(os.Stderr)
+		}
+		stop(0)
+	}
+
+	ms := yang.NewModules()
+	ms.ParseOptions.IgnoreSubmoduleCircularDependencies = ignoreSubmoduleCircularDependencies
+
+	for _, path := range paths {
+		expanded, err := yang.PathsWithModules(path)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			continue
+		}
+		ms.AddPath(expanded...)
+	}
+
+	if format == "" {
+		format = "tree"
+	}
+	if _, ok := formatters[format]; !ok {
+		fmt.Fprintf(os.Stderr, "%s: invalid format.  Choices are %s\n", format, strings.Join(formats, ", "))
+		stop(1)
+
+	}
+
+	files := getopt.Args()
+
+	if len(files) == 0 {
+		data, err := ioutil.ReadAll(os.Stdin)
+		if err == nil {
+			err = ms.Parse(string(data), "<STDIN>")
+		}
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			stop(1)
+		}
+	}
+
+	for _, name := range files {
+		if err := ms.Read(name); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			continue
+		}
+	}
+
+	// Process the read files, exiting if any errors were found.
+	exitIfError(ms.Process())
+
+	// Keep track of the top level modules we read in.
+	// Those are the only modules we want to print below.
+	mods := map[string]*yang.Module{}
+	var names []string
+
+	for _, m := range ms.Modules {
+		if mods[m.Name] == nil {
+			mods[m.Name] = m
+			names = append(names, m.Name)
+		}
+	}
+	sort.Strings(names)
+	entries := make([]*yang.Entry, len(names))
+	for x, n := range names {
+		entries[x] = yang.ToEntry(mods[n])
+	}
+
+	formatters[format].f(os.Stdout, entries)
+}

src/webui/internal/handlers/common.go

@@ -17,6 +17,7 @@ type PageData struct {
 	PageTitle    string
 	ActivePage   string
 	Capabilities *Capabilities
+	CfgUnsaved   bool // running config differs from startup (Apply was used without ApplyAndSave)
 }
 
 func csrfToken(ctx context.Context) string {
@@ -24,11 +25,13 @@ func csrfToken(ctx context.Context) string {
 }
 
 func newPageData(r *http.Request, page, title string) PageData {
+	_, cookieErr := r.Cookie(cfgUnsavedCookie)
 	return PageData{
 		Username:     restconf.CredentialsFromContext(r.Context()).Username,
 		CsrfToken:    csrfToken(r.Context()),
 		PageTitle:    title,
 		ActivePage:   page,
 		Capabilities: CapabilitiesFromContext(r.Context()),
+		CfgUnsaved:   cookieErr == nil,
 	}
 }

src/webui/internal/handlers/configure.go

@@ -9,11 +9,21 @@ import (
 	"github.com/kernelkit/webui/internal/restconf"
 )
 
+const cfgUnsavedCookie = "cfg-unsaved"
+
 // ConfigureHandler manages the candidate datastore lifecycle.
 type ConfigureHandler struct {
 	RC restconf.Fetcher
 }
 
+func setCfgUnsaved(w http.ResponseWriter) {
+	http.SetCookie(w, &http.Cookie{Name: cfgUnsavedCookie, Value: "1", Path: "/", MaxAge: 86400, SameSite: http.SameSiteLaxMode})
+}
+
+func clearCfgUnsaved(w http.ResponseWriter) {
+	http.SetCookie(w, &http.Cookie{Name: cfgUnsavedCookie, Value: "", Path: "/", MaxAge: -1, SameSite: http.SameSiteLaxMode})
+}
+
 // Enter copies running → candidate, initialising a fresh edit session.
 // Called when the user opens the Configure accordion.
 // POST /configure/enter
@@ -27,6 +37,7 @@ func (h *ConfigureHandler) Enter(w http.ResponseWriter, r *http.Request) {
 }
 
 // Apply copies candidate → running, activating all staged changes atomically.
+// Sets the cfg-unsaved cookie so the persistent banner appears until startup is saved.
 // POST /configure/apply
 func (h *ConfigureHandler) Apply(w http.ResponseWriter, r *http.Request) {
 	if err := h.RC.CopyDatastore(r.Context(), "candidate", "running"); err != nil {
@@ -34,7 +45,8 @@ func (h *ConfigureHandler) Apply(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "Could not apply configuration: "+err.Error(), http.StatusBadGateway)
 		return
 	}
-	w.Header().Set("HX-Redirect", "/")
+	setCfgUnsaved(w)
+	w.Header().Set("HX-Refresh", "true")
 	w.WriteHeader(http.StatusNoContent)
 }
 
@@ -43,13 +55,14 @@ func (h *ConfigureHandler) Apply(w http.ResponseWriter, r *http.Request) {
 func (h *ConfigureHandler) Abort(w http.ResponseWriter, r *http.Request) {
 	if err := h.RC.CopyDatastore(r.Context(), "running", "candidate"); err != nil {
 		log.Printf("configure abort: %v", err)
-		// Best-effort reset; redirect regardless so the user can get out.
+		// Best-effort reset; refresh regardless.
 	}
-	w.Header().Set("HX-Redirect", "/")
+	w.Header().Set("HX-Refresh", "true")
 	w.WriteHeader(http.StatusNoContent)
 }
 
 // ApplyAndSave copies candidate → running then running → startup in one step.
+// Clears the cfg-unsaved cookie.
 // POST /configure/apply-and-save
 func (h *ConfigureHandler) ApplyAndSave(w http.ResponseWriter, r *http.Request) {
 	if err := h.RC.CopyDatastore(r.Context(), "candidate", "running"); err != nil {
@@ -62,6 +75,21 @@ func (h *ConfigureHandler) ApplyAndSave(w http.ResponseWriter, r *http.Request)
 		http.Error(w, "Could not save configuration: "+err.Error(), http.StatusBadGateway)
 		return
 	}
-	w.Header().Set("HX-Redirect", "/")
+	clearCfgUnsaved(w)
+	w.Header().Set("HX-Refresh", "true")
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// Save copies running → startup, persisting the active configuration.
+// Clears the cfg-unsaved cookie and does a full-page refresh so the banner disappears.
+// POST /configure/save
+func (h *ConfigureHandler) Save(w http.ResponseWriter, r *http.Request) {
+	if err := h.RC.CopyDatastore(r.Context(), "running", "startup"); err != nil {
+		log.Printf("configure save: %v", err)
+		http.Error(w, "Could not save configuration: "+err.Error(), http.StatusBadGateway)
+		return
+	}
+	clearCfgUnsaved(w)
+	w.Header().Set("HX-Refresh", "true")
 	w.WriteHeader(http.StatusNoContent)
 }

src/webui/internal/handlers/configure_system.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 
 	"github.com/kernelkit/webui/internal/restconf"
+	"github.com/kernelkit/webui/internal/schema"
 )
 
 // ─── RESTCONF JSON types (candidate datastore) ────────────────────────────────
@@ -70,6 +71,7 @@ type cfgDNSAddrJSON struct {
 
 type cfgSystemPageData struct {
 	PageData
+	Loading    bool   // true while YANG schema is still downloading
 	Error      string
 	Hostname   string
 	Contact    string
@@ -79,6 +81,11 @@ type cfgSystemPageData struct {
 	DNS        cfgDNSJSON
 	MotdBanner string // decoded from YANG binary
 	TextEditor string // e.g. "infix-system:emacs"
+
+	// Schema-enriched fields — only populated when Loading is false.
+	TextEditorOptions []schema.IdentityOption
+	TimezoneOptions   []string          // bare timezone names for select
+	Desc              map[string]string // leaf name → YANG description
 }
 
 // ─── Handler ─────────────────────────────────────────────────────────────────
@@ -87,6 +94,7 @@ type cfgSystemPageData struct {
 type ConfigureSystemHandler struct {
 	Template *template.Template
 	RC       restconf.Fetcher
+	Schema   *schema.Cache
 }
 
 const candidatePath = "/ds/ietf-datastores:candidate"
@@ -127,6 +135,32 @@ func (h *ConfigureSystemHandler) Overview(w http.ResponseWriter, r *http.Request
 		data.TextEditor = s.TextEditor
 	}
 
+	mgr := h.Schema.Manager()
+	data.Loading = mgr == nil
+	if mgr != nil {
+		const sys = "/ietf-system:system"
+		data.TextEditorOptions = schema.OptionsFor(mgr, sys+"/infix-system:text-editor")
+		if data.TextEditor == "" {
+			for _, opt := range data.TextEditorOptions {
+				if opt.IsDefault {
+					data.TextEditor = opt.Value
+					break
+				}
+			}
+		}
+		data.Desc = map[string]string{
+			"hostname":    schema.DescriptionOf(mgr, sys+"/hostname"),
+			"contact":     schema.DescriptionOf(mgr, sys+"/contact"),
+			"location":    schema.DescriptionOf(mgr, sys+"/location"),
+			"timezone":    schema.DescriptionOf(mgr, sys+"/clock/timezone-name"),
+			"text-editor": schema.DescriptionOf(mgr, sys+"/infix-system:text-editor"),
+			"motd-banner": schema.DescriptionOf(mgr, sys+"/infix-system:motd-banner"),
+		}
+		for _, opt := range schema.OptionsFor(mgr, sys+"/clock/timezone-name") {
+			data.TimezoneOptions = append(data.TimezoneOptions, schema.StripModulePrefix(opt.Value))
+		}
+	}
+
 	tmplName := "configure-system.html"
 	if r.Header.Get("HX-Request") == "true" {
 		tmplName = "content"

src/webui/internal/handlers/sibling_test.go

@@ -0,0 +1,106 @@
+package handlers
+
+import (
+	"encoding/json"
+	"reflect"
+	"testing"
+)
+
+func TestUnwrapForPutContainer(t *testing.T) {
+	raw := []byte(`{"infix-services:web":{"certificate":"gencert","enabled":true}}`)
+	var doc map[string]any
+	if err := json.Unmarshal(raw, &doc); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	obj, wrap, err := unwrapForPut(doc, "/infix-services:web")
+	if err != nil {
+		t.Fatalf("unwrap: %v", err)
+	}
+	if wrap != "infix-services:web" {
+		t.Errorf("wrap = %q, want %q", wrap, "infix-services:web")
+	}
+	if obj["certificate"] != "gencert" {
+		t.Errorf("certificate = %v, want gencert", obj["certificate"])
+	}
+}
+
+func TestUnwrapForPutListInstance(t *testing.T) {
+	raw := []byte(`{"ietf-interfaces:interfaces":{"interface":[{"name":"lan3","type":"ethernet","infix-interfaces:bridge-port":{"bridge":"br0"}}]}}`)
+	var doc map[string]any
+	if err := json.Unmarshal(raw, &doc); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	obj, wrap, err := unwrapForPut(doc, "/ietf-interfaces:interfaces/interface=lan3")
+	if err != nil {
+		t.Fatalf("unwrap: %v", err)
+	}
+	if wrap != "interface" {
+		t.Errorf("wrap = %q, want %q", wrap, "interface")
+	}
+	if obj["name"] != "lan3" {
+		t.Errorf("name = %v, want lan3", obj["name"])
+	}
+	if _, ok := obj["infix-interfaces:bridge-port"]; !ok {
+		t.Errorf("expected bridge-port key in unwrapped entry, got: %v", obj)
+	}
+}
+
+func TestUnwrapForPutEmpty(t *testing.T) {
+	doc := map[string]any{}
+	if _, _, err := unwrapForPut(doc, "/x"); err == nil {
+		t.Errorf("expected error for empty doc")
+	}
+}
+
+func TestExtractFieldValuesWithSibling(t *testing.T) {
+	data := []byte(`{
+      "ietf-interfaces:interfaces": {
+        "interface": [
+          {"name": "lan1", "type": "ethernet"},
+          {"name": "br0", "type": "bridge", "infix-interfaces:bridge": {"vlans": {}}},
+          {"name": "br1", "type": "bridge", "infix-interfaces:bridge": {}},
+          {"name": "lan3", "type": "ethernet", "infix-interfaces:bridge-port": {"bridge":"br0"}}
+        ]
+      }
+    }`)
+	got := extractFieldValuesWithSibling(data, "name", "bridge")
+	want := []string{"br0", "br1"}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}
+
+// TestExtractFieldValuesNestedRecord guards against the bug where a
+// leafref dropdown for /ietf-keystore:keystore/asymmetric-keys/
+// asymmetric-key/name picked up "self-signed" — which lives in the
+// nested certificates/certificate[]/name list inside each asymmetric
+// key entry. The walker has to treat the asymmetric-key map as a
+// record boundary and not descend into siblings once it has found
+// the field there.
+func TestExtractFieldValuesNestedRecord(t *testing.T) {
+	data := []byte(`{
+      "ietf-keystore:keystore": {
+        "asymmetric-keys": {
+          "asymmetric-key": [
+            {
+              "name": "gencert",
+              "certificates": {
+                "certificate": [
+                  {"name": "self-signed"}
+                ]
+              }
+            },
+            {
+              "name": "genkey",
+              "certificates": {}
+            }
+          ]
+        }
+      }
+    }`)
+	got := extractFieldValues(data, "name")
+	want := []string{"gencert", "genkey"}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}

