StreamIDTooLowError when trying to send headers into closed stream

Empieza en h2/connection.py, en H2Connection._get_or_create_stream y send_headers, y después inspecciona cómo se mantienen los streams y _closed_streams después de RST_STREAM. Reproduce la ruta de stream cerrado y comprueba las pruebas HTTP/2 existentes; se considera terminado cuando enviar headers en un stream reiniciado produce de forma consistente el error esperado de stream cerrado en lugar de StreamIDTooLowError.

Hi!

I'm getting errors like this on the server-side:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/grpclib/server.py", line 310, in request_handler
    await method.func(stream)
  File "/usr/local/lib/python3.6/dist-packages/featureflags/server/rpc/service.py", line 51, in Exchange
    await self._queue.StoreStats.add(task, timeout=timeout)
  File "/usr/local/lib/python3.6/dist-packages/taskqueue/client/queue.py", line 21, in add
    await self._task_queue_stub.Add(task, timeout=timeout)
  File "/usr/local/lib/python3.6/dist-packages/grpclib/client.py", line 473, in __call__
    return await stream.recv_message()
  File "/usr/local/lib/python3.6/dist-packages/grpclib/client.py", line 286, in recv_message
    await self.recv_initial_metadata()
  File "/usr/local/lib/python3.6/dist-packages/grpclib/client.py", line 221, in recv_initial_metadata
    headers = await self._stream.recv_headers()
  File "/usr/local/lib/python3.6/dist-packages/grpclib/protocol.py", line 215, in recv_headers
    return await self.__headers__.get()
  File "/usr/lib/python3.6/asyncio/queues.py", line 167, in get
    yield from getter
concurrent.futures._base.CancelledError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/h2/connection.py", line 585, in _get_or_create_stream
    return self.streams[stream_id]
KeyError: 48141

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/grpclib/server.py", line 325, in request_handler
    raise
  File "/usr/local/lib/python3.6/dist-packages/grpclib/server.py", line 220, in __aexit__
    status_message=status_message)
  File "/usr/local/lib/python3.6/dist-packages/grpclib/server.py", line 170, in send_trailing_metadata
    await self._stream.send_headers(headers, end_stream=True)
  File "/usr/local/lib/python3.6/dist-packages/grpclib/protocol.py", line 267, in send_headers
    end_stream=end_stream)
  File "/usr/local/lib/python3.6/dist-packages/h2/connection.py", line 763, in send_headers
    stream_id, AllowedStreamIDs(self.config.client_side)
  File "/usr/local/lib/python3.6/dist-packages/h2/connection.py", line 587, in _get_or_create_stream
    return self._begin_new_stream(stream_id, allowed_ids)
  File "/usr/local/lib/python3.6/dist-packages/h2/connection.py", line 454, in _begin_new_stream
    raise StreamIDTooLowError(stream_id, highest_stream_id)
h2.exceptions.StreamIDTooLowError: StreamIDTooLowError: 48141 is lower than 48143

This happens when client cancels stream with RST_STREAM, and on the server-side I have a logic which looks like this:

try:
    conn.send_headers(stream_id, [...])
except h2.exceptions.StreamClosedError:
    pass

And sometimes I'm getting StreamIDTooLowError exception instead of StreamClosedError, because this behavior depends on H2Connection.streams dictionary, where streams are removed nondeterministically.

I think that H2Connection._get_or_create_stream function should check not only H2Connection.streams but also H2Connection._closed_streams.

Of course I can refactor my code and check that stream is closed by myself, but I still think that there is a bug in H2Connection.send_headers method.