statd: log critical yanger errors to syslog

Switch to logger, with syslog backend, instead of print() for logging
errors.  This way we can log errors/warnings yet still return partial
JSON data back to statd.  For example, failing to read JSON counters
from ethtool should not break "show interfaces", just return empty
array and log failure to run command.

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

src/statd/python/yanger/yanger.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
-
+import logging
+import logging.handlers
 import subprocess
 import json
 import sys  # (built-in module)
@@ -8,6 +9,7 @@ import argparse
 from datetime import datetime
 
 TESTPATH = ""
+logger = None
 
 
 def json_get_yang_type(iface_in):
@@ -79,7 +81,7 @@ def get_proc_value(procfile):
         # This is considered OK
         return None
     except IOError:
-        print(f"Error: reading from {procfile}", file=sys.stderr)
+        logger.error(f"failed reading from {procfile}")
 
 
 def lookup(obj, *keys):
@@ -118,8 +120,8 @@ def run_cmd(cmd, testfile):
     try:
         output = subprocess.check_output(cmd, stderr=subprocess.DEVNULL, text=True)
         return output.splitlines()
-    except subprocess.CalledProcessError:
-        print("Error: command returned error", file=sys.stderr)
+    except subprocess.CalledProcessError as err:
+        logger.error(f"{err}")
         sys.exit(1)
 
 
@@ -135,9 +137,11 @@ def run_json_cmd(cmd, testfile):
         output = result.stdout
         data = json.loads(output)
     except subprocess.CalledProcessError as err:
+        logger.error(f"{err}")
         data = {}
     except json.JSONDecodeError as err:
-        print(f"Error: parsing JSON output: {err.msg}", file=sys.stderr)
+        logger.error(f"failed parsing JSON output of command: {' '.join(cmd)}"
+                     f", error: {err}")
         sys.exit(1)
     return data
 
@@ -540,7 +544,7 @@ def add_ip_link(ifname, iface_out):
     data = run_json_cmd(['ip', '-s', '-d', '-j', 'link', 'show', 'dev', ifname],
                         f"ip-link-show-dev-{ifname}.json")
     if len(data) != 1:
-        print("Error: expected ip link output to be array with length 1", file=sys.stderr)
+        logger.error("expected ip link output to be array with length 1")
         sys.exit(1)
 
     iface_in = data[0]
@@ -601,7 +605,7 @@ def add_ip_addr(ifname, iface_out):
     data = run_json_cmd(['ip', '-j', 'addr', 'show', 'dev', ifname],
                         f"ip-addr-show-dev-{ifname}.json")
     if len(data) != 1:
-        print("Error: expected ip addr output to be array with length 1", file=sys.stderr)
+        logger.error("expected ip addr output to be array with length 1")
         sys.exit(1)
 
     iface_in = data[0]
@@ -622,7 +626,7 @@ def add_ip_addr(ifname, iface_out):
             new = {}
 
             if 'family' not in addr:
-                print("Error: 'family' missing from 'addr_info'", file=sys.stderr)
+                logger.error("'family' missing from 'addr_info'")
                 continue
 
             if 'local' in addr:
@@ -637,7 +641,7 @@ def add_ip_addr(ifname, iface_out):
             elif addr['family'] == "inet6":
                 inet6.append(new)
             else:
-                print("Error: invalid 'family' in 'addr_info'", file=sys.stderr)
+                logger.error("invalid 'family' in 'addr_info'")
                 sys.exit(1)
 
         insert(iface_out, "ietf-ip:ipv4", "address", inet)
@@ -650,7 +654,7 @@ def add_ethtool_groups(ifname, iface_out):
     data = run_json_cmd(['ethtool', '--json', '-S', ifname, '--all-groups'],
                         f"ethtool-groups-{ifname}.json")
     if len(data) != 1:
-        print(f"Error: no counters available for {ifname}, skipping.")
+        logger.warning(f"{ifname}: no counters available, skipping.")
         return
 
     iface_in = data[0]
@@ -827,6 +831,7 @@ def add_vlans_to_bridge(brname, iface_out, mc_status):
 
 def main():
     global TESTPATH
+    global logger
 
     parser = argparse.ArgumentParser(description="YANG data creator")
     parser.add_argument("model", help="YANG Model")
@@ -839,6 +844,14 @@ def main():
     else:
         TESTPATH = ""
 
+    # Set up syslog output for critical errors to aid debugging
+    logger = logging.getLogger('yanger')
+    log = logging.handlers.SysLogHandler(address='/dev/log')
+    fmt = logging.Formatter('%(name)s[%(process)d]: %(message)s')
+    log.setFormatter(fmt)
+    logger.setLevel(logging.INFO)
+    logger.addHandler(log)
+
     if args.model == 'ietf-interfaces':
         # For now, we handle each interface separately, as this is how it's
         # currently implemented in sysrepo. I.e sysrepo will subscribe to
@@ -916,7 +929,7 @@ def main():
         add_container(yang_data['infix-containers:containers']['container'])
 
     else:
-        print(f"Unsupported model {args.model}", file=sys.stderr)
+        logger.warning(f"Unsupported model {args.model}", file=sys.stderr)
         sys.exit(1)
 
     print(json.dumps(yang_data, indent=2))