Channel.process_frames crashes when channel-close listener raises an exception

[vitaly-krugl]

[This is related to https://github.com//issues/11 and https://github.com//issues/12]

1. Create a channel-close listener function that raises Exception() and register it via Channel.add_close_listener(); the exception doesn't have to come explicitly from the channel-closer listener: if the listener calls a Gevent API that results in context switch and then another greenlet kills the greenlet that was executing the channel-close listener, then a GreenletExit (or another exception such as LinkedFailed, etc.) would be injected into that greenlet, causing the exception to be raised in channel-close listener function.
2. Then do something that causes the broker to close your channel; this happened to me with RabbitMQ when I set qos as ch.basic.qos(prefetch_count=1), but forgot to pass no_ack=False to ch.basic.consume(), and then sent some messages to an exchange that was bound to the consumer's queue; when my code ACK'ed the incoming message, the broker no longer had a matching message in the queue (since no_ack was True by default) and closed the channel to signal an error condition.

If the channel-close listener callback is called from the scope of self.dispatch(), then by the time the exception that was raised in my channel-close listener is caught by process_frames(), both self._connection and self._logger of the Channel instance are None (cleared by Channel._closed_cb()). Since self.logger maps to self._connection.logger and self.close() maps to self.channel.close(), both of these calls would result in AttributeError exception. E.g.,

  File "/Users/vkruglikov/Packages/haigha/agoragames-haigha-6540e82/build/lib/haigha/connection.py", line 318, in read_frames
    self._transport.process_channels( p_channels )
  File "/Users/vkruglikov/Packages/haigha/agoragames-haigha-6540e82/build/lib/haigha/transports/transport.py", line 32, in process_channels
    channel.process_frames()
  File "/Users/vkruglikov/Packages/haigha/agoragames-haigha-6540e82/build/lib/haigha/channel.py", line 148, in process_frames
    self.logger.error(
  File "/Users/vkruglikov/Packages/haigha/agoragames-haigha-6540e82/build/lib/haigha/channel.py", line 60, in logger
    return self._connection.logger
AttributeError: 'NoneType' object has no attribute 'logger'

def process_frames(self):
  """
  Process the input buffer.
  """
  while len(self._frame_buffer):
    try:
      # It would make sense to call next_frame, but it's technically faster
      # to repeat the code here.
      frame = self._frame_buffer.popleft()
      self.dispatch( frame )
    except ProtocolClass.FrameUnderflow:
      return
    except:
      self.logger.error( 
        "Failed to dispatch %s", frame, exc_info=True )
      self.close( 500, "Failed to dispatch %s"%(str(frame)) )
      return

[awestendorf]

I think that this is resolved in master due to :

• Channel state is now stored in the Channel object and is left alone after it is closed
• No longer log in Channel.process_frames; exception is raised and user code can handle it

This is a complicated case that I can't readily repeat so please re-open if this is still broken. Fix will go out with today's release.