Paho mqtt client got connection lost - c

Question

I have a little problem about paho mqtt library.
I register a callback function MQTTClient_messageArrived and MQTTClient_connectionLost.
And I call MQTTClient_subscribe() or MQTTClient_unsubscribe() in this callback function. After running this callback function. I got a error code (-3) from MQTTClient_connectionLost. Furthermore, I print the cause is NULL.
Is any possible problem to my problem? Thanks
Here are my initialize function and callback function:
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

Did you try connecting any other client to same broker with same client id? That could be a possible case if you are getting connection lost. Also if your callback throws exception, it will cause connection lost, however in this case paho will reconnect.