From 36716dab42031ac42496ca9cd27acdbcd509bf19 Mon Sep 17 00:00:00 2001
From: Tobias Waldekranz <tobias@waldekranz.com>
Date: Tue, 16 Apr 2024 10:18:00 +0200
Subject: [PATCH] utils: ixll: Add link-local wrappers for ping/ssh/scp

---
 utils/ixll     |  92 +++++++++++++++++++++++++++++++
 utils/libll.sh | 146 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 238 insertions(+)
 create mode 100755 utils/ixll
 create mode 100644 utils/libll.sh

diff --git a/utils/ixll b/utils/ixll
new file mode 100755
index 00000000..f4121709
--- /dev/null
+++ b/utils/ixll
@@ -0,0 +1,92 @@
+#!/bin/sh
+
+set -e
+
+. $(dirname $(readlink -f "$0"))/libll.sh
+
+usage()
+{
+    local me="$(basename $0)"
+
+    cat <<EOF
+usage: $me [-A] <command> [<args>]
+
+Wrap various existing network facilities such that an interface name
+may be supplied in places where a hostname is otherwise expected.
+
+  Options:
+
+    -A
+      For commands requiring authentication, use password
+      authentication with username "admin" and password "admin".
+
+  Commands:
+
+    peer <iface>
+      Return the address of the first IPv6 neighbor to respond on
+      <iface>'s local LAN.
+
+    ping <iface>
+      Send ping to all-hosts group, with link-local scope, on <iface>,
+      suppressing loopbacked packets.
+
+    ssh <iface> [<ssh-arguments>]
+      ssh(1) to the neighboring host on <iface>.
+
+    scp <src> <dst>
+      scp(1) from <src> to <dst>, but any host specified in either
+      <src> or <dst> is assumed to be an interface name, which is
+      expanded to a neighboring host on that interface.
+
+    ${0} help
+      Display this message.
+
+  Examples:
+
+    Start interactive ssh(1) session to the neighbor to eth0
+      $me ssh eth0
+
+    Copy /etc/hostname from the neighbor to eth0, using admin/admin
+      $me -A scp eth0:/etc/hostname /tmp/hostname
+
+EOF
+}
+
+while getopts "A" opt; do
+    case ${opt} in
+	A)
+	    LLSSH_USER=admin
+	    LLSSH_PASS=admin
+	    ;;
+    esac
+done
+shift $((OPTIND - 1))
+
+if [ $# -lt 1 ]; then
+    usage && exit 1
+fi
+
+cmd="$1"
+shift
+
+case "$cmd" in
+    help)
+	usage && exit 0
+	;;
+    peer)
+	llpeer "$@"
+	;;
+    ping)
+	llping "$@"
+	;;
+    scp)
+	llscp "$@"
+	;;
+    ssh)
+	llssh "$@"
+	;;
+    *)
+	echo "Unknown command \"$cmd\"" >2
+	exit 1
+	;;
+esac
diff --git a/utils/libll.sh b/utils/libll.sh
new file mode 100644
index 00000000..d42f94ab
--- /dev/null
+++ b/utils/libll.sh
@@ -0,0 +1,146 @@
+# Utility functions for communicating with IPv6 neighbors on the local
+# LAN
+
+# Usage: llping <iface>
+#
+# Send ping to all-hosts group, with link-local scope, on <iface>,
+# suppressing loopbacked packets.
+llping()
+{
+    local iface="$1"
+    shift
+    ping -L ff02::1%$iface "$@"
+}
+
+
+# Usage: llpeer <iface>
+#
+# Return the address of the first IPv6 neighbor to respond on
+# <iface>'s local LAN. It is thus typically only useful in scenarios
+# where only one neighbor exists
+llpeer()
+{
+    local iface="$1"
+    shift
+    llping $iface -c1 "$@" | \
+	awk '/bytes from/ { sub(/:$/, "", $4); print($4); exit(0); }'
+}
+
+llssh_expand()
+{
+    local old_ifs="$IFS"
+
+    local orig="$1"
+    local fmt="$2"
+
+    local peer=
+    local user=
+    local iface=
+
+    IFS=@
+    set $1
+    IFS="$old_ifs"
+    case $# in
+	1)
+	    user="$LLSSH_USER"
+	    iface="$1"
+	    ;;
+	2)
+	    user="$1"
+	    iface="$2"
+	    ;;
+	*)
+	    echo "Error: Invalid peer \"$orig1\"" >&2
+	    return 1
+	    ;;
+    esac
+
+    if [ -d "/sys/class/net/$iface" ]; then
+	peer="$(llpeer $iface -w3)"
+    else
+	peer="$iface"
+    fi
+
+    if [ ! "$peer" ]; then
+	echo "Error: No peer responded on $iface" >&2
+	return 1
+    fi
+
+    case "$fmt" in
+	ssh)
+	    ;;
+	scp)
+	    peer="[$peer]"
+	    ;;
+	*)
+	    echo "Internal error: Invalid format \"$fmt\"" >&2
+	    return 1
+	    ;;
+    esac
+
+    [ "$user" ] && peer="$user@$peer"
+    echo $peer
+}
+
+# Usage: llssh <destination> [<ssh-args>]
+#
+# ssh(1) to <destination>, but if the host matches an existing
+# interface name, expand it to a neighboring host on that interface.
+llssh()
+{
+    local remote="$1"
+    shift
+
+    local peer="$(llssh_expand $remote ssh)"
+    [ "$peer" ] || return 1
+
+    local sshpasscmd=
+    [ "$LLSSH_PASS" ] && sshpasscmd="sshpass -p$LLSSH_PASS $LLSSHPASS_OPTS"
+
+    $sshpasscmd ssh $LLSSH_OPTS $peer "$@"
+}
+
+llscp_expand()
+{
+    local orig="$1"
+    local old_ifs="$IFS"
+
+    local peer=
+
+    IFS=:
+    set $@
+    IFS="$old_ifs"
+    case $# in
+	1)
+	    echo "$1"
+	    ;;
+	2)
+	    peer="$(llssh_expand $1 scp)"
+	    [ "$peer" ] || return 1
+
+	    echo "$peer:$2"
+	    ;;
+	*)
+	    echo "Error: Invalid location \"$orig1\"" >&2
+	    return 1
+	    ;;
+    esac
+}
+
+# Usage: llscp <src> <dst>
+#
+# scp(1) from <src> to <dst>, but expand any host specified in either
+# <src> or <dst>, which matches an existing interface name, to a
+# neighboring host on that interface.
+llscp()
+{
+    local src="$(llscp_expand $1)"
+    local dst="$(llscp_expand $2)"
+    [ "$src" -a "$dst" ] || return 1
+    shift 2
+
+    local sshpasscmd=
+    [ "$LLSSH_PASS" ] && sshpasscmd="sshpass -p$LLSSH_PASS $LLSSHPASS_OPTS"
+
+    $sshpasscmd scp $LLSCP_OPTS "$src" "$dst"
+}