I'm not exactly sure what caused this error, but I was a client receiving messages on a websocket for a while (about 12 hours). Suddenly all incoming data stopped, then nothing happened for about 5 hours. Finally, I received a ConnectionClosed and the following appeared on stdout:

```
Fatal error on SSL transport
protocol: <asyncio.sslproto.SSLProtocol object at 0x7f17ae393e48>
transport: <_SelectorSocketTransport closing fd=15 read=idle write=<idle, bufsize=0>>
Traceback (most recent call last):
  File "/usr/lib/python3.6/asyncio/sslproto.py", line 636, in _process_write_backlog
    ssldata, offset = self._sslpipe.feed_appdata(data, offset)
AttributeError: 'NoneType' object has no attribute 'feed_appdata'
```

I can't imagine this is what was supposed to happen. This has happened about three times now, so I can confirm it is reproducible. I'm writing a minimalist client now to see if I can isolate the problem any further. It's still unclear, though, which layer is responsible---websockets or asyncio. The websockets issue is here:

https://github.com/aaugustin/websockets/issues/356