def _setClient(self, client):
        """
        Called when the connection was established to the forwarding
        destination.

        @param client: Client protocol connected to the forwarding destination.
        @type  client: L{protocol.Protocol}
        """
        self.client = client
        log.msg("connected to %s:%i" % self.hostport)
        if self.clientBuf:
            self.client.transport.write(self.clientBuf)
            self.clientBuf = None
        if self.client.buf[1:]:
            self.write(self.client.buf[1:])
        self.client.buf = b''

        Called when the connection was established to the forwarding
        destination.

        @param client: Client protocol connected to the forwarding destination.
        @type  client: L{protocol.Protocol}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/ssh/forwarding.py