src/webui/internal/handlers/yang_data.go

@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: MIT
+
+package handlers
+
+import (
+	"bytes"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/kernelkit/webui/internal/restconf"
+	"github.com/kernelkit/webui/internal/schema"
+)
+
+const candidateDS = "/ds/ietf-datastores:candidate"
+
+// DataHandler serves GET /api/data — raw RESTCONF JSON for a path.
+// PUT and DELETE are handled by TreeHandler to share template rendering.
+type DataHandler struct {
+	RC     restconf.Fetcher
+	Schema *schema.Cache
+}
+
+// Get serves GET /api/data?path=...
+// Returns the raw RESTCONF JSON subtree from candidate (falls back to running).
+func (h *DataHandler) Get(w http.ResponseWriter, r *http.Request) {
+	path := r.URL.Query().Get("path")
+	if path == "" {
+		http.Error(w, "path required", http.StatusBadRequest)
+		return
+	}
+
+	data, err := h.RC.GetRaw(r.Context(), candidateDS+path)
+	if err != nil {
+		data, err = h.RC.GetRaw(r.Context(), "/data"+path)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusNotFound)
+			return
+		}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.Write(data)
+}
+
+// navigateToNode traverses a RESTCONF JSON response using path segments to
+// reach the target node.  The server always wraps responses in the full
+// module-root hierarchy ({"module:root": {"list": [{...}]}}), so we walk each
+// segment; for list segments with a key predicate (e.g. "interface=eth0") we
+// enter the array and take the first (only) element.
+// Returns nil when any segment cannot be found.
+func navigateToNode(data []byte, path string) json.RawMessage {
+	segs := strings.Split(strings.TrimPrefix(path, "/"), "/")
+	current := json.RawMessage(data)
+	for _, seg := range segs {
+		hasPred := strings.ContainsAny(seg, "[=")
+		_, localName := splitModPrefix(stripModPredicate(seg))
+		var obj map[string]json.RawMessage
+		if err := json.Unmarshal(current, &obj); err != nil {
+			return nil
+		}
+		var found json.RawMessage
+		for k, v := range obj {
+			_, local := splitModPrefix(k)
+			if local == localName {
+				found = v
+				break
+			}
+		}
+		if found == nil {
+			return nil
+		}
+		if hasPred {
+			var arr []json.RawMessage
+			if err := json.Unmarshal(found, &arr); err != nil || len(arr) == 0 {
+				return nil
+			}
+			// Extract key value from predicate: "name=eth0" → "eth0".
+			keyVal := ""
+			if i := strings.IndexByte(seg, '='); i >= 0 {
+				keyVal = seg[i+1:]
+			}
+			matched := arr[0] // fallback: first element
+			if keyVal != "" {
+				for _, elem := range arr {
+					var row map[string]json.RawMessage
+					if json.Unmarshal(elem, &row) != nil {
+						continue
+					}
+					for _, v := range row {
+						var s string
+						if json.Unmarshal(v, &s) == nil && s == keyVal {
+							matched = elem
+							goto nextSeg
+						}
+					}
+				}
+			}
+		nextSeg:
+			found = matched
+		}
+		current = found
+	}
+	return current
+}
+
+// flattenNodeValues extracts direct scalar leaf values from a JSON object,
+// returning a map of bare-name → string.  Nested objects and arrays (which
+// represent sub-containers and sub-lists) are silently skipped.
+func flattenNodeValues(raw json.RawMessage) map[string]string {
+	var obj map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &obj); err != nil {
+		return nil
+	}
+	result := make(map[string]string, len(obj))
+	for k, v := range obj {
+		if len(v) > 0 && v[0] == '[' {
+			// YANG empty type is encoded as [null] in JSON (RFC 7951 §6.9).
+			// Represent presence as "true"; skip real arrays (sub-lists).
+			trimmed := bytes.TrimSpace(v)
+			if bytes.Equal(trimmed, []byte("[null]")) {
+				_, local := splitModPrefix(k)
+				result[local] = "true"
+			}
+			continue
+		}
+		if len(v) > 0 && v[0] == '{' {
+			continue // sub-container — not a direct leaf
+		}
+		_, local := splitModPrefix(k)
+		result[local] = extractScalar(v)
+	}
+	return result
+}
+
+// stripModPredicate removes both a module prefix and a RESTCONF key predicate
+// from a path segment, e.g. "ietf-interfaces:interface=eth0" → "interface".
+func stripModPredicate(seg string) string {
+	if i := strings.IndexByte(seg, '['); i >= 0 {
+		seg = seg[:i]
+	}
+	if i := strings.IndexByte(seg, '='); i >= 0 {
+		seg = seg[:i]
+	}
+	return seg
+}
+
+// extractLeafValue unwraps the single-key RESTCONF JSON envelope that wraps a
+// leaf value: {"module:name": <value>} → string representation of <value>.
+// Recursively unwraps single-key nested objects so that a response like
+// {"module:parent": {"certificate": "gencert"}} → "gencert".
+func extractLeafValue(data []byte) string {
+	var m map[string]json.RawMessage
+	if err := json.Unmarshal(data, &m); err != nil {
+		return ""
+	}
+	for _, raw := range m {
+		return extractScalar(raw)
+	}
+	return ""
+}
+
+// extractScalar converts a JSON value to a display string.
+// Single-key objects are recursively unwrapped (RESTCONF sometimes wraps leaf
+// values in a choice/case or container envelope).
+func extractScalar(raw json.RawMessage) string {
+	// Plain string.
+	var s string
+	if json.Unmarshal(raw, &s) == nil {
+		return s
+	}
+	// Bool or number (unquoted JSON token).
+	v := string(raw)
+	if v == "true" || v == "false" || (len(v) > 0 && (v[0] == '-' || (v[0] >= '0' && v[0] <= '9'))) {
+		return v
+	}
+	// Single-key object: unwrap one level and recurse.
+	var nested map[string]json.RawMessage
+	if err := json.Unmarshal(raw, &nested); err == nil && len(nested) == 1 {
+		for _, inner := range nested {
+			return extractScalar(inner)
+		}
+	}
+	// Fallback: return the raw token (strips outer quotes if present).
+	if len(v) >= 2 && v[0] == '"' && v[len(v)-1] == '"' {
+		return v[1 : len(v)-1]
+	}
+	return v
+}
+
+// coerceLeafValue converts the raw form string to the JSON type that RESTCONF
+// expects for the leaf based on the schema Node type.
+func coerceLeafValue(raw string, node *schema.Node) any {
+	if node == nil || node.Type == nil {
+		return raw
+	}
+	switch node.Type.Kind {
+	case "boolean":
+		return raw == "on" || raw == "true"
+	case "int8", "int16", "int32", "int64",
+		"uint8", "uint16", "uint32", "uint64":
+		var n int64
+		if _, err := fmt.Sscanf(raw, "%d", &n); err == nil {
+			return n
+		}
+	case "binary":
+		// Strip whitespace that textarea input may add (trailing newlines, spaces).
+		// If the cleaned value is valid base64, send it as-is; otherwise encode.
+		cleaned := strings.Map(func(r rune) rune {
+			if r == ' ' || r == '\t' || r == '\n' || r == '\r' {
+				return -1
+			}
+			return r
+		}, raw)
+		if _, err := base64.StdEncoding.DecodeString(cleaned); err == nil {
+			return cleaned
+		}
+		return base64.StdEncoding.EncodeToString([]byte(raw))
+	}
+	return raw
+}

src/webui/internal/restconf/client.go

@@ -187,6 +187,40 @@ func (c *Client) writeJSON(ctx context.Context, method, path string, body any) e
 	return nil
 }
 
+// GetYANG downloads a YANG module file. YANG files are served outside the
+// RESTCONF tree at /yang/{name}@{revision}.yang on the device host — mirroring
+// the approach used by the Infamy test framework (yang_url = base_url + "/yang").
+func (c *Client) GetYANG(ctx context.Context, name, revision string) ([]byte, error) {
+	// Strip the /restconf suffix to get the host-level base URL.
+	yangBase := c.baseURL
+	if i := strings.LastIndex(yangBase, "/restconf"); i >= 0 {
+		yangBase = yangBase[:i]
+	}
+
+	path := "/yang/" + name
+	if revision != "" {
+		path += "@" + revision
+	}
+	path += ".yang"
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, yangBase+path, nil)
+	if err != nil {
+		return nil, err
+	}
+	creds := CredentialsFromContext(ctx)
+	req.SetBasicAuth(creds.Username, creds.Password)
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("restconf request failed: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, parseError(resp)
+	}
+	return io.ReadAll(resp.Body)
+}
+
 // GetRaw fetches a RESTCONF resource and returns the raw JSON bytes.
 func (c *Client) GetRaw(ctx context.Context, path string) ([]byte, error) {
 	resp, err := c.doRequest(ctx, http.MethodGet, path)

src/webui/internal/restconf/errors.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 )
 
 // AuthError is returned when RESTCONF rejects credentials (401/403).
@@ -35,7 +36,7 @@ func (e *Error) Error() string {
 
