'Called when the low-level connection is lost or closed.
The argument is an exception object or None (the latter
meaning a regular EOF is received or the connection was
aborted or closed).'

def connection_lost(self, exc):

    if self._session_established:
        self._session_established = False
        self._loop.call_soon(self._app_protocol.connection_lost, exc)
    self._transport = None
    self._app_transport = None
    self._wakeup_waiter(exc)
