Handle exception to avoid lldp_syncd crash

[ZhaohuiS]

Issue description

When there is invalid string in chassis name or other fields, json.load could throw exception and return None in function _scrap_output, it could cause TypeError: 'NoneType' object does not support item assignment when running the following code:

lldp_json['lldp_loc_chassis'] = self._scrap_output(cmd_local

Traceback looks like below and cause lldp_syncd crash:

May  6 21:31:23.136172 docker ps ERR lldp#lldp-syncd [lldp_syncd] ERROR: Failed to parse lldpctl output#012Traceback (most recent call last):#012  File "/usr/local/lib/python3.9/dist-packages/lldp_syncd/daemon.py", line 180, in _scrap_output#012    lldpctl_json = json.loads(lldpctl_output)#012  File "/usr/lib/python3.9/json/__init__.py", line 346, in loads#012    return _default_decoder.decode(s)#012  File "/usr/lib/python3.9/json/decoder.py", line 337, in decode#012    obj, end = self.raw_decode(s, idx=_w(s, 0).end())#012  File "/usr/lib/python3.9/json/decoder.py", line 353, in raw_decode#012    obj, end = self.scan_once(s, idx)#012json.decoder.JSONDecodeError: Invalid \escape: line 130 column 14 (char 3552)
May  6 21:31:23.147700 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd Exception in thread LldpSyncDaemon:
May  6 21:31:23.147700 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd Traceback (most recent call last):
May  6 21:31:23.147700 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd   File "/usr/lib/python3.9/threading.py", line 954, in _bootstrap_inner
May  6 21:31:23.148327 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd     self.run()
May  6 21:31:23.148327 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd   File "/usr/local/lib/python3.9/dist-packages/sonic_syncd/interface.py", line 43, in run
May  6 21:31:23.148725 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd     update_obj = self.source_update()
May  6 21:31:23.148763 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd   File "/usr/local/lib/python3.9/dist-packages/lldp_syncd/daemon.py", line 197, in source_update
May  6 21:31:23.148782 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd     lldp_json['lldp_loc_chassis'] = self._scrap_output(cmd_local)
May  6 21:31:23.148800 LON21-0101-0105-12T1 INFO lldp#supervisord: lldp-syncd TypeError: 'NoneType' object does not support item assignment
May  6 21:31:23.183356 LON21-0101-0105-12T1 INFO lldp#supervisord 2024-05-06 21:31:23,182 INFO exited: lldp-syncd (exit status 0; expected)

How to fix

Handle None returned value in source_update and return None if can't parse the lldpctl json output.
This can avoid lldp_syncd crash.

The expected syslog for invalid output in lldpctl command:
May 21 07:11:35.135275 hostname WARNING lldp#lldp-syncd [sonic_syncd] WARNING: No source information returned during last update. Skipping sync.

workitem

28004915

[bingwang-ms]

LGTM. Thanks for the fix!

[ZhaohuiS]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[StormLiangMS]

hi @yxieca need cherry pick for 202311.

[StormLiangMS]

hi @ZhaohuiS could you update the ADO in this PR? And also the test result with 202305 and 202311?

[mssonicbld]

Cherry-pick PR to 202311: #69