mongoose7 mqtt例程

以下是使用mongoose7库实现MQTT协议的例程：

#include "mgos.h"
#include "mgos_mqtt.h"

static void mqtt_ev_handler(struct mg_connection *nc, int ev, void *ev_data, void *user_data) {
  struct mg_mqtt_message *msg = (struct mg_mqtt_message *) ev_data;
  switch (ev) {
    case MG_EV_MQTT_CONNACK:
      mgos_mqtt_pub("/my/topic", "hello", 5, 0, false);
      break;
    case MG_EV_MQTT_SUBACK:
      LOG(LL_INFO, ("Subscription %d acknowledged", msg->message_id));
      break;
    case MG_EV_MQTT_PUBLISH:
      LOG(LL_INFO, ("Got publish [%.*s]", (int) msg->payload.len, msg->payload.p));
      break;
    default:
      break;
  }
}

enum mgos_app_init_result mgos_app_init(void) {
  struct mg_connection *nc = mgos_mqtt_connect("mqtt://test.mosquitto.org", mqtt_ev_handler, NULL);
  if (nc == NULL) {
    return MGOS_APP_INIT_ERROR;
  }
  mgos_mqtt_sub("/my/topic", NULL);
  return MGOS_APP_INIT_SUCCESS;
}

这个例程连接到了test.mosquitto.org的MQTT服务器，并订阅了/my/topic主题。当连接成功后，它会发布一条消息到/my/topic主题。当收到订阅的消息时，它会打印出消息内容。