 // parseError reads a RESTCONF error response body and returns an *Error.
 func parseError(resp *http.Response) error {
-	body, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+	body, _ := io.ReadAll(io.LimitReader(resp.Body, 8192))
 
 	re := &Error{StatusCode: resp.StatusCode}
 
@@ -45,16 +46,28 @@ func parseError(resp *http.Response) error {
 			Error []struct {
 				ErrorType    string `json:"error-type"`
 				ErrorTag     string `json:"error-tag"`
+				ErrorPath    string `json:"error-path"`
 				ErrorMessage string `json:"error-message"`
+				ErrorInfo    any    `json:"error-info"`
 			} `json:"error"`
 		} `json:"ietf-restconf:errors"`
 	}
 
 	if json.Unmarshal(body, &envelope) == nil && len(envelope.Errors.Error) > 0 {
-		first := envelope.Errors.Error[0]
-		re.Type = first.ErrorType
-		re.Tag = first.ErrorTag
-		re.Message = first.ErrorMessage
+		var parts []string
+		for _, e := range envelope.Errors.Error {
+			msg := e.ErrorMessage
+			if msg == "" {
+				msg = e.ErrorTag
+			}
+			if e.ErrorPath != "" {
+				msg += " (path: " + e.ErrorPath + ")"
+			}
+			parts = append(parts, msg)
+		}
+		re.Type = envelope.Errors.Error[0].ErrorType
+		re.Tag = envelope.Errors.Error[0].ErrorTag
+		re.Message = strings.Join(parts, "; ")
 	} else {
 		re.Message = http.StatusText(resp.StatusCode)
 	}

src/webui/internal/restconf/fetcher.go

@@ -12,6 +12,9 @@ import (
 type Fetcher interface {
 	Get(ctx context.Context, path string, target any) error
 	GetRaw(ctx context.Context, path string) ([]byte, error)
+	// GetYANG downloads a YANG module file from /yang/{name}@{revision}.yang
+	// on the device host (outside the /restconf tree).
+	GetYANG(ctx context.Context, name, revision string) ([]byte, error)
 	Post(ctx context.Context, path string) error
 	PostJSON(ctx context.Context, path string, body any) error
 

src/webui/internal/schema/fetch.go

@@ -0,0 +1,125 @@
+package schema
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+
+	"github.com/kernelkit/webui/internal/restconf"
+)
+
+// ModuleInfo identifies a YANG module by name and revision.
+type ModuleInfo struct {
+	Name     string
+	Revision string
+}
+
+func (m ModuleInfo) filename() string {
+	if m.Revision == "" {
+		return m.Name + ".yang"
+	}
+	return m.Name + "@" + m.Revision + ".yang"
+}
+
+// rfc7895ModulesState is the RFC 7895 /modules-state response structure.
+type rfc7895ModulesState struct {
+	ModulesState struct {
+		Module []struct {
+			Name       string `json:"name"`
+			Revision   string `json:"revision"`
+			Submodule  []struct {
+				Name     string `json:"name"`
+				Revision string `json:"revision"`
+			} `json:"submodule"`
+		} `json:"module"`
+	} `json:"ietf-yang-library:modules-state"`
+}
+
+// rfc8525YangLibrary is the RFC 8525 /yang-library response structure (fallback).
+type rfc8525YangLibrary struct {
+	YangLibrary struct {
+		ModuleSet []struct {
+			Module []struct {
+				Name     string `json:"name"`
+				Revision string `json:"revision"`
+			} `json:"module"`
+		} `json:"module-set"`
+	} `json:"ietf-yang-library:yang-library"`
+}
+
+// FetchModules downloads any YANG files not already cached in cacheDir.
+// It first tries the RFC 7895 modules-state endpoint, then falls back to
+// the RFC 8525 yang-library endpoint (same as capabilities.go).
+// Each module and its submodules are downloaded from /yang/{name}@{rev}.yang.
+func FetchModules(ctx context.Context, rc restconf.Fetcher, cacheDir string) ([]ModuleInfo, error) {
+	if err := os.MkdirAll(cacheDir, 0750); err != nil {
+		return nil, fmt.Errorf("schema: create cache dir: %w", err)
+	}
+
+	modules, err := listModules(ctx, rc)
+	if err != nil {
+		return nil, err
+	}
+
+	var downloaded []ModuleInfo
+	for _, m := range modules {
+		if err := downloadIfMissing(ctx, rc, cacheDir, m); err != nil {
+			log.Printf("schema: skip %s: %v", m.filename(), err)
+			continue
+		}
+		downloaded = append(downloaded, m)
+	}
+	return downloaded, nil
+}
+
+// listModules queries the device for the list of implemented YANG modules.
+func listModules(ctx context.Context, rc restconf.Fetcher) ([]ModuleInfo, error) {
+	// Try RFC 7895 modules-state first.
+	var ms rfc7895ModulesState
+	if err := rc.Get(ctx, "/data/ietf-yang-library:modules-state", &ms); err == nil {
+		var mods []ModuleInfo
+		for _, m := range ms.ModulesState.Module {
+			mods = append(mods, ModuleInfo{Name: m.Name, Revision: m.Revision})
+			for _, sub := range m.Submodule {
+				mods = append(mods, ModuleInfo{Name: sub.Name, Revision: sub.Revision})
+			}
+		}
+		if len(mods) > 0 {
+			return mods, nil
+		}
+	}
+
+	// Fall back to RFC 8525 yang-library.
+	var yl rfc8525YangLibrary
+	if err := rc.Get(ctx, "/data/ietf-yang-library:yang-library", &yl); err != nil {
+		return nil, fmt.Errorf("schema: list modules: %w", err)
+	}
+	var mods []ModuleInfo
+	for _, ms := range yl.YangLibrary.ModuleSet {
+		for _, m := range ms.Module {
+			mods = append(mods, ModuleInfo{Name: m.Name, Revision: m.Revision})
+		}
+	}
+	return mods, nil
+}
+
+// downloadIfMissing fetches a single YANG file from the device if not cached.
+func downloadIfMissing(ctx context.Context, rc restconf.Fetcher, cacheDir string, m ModuleInfo) error {
+	dest := filepath.Join(cacheDir, m.filename())
+	if _, err := os.Stat(dest); err == nil {
+		return nil // already cached
+	}
+
+	data, err := rc.GetYANG(ctx, m.Name, m.Revision)
+	if err != nil {
+		return fmt.Errorf("GET /yang/%s: %w", m.filename(), err)
+	}
+
+	if err := os.WriteFile(dest, data, 0640); err != nil {
+		return fmt.Errorf("write %s: %w", dest, err)
+	}
+	log.Printf("schema: cached %s", m.filename())
+	return nil
+}

src/webui/internal/schema/helpers.go

@@ -0,0 +1,55 @@
+package schema
+
+import "strings"
+
+// IdentityOption is a schema-resolved identity/enum value for use in select dropdowns.
+type IdentityOption struct {
+	Value     string // full identity, e.g. "infix-system:clish" — submitted to RESTCONF
+	Label     string // display label with module prefix stripped, e.g. "clish"
+	IsDefault bool   // true if this matches the leaf's YANG default
+}
+
+// StripModulePrefix strips the "module:" prefix from an identity or enum value.
+func StripModulePrefix(v string) string {
+	if i := strings.LastIndex(v, ":"); i >= 0 {
+		return v[i+1:]
+	}
+	return v
+}
+
+// OptionsFor returns IdentityOption entries for the identityref or enumeration
+// leaf at path. Returns nil when schema is unavailable or the leaf has no options.
+func OptionsFor(mgr *Manager, path string) []IdentityOption {
+	if mgr == nil {
+		return nil
+	}
+	node, err := mgr.NodeAt(path)
+	if err != nil || node == nil || node.Type == nil {
+		return nil
+	}
+	values := node.Type.Identities
+	if len(values) == 0 {
+		values = node.Type.Enums
+	}
+	opts := make([]IdentityOption, 0, len(values))
+	for _, v := range values {
+		opts = append(opts, IdentityOption{
+			Value:     v,
+			Label:     StripModulePrefix(v),
+			IsDefault: node.Default != "" && v == node.Default,
+		})
+	}
+	return opts
+}
+
+// DescriptionOf returns the YANG description for the leaf at path, or "".
+func DescriptionOf(mgr *Manager, path string) string {
+	if mgr == nil {
+		return ""
+	}
+	node, err := mgr.NodeAt(path)
+	if err != nil || node == nil {
+		return ""
+	}
+	return node.Description
+}

src/webui/internal/schema/leafref_test.go

@@ -0,0 +1,166 @@
+package schema
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const testTargetYang = `
+module test-target {
+  yang-version 1.1;
+  namespace "urn:test:target";
+  prefix tt;
+
+  container interfaces {
+    list interface {
+      key name;
+      leaf name { type string; }
+      leaf type { type string; }
+    }
+  }
+}
+`
+
+const testReferYang = `
+module test-refer {
+  yang-version 1.1;
+  namespace "urn:test:refer";
+  prefix tr;
+
+  import test-target { prefix tt; }
+
+  container config {
+    leaf port {
+      type leafref {
+        path "/tt:interfaces/tt:interface/tt:name";
+      }
+      must "deref(.)/../tt:type" {
+        error-message "target must have type";
+      }
+    }
+  }
+}
+`
+
+func TestLeafrefCanonicalize(t *testing.T) {
+	dir := t.TempDir()
+	mustWrite(t, dir, "test-target.yang", testTargetYang)
+	mustWrite(t, dir, "test-refer.yang", testReferYang)
+
+	mgr, err := Load(dir)
+	if err != nil {
+		t.Fatalf("new manager: %v", err)
+	}
+
+	n, err := mgr.NodeAt("/test-refer:config/port")
+	if err != nil {
+		t.Fatalf("NodeAt: %v", err)
+	}
+	if n == nil || n.Type == nil {
+		t.Fatalf("missing node or type: %+v", n)
+	}
+	t.Logf("Leafref path = %q", n.Type.Leafref)
+	t.Logf("LeafrefSibling = %q", n.Type.LeafrefSibling)
+
+	if strings.Contains(n.Type.Leafref, "tt:") {
+		t.Errorf("Leafref still has unresolved prefix: %q", n.Type.Leafref)
+	}
+	want := "/test-target:interfaces/interface/name"
+	if n.Type.Leafref != want {
+		t.Errorf("Leafref = %q, want %q (RESTCONF canonical, no repeated module prefixes)", n.Type.Leafref, want)
+	}
+	if n.Type.LeafrefSibling != "type" {
+		t.Errorf("LeafrefSibling = %q, want \"type\"", n.Type.LeafrefSibling)
+	}
+}
+
+func mustWrite(t *testing.T, dir, name, content string) {
+	if err := os.WriteFile(filepath.Join(dir, name), []byte(content), 0644); err != nil {
+		t.Fatalf("write %s: %v", name, err)
+	}
+}
+
+// TestLeafrefParentIsList verifies that NodeAt reports the correct Kind
+// for each segment of a canonical leafref path so fetchLeafrefValues can
+// walk up past the list to its container parent (RESTCONF refuses bare
+// list paths). Mirrors the bridge-port/bridge case where the path
+// ends in /interfaces/interface/name and we have to GET /interfaces.
+func TestLeafrefParentIsList(t *testing.T) {
+	dir := t.TempDir()
+	mustWrite(t, dir, "test-target.yang", testTargetYang)
+	mgr, err := Load(dir)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	cases := []struct{ path, kind string }{
+		{"/test-target:interfaces", "container"},
+		{"/test-target:interfaces/interface", "list"},
+		{"/test-target:interfaces/interface/name", "leaf"},
+	}
+	for _, tc := range cases {
+		n, err := mgr.NodeAt(tc.path)
+		if err != nil || n == nil {
+			t.Fatalf("NodeAt(%q): %v", tc.path, err)
+		}
+		if n.Kind != tc.kind {
+			t.Errorf("NodeAt(%q).Kind = %q, want %q", tc.path, n.Kind, tc.kind)
+		}
+	}
+}
+
+const testBridgeYang = `
+module test-br {
+  yang-version 1.1;
+  namespace "urn:test:br";
+  prefix tb;
+
+  import test-target { prefix tt; }
+
+  grouping br-port {
+    leaf bridge {
+      type leafref {
+        path "/tt:interfaces/tt:interface/tt:name";
+      }
+      must "deref(.)/../bridge and not(. = ../../tt:name)";
+    }
+  }
+
+  augment "/tt:interfaces/tt:interface" {
+    container bridge-port {
+      uses br-port;
+    }
+  }
+}
+`
+
+func TestLeafrefBridgeAugment(t *testing.T) {
+	dir := t.TempDir()
+	mustWrite(t, dir, "test-target.yang", testTargetYang)
+	mustWrite(t, dir, "test-br.yang", testBridgeYang)
+	mgr, err := Load(dir)
+	if err != nil {
+		t.Fatalf("load: %v", err)
+	}
+	n, err := mgr.NodeAt("/test-target:interfaces/interface/test-br:bridge-port/bridge")
+	if err != nil {
+		t.Logf("first NodeAt failed: %v", err)
+		n, err = mgr.NodeAt("/test-target:interfaces/test-target:interface/test-br:bridge-port/test-br:bridge")
+		if err != nil {
+			t.Fatalf("NodeAt: %v", err)
+		}
+	}
+	if n == nil || n.Type == nil {
+		t.Fatalf("missing: %+v", n)
+	}
+	t.Logf("Leafref = %q", n.Type.Leafref)
+	t.Logf("LeafrefSibling = %q", n.Type.LeafrefSibling)
+	if n.Type.LeafrefSibling != "bridge" {
+		t.Errorf("LeafrefSibling = %q, want \"bridge\"", n.Type.LeafrefSibling)
+	}
+	want := "/test-target:interfaces/interface/name"
+	if n.Type.Leafref != want {
+		t.Errorf("Leafref = %q, want %q", n.Type.Leafref, want)
+	}
+}

