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

Eric, what is needed to try and reproduce this issue accurately?  Would it be installing websockets and setting up your client to ping to the server forever (12 hours in this case)?  If you are able to provide a client I would be willing to setup a test case on my end.

Looks like https://bugs.python.org/issue33037

Well, that looks good! Looking forward to 3.6.5!

Thanks for the report and for the analysis!  Closing as duplicate.