使 esp32 成为 mqtt 代理的 c 示例代码

以下是一个简单的C语言示例代码，用于将ESP32设备作为MQTT代理：

#include <stdio.h>
#include <string.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_system.h"
#include "esp_event.h"
#include "esp_log.h"
#include "mqtt_client.h"

static const char *TAG = "MQTT_EXAMPLE";

static esp_err_t mqtt_event_handler_cb(esp_mqtt_event_handle_t event)
{
esp_mqtt_client_handle_t client = event->client;
int msg_id;
// your event handling code here
switch (event->event_id) {
case MQTT_EVENT_CONNECTED:
ESP_LOGI(TAG, "MQTT_EVENT_CONNECTED");
msg_id = esp_mqtt_client_publish(client, "/topic/qos0", "data_3", 0, 0, 0);
ESP_LOGI(TAG, "sent publish successful, msg_id=%d", msg_id);

msg_id = esp_mqtt_client_subscribe(client, "/topic/qos1", 1);
ESP_LOGI(TAG, "sent subscribe successful, msg_id=%d", msg_id);

msg_id = esp_mqtt_client_subscribe(client, "/topic/qos0", 0);
ESP_LOGI(TAG, "sent subscribe successful, msg_id=%d", msg_id);
break;
case MQTT_EVENT_DISCONNECTED:
ESP_LOGI(TAG, "MQTT_EVENT_DISCONNECTED");
break;

case MQTT_EVENT_SUBSCRIBED:
ESP_LOGI(TAG, "MQTT_EVENT_SUBSCRIBED, msg_id=%d", event->msg_id);
msg_id = esp_mqtt_client_publish(client, "/topic/qos0", "data", 0, 0, 0);
ESP_LOGI(TAG, "sent publish successful, msg_id=%d", msg_id);
break;
case MQTT_EVENT_UNSUBSCRIBED:
ESP_LOGI(TAG, "MQTT_EVENT_UNSUBSCRIBED, msg_id=%d", event->msg_id);
break;
case MQTT_EVENT_PUBLISHED:
ESP_LOGI(TAG, "MQTT_EVENT_PUBLISHED, msg_id=%d", event->msg_id);
break;
case MQTT_EVENT_DATA:
ESP_LOGI(TAG, "MQTT_EVENT_DATA");
printf("TOPIC=%.*s\r\n", event->topic_len, event->topic);
printf("DATA=%.*s\r\n", event->data_len, event->data);
break;
case MQTT_EVENT_ERROR:
ESP_LOGI(TAG, "MQTT_EVENT_ERROR");
break;
}
return ESP_OK;
}

void mqtt_app_start(void)
{
esp_mqtt_client_config_t mqtt_cfg = {
.uri = "mqtt://test.mosquitto.org",
.event_handle = mqtt_event_handler_cb,
};
esp_mqtt_client_handle_t client = esp_mqtt_client_init(&mqtt_cfg);
esp_mqtt_client_start(client);
}

void app_main()
{
mqtt_app_start();
}

请注意，这只是一个简单的示例代码，您需要根据您的具体需求进行修改和定制。