src/webui/internal/schema/manager.go

@@ -0,0 +1,899 @@
+package schema
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"reflect"
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/openconfig/goyang/pkg/yang"
+)
+
+// Manager holds a fully processed goyang module set and provides schema queries.
+// All modules are loaded before Process() is called so that cross-module
+// identityref resolution and augments work correctly.
+type Manager struct {
+	ms *yang.Modules
+}
+
+// Load parses all .yang files in yangDir and returns a Manager.
+// Errors from Process() that are non-fatal (e.g. unresolved augments for
+// modules that were not downloaded) are logged but do not abort loading.
+func Load(yangDir string) (*Manager, error) {
+	ms := yang.NewModules()
+	ms.Path = []string{yangDir}
+
+	entries, err := os.ReadDir(yangDir)
+	if err != nil {
+		return nil, fmt.Errorf("schema: read yang dir: %w", err)
+	}
+
+	for _, e := range entries {
+		if e.IsDir() || !strings.HasSuffix(e.Name(), ".yang") {
+			continue
+		}
+		if err := ms.Read(filepath.Join(yangDir, e.Name())); err != nil {
+			// Non-fatal: goyang may still register the module partially.
+			log.Printf("schema: parse (non-fatal) %s: %v", e.Name(), err)
+		}
+	}
+
+	errs := ms.Process()
+	for _, err := range errs {
+		// goyang v1.6.3 has known YANG 1.1 gaps (must/when substatements,
+		// duplicate augments).  These are non-fatal; log at debug level.
+		log.Printf("schema: process (non-fatal): %v", err)
+	}
+
+	return &Manager{ms: ms}, nil
+}
+
+// Children returns the direct config-relevant child Nodes of the node at path.
+// Use path "/" for the top-level module list.
+// choice/case nodes are inlined transparently (their children are promoted).
+func (m *Manager) Children(path string) ([]*Node, error) {
+	if path == "" || path == "/" {
+		return m.topLevelNodes(), nil
+	}
+	e, err := m.entryAt(path)
+	if err != nil {
+		return nil, err
+	}
+	if e.Dir == nil {
+		return nil, nil
+	}
+	return dirToNodes(e.Dir, path), nil
+}
+
+// ChildrenAll is like Children but includes config:false nodes, making it
+// suitable for the operational/status tree where state data reuses read-write
+// schema nodes. Only RPCs, notifications, anydata/anyxml, and deprecated or
+// obsolete nodes are excluded.
+func (m *Manager) ChildrenAll(path string) ([]*Node, error) {
+	if path == "" || path == "/" {
+		return m.topLevelNodesAll(), nil
+	}
+	e, err := m.entryAt(path)
+	if err != nil {
+		return nil, err
+	}
+	if e.Dir == nil {
+		return nil, nil
+	}
+	return dirToNodesAll(e.Dir, path), nil
+}
+
+// NodeAt returns a Node for the YANG schema node at path (without children).
+func (m *Manager) NodeAt(path string) (*Node, error) {
+	if path == "" || path == "/" {
+		return &Node{Path: "/", Name: "", Kind: "container", Config: true}, nil
+	}
+	e, err := m.entryAt(path)
+	if err != nil {
+		return nil, err
+	}
+	return entryToNode(e, path), nil
+}
+
+// IdentitiesOf returns the names of all identities derived (directly or
+// transitively) from baseName. baseName may be "name" or "module:name".
+// Searches across all loaded modules.
+func (m *Manager) IdentitiesOf(baseName string) []string {
+	// Strip module prefix if present; search by identity name.
+	_, localName := splitPrefix(baseName)
+
+	for _, mod := range m.ms.Modules {
+		for _, id := range mod.Identities() {
+			if id.Name == localName {
+				var names []string
+				for _, v := range id.Values {
+					names = append(names, v.Name)
+				}
+				sort.Strings(names)
+				return names
+			}
+		}
+	}
+	return nil
+}
+
+// ResolveLeafref converts a YANG leafref path expression to an absolute schema
+// path that can be fetched via RESTCONF. contextPath is the schema path of the
+// leaf that holds the leafref (needed for relative `../` resolution).
+// Returns empty string if the path cannot be resolved.
+func (m *Manager) ResolveLeafref(leafrefPath, contextPath string) string {
+	if strings.HasPrefix(leafrefPath, "/") {
+		return normalizeLeafrefPath(leafrefPath)
+	}
+	// Relative path: resolve `../` against the context, stripping the leaf itself.
+	parts := strings.Split(strings.TrimPrefix(contextPath, "/"), "/")
+	if len(parts) > 0 {
+		parts = parts[:len(parts)-1] // remove the leaf; start from its parent
+	}
+	for _, seg := range strings.Split(leafrefPath, "/") {
+		switch seg {
+		case "..":
+			if len(parts) > 0 {
+				parts = parts[:len(parts)-1]
+			}
+		case ".", "":
+			// skip
+		default:
+			parts = append(parts, stripPredicate(seg))
+		}
+	}
+	if len(parts) == 0 {
+		return ""
+	}
+	return "/" + strings.Join(parts, "/")
+}
+
+// normalizeLeafrefPath strips XPath predicates from each segment of an
+// absolute YANG leafref path so it can be used as a schema lookup path.
+func normalizeLeafrefPath(p string) string {
+	segs := strings.Split(strings.TrimPrefix(p, "/"), "/")
+	for i, s := range segs {
+		segs[i] = stripPredicate(s)
+	}
+	return "/" + strings.Join(segs, "/")
+}
+
+// canonicalizeLeafrefPath rewrites a YANG leafref path into the RESTCONF
+// canonical form (RFC 8040 §3.5.3): each segment's prefix alias is
+// resolved to its canonical module name, and the "module:" qualifier
+// is dropped from segments whose module matches the preceding
+// qualified segment. Unknown prefixes are left untouched.
+//
+// Example: "/if:interfaces/if:interface/if:name" with the `if` prefix
+// pointing at `ietf-interfaces` becomes
+// "/ietf-interfaces:interfaces/interface/name", which is what
+// nodeSegment() produces for ordinary paths and what RESTCONF expects.
+func canonicalizeLeafrefPath(node yang.Node, p string) string {
+	if node == nil || p == "" {
+		return p
+	}
+	segs := strings.Split(p, "/")
+	var lastMod string
+	for i, seg := range segs {
+		if seg == "" || seg == ".." || seg == "." {
+			continue
+		}
+		bare, pred := seg, ""
+		if b := strings.IndexByte(seg, '['); b >= 0 {
+			bare, pred = seg[:b], seg[b:]
+		}
+		colon := strings.IndexByte(bare, ':')
+		if colon < 0 {
+			// Unprefixed segments inherit the prevailing module.
+			continue
+		}
+		prefix, rest := bare[:colon], bare[colon+1:]
+		mod := yang.FindModuleByPrefix(node, prefix)
+		if mod == nil {
+			continue
+		}
+		modName := mod.Name
+		if mod.BelongsTo != nil {
+			modName = mod.BelongsTo.Name
+		}
+		if modName == lastMod {
+			segs[i] = rest + pred
+		} else {
+			segs[i] = modName + ":" + rest + pred
+			lastMod = modName
+		}
+	}
+	return strings.Join(segs, "/")
+}
+
+// derefSiblingPattern captures the `deref(.)/../<sibling>` XPath idiom
+// used by Infix YANG must statements to constrain a leafref's target
+// to objects that carry a specific sibling node (e.g. `bridge-port/
+// bridge`'s must says the referenced interface must have a `bridge`
+// container — i.e. it has to be a bridge). The capture group is the
+// local sibling name; any prefix (`tt:type`) is matched non-capturing
+// so callers don't have to strip it.
+var derefSiblingPattern = regexp.MustCompile(`deref\s*\(\s*\.\s*\)\s*/\s*\.\.\s*/\s*(?:[a-zA-Z][\w-]*:)?([a-zA-Z][\w-]*)`)
+
+// leafrefSiblingFilter looks at the leaf's must statements (only Leaf
+// nodes carry must in goyang's Entry tree) for the deref(.)/../X
+// pattern and returns X, or "" when no such constraint exists.
+func leafrefSiblingFilter(e *yang.Entry) string {
+	leaf, ok := e.Node.(*yang.Leaf)
+	if !ok {
+		return ""
+	}
+	for _, m := range leaf.Must {
+		if m == nil {
+			continue
+		}
+		if match := derefSiblingPattern.FindStringSubmatch(m.Name); len(match) == 2 {
+			return match[1]
+		}
+	}
+	return ""
+}
+
+// Default returns the YANG default value for the leaf at path, if any.
+func (m *Manager) Default(path string) (string, bool) {
+	e, err := m.entryAt(path)
+	if err != nil {
+		return "", false
+	}
+	return e.SingleDefaultValue()
+}
+
+// ModuleName returns the module name for the schema node at path.
+func (m *Manager) ModuleName(path string) (string, error) {
+	e, err := m.entryAt(path)
+	if err != nil {
+		return "", err
+	}
+	return e.InstantiatingModule()
+}
+
+// ModuleQualifiedName returns "module:name" for the schema node at path.
+// This is the JSON object key used when PUT/PATCHing that node directly via
+// RESTCONF (RFC 7951 §4 — namespace-qualified name at module boundaries).
+func (m *Manager) ModuleQualifiedName(path string) (string, error) {
+	e, err := m.entryAt(path)
+	if err != nil {
+		return "", err
+	}
+	modName, err := e.InstantiatingModule()
+	if err != nil {
+		return "", err
+	}
+	return modName + ":" + e.Name, nil
+}
+
+// internalOperationalTopNodes lists bare node names that must not appear at
+// the top level of the operational/status tree.  These are all transport- or
+// server-monitoring nodes of no interest to end users.  They are already
+// absent from the configure tree because they are config:false; this list
+// applies the same exclusion to topLevelNodesAll.
+var internalOperationalTopNodes = map[string]bool{
+	"netconf":              true, // NETCONF session/lock monitoring
+	"netconf-state":        true, // ietf-netconf-monitoring (RFC 6022)
+	"notification":         true, // nc-notifications stream container
+	"restconf-state":       true, // ietf-restconf-monitoring (RFC 8527)
+	"supported-algorithms": true, // SSH/TLS algorithm capability advertisement
+	"system-capabilities":  true, // ietf-system-capabilities (RFC 9196)
+}
+
+// internalModules is the deny-list of YANG modules that are infrastructure-only
+// and must not appear in the user-facing configure tree.
+// Mirrors sr_module_is_internal() from klish-plugin-sysrepo/src/pline.c.
