c - Paho mqtt 客户端失去连接

Question

我对 paho mqtt 库有一个小问题。我注册了回调函数 MQTTClient_messageArrived 和 MQTTClient_connectionLost。

我在此回调函数中调用 MQTTClient_subscribe() 或 MQTTClient_unsubscribe()。运行此回调函数后。我从 MQTTClient_connectionLost 收到错误代码 (-3)。此外，我打印的原因是NULL。

我的问题有什么可能的问题吗？谢谢

这是我的初始化函数和回调函数:

void mqtt_initialize(void){
    int rc;

    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;

    if(MQTTClient_create(&g_MQTT_client, BROKER_ADDR, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL) < 0){
        g_mqtt_exist = MQTT_INSTANCE_NOT_EXIST;
    } else {
        g_mqtt_exist = MQTT_INSTANCE_EXIST;
    }

    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;

    MQTTClient_setCallbacks(g_MQTT_client, NULL, mqtt_connlost_cb, mqtt_arrived_cb, mqtt_delivered_cb);

    if ((rc = MQTTClient_connect(g_MQTT_client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
        MAIN_PRINT_DEBUG(0, "Failed to connect MQTT broker, return code %d\n", rc);
        mqtt_free();
    } 

    /* set subscribe control topic */
    MQTTClient_subscribe(g_MQTT_client, "topic_1", MQTT_QOS);
}


int mqtt_arrived_cb(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
    int ret = 0;
    printf("topic: %s\n", topicName);
    if(!strcmp(topicName, "topic_1")){
        printf("topic_1\n");
        ret = MQTTClient_subscribe(g_MQTT_client, "topic_2", 0);
        if (ret < 0){
            printf("mqtt operation fail\n");
        }       
    } 
    return 1;

}

void mqtt_connlost_cb(void *context, char *cause)
{
    MAIN_PRINT_DEBUG(0, "\n MQTT Connection lost\n");
    MAIN_PRINT_DEBUG(0,"     cause: %s\n", cause);
}

Answer 1

您是否尝试将任何其他客户端连接到具有相同客户端 ID 的同一代理？如果您失去连接，这可能是一种情况。另外，如果您的回调抛出异常，则会导致连接丢失，但在这种情况下，paho 将重新连接。