GerritEventLogPoller.getFiles has no error handling

[flichtenheld]

If the API call fails, e.g. due to change being deleted, or buildbot not having access to that project, it throws an exception:

2024-05-15 10:12:38+0000 [-] while polling for changes
	Traceback (most recent call last):
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 913, in errback
	    self._startRunCallbacks(fail)
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 981, in _startRunCallbacks
	    self._runCallbacks()
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 1075, in _runCallbacks
	    current.result = callback(  # type: ignore[misc]
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 1946, in _gotResultInlineCallbacks
	    _inlineCallbacks(r, gen, status, context)
	--- <exception caught here> ---
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 1996, in _inlineCallbacks
	    result = context.run(
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/python/failure.py", line 519, in throwExceptionIntoGenerator
	    return g.throw(self.type, self.value, self.tb)
	  File "/buildbot_venv/lib/python3.9/site-packages/buildbot/changes/gerritchangesource.py", line 566, in poll
	    yield self.lineReceived(line)
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 1996, in _inlineCallbacks
	    result = context.run(
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/python/failure.py", line 519, in throwExceptionIntoGenerator
	    return g.throw(self.type, self.value, self.tb)
	  File "/buildbot_venv/lib/python3.9/site-packages/buildbot/changes/gerritchangesource.py", line 570, in eventReceived
	    res = yield super().eventReceived(event)
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 1996, in _inlineCallbacks
	    result = context.run(
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/python/failure.py", line 519, in throwExceptionIntoGenerator
	    return g.throw(self.type, self.value, self.tb)
	  File "/buildbot_venv/lib/python3.9/site-packages/buildbot/changes/gerritchangesource.py", line 254, in addChangeFromEvent
	    files = yield self.getFiles(
	  File "/buildbot_venv/lib/python3.9/site-packages/twisted/internet/defer.py", line 2000, in _inlineCallbacks
	    result = context.run(gen.send, result)
	  File "/buildbot_venv/lib/python3.9/site-packages/buildbot/changes/gerritchangesource.py", line 580, in getFiles
	    res = res.splitlines()[1].decode('utf8')  # the first line of every response is `)]}'`
	builtins.IndexError: list index out of range

This causes buildbot to loop over the event log again and again, with no easy way to get out of it except to disable get_files (and whatever code needed that information).

When looking at the code the problem is obvious:

@defer.inlineCallbacks
    def getFiles(self, change, patchset):
        res = yield self._http.get(f"/changes/{change}/revisions/{patchset}/files/")
        res = yield res.content()

        res = res.splitlines()[1].decode('utf8')  # the first line of every response is `)]}'`
        return list(json.loads(res))

Probably should return gracefully ("unknown") when res is shorter than 2 lines.

[mokibit]

Hi, @flichtenheld,
Thanks for opening the issue.
It has been fixed in PR #7647.