While debugging bpo-32458 (functional test on START TLS), I found a race condition in SSLProtocol of asyncio/sslproto.py.
Sometimes, _sslpipe.feed_ssldata() is called before _sslpipe.shutdown().
* SSLProtocol.connection_made() -> SSLProtocol._start_handshake(): self._loop.call_soon(self._process_write_backlog)
* SSLProtoco.data_received(): direct call to self._sslpipe.feed_ssldata(data)
* Later, self._process_write_backlog() calls self._sslpipe.do_handshake()
The first write is delayed by call_soon(), whereas the first read is a direct call to the SSL pipe.