def unicast(self, socket_id, event, data):
        """Sends an event to a single socket.  Returns `True` if that
        worked or `False` if not.
        """
        payload = self._server.serialize_event(event, data)
        rv = self._server.sockets.get(socket_id)
        if rv is not None:
            rv.socket.send(payload)
            return True
        return False
Sends an event to a single socket.  Returns `True` if that
        worked or `False` if not.