On the client side, handle a server shutdown.

[miracle2k]

I have a client that is reading a stream from the server. When the server shuts down, the client hangs, basically because it is waiting here:

  File ".../grpclib/grpclib/protocol.py", line 93, in read
    await self._ready_event.wait()

Making sure that when we get connection_lost from the asyncio protocol that all the streams are closed fixes it for me (this will set the ready_event in the buffer).

In addition, I had to make sure that the async with api.Method.open() as stream: context manager doesn't hang in __aexit__ after that trying to read the trailing metadata.

What else is needed?

[vmagamedov]

There are two things client/server can wait: HEADERS and DATA. I think we should put some indicator into the grpclib.protocol.Stream.__headers__ queue in the grpclib.protocol.Stream.__ended__ method to wake up recv_headers coroutine. There is a corresponding issue - #8.

I think it is necessary to distinguish normal Stream.__ended__() and other causes (errors). So when connection is lost, we should raise exceptions in recv_headers and recv_data coroutines.

[vmagamedov]

I forgot another two things client/server can wait: WINDOW_UPDATED and H2Protocol.resume_writing. It would be too complex to fix all of these in one PR, so I will update #8 issue.

[vmagamedov]

Thank you for your contribution. Going to complete this fix as soon as possible to make new release.