func (m *muxClient) roundtrip(h HandlerID, req []byte) ([]byte, error) {
	if m.init {
		return nil, errors.New("mux client already used")
	}
	m.init = true
	m.singleResp = true
	msg := message{
		Op:         OpRequest,
		MuxID:      m.MuxID,
		Handler:    h,
		Flags:      m.BaseFlags | FlagEOF,
		Payload:    req,
		DeadlineMS: uint32(m.deadline.Milliseconds()),
	}
	if m.subroute != nil {
		msg.Flags |= FlagSubroute
	}

		c.handleDisconnectServerMux(m)
	case OpDisconnectClientMux:
		c.handleDisconnectClientMux(m)
	case OpPing:
		c.handlePing(ctx, m)
	case OpPong:
		c.handlePong(ctx, m)
	case OpRequest:
		c.handleRequest(ctx, m, subID)
	case OpAckMux:
		c.handleAckMux(ctx, m)
	case OpConnectMux:
		c.handleConnectMux(ctx, m, subID)
	case OpMuxConnectError:
		c.handleConnectMuxError(ctx, m)