+// Note: ietf-netconf-acm is intentionally NOT listed here — Infix exposes NACM
+// configuration to users.
+var internalModules = map[string]bool{
+	// libyang built-ins
+	"ietf-yang-metadata": true,
+	"yang":               true,
+	"ietf-inet-types":    true,
+	"ietf-yang-types":    true,
+	// YANG library / schema mount
+	"ietf-datastores":         true,
+	"ietf-yang-schema-mount":  true,
+	"ietf-yang-library":       true,
+	// NETCONF infrastructure
+	"ietf-netconf":                  true,
+	"ietf-netconf-with-defaults":    true,
+	"ietf-origin":                   true,
+	"ietf-netconf-notifications":    true,
+	// sysrepo internals
+	"sysrepo":            true,
+	"sysrepo-monitoring": true,
+	"sysrepo-plugind":    true,
+	// Infix test/debug subtree and meta-data — not user-facing
+	"infix-test": true,
+	"infix-meta": true,
+	// NETCONF server / transport infrastructure — managed by the system, not users
+	"ietf-netconf-server":          true,
+	"libnetconf2-netconf-server":   true,
+	"ietf-truststore":              true,
+	// Notification subscriptions and filters — not user-configurable via WebUI
+	"ietf-subscribed-notifications": true,
+	// ACL, key-chains, network-instances — not exposed in WebUI yet
+	"ietf-access-control-list":  true,
+	"ietf-key-chain":            true,
+	"ietf-network-instance":     true,
+}
+
+// topLevelNodes returns a Node for each config-relevant top-level schema node
+// across all loaded modules. Submodules, versioned aliases, internal modules,
+// and config:false top-level nodes are all excluded.
+func (m *Manager) topLevelNodes() []*Node {
+	var nodes []*Node
+	for key, mod := range m.ms.Modules {
+		if strings.Contains(key, "@") {
+			continue // versioned alias (e.g. "ieee802-dot1ab-lldp@2022-03-15") — duplicate
+		}
+		if mod.BelongsTo != nil {
+			continue // submodule — content appears under the parent module
+		}
+		if internalModules[key] {
+			continue
+		}
+		e := yang.ToEntry(mod)
+		if e == nil || e.Dir == nil {
+			continue
+		}
+		for _, child := range sortedEntries(e.Dir) {
+			if isNonConfigNode(child) {
+				continue
+			}
+			nodePath := "/" + key + ":" + child.Name
+			if isContainerList(child) {
+				if lc := listChildOf(child); lc != nil {
+					nodes = append(nodes, entryToNode(lc, nodePath+"/"+nodeSegment(lc, key)))
+				}
+				continue
+			}
+			nodes = append(nodes, entryToNode(child, nodePath))
+		}
+	}
+	// Sort by node name (not module-qualified path) for a clean alphabetical list.
+	sort.Slice(nodes, func(i, j int) bool { return nodes[i].Name < nodes[j].Name })
+	return nodes
+}
+
+// entryAt resolves a RESTCONF-style path to a goyang Entry.
+// Path format: /module:top-node/child[key='val']/grandchild
+// Key predicates ([key='val']) are stripped — they carry instance identity,
+// not schema identity. choice/case nodes are skipped during traversal.
+func (m *Manager) entryAt(path string) (*yang.Entry, error) {
+	path = strings.TrimPrefix(path, "/")
+	parts := strings.SplitN(path, "/", 2)
+
+	head := stripPredicate(parts[0])
+	moduleName, nodeName := splitPrefix(head)
+
+	if moduleName == "" {
+		return nil, fmt.Errorf("schema: path must start with module prefix: %s", path)
+	}
+
+	mod, ok := m.ms.Modules[moduleName]
+	if !ok {
+		return nil, fmt.Errorf("schema: module not found: %s", moduleName)
+	}
+
+	root := yang.ToEntry(mod)
+	if root == nil {
+		return nil, fmt.Errorf("schema: no entry for module: %s", moduleName)
+	}
+
+	e := findInDir(root.Dir, nodeName)
+	if e == nil {
+		return nil, fmt.Errorf("schema: %s not found in %s", nodeName, moduleName)
+	}
+
+	if len(parts) == 1 {
+		return e, nil
+	}
+
+	// Traverse remaining path segments, stripping key predicates.
+	for _, seg := range strings.Split(parts[1], "/") {
+		if seg == "" {
+			continue
+		}
+		_, localName := splitPrefix(stripPredicate(seg))
+		child := findInDir(e.Dir, localName)
+		if child == nil {
+			return nil, fmt.Errorf("schema: %s not found under %s", localName, e.Name)
+		}
+		e = child
+	}
+	return e, nil
+}
+
+// stripPredicate removes a key predicate from a path segment.
+// Handles both RESTCONF ("interface=eth0" → "interface") and
+// XPath ("interface[name='eth0']" → "interface") forms.
+func stripPredicate(seg string) string {
+	if i := strings.IndexByte(seg, '['); i >= 0 {
+		return seg[:i]
+	}
+	if i := strings.IndexByte(seg, '='); i >= 0 {
+		return seg[:i]
+	}
+	return seg
+}
+
+// findInDir looks up name in a dir map, transparently descending into
+// choice/case nodes which are not part of the RESTCONF path.
+func findInDir(dir map[string]*yang.Entry, name string) *yang.Entry {
+	if dir == nil {
+		return nil
+	}
+	// Direct match — but if it is a choice/case, descend into it because YANG
+	// commonly names a case identically to the leaf it contains (e.g. the
+	// ietf-system timezone-name case wrapping the timezone-name leaf).
+	if e, ok := dir[name]; ok {
+		if !e.IsChoice() && !e.IsCase() {
+			return e
+		}
+		if found := findInDir(e.Dir, name); found != nil {
+			return found
+		}
+	}
+	// Search inside all choice/case children.
+	for _, e := range dir {
+		if e.IsChoice() || e.IsCase() {
+			if found := findInDir(e.Dir, name); found != nil {
+				return found
+			}
+		}
+	}
+	return nil
+}
+
+// isContainerList returns true for containers that wrap exactly one list and
+// nothing else — the classic YANG container/list idiom (e.g. /interfaces wrapping
+// /interfaces/interface).  Mirrors klysc_is_container_list() in klish-plugin-sysrepo
+// exactly: ALL direct children are inspected, including config:false ones.  Any
+// non-list child (a leaf, another container, …) prevents collapsing.  This is why
+// "hardware" does not collapse — it has a config:false "last-change" leaf alongside
+// "component", so the default case fires and returns false.
+//
+// Hard exceptions:
+//   - "static-routes"  always collapses (ietf-routing, asymmetric naming)
+//   - "mdb"            never collapses
+//   - "ipv4", "ipv6"   never collapse (would confuse routing subtrees)
+func isContainerList(e *yang.Entry) bool {
+	if !e.IsContainer() || e.Dir == nil {
+		return false
+	}
+	if e.Name == "mdb" || e.Name == "ipv4" || e.Name == "ipv6" {
+		return false
+	}
+	if e.Name == "static-routes" {
+		return true
+	}
+	listCount := 0
+	for _, child := range e.Dir {
+		if !child.IsList() {
+			return false // any non-list child (even config:false) prevents collapse
+		}
+		listCount++
+	}
+	return listCount == 1
+}
+
+// listChildOf returns the single list child of a collapsible container (panics if
+// called on a non-collapsible container — callers must guard with isContainerList).
+func listChildOf(e *yang.Entry) *yang.Entry {
+	for _, child := range e.Dir {
+		if child.IsList() && !isNonConfigNode(child) {
+			return child
+		}
+	}
+	return nil
+}
+
+// listChildOfAll is like listChildOf but uses the data-node filter (includes
+// config:false lists), used by dirToNodesAll / the operational status tree.
+func listChildOfAll(e *yang.Entry) *yang.Entry {
+	for _, child := range e.Dir {
+		if child.IsList() && !isNonDataNode(child) {
+			return child
+		}
+	}
+	return nil
+}
+
+// topLevelNodesAll is like topLevelNodes but includes config:false top-level
+// nodes, for use by the operational status tree.
+func (m *Manager) topLevelNodesAll() []*Node {
+	var nodes []*Node
+	for key, mod := range m.ms.Modules {
+		if strings.Contains(key, "@") {
+			continue
+		}
+		if mod.BelongsTo != nil {
+			continue
+		}
+		if internalModules[key] {
+			continue
+		}
+		e := yang.ToEntry(mod)
+		if e == nil || e.Dir == nil {
+			continue
+		}
+		for _, child := range sortedEntries(e.Dir) {
+			if isNonDataNode(child) {
+				continue
+			}
+			if internalOperationalTopNodes[child.Name] {
+				continue
+			}
+			nodePath := "/" + key + ":" + child.Name
+			if isContainerList(child) {
+				if lc := listChildOfAll(child); lc != nil {
+					nodes = append(nodes, entryToNode(lc, nodePath+"/"+nodeSegment(lc, key)))
+				}
+				continue
+			}
+			nodes = append(nodes, entryToNode(child, nodePath))
+		}
+	}
+	sort.Slice(nodes, func(i, j int) bool { return nodes[i].Name < nodes[j].Name })
+	return nodes
+}
+
+// dirToNodesAll is like dirToNodes but uses isNonDataNode, including
+// config:false leaves and containers in the result.
+func dirToNodesAll(dir map[string]*yang.Entry, parentPath string) []*Node {
+	parentMod := extractModuleFromPath(parentPath)
+	var nodes []*Node
+	for _, e := range sortedEntries(dir) {
+		if e.IsChoice() || e.IsCase() {
+			caseWhen := extractWhen(e)
+			for _, child := range dirToNodesAll(e.Dir, parentPath) {
+				if caseWhen != "" && child.When == "" {
+					child.When = caseWhen
+				}
+				nodes = append(nodes, child)
+			}
+			continue
+		}
+		if isNonDataNode(e) {
+			continue
+		}
+		nodePath := parentPath + "/" + nodeSegment(e, parentMod)
+		if isContainerList(e) {
+			if lc := listChildOfAll(e); lc != nil {
+				nodes = append(nodes, entryToNode(lc, nodePath+"/"+nodeSegment(lc, parentMod)))
+			}
+			continue
+		}
+		nodes = append(nodes, entryToNode(e, nodePath))
+	}
+	return nodes
+}
+
+// dirToNodes converts a goyang Dir map to a sorted slice of Nodes.
+// choice/case children are inlined (their contents promoted to this level).
+// Collapsible container-list wrappers are transparent: the list child is surfaced
+// directly under the parent with the full (un-collapsed) RESTCONF path.
+// RPC, notification, anydata, anyxml and config:false nodes are excluded.
+//
+// RESTCONF requires module qualification ("module:name") whenever a node's
