mqtt协议理解（结合libemqtt，subscribe部分）
1. connect在libemqtt代码中，客户端的connect代码是调用的mqtt_connect函数，代码如下：int mqtt_connect(mqtt_broker_handle_t* broker){ uint8_t flags = 0x00; uint16_t clientidlen = strlen(broker->clientid); uint16_t usern
