Close `ijson` coroutines ourselves instead of letting the GC close them

[squahtx]

synapse/synapse/federation/transport/client.py

Lines 928 to 930 in d9f0922

	def finish(self) -> SendJoinResponse:
	for c in self._coros:
	c.close()

synapse/synapse/federation/transport/client.py

Lines 972 to 974 in d9f0922

	def finish(self) -> StateRequestResponse:
	for c in self._coros:
	c.close()

These close() calls were added in #12875, but I overlooked that we'd only close the first coroutine if it raised an IncompleteJSONError.
We need to close all coroutines, even when any of them raise an error.

Until we fix this properly, we'll get unhelpful Exception ignored in: <generator object utf8_encoder at 0x7f87c9b1ccf0> errors in sentry without a stack trace or logging context.

[DMRobertson]

What's the fix here? Wrap each close call in a try: ... except Exception: pass?

[squahtx]

What's the fix here? Wrap each close call in a try: ... except Exception: pass?

I think we'd want to let the exception bubble up still. Maybe something like

exc = None
for c in self._coros:
    try:
        c.close()
    except Exception as e:
        exc = e
if exc is not None:
    raise exc

if that doesn't mess up the exception stack traces.

[richvdh]

if that doesn't mess up the exception stack traces.

I think (untested) that stack traces would be fine (if an exception already has a traceback object when you raise it, it is not replaced), but you'd need to worry about exception chaining. I note that contextlib.ExitStack has some horrid workarounds to deal with that.

[DMRobertson]

(Would https://peps.python.org/pep-0654/ 's ExceptionGroups be helpful? Not that this is available to us any time soon.)