Broken HTTP2 cancellations tests

[karpetrosyan]

Sometimes http2 connection cancellation tests fail, but other times they succeed.

The issue appears to be in AsyncHTTP2Connection's async_handle_request method, which cannot always handle cancelled errors.

If the cancellation happens in this section of the code, the connection will not call the response_closed method.

[tomchristie]

(As a starting point...)

Sometimes http2 connection cancellation tests fail, but other times they succeed.

Could you provide a link/example for this?

[zanieb]

https://github.com/encode/httpcore/actions/runs/5532888849/jobs/10095604921#step:7:66

[karpetrosyan]

You can get that error by inserting anyio.sleep in the middle of this code block.

Like so

                self._sent_connection_init = True

                # Initially start with just 1 until the remote server provides
                # its max_concurrent_streams value
                self._max_streams = 1

                local_settings_max_streams = (
                    self._h2_state.local_settings.max_concurrent_streams
                )
                self._max_streams_semaphore = AsyncSemaphore(local_settings_max_streams)
                await anyio.sleep(0.5)
                for _ in range(local_settings_max_streams - self._max_streams):
                    await self._max_streams_semaphore.acquire()

        await self._max_streams_semaphore.acquire()

This line may cause a Canceled Error, which we do not handle. We use timeout 0.01 in tests, so I frequently get failing tests on my local machine.

await self._max_streams_semaphore.acquire()

[karpetrosyan]

Issue: #756