rosserial publish发布消息时的id问题

virtual int publish(int id, const Msg * msg)
  {
    if (id >= 100 && !configured_) // id>=100 消息发布失败
      return 0;
    /* serialize message */
    int l = msg->serialize(message_out + 7);
    rt_kprintf("virtual int publish1 %d\r\n",l);
    /* setup the header */
    message_out[0] = 0xff;
    message_out[1] = PROTOCOL_VER;
    message_out[2] = (uint8_t)((uint16_t)l & 255);
    message_out[3] = (uint8_t)((uint16_t)l >> 8);
    message_out[4] = 255 - ((message_out[2] + message_out[3]) % 256);
    message_out[5] = (uint8_t)((int16_t)id & 255);
    message_out[6] = (uint8_t)((int16_t)id >> 8);
    /* calculate checksum */
    int chk = 0;
    for (int i = 5; i < l + 7; i++)
      chk += message_out[i];
    l += 7;
    message_out[l++] = 255 - (chk % 256);
    if (l <= OUTPUT_SIZE)
    {
      hardware_.write(message_out, l);
      return l;
    }
    else
    {
      logerror("Message from device dropped: message larger than buffer.");
      return -1;
    }
  }