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AttributeError: 'WebSocketProtocol' object has no attribute 'reply_channel'

See original GitHub issue

With an incorrect nginx setup (one that does not include proxy_set_header Connection "upgrade";) Daphne crashes resulting in a client-side 502 Bad gateway.

When the log statement from daphne/http_protocol.py:107 is removed Daphne no longer crashes resulting in a client-side 400 HTTP Connection headers do not include ‘upgrade’ value (case-insensitive) : close, which is more helpful in determining what is wrong with the setup.

Stacktrace:

2016-06-26 22:02:12,500 ERROR    Traceback (most recent call last):
  File "<...>/virtual/lib/python3.4/site-packages/daphne/http_protocol.py", line 107, in process
    logger.debug("Upgraded connection %s to WebSocket %s", self.reply_channel, protocol.reply_channel)
AttributeError: 'WebSocketProtocol' object has no attribute 'reply_channel'

Unhandled Error
Traceback (most recent call last):
  File "<...>/virtual/lib/python3.4/site-packages/twisted/python/log.py", line 101, in callWithLogger
    return callWithContext({"system": lp}, func, *args, **kw)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/python/log.py", line 84, in callWithContext
    return context.call({ILogContext: newCtx}, func, *args, **kw)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/python/context.py", line 118, in callWithContext
    return self.currentContext().callWithContext(ctx, func, *args, **kw)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/python/context.py", line 81, in callWithContext
    return func(*args,**kw)
--- <exception caught here> ---
  File "<...>/virtual/lib/python3.4/site-packages/twisted/internet/posixbase.py", line 597, in _doReadOrWrite
    why = selectable.doRead()
  File "<...>/virtual/lib/python3.4/site-packages/twisted/internet/tcp.py", line 209, in doRead
    return self._dataReceived(data)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/internet/tcp.py", line 215, in _dataReceived
    rval = self.protocol.dataReceived(data)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/protocols/basic.py", line 571, in dataReceived
    why = self.lineReceived(line)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/web/http.py", line 1692, in lineReceived
    self.allContentReceived()
  File "<...>/virtual/lib/python3.4/site-packages/twisted/web/http.py", line 1781, in allContentReceived
    req.requestReceived(command, path, version)
  File "<...>/virtual/lib/python3.4/site-packages/twisted/web/http.py", line 768, in requestReceived
    self.process()
  File "<...>/virtual/lib/python3.4/site-packages/daphne/http_protocol.py", line 147, in process
    self.basic_error(500, b"Internal Server Error", "HTTP processing error")
  File "<...>/virtual/lib/python3.4/site-packages/daphne/http_protocol.py", line 256, in basic_error
    }).encode("utf8"),
  File "<...>/virtual/lib/python3.4/site-packages/daphne/http_protocol.py", line 216, in serverResponse
    http.Request.write(self, message['content'])
  File "<...>/virtual/lib/python3.4/site-packages/twisted/web/http.py", line 951, in write
    self.transport.writeSequence(l)
builtins.AttributeError: 'NoneType' object has no attribute 'writeSequence'