+// module differs from its parent's — the common case being augmented nodes.
+// e.g. infix-lldp augments ieee802-dot1ab-lldp:lldp, so the path is
+// /ieee802-dot1ab-lldp:lldp/infix-lldp:enabled, not /…/enabled.
+func dirToNodes(dir map[string]*yang.Entry, parentPath string) []*Node {
+	parentMod := extractModuleFromPath(parentPath)
+	var nodes []*Node
+	for _, e := range sortedEntries(dir) {
+		if e.IsChoice() || e.IsCase() {
+			// Extract when from the choice/case before inlining its children.
+			// Cases contributed by augments carry the augment's when (e.g.
+			// lag-port only for ethernetCsmacd, bridge-port only for bridge).
+			// Propagate that constraint to each promoted child that has no when of
+			// its own; if the child already has one, leave it alone.
+			caseWhen := extractWhen(e)
+			for _, child := range dirToNodes(e.Dir, parentPath) {
+				if caseWhen != "" && child.When == "" {
+					child.When = caseWhen
+				}
+				nodes = append(nodes, child)
+			}
+			continue
+		}
+		if isNonConfigNode(e) {
+			continue
+		}
+		nodePath := parentPath + "/" + nodeSegment(e, parentMod)
+		if isContainerList(e) {
+			if lc := listChildOf(e); lc != nil {
+				// Container is collapsed; qualify list child against parentMod.
+				nodes = append(nodes, entryToNode(lc, nodePath+"/"+nodeSegment(lc, parentMod)))
+			}
+			continue
+		}
+		nodes = append(nodes, entryToNode(e, nodePath))
+	}
+	return nodes
+}
+
+// nodeSegment returns the path segment for e, qualified as "module:name" when
+// e's instantiating module differs from parentMod (RESTCONF RFC 8040 §3.5.3).
+func nodeSegment(e *yang.Entry, parentMod string) string {
+	mod, err := e.InstantiatingModule()
+	if err != nil || mod == parentMod {
+		return e.Name
+	}
+	return mod + ":" + e.Name
+}
+
+// extractModuleFromPath returns the module from the rightmost module-qualified
+// segment in a RESTCONF path, e.g. "/ieee802-dot1ab-lldp:lldp/port" → "ieee802-dot1ab-lldp".
+func extractModuleFromPath(path string) string {
+	segs := strings.Split(strings.TrimPrefix(path, "/"), "/")
+	for i := len(segs) - 1; i >= 0; i-- {
+		seg := stripPredicate(segs[i])
+		if j := strings.IndexByte(seg, ':'); j > 0 {
+			return seg[:j]
+		}
+	}
+	return ""
+}
+
+// isNonConfigNode returns true for schema nodes that do not belong in the
+// configuration tree: RPCs, notifications, anydata/anyxml, config:false subtrees,
+// and nodes with YANG status deprecated or obsolete.
+// goyang propagates config:false from parent to children during Process(), so a
+// single check at each level is sufficient to prune entire read-only subtrees.
+func isNonConfigNode(e *yang.Entry) bool {
+	return e.RPC != nil ||
+		e.Kind == yang.NotificationEntry ||
+		e.Kind == yang.AnyDataEntry ||
+		e.Kind == yang.AnyXMLEntry ||
+		e.Config == yang.TSFalse ||
+		isDeprecatedOrObsolete(e)
+}
+
+// isNonDataNode is like isNonConfigNode but keeps config:false nodes.
+// Used by ChildrenAll / the operational status tree which shows all data —
+// operational state reuses read-write schema nodes alongside state-only leaves.
+func isNonDataNode(e *yang.Entry) bool {
+	return e.RPC != nil ||
+		e.Kind == yang.NotificationEntry ||
+		e.Kind == yang.AnyDataEntry ||
+		e.Kind == yang.AnyXMLEntry ||
+		isDeprecatedOrObsolete(e)
+}
+
+// entryPresence returns the YANG presence statement string for e, or "".
+// Presence is stored on the underlying Container Node via reflection because
+// yang.Entry does not expose it directly.
+func entryPresence(e *yang.Entry) string {
+	if e.Node == nil {
+		return ""
+	}
+	v := reflect.ValueOf(e.Node)
+	if v.Kind() == reflect.Ptr {
+		v = v.Elem()
+	}
+	f := v.FieldByName("Presence")
+	if !f.IsValid() || f.Kind() != reflect.Ptr || f.IsNil() {
+		return ""
+	}
+	name := f.Elem().FieldByName("Name")
+	if !name.IsValid() {
+		return ""
+	}
+	return name.String()
+}
+
+// isDeprecatedOrObsolete returns true when the YANG node carries
+// "status deprecated" or "status obsolete". goyang does not expose status
+// directly on Entry, so we reach through to the underlying Node via reflection.
+// All concrete yang node types (Container, Leaf, List, …) have Status *Value.
+func isDeprecatedOrObsolete(e *yang.Entry) bool {
+	if e.Node == nil {
+		return false
+	}
+	v := reflect.ValueOf(e.Node)
+	if v.Kind() == reflect.Ptr {
+		v = v.Elem()
+	}
+	f := v.FieldByName("Status")
+	if !f.IsValid() || f.Kind() != reflect.Ptr || f.IsNil() {
+		return false
+	}
+	name := f.Elem().FieldByName("Name")
+	if !name.IsValid() {
+		return false
+	}
+	s := name.String()
+	return s == "deprecated" || s == "obsolete"
+}
+
+// entryToNode converts a goyang Entry to a schema Node (no children populated).
+func entryToNode(e *yang.Entry, path string) *Node {
+	n := &Node{
+		Path:        path,
+		Name:        e.Name,
+		Kind:        entryKind(e),
+		Description: e.Description,
+		Config:      e.Config != yang.TSFalse,
+		Mandatory:   e.Mandatory == yang.TSTrue,
+		When:        extractWhen(e),
+		Presence:    entryPresence(e),
+	}
+
+	if def, ok := e.SingleDefaultValue(); ok {
+		n.Default = def
+	}
+
+	if strings.Contains(e.Key, " ") || e.Key != "" {
+		n.Keys = strings.Fields(e.Key)
+	}
+
+	if e.IsLeaf() || e.IsLeafList() {
+		n.Type = yangTypeInfo(e)
+	}
+
+	return n
+}
+
+// prefixInXPath matches a "prefix:X" token where X is a letter or underscore,
+// the first character of an identifier.  The matched letter is included so
+// ReplaceAllStringFunc can reattach it after resolving the prefix.
+var prefixInXPath = regexp.MustCompile(`[a-zA-Z][a-zA-Z0-9_\-]*:[a-zA-Z_]`)
+
+// extractWhen returns the pre-resolved YANG when expression for e, or "".
+// It first checks e itself (when directly on the node), then checks parent
+// augments — the Infix convention is to put when on the augment, not on the
+// top-level container inside the augment.
+func extractWhen(e *yang.Entry) string {
+	if xpath, ok := e.GetWhenXPath(); ok && xpath != "" {
+		return resolveWhenPrefixes(e.Node, xpath)
+	}
+	// Check parent's augment list: the augment may carry the when expression
+	// even though the individual container inside it does not.
+	if e.Parent == nil {
+		return ""
+	}
+	for _, aug := range e.Parent.Augmented {
+		if _, found := aug.Dir[e.Name]; !found {
+			continue
+		}
+		if xpath, ok := aug.GetWhenXPath(); ok && xpath != "" {
+			return resolveWhenPrefixes(aug.Node, xpath)
+		}
+	}
+	return ""
+}
+
+// resolveWhenPrefixes replaces "prefix:x" tokens in an XPath expression with
+// the canonical "module:x" form using FindModuleByPrefix on the given node.
+// Unknown prefixes (not imported by the node's module) are left unchanged.
+func resolveWhenPrefixes(node yang.Node, xpath string) string {
+	return prefixInXPath.ReplaceAllStringFunc(xpath, func(m string) string {
+		colon := strings.IndexByte(m, ':')
+		prefix := m[:colon]
+		rest := m[colon+1:] // the single identifier-start character
+		mod := yang.FindModuleByPrefix(node, prefix)
+		if mod == nil {
+			return m
+		}
+		modName := mod.Name
+		if mod.BelongsTo != nil {
+			modName = mod.BelongsTo.Name
+		}
+		return modName + ":" + rest
+	})
+}
+
+// entryKind maps a goyang Entry to a kind string.
+func entryKind(e *yang.Entry) string {
+	switch {
+	case e.IsLeaf():
+		return "leaf"
+	case e.IsLeafList():
+		return "leaf-list"
+	case e.IsList():
+		return "list"
+	case e.IsContainer():
+		return "container"
+	case e.IsChoice():
+		return "choice"
+	case e.IsCase():
+		return "case"
+	case e.Kind == yang.AnyDataEntry:
+		return "anydata"
+	case e.Kind == yang.AnyXMLEntry:
+		return "anyxml"
+	case e.RPC != nil:
+		return "rpc"
+	default:
+		return "unknown"
+	}
+}
+
+// yangTypeInfo builds a TypeInfo from a leaf's YangType.
+func yangTypeInfo(e *yang.Entry) *TypeInfo {
+	t := e.Type
+	if t == nil {
+		return nil
+	}
+
+	info := &TypeInfo{
+		Kind: yang.TypeKindToName[t.Kind],
+	}
+
+	switch t.Kind {
+	case yang.Yenum:
+		if t.Enum != nil {
+			info.Enums = t.Enum.Names()
+			sort.Strings(info.Enums)
+		}
+	case yang.Yidentityref:
+		if t.IdentityBase != nil {
+			for _, v := range t.IdentityBase.Values {
+				name := v.Name
+				if root := yang.RootNode(v); root != nil {
+					modName := root.Name
+					if root.Kind() == "submodule" && root.BelongsTo != nil {
+						modName = root.BelongsTo.Name
+					}
+					name = modName + ":" + v.Name
+				}
+				info.Identities = append(info.Identities, name)
+			}
+			sort.Strings(info.Identities)
+		}
+	case yang.Yleafref:
+		info.Leafref = canonicalizeLeafrefPath(e.Node, t.Path)
+		info.LeafrefSibling = leafrefSiblingFilter(e)
+	case yang.Yunion:
+		for _, sub := range t.Type {
+			if sub.Kind == yang.Yenum && sub.Enum != nil {
+				info.Enums = append(info.Enums, sub.Enum.Names()...)
+			}
+		}
+		if len(info.Enums) > 0 {
+			sort.Strings(info.Enums)
+		}
+	}
+
+	if len(t.Pattern) > 0 {
+		info.Pattern = strings.Join(t.Pattern, "|")
+	}
+
+	if len(t.Range) > 0 {
+		info.Range = t.Range.String()
+	}
+
+	return info
+}
+
+// splitPrefix splits "module:name" into ("module", "name").
+// If there is no prefix, it returns ("", name).
+func splitPrefix(s string) (prefix, name string) {
+	if i := strings.Index(s, ":"); i >= 0 {
+		return s[:i], s[i+1:]
+	}
+	return "", s
+}
+
+// sortedEntries returns the entries in a Dir map sorted by name.
+func sortedEntries(dir map[string]*yang.Entry) []*yang.Entry {
+	keys := make([]string, 0, len(dir))
+	for k := range dir {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	result := make([]*yang.Entry, 0, len(keys))
+	for _, k := range keys {
+		result = append(result, dir[k])
+	}
+	return result
+}

