I think there's been some confusion about what PR 480 was meant to fix - it helps in cases where connections are closed during handshake, but if a server connection is waiting for a handshake but never receives any data at all then it stays in that state forever.

As for a fix, how about giving SSLProtocol a method like:

    def checkHandshakeDone(self):
        if self._in_handshake == True:
            self._abort()

and then at the end of _start_handshake() adding:

    self._loop.call_later(10, self.checkHandshakeDone)

Then if the handshake is not complete within ten seconds of starting, the connection will be aborted.