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Paho MQTT

Paho MQTT‌ 是 Eclipse 基金会下的一个开源项目，旨在为多种编程语言提供 ‌MQTT 协议‌的客户端实现。MQTT（Message Queuing Telemetry Transport）是一种轻量级的发布/订阅（Pub/Sub）消息传输协议，专为物联网（IoT）等低带宽、高延迟或不稳定网络环境设计。

关键信息：

1. ‌定义‌：

   • ‌Paho‌ 是 Eclipse IoT 技术栈的一部分，提供跨平台的 MQTT 客户端库，支持设备与服务器之间的双向通信。
   • ‌paho.mqtt‌ 通常指特定语言的客户端库，例如 paho-mqtt 是 Python 的客户端库名称。

2. ‌支持的语言‌：

   • ‌Python‌: paho-mqtt（通过 pip install paho-mqtt 安装）
   • ‌Java‌: Eclipse Paho Java Client
   • ‌C/C++‌: Eclipse Paho C/C++
   • ‌JavaScript‌: Paho MQTT over WebSocket（适用于浏览器）
   • 其他语言（如 Go、.NET 等）也有社区支持的实现。

3. ‌核心功能‌：

   • 发布消息到 MQTT Broker（如 Mosquitto、EMQX、AWS IoT Core）。
   • 订阅主题并接收消息。
   • 支持 MQTT 3.1.1 和 5.0 协议版本。
   • 提供 QoS（服务质量）级别（0/1/2），确保消息可靠性。
   • 支持 TLS/SSL 加密、持久会话、遗嘱消息（Last Will）等特性。

4. ‌典型应用场景‌：

   • 物联网设备与云平台通信（如传感器上报数据、远程控制设备）。
   • 移动端与服务器实时消息推送。
   • 跨系统异步通信（如微服务架构中的事件驱动）。

测试Demo

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1. 安装MQTT Broker（Mosquitto）

# 安装Mosquitto Broker及客户端工具
sudo apt-get update
sudo apt-get install -y mosquitto mosquitto-clients# 启动Mosquitto服务（部分系统需手动启动）
sudo systemctl start mosquitto
sudo systemctl enable mosquitto# 验证Broker是否运行
sudo systemctl status mosquitto

2. 安装C语言MQTT库（推荐Paho MQTT C库）

# 安装依赖项
sudo apt-get install build-essential cmake openssl libssl-dev# 下载并编译Paho MQTT C库
git clone https://github.com/eclipse/paho.mqtt.c.git
cd paho.mqtt.c
mkdir build
cd build
cmake ..
make
sudo make install
sudo ldconfig  # 更新动态库缓存

3. 编写MQTT测试程序

‌发布者（publisher.c）
------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "Publisher"
#define TOPIC       "test/topic"
#define QOS         1
#define TIMEOUT     10000Lint main() {MQTTClient client;MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;MQTTClient_message pubmsg = MQTTClient_message_initializer;MQTTClient_deliveryToken token;int rc;// 创建客户端实例rc = MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);if (rc != MQTTCLIENT_SUCCESS) {fprintf(stderr, "Failed to create client: %d\n", rc);exit(EXIT_FAILURE);}// 连接Brokerconn_opts.keepAliveInterval = 20;conn_opts.cleansession = 1;rc = MQTTClient_connect(client, &conn_opts);if (rc != MQTTCLIENT_SUCCESS) {fprintf(stderr, "Failed to connect: %d\n", rc);MQTTClient_destroy(&client);exit(EXIT_FAILURE);}// 发送消息pubmsg.payload = (void*)"Hello from C MQTT!";pubmsg.payloadlen = strlen(pubmsg.payload);pubmsg.qos = QOS;pubmsg.retained = 0;rc = MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);if (rc != MQTTCLIENT_SUCCESS) {fprintf(stderr, "Failed to publish: %d\n", rc);exit(EXIT_FAILURE);}printf("Message published. Token: %d\n", token);// 断开连接并清理MQTTClient_disconnect(client, 10000);MQTTClient_destroy(&client);return 0;
}

‌订阅者（subscriber.c）
----------------------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "Subscriber"
#define TOPIC       "test/topic"
#define QOS         1
#define TIMEOUT     10000Lvolatile MQTTClient_deliveryToken deliveredtoken;void delivered(void *context, MQTTClient_deliveryToken dt) {deliveredtoken = dt;
}int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message) {printf("Received message: %.*s\n", message->payloadlen, (char*)message->payload);MQTTClient_freeMessage(&message);MQTTClient_free(topicName);return 1;
}void connlost(void *context, char *cause) {fprintf(stderr, "Connection lost. Cause: %s\n", cause);
}int main() {MQTTClient client;MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;int rc;rc = MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);if (rc != MQTTCLIENT_SUCCESS) {fprintf(stderr, "Failed to create client: %d\n", rc);exit(EXIT_FAILURE);}// 设置回调函数MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);conn_opts.keepAliveInterval = 20;conn_opts.cleansession = 1;rc = MQTTClient_connect(client, &conn_opts);if (rc != MQTTCLIENT_SUCCESS) {fprintf(stderr, "Failed to connect: %d\n", rc);MQTTClient_destroy(&client);exit(EXIT_FAILURE);}// 订阅主题rc = MQTTClient_subscribe(client, TOPIC, QOS);if (rc != MQTTCLIENT_SUCCESS) {fprintf(stderr, "Failed to subscribe: %d\n", rc);exit(EXIT_FAILURE);}printf("Subscribed to topic: %s\n", TOPIC);printf("Press Q<Enter> to quit\n");while(getchar() != 'Q');// 清理MQTTClient_unsubscribe(client, TOPIC);MQTTClient_disconnect(client, TIMEOUT);MQTTClient_destroy(&client);return 0;
}

4. 编译程序

# 编译发布者
gcc publisher.c -o publisher -lpaho-mqtt3c# 编译订阅者
gcc subscriber.c -o subscriber -lpaho-mqtt3c

‌5. 运行测试