observer-mdns fails on unicode issue

[Mark Shuttleworth]

I see this in logs with 2.4.0:

May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: Traceback (most recent call last):
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/maas/maas-common", line 87, in <module>
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: main()
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/maas/maas-common", line 83, in main
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: run()
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/maas/maas-common", line 52, in run
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: from provisioningserver.__main__ import main
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/__main__.py", line 55, in <module>
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: main()
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/utils/script.py", line 91, in __call__
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: self.execute(argv)
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/utils/script.py", line 86, in execute
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: args.handler.run(args)
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/utils/avahi.py", line 221, in run
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: _observe_mdns(reader, output, args.verbose)
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/utils/avahi.py", line 145, in _observe_mdns
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: for event in observer(events):
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/utils/avahi.py", line 161, in _observe_resolver_found
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: for event in filter(_p_resolver_found, events):
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3/dist-packages/provisioningserver/utils/avahi.py", line 125, in _extract_mdns_events
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: for event in map(parse_avahi_event, lines):
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: File "/usr/lib/python3.6/codecs.py", line 321, in decode
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: (result, consumed) = self._buffer_decode(data, self.errors, final)
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [info] observe-mdns: UnicodeDecodeError: 'utf-8' codec can't decode byte 0x98 in position 276: invalid start byte
May 27 16:39:53 maas-1 sh[27877]: 2018-05-27 16:39:53 provisioningserver.utils.services: [critical] mDNS observation process failed.
May 27 16:39:53 maas-1 sh[27877]: #011Traceback (most recent call last):
May 27 16:39:53 maas-1 sh[27877]: #011Failure: twisted.internet.error.ProcessTerminated: A process has ended with a probable error condition: process ended with exit code 1.
May 27 16:39:53 maas-1 sh[27877]: #011

[Andres Rodriguez (andreserl)]

I did more investigation on this, and found [1]. As per Mike, this is an issue where avahi is sending unicode, when it probably shouldn't [3]. That said, MAAS should be bullet proof and deal with this case and not just crash the way it has.

[1]: https://bugs.launchpad.net/maas/+bug/1752737
[2]: https://bugs.launchpad.net/maas/+bug/1752737/comments/1
[3]: https://github.com/lathiat/avahi/issues/169

[Mark Shuttleworth (sabdfl)]

The measure of software quality is how it deals with the unexpected, so
let's focus on MAAS quality ;)