src/webui/internal/schema/refresh.go

@@ -0,0 +1,126 @@
+package schema
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"sync"
+
+	"github.com/kernelkit/webui/internal/restconf"
+)
+
+// Cache holds a lazily-loaded schema Manager and refreshes it at startup.
+// All methods are safe for concurrent use.
+type Cache struct {
+	mu       sync.RWMutex
+	manager  *Manager
+	syncing  bool // guarded by mu
+	dir      string
+	rc       restconf.Fetcher
+}
+
+// NewCache creates a Cache.
+// Call LoadFromCacheBackground at startup, then RefreshBackground after login.
+func NewCache(rc restconf.Fetcher, dir string) *Cache {
+	return &Cache{rc: rc, dir: dir}
+}
+
+// LoadFromCache parses whatever .yang files are already in the cache
+// directory.  It makes no HTTP requests and needs no credentials.
+// This is fast — suitable for server startup.  If the directory is empty
+// or has too few files to form a useful schema, the Manager is left nil.
+func (c *Cache) LoadFromCache() error {
+	entries, err := os.ReadDir(c.dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil // nothing cached yet — that is fine
+		}
+		return err
+	}
+	var count int
+	for _, e := range entries {
+		if !e.IsDir() && len(e.Name()) > 5 { // len(".yang") == 5
+			if e.Name()[len(e.Name())-5:] == ".yang" {
+				count++
+			}
+		}
+	}
+	if count == 0 {
+		return nil // empty cache — wait for first Refresh
+	}
+
+	mgr, err := Load(c.dir)
+	if err != nil {
+		return fmt.Errorf("schema: load from cache: %w", err)
+	}
+	c.mu.Lock()
+	c.manager = mgr
+	c.mu.Unlock()
+	log.Printf("schema: loaded %d cached YANG file(s) from %s", count, c.dir)
+	return nil
+}
+
+// LoadFromCacheBackground calls LoadFromCache in a goroutine. Errors are logged.
+func (c *Cache) LoadFromCacheBackground() {
+	go func() {
+		if err := c.LoadFromCache(); err != nil {
+			log.Printf("schema: cache load failed: %v", err)
+		}
+	}()
+}
+
+// Refresh downloads any missing YANG files from the device (credentials must
+// be present in ctx) and then reloads the schema Manager.
+// Only one refresh runs at a time; concurrent calls return immediately.
+func (c *Cache) Refresh(ctx context.Context) error {
+	c.mu.Lock()
+	if c.syncing {
+		c.mu.Unlock()
+		return nil
+	}
+	c.syncing = true
+	c.mu.Unlock()
+
+	defer func() {
+		c.mu.Lock()
+		c.syncing = false
+		c.mu.Unlock()
+	}()
+
+	if _, err := FetchModules(ctx, c.rc, c.dir); err != nil {
+		return fmt.Errorf("schema refresh: fetch: %w", err)
+	}
+
+	mgr, err := Load(c.dir)
+	if err != nil {
+		return fmt.Errorf("schema refresh: load: %w", err)
+	}
+
+	c.mu.Lock()
+	c.manager = mgr
+	c.mu.Unlock()
+
+	log.Printf("schema: refreshed successfully from %s", c.dir)
+	return nil
+}
+
+// RefreshBackground calls Refresh in a goroutine. Errors are logged.
+// The context's values (credentials) are preserved but its cancellation is
+// detached so the goroutine is not killed when the originating HTTP request
+// completes.
+func (c *Cache) RefreshBackground(ctx context.Context) {
+	detached := context.WithoutCancel(ctx)
+	go func() {
+		if err := c.Refresh(detached); err != nil {
+			log.Printf("schema: background refresh failed: %v", err)
+		}
+	}()
+}
+
+// Manager returns the current Manager, or nil if not yet loaded.
+func (c *Cache) Manager() *Manager {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return c.manager
+}

src/webui/internal/schema/types.go

@@ -0,0 +1,41 @@
+package schema
+
+// Node is a JSON-serialisable representation of a single YANG schema node.
+// Children are omitted (nil) by default; use Manager.Children to lazy-load them.
+type Node struct {
+	Path        string    `json:"path"`
+	Name        string    `json:"name"`
+	Kind        string    `json:"kind"` // container|list|leaf|leaf-list|choice|case|rpc|notification
+	Description string    `json:"description,omitempty"`
+	Keys        []string  `json:"keys,omitempty"`
+	Children    []*Node   `json:"children,omitempty"`
+	Config      bool      `json:"config"`
+	Mandatory   bool      `json:"mandatory"`
+	Default     string    `json:"default,omitempty"`
+	Type        *TypeInfo `json:"type,omitempty"`
+	// When holds the pre-resolved YANG when expression (prefix aliases replaced
+	// by canonical module names). Empty when there is no constraint.
+	When string `json:"when,omitempty"`
+	// Presence is non-empty for presence containers; its value is the YANG
+	// presence statement string (describes what the container's existence means).
+	Presence string `json:"presence,omitempty"`
+}
+
+// TypeInfo describes the type of a leaf or leaf-list node.
+type TypeInfo struct {
+	Kind       string   `json:"kind"` // string|boolean|int8..uint64|enumeration|identityref|leafref|binary|empty|...
+	Enums      []string `json:"enums,omitempty"`      // enumeration values
+	Identities []string `json:"identities,omitempty"` // identityref derived identity names
+	Range      string   `json:"range,omitempty"`
+	Pattern    string   `json:"pattern,omitempty"`
+	// Leafref is the leafref target path with YANG prefix aliases
+	// resolved to canonical "module:name" form, so it can be fed
+	// straight to mgr.NodeAt / RESTCONF without further mapping.
+	Leafref string `json:"leafref,omitempty"`
+	// LeafrefSibling is the sibling-leaf or sibling-container name
+	// extracted from the leaf's `must "deref(.)/../<X>"` constraint,
+	// if any. Callers filter the dropdown to those leafref targets
+	// whose parent object exposes this sibling — the common idiom
+	// for "this leafref must point at an object of kind <X>".
+	LeafrefSibling string `json:"leafref-sibling,omitempty"`
+}

src/webui/internal/schema/when.go

@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: MIT
+
+package schema
+
+import "strings"
+
+// EvaluateWhen evaluates a pre-resolved YANG when XPath expression against
+// the flat key→value map of the context node's parent data.
+//
+// Handles the practical subset used in Infix YANG models:
+//   - derived-from-or-self(path, 'module:identity')
+//   - derived-from(path, 'module:identity')
+//   - combinations joined with 'or' / 'and'
+//
+// Conservative: any unrecognised expression or absent data returns true (show).
+func EvaluateWhen(mgr *Manager, expr string, values map[string]string) bool {
+	if expr == "" || values == nil {
+		return true
+	}
+	return evalOr(mgr, strings.TrimSpace(expr), values)
+}
+
+func evalOr(mgr *Manager, expr string, values map[string]string) bool {
+	parts := splitOnKeyword(expr, "or")
+	for _, p := range parts {
+		if evalAnd(mgr, strings.TrimSpace(p), values) {
+			return true
+		}
+	}
+	return false
+}
+
+func evalAnd(mgr *Manager, expr string, values map[string]string) bool {
+	parts := splitOnKeyword(expr, "and")
+	for _, p := range parts {
+		if !evalAtom(mgr, strings.TrimSpace(p), values) {
+			return false
+		}
+	}
+	return true
+}
+
+func evalAtom(mgr *Manager, expr string, values map[string]string) bool {
+	if expr == "" {
+		return true // empty: conservative
+	}
+	if strings.HasPrefix(expr, "derived-from-or-self(") && strings.HasSuffix(expr, ")") {
+		inner := expr[len("derived-from-or-self(") : len(expr)-1]
+		return evalDerivedFrom(mgr, inner, values, true)
+	}
+	if strings.HasPrefix(expr, "derived-from(") && strings.HasSuffix(expr, ")") {
+		inner := expr[len("derived-from(") : len(expr)-1]
+		return evalDerivedFrom(mgr, inner, values, false)
+	}
+	return true // unknown expression: conservative show
+}
+
+func evalDerivedFrom(mgr *Manager, inner string, values map[string]string, orSelf bool) bool {
+	comma := strings.Index(inner, ",")
+	if comma < 0 {
+		return true // malformed: conservative
+	}
+	xpathPath := strings.TrimSpace(inner[:comma])
+	identity := strings.Trim(strings.TrimSpace(inner[comma+1:]), "'\"")
+
+	leafName := xpathLeafName(xpathPath)
+	if leafName == "" {
+		return true // unresolvable path: conservative
+	}
+
+	current := values[leafName]
+	if current == "" {
+		return true // no data: conservative show
+	}
+	return checkIdentity(mgr, current, identity, orSelf)
+}
+
+// xpathLeafName extracts the bare leaf name from a simple XPath step.
+//   - "module:name" or "name"        → "name"
+//   - "../module:name"               → "name"  (single parent step)
+//   - "../../../…" or path with "/"  → ""  (multi-level: conservative)
+func xpathLeafName(path string) string {
+	if strings.HasPrefix(path, "../") {
+		path = path[3:]
+		// After one parent step, path must be a bare leaf name.
+		if strings.Contains(path, "/") || strings.HasPrefix(path, "..") {
+			return ""
+		}
+	} else if strings.Contains(path, "/") {
+		return "" // forward traversal: conservative
+	}
+	_, local := splitPrefix(strings.TrimSpace(path))
+	return local
+}
+
+// checkIdentity reports whether currentValue is equal to or derived from
+// targetIdentity according to the YANG identity hierarchy.
+func checkIdentity(mgr *Manager, currentValue, targetIdentity string, orSelf bool) bool {
+	_, currentLocal := splitPrefix(currentValue)
+	_, targetLocal := splitPrefix(targetIdentity)
+
+	if orSelf && currentLocal == targetLocal {
+		return true
+	}
+	for _, d := range mgr.IdentitiesOf(targetLocal) {
+		if d == currentLocal {
+			return true
+		}
+	}
+	return false
+}
+
+// splitOnKeyword splits expr on the XPath keyword kw at parenthesis depth 0,
+// but NOT when kw is part of a compound name (e.g. "derived-from-or-self"
+// contains "or"; "derived-from-and-…" would contain "and").
+// A keyword match is suppressed when immediately preceded by a hyphen.
+//
+// The Infix YANG files contain a concatenation bug where the 'or' keyword is
+// immediately followed by the next function name without a separating space
+// (e.g. "…') orderived-from-or-self(…)").  This splitter handles that case
+// by treating any 'or'/'and' that is not preceded by '-' as a keyword.
+func splitOnKeyword(expr, kw string) []string {
+	n := len(kw)
+	var parts []string
+	depth := 0
+	start := 0
+	for i := 0; i < len(expr); i++ {
+		switch expr[i] {
+		case '(':
+			depth++
+		case ')':
+			depth--
+		}
+		if depth != 0 || i+n > len(expr) || expr[i:i+n] != kw {
+			continue
+		}
+		// Suppress if immediately preceded by '-' (part of compound name).
+		if i > 0 && expr[i-1] == '-' {
+			continue
+		}
+		// Found keyword: save part, trim trailing space before keyword.
+		end := i
+		if end > start && expr[end-1] == ' ' {
+			end--
+		}
+		parts = append(parts, strings.TrimSpace(expr[start:end]))
+		start = i + n
+		if start < len(expr) && expr[start] == ' ' {
+			start++
+		}
+		i = start - 1 // loop will increment
+	}
+	parts = append(parts, strings.TrimSpace(expr[start:]))
+	return parts
+}

