MQTT

5 mqtt软件包通讯使用问题

发布于 2021-07-06 09:19:38 浏览：1169 订阅该版

5 个回答

lx1024 2024-02-29

这家伙很懒，什么也没写！

![Mqtt Publish Error.jpg](https://oss-club.rt-thread.org/uploads/20240229/36c1a296da88562c1e01f13e0865bd07.jpg.webp)

Mosquitto Broker收到Puslish Message报文后，其Message Identifier为0时，Broker会断开TCP连接。

Mosquitto Broker日志：
1709176157: Sending SUBACK to abcd1234
1709176158: Client abcd1234 disconnected due to protocol error.

```c
typedef struct MQTTMessage
{
    enum QoS qos;
    unsigned char retained;
    unsigned char dup;
    unsigned short id;
    void *payload;
    size_t payloadlen;
} MQTTMessage;
```
没有找到设置MQTTMessage结构体中id的语句，在paho_mqtt_publish函数中添加id自增动语句测试后，能正常发布消息，且不会再断开TCP。

```c
int paho_mqtt_publish(MQTTClient *client, enum QoS qos, const char *topic, const char *msg_str)
{
    static unsigned short id = 0;
    MQTTMessage message = {0};

if (qos != QOS1)
    {
        LOG_E("Not support Qos(%d) config, only support Qos(d).", qos, QOS1);
        return PAHO_FAILURE;
    }

if (++id == 0)
    {
        ++id;
    }

message.qos = qos;
    message.retained = 0;
    message.id = id;
    message.payload = (void *)msg_str;
    message.payloadlen = rt_strlen(message.payload);

if (client->isblocking && client->pub_sem)
    {
        if(rt_sem_take(client->pub_sem, 5 * RT_TICK_PER_SECOND) < 0)
        {
            return PAHO_FAILURE;
        }
    }

return MQTTPublish(client, topic, &message);
}
```
在 https://mqtt.p2hp.com/mqtt311 2.3.1 包唯一标识中找到关闭唯一标识的描述：
SUBSCRIBE，UNSUBSCRIBE，PUBLISH（QoS > 0 的时候）控制包必须包含**非零**的唯一标识[MQTT-2.3.1-1]。每次客户端发送上述控制包的时候，必须分配一个未使用过的唯一标识[MQTT-2.3.1-2]。如果一个客户端重新发送一个特别的控制包，必须使用相同的唯一标识符。唯一标识会在客户端收到相应的确认包之后变为可用。例如PUBLIST在QoS1的时候对应PUBACK；在QoS2时对应PUBCOMP。对于SUBSCRIBE和UNSUBSCRIBE对应SUBACK和UNSUBACK[MQTT-2.3.1-3]。服务端发送QoS>0的PUBLISH时，上述内容同样适用。