1 说明

   采用 mosquitto 库，实现订阅主题，并接收消息。其中服务器有做限制，需要对应的 cilent id ，cafile 、certfile  、keyfile 等配置

2 环境

采用ubuntu 直接编译调试
安装mosquitto 库

sudo apt install libmosquitto-dev
sudo apt-get install mosquitto

3 代码实现

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mosquitto.h>#define MQTT_HOST "akhrsh85xmt1q-ats.iot.us-east-1.amazonaws.com"
#define MQTT_PORT 8883
#define MQTT_TOPIC "test_topic/recv"
#define MQTT_CERT_PATH "/home/sky/develop/test/mosqito/cert.pem"
#define MQTT_KEY_PATH "/home/sky/develop/test/mosqito/key.pem"
#define MQTT_CA_PATH "/home/sky/develop/test/mosqito/ca.pem"
#define MQTT_CLIENT_ID "ID_666"void on_message(struct mosquitto *mosq, void *userdata, const struct mosquitto_message *message) {printf("Received message: %s\n", (char *)message->payload);
}int main() {struct mosquitto *mosq = NULL;int rc;// 初始化 mosquitto 库mosquitto_lib_init();// 创建 mosquitto 客户端实例mosq = mosquitto_new(MQTT_CLIENT_ID, true, NULL);if (!mosq) {printf("Failed to create mosquitto instance.\n");return 1;}// 设置 TLS 证书rc = mosquitto_tls_set(mosq, MQTT_CA_PATH, NULL, MQTT_CERT_PATH, MQTT_KEY_PATH, NULL);if (rc != MOSQ_ERR_SUCCESS) {printf("Failed to set TLS certificate.\n");return 1;}// 连接 MQTT 服务器rc = mosquitto_connect(mosq, MQTT_HOST, 8883, 60);if (rc != MOSQ_ERR_SUCCESS) {printf("Failed to connect to MQTT server.\n");return 1;}// 订阅主题rc = mosquitto_subscribe(mosq, NULL, MQTT_TOPIC, 0);if (rc != MOSQ_ERR_SUCCESS) {printf("Failed to subscribe to topic.\n");return 1;}// 设置消息回调函数mosquitto_message_callback_set(mosq, on_message);// 循环处理消息while (1) {rc = mosquitto_loop(mosq, -1, 1);if (rc != MOSQ_ERR_SUCCESS) {printf("Failed to process messages.\n");break;}}// 断开连接并清理资源mosquitto_disconnect(mosq);mosquitto_destroy(mosq);mosquitto_lib_cleanup();return 0;
}

对应的makefile

all: mqtt_submqtt_sub: mqtt_sub.ogcc -o mqtt_sub mqtt_sub.o -lmosquittomqtt_sub.o: mqtt_sub.cgcc -c mqtt_sub.cclean:rm -f mqtt_sub mqtt_sub.o

4 调试

4.1 编译

sky@ubuntu:~/develop/test/mosqito$ make
gcc -c mqtt_sub.c
gcc -o mqtt_sub mqtt_sub.o -lmosquitto

4.2 对应发送端的发送

此工具为 亚马逊的测试平台，可根据自己的实际情况，采用其他的测试工具或者linux下的发送命令

4.3 接收端

sky@ubuntu:~/develop/test/mosqito$ 
sky@ubuntu:~/develop/test/mosqito$ ./mqtt_sub
Received message: {"message": "1111"
}