src/webui/internal/schema/when_test.go

@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: MIT
+
+package schema
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestSplitOnKeyword(t *testing.T) {
+	tests := []struct {
+		name string
+		expr string
+		kw   string
+		want []string
+	}{
+		{
+			name: "single_term_no_split",
+			expr: "derived-from-or-self(if:type, 'gre')",
+			kw:   "or",
+			want: []string{"derived-from-or-self(if:type, 'gre')"},
+		},
+		{
+			name: "two_terms_with_space",
+			expr: "derived-from-or-self(if:type, 'gre') or derived-from-or-self(if:type, 'gretap')",
+			kw:   "or",
+			want: []string{
+				"derived-from-or-self(if:type, 'gre')",
+				"derived-from-or-self(if:type, 'gretap')",
+			},
+		},
+		{
+			name: "two_terms_no_space_after_or", // Infix YANG concatenation bug
+			expr: "derived-from-or-self(if:type, 'gre') orderived-from-or-self(if:type, 'gretap')",
+			kw:   "or",
+			want: []string{
+				"derived-from-or-self(if:type, 'gre')",
+				"derived-from-or-self(if:type, 'gretap')",
+			},
+		},
+		{
+			name: "or_inside_parens_not_split",
+			expr: "derived-from-or-self(if:type, 'foo or bar')",
+			kw:   "or",
+			want: []string{"derived-from-or-self(if:type, 'foo or bar')"},
+		},
+		{
+			name: "and_keyword",
+			expr: "cond-a and cond-b",
+			kw:   "and",
+			want: []string{"cond-a", "cond-b"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := splitOnKeyword(tt.expr, tt.kw)
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("splitOnKeyword(%q, %q) = %v; want %v", tt.expr, tt.kw, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestXpathLeafName(t *testing.T) {
+	tests := []struct {
+		path string
+		want string
+	}{
+		{"if:type", "type"},
+		{"ietf-interfaces:type", "type"},
+		{"type", "type"},
+		{"../iehw:class", "class"},
+		{"../infix-hardware:class", "class"},
+		{"../../something", ""},
+		{"../../../rt:address-family", ""},
+		{"a/b", ""},
+		{"/abs/path", ""},
+	}
+	for _, tt := range tests {
+		got := xpathLeafName(tt.path)
+		if got != tt.want {
+			t.Errorf("xpathLeafName(%q) = %q; want %q", tt.path, got, tt.want)
+		}
+	}
+}
+
+func TestEvaluateWhenConservative(t *testing.T) {
+	// nil values → conservative true
+	if !EvaluateWhen(nil, "derived-from-or-self(if:type, 'foo')", nil) {
+		t.Error("nil values should be conservative true")
+	}
+	// empty expr → true
+	if !EvaluateWhen(nil, "", map[string]string{"type": "bar"}) {
+		t.Error("empty expr should be conservative true")
+	}
+	// nil manager with unknown expr → true
+	if !EvaluateWhen(nil, "unknown-function(x)", map[string]string{"x": "y"}) {
+		t.Error("unknown expr should be conservative true")
+	}
+}
+
+func TestEvaluateWhenDerivedFromOrSelf(t *testing.T) {
+	// Minimal mock manager: IdentitiesOf("gre") → ["gretap"]
+	mgr := &Manager{ms: nil} // ms is nil, but IdentitiesOf will handle it gracefully
+
+	// We need a real identity hierarchy. Use a Manager with minimal modules.
+	// Since setting up goyang modules is complex, test via checkIdentity directly.
+	tests := []struct {
+		name     string
+		current  string
+		target   string
+		orSelf   bool
+		derived  []string // what IdentitiesOf would return; we test checkIdentity
+		want     bool
+	}{
+		{"or-self exact match", "gre", "gre", true, nil, true},
+		{"or-self different", "bridge", "gre", true, nil, false},
+		{"derived match", "gretap", "gre", false, []string{"gretap"}, true},
+		{"derived no match", "bridge", "gre", false, []string{"gretap"}, false},
+		{"module-qualified current", "infix-if-type:gre", "gre", true, nil, true},
+		{"module-qualified target", "gre", "infix-if-type:gre", true, nil, true},
+		{"both qualified exact", "infix-if-type:gre", "infix-if-type:gre", true, nil, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Override IdentitiesOf by testing checkIdentity directly with a mock.
+			// Build a mini-mgr that returns tt.derived for any base name.
+			got := checkIdentityTest(tt.current, tt.target, tt.orSelf, tt.derived)
+			if got != tt.want {
+				t.Errorf("checkIdentity(%q, %q, orSelf=%v) = %v; want %v",
+					tt.current, tt.target, tt.orSelf, got, tt.want)
+			}
+		})
+	}
+	_ = mgr
+}
+
+// checkIdentityTest is a test helper that bypasses the Manager.IdentitiesOf call.
+func checkIdentityTest(currentValue, targetIdentity string, orSelf bool, derivedNames []string) bool {
+	_, currentLocal := splitPrefix(currentValue)
+	_, targetLocal := splitPrefix(targetIdentity)
+	if orSelf && currentLocal == targetLocal {
+		return true
+	}
+	for _, d := range derivedNames {
+		if d == currentLocal {
+			return true
+		}
+	}
+	return false
+}

src/webui/internal/server/server.go

@@ -3,6 +3,7 @@
 package server
 
 import (
+	"context"
 	"html/template"
 	"io/fs"
 	"net/http"
@@ -10,12 +11,14 @@ import (
 	"github.com/kernelkit/webui/internal/auth"
 	"github.com/kernelkit/webui/internal/handlers"
 	"github.com/kernelkit/webui/internal/restconf"
+	"github.com/kernelkit/webui/internal/schema"
 )
 
 // New creates a fully wired http.Handler with all routes and middleware.
 func New(
 	store *auth.SessionStore,
 	rc *restconf.Client,
+	schemaCache *schema.Cache,
 	templateFS fs.FS,
 	staticFS fs.FS,
 ) (http.Handler, error) {
@@ -101,11 +104,31 @@ func New(
 	if err != nil {
 		return nil, err
 	}
+	yangTreeTmpl, err := template.ParseFS(templateFS,
+		"layouts/*.html",
+		"fragments/configure-toolbar.html",
+		"fragments/yang-tree-node.html",
+		"pages/yang-tree.html")
+	if err != nil {
+		return nil, err
+	}
+	yangFuncs := template.FuncMap{"stripPrefix": schema.StripModulePrefix}
+	yangFragTmpl, err := template.New("frag").Funcs(yangFuncs).ParseFS(templateFS,
+		"fragments/yang-tree-node.html",
+		"fragments/yang-node-detail.html",
+		"fragments/yang-leaf-group.html",
+		"fragments/yang-list-table.html")
+	if err != nil {
+		return nil, err
+	}
 
 	login := &auth.LoginHandler{
 		Store:    store,
 		RC:       rc,
 		Template: loginTmpl,
+		OnLogin: func(ctx context.Context) {
+			schemaCache.RefreshBackground(ctx)
+		},
 	}
 
 	dash := &handlers.DashboardHandler{
@@ -146,8 +169,16 @@ func New(
 	services := &handlers.ServicesHandler{Template: servicesTmpl, RC: rc}
 	containers := &handlers.ContainersHandler{Template: containersTmpl, RC: rc}
 	cfg := &handlers.ConfigureHandler{RC: rc}
-	cfgSys := &handlers.ConfigureSystemHandler{Template: cfgSysTmpl, RC: rc}
-	cfgUsers := &handlers.ConfigureUsersHandler{Template: cfgUsersTmpl, RC: rc}
+	cfgSys := &handlers.ConfigureSystemHandler{Template: cfgSysTmpl, RC: rc, Schema: schemaCache}
+	cfgUsers := &handlers.ConfigureUsersHandler{Template: cfgUsersTmpl, RC: rc, Schema: schemaCache}
+	schemaH := &handlers.SchemaHandler{Cache: schemaCache}
+	dataH := &handlers.DataHandler{RC: rc, Schema: schemaCache}
+	treeH := &handlers.TreeHandler{
+		Cache:    schemaCache,
+		RC:       rc,
+		PageTmpl: yangTreeTmpl,
+		FragTmpl: yangFragTmpl,
+	}
 
 	mux := http.NewServeMux()
 
@@ -185,10 +216,11 @@ func New(
 	mux.HandleFunc("GET /containers", containers.Overview)
 
 	// Configure routes.
-	mux.HandleFunc("POST /configure/enter",           cfg.Enter)
-	mux.HandleFunc("POST /configure/apply",           cfg.Apply)
-	mux.HandleFunc("POST /configure/apply-and-save",  cfg.ApplyAndSave)
-	mux.HandleFunc("POST /configure/abort",           cfg.Abort)
+	mux.HandleFunc("POST /configure/enter",          cfg.Enter)
+	mux.HandleFunc("POST /configure/apply",          cfg.Apply)
+	mux.HandleFunc("POST /configure/apply-and-save", cfg.ApplyAndSave)
+	mux.HandleFunc("POST /configure/abort",          cfg.Abort)
+	mux.HandleFunc("POST /configure/save",           cfg.Save)
 	mux.HandleFunc("GET /configure/system",           cfgSys.Overview)
 	mux.HandleFunc("POST /configure/system/identity",     cfgSys.SaveIdentity)
 	mux.HandleFunc("POST /configure/system/clock",        cfgSys.SaveClock)
@@ -205,6 +237,27 @@ func New(
 	mux.HandleFunc("POST /configure/users/groups/{name}/members",          cfgUsers.AddGroupMembers)
 	mux.HandleFunc("DELETE /configure/users/groups/{name}/members/{user}", cfgUsers.RemoveGroupMember)
 
+	// Schema API routes (authenticated).
+	mux.HandleFunc("GET /api/schema",          schemaH.Schema)
+	mux.HandleFunc("GET /api/schema/children", schemaH.Children)
+
+	// Data API route (authenticated) — raw RESTCONF JSON passthrough.
+	mux.HandleFunc("GET /api/data", dataH.Get)
+
+	// YANG tree UI routes (authenticated).
+	mux.HandleFunc("GET /configure/tree",           treeH.Overview)
+	mux.HandleFunc("GET /configure/tree/children",  treeH.TreeChildren)
+	mux.HandleFunc("GET /configure/tree/node",      treeH.TreeNode)
+	mux.HandleFunc("PUT /configure/tree/node",      treeH.SaveLeaf)
+	mux.HandleFunc("DELETE /configure/tree/node",   treeH.DeleteLeaf)
+	mux.HandleFunc("PUT /configure/tree/group",      treeH.SaveGroup)
+	mux.HandleFunc("GET /configure/tree/list-add",   treeH.AddListRowForm)
+	mux.HandleFunc("POST /configure/tree/list-row",  treeH.SaveListRow)
+	mux.HandleFunc("DELETE /configure/tree/list-row", treeH.DeleteListRow)
+	mux.HandleFunc("PUT /configure/tree/presence",    treeH.TogglePresence)
+	mux.HandleFunc("DELETE /configure/tree/presence", treeH.TogglePresence)
+	mux.HandleFunc("DELETE /configure/tree/container", treeH.DeleteContainer)
+
 	handler := authMiddleware(store, mux)
 	handler = csrfMiddleware(handler)
 	handler = securityHeadersMiddleware(handler)

src/webui/internal/testutil/helpers.go

@@ -94,9 +94,10 @@ func (m *MockFetcher) PostJSON(_ context.Context, path string, _ any) error {
 	return nil
 }
 
-func (m *MockFetcher) Put(_ context.Context, _ string, _ any) error        { return nil }
-func (m *MockFetcher) Patch(_ context.Context, _ string, _ any) error      { return nil }
-func (m *MockFetcher) Delete(_ context.Context, _ string) error            { return nil }
+func (m *MockFetcher) GetYANG(_ context.Context, _, _ string) ([]byte, error) { return nil, nil }
+func (m *MockFetcher) Put(_ context.Context, _ string, _ any) error          { return nil }
+func (m *MockFetcher) Patch(_ context.Context, _ string, _ any) error        { return nil }
+func (m *MockFetcher) Delete(_ context.Context, _ string) error              { return nil }
 
 func (m *MockFetcher) GetDatastore(_ context.Context, _ string) (json.RawMessage, error) {
 	return json.RawMessage("{}"), nil