fix: event handler error breaks stream

[peterschutt]

Pull Request Checklist

• New code has 100% test coverage
• (If applicable) The prose documentation has been updated to reflect the changes introduced by this PR
• (If applicable) The reference documentation has been updated to reflect the changes introduced by this PR
• Pre-Commit Checks were ran and passed
• Tests were ran and passed

Description

This PR prevents exceptions raised from within event handlers from closing the event receive stream, and from further propagation beyond the event emitter backend.

When an exception is caught from an event handler, we log it at ERROR level.

Close Issue(s)

Closes #2809

[peterschutt]

Before this PR, the request that triggers the error event returns OK, then we get a weird asgi message, and on next request that emits an event we get a 500 error:

INFO:     127.0.0.1:44188 - "GET /check-value/3 HTTP/1.1" 200 OK
INFO:     ASGI 'lifespan' protocol appears unsupported.
ERROR - 2023-12-01 09:09:25,746 - litestar - config - exception raised on http connection to route /check-value/2

Traceback (most recent call last):
  File "/home/peter/PycharmProjects/litestar/litestar/middleware/exceptions/middleware.py", line 191, in __call__
    await self.app(scope, receive, send)
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 81, in handle
    response = await self._get_response_for_request(
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 133, in _get_response_for_request
    return await self._call_handler_function(
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 153, in _call_handler_function
    response_data, cleanup_group = await self._get_response_data(
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 201, in _get_response_data
    data = await route_handler.fn(**parsed_kwargs)
  File "/home/peter/PycharmProjects/litestar-hello-world/app.py", line 23, in check_value
    request.app.emit("raise_exception", value)
  File "/home/peter/PycharmProjects/litestar/litestar/app.py", line 875, in emit
    self.event_emitter.emit(event_id, *args, **kwargs)
  File "/home/peter/PycharmProjects/litestar/litestar/events/emitter.py", line 134, in emit
    self._send_stream.send_nowait((listener.fn, args, kwargs))
  File "/home/peter/.local/share/pdm/venvs/litestar-hello-world-qe1MW6VZ-3.8/lib/python3.8/site-packages/anyio/streams/memory.py", line 189, in send_nowait
    raise ClosedResourceError
anyio.ClosedResourceError
Traceback (most recent call last):
  File "/home/peter/PycharmProjects/litestar/litestar/middleware/exceptions/middleware.py", line 191, in __call__
    await self.app(scope, receive, send)
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 81, in handle
    response = await self._get_response_for_request(
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 133, in _get_response_for_request
    return await self._call_handler_function(
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 153, in _call_handler_function
    response_data, cleanup_group = await self._get_response_data(
  File "/home/peter/PycharmProjects/litestar/litestar/routes/http.py", line 201, in _get_response_data
    data = await route_handler.fn(**parsed_kwargs)
  File "/home/peter/PycharmProjects/litestar-hello-world/app.py", line 23, in check_value
    request.app.emit("raise_exception", value)
  File "/home/peter/PycharmProjects/litestar/litestar/app.py", line 875, in emit
    self.event_emitter.emit(event_id, *args, **kwargs)
  File "/home/peter/PycharmProjects/litestar/litestar/events/emitter.py", line 134, in emit
    self._send_stream.send_nowait((listener.fn, args, kwargs))
  File "/home/peter/.local/share/pdm/venvs/litestar-hello-world-qe1MW6VZ-3.8/lib/python3.8/site-packages/anyio/streams/memory.py", line 189, in send_nowait
    raise ClosedResourceError
anyio.ClosedResourceError
INFO:     127.0.0.1:50308 - "GET /check-value/2 HTTP/1.1" 500 Internal Server Error

After this PR the exception is caught and logged, and the next event emitting request succeeds:

INFO:     127.0.0.1:54846 - "GET /check-value/3 HTTP/1.1" 200 OK
ERROR - 2023-12-01 09:11:27,768 - litestar.events.emitter - emitter - Error in event listener: unhandled errors in a TaskGroup (1 sub-exception)
  + Exception Group Traceback (most recent call last):
  |   File "/home/peter/PycharmProjects/litestar/litestar/events/emitter.py", line 96, in _worker
  |     task_group.start_soon(fn, *args)
  |   File "/home/peter/.local/share/pdm/venvs/litestar-hello-world-qe1MW6VZ-3.8/lib/python3.8/site-packages/anyio/_backends/_asyncio.py", line 664, in __aexit__
  |     raise BaseExceptionGroup(
  | exceptiongroup.ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/home/peter/PycharmProjects/litestar-hello-world/app.py", line 12, in raise_exception_if_odd
    |     raise ValueError(f"{value} is odd")
    | ValueError: 3 is odd
    +------------------------------------
INFO:     127.0.0.1:54846 - "GET /check-value/2 HTTP/1.1" 200 OK

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

100.0% Coverage
0.0% Duplication

[github-actions]

Documentation preview will be available shortly at https://litestar-org.github.io/litestar-docs-preview/2810

[provinzkraut]

This solution is a bit of an issue unfortunately, as creating a new task group for every received item will prevent them running concurrently. I think the proper fix here would be to wrap the listeners in an exception handler and then run those in the task group

[provinzkraut]

@peterschutt I can cook up a PR for this later unless you want to fix it :)

[peterschutt]

OK, I'll leave it to you - thanks.

[peterschutt]

Actually, I got it - my mess, I'll clean it up.