func (z *ZtunnelConnection) sendDataAndWaitForAck(data []byte, fd *int) (*zdsapi.WorkloadResponse, error) {
	var rights []byte
	if fd != nil {
		rights = unix.UnixRights(*fd)
	}
	err := z.u.SetWriteDeadline(time.Now().Add(readWriteDeadline))
	if err != nil {
		return nil, err
	}

	_, _, err = z.u.WriteMsgUnix(data, rights, nil)
	if err != nil {
		return nil, err
	}

	// wait for ack