#  MQTT 示例程序

## 示例代码讲解

下面讲解 RT-Thread 提供的  MQTT 示例代码，测试服务器使用 Eclipse 的测试服务器，地址 `iot.eclipse.org` ，端口 `1883`，MQTT 功能示例代码如下：

```c
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

#include <rtthread.h>

#define DBG_ENABLE
#define DBG_SECTION_NAME    "mqtt.sample"
#define DBG_LEVEL           DBG_LOG
#define DBG_COLOR
#include <rtdbg.h>

#include "paho_mqtt.h"

/**
 * MQTT URI farmat:
 * domain mode
 * tcp://iot.eclipse.org:1883
 *
 * ipv4 mode
 * tcp://192.168.10.1:1883
 * ssl://192.168.10.1:1884
 *
 * ipv6 mode
 * tcp://[fe80::20c:29ff:fe9a:a07e]:1883
 * ssl://[fe80::20c:29ff:fe9a:a07e]:1884
 */
#define MQTT_URI                "tcp://iot.eclipse.org:1883"   // 配置测试服务器地址
#define MQTT_USERNAME           "admin"   
#define MQTT_PASSWORD           "admin"
#define MQTT_SUBTOPIC           "/mqtt/test"                   // 设置订阅主题
#define MQTT_PUBTOPIC           "/mqtt/test"                   // 设置推送主题
#define MQTT_WILLMSG            "Goodbye!"                     // 设置遗言消息

/* 定义 MQTT 客户端环境结构体 */
static MQTTClient client;
static int is_started = 0;

/* MQTT 订阅事件自定义回调函数 */
static void mqtt_sub_callback(MQTTClient *c, MessageData *msg_data)
{
    *((char *)msg_data->message->payload + msg_data->message->payloadlen) = '\0';
    LOG_D("mqtt sub callback: %.*s %.*s",
               msg_data->topicName->lenstring.len,
               msg_data->topicName->lenstring.data,
               msg_data->message->payloadlen,
               (char *)msg_data->message->payload);
}

/* MQTT 订阅事件默认回调函数 */
static void mqtt_sub_default_callback(MQTTClient *c, MessageData *msg_data)
{
    *((char *)msg_data->message->payload + msg_data->message->payloadlen) = '\0';
    LOG_D("mqtt sub default callback: %.*s %.*s",
               msg_data->topicName->lenstring.len,
               msg_data->topicName->lenstring.data,
               msg_data->message->payloadlen,
               (char *)msg_data->message->payload);
}

/* MQTT 连接事件回调函数 */
static void mqtt_connect_callback(MQTTClient *c)
{
    LOG_D("inter mqtt_connect_callback!");
}

/* MQTT 上线事件回调函数 */
static void mqtt_online_callback(MQTTClient *c)
{
    LOG_D("inter mqtt_online_callback!");
}

/* MQTT 下线事件回调函数 */
static void mqtt_offline_callback(MQTTClient *c)
{
    LOG_D("inter mqtt_offline_callback!");
}

static int mqtt_start(int argc, char **argv)
{
    /* 使用 MQTTPacket_connectData_initializer 初始化 condata 参数 */
    MQTTPacket_connectData condata = MQTTPacket_connectData_initializer;
    static char cid[20] = { 0 };

    if (argc != 1)
    {
        rt_kprintf("mqtt_start    --start a mqtt worker thread.\n");
        return -1;
    }

    if (is_started)
    {
        LOG_E("mqtt client is already connected.");
        return -1;
    }
     /* 配置 MQTT 结构体内容参数 */
    {
        client.isconnected = 0;
        client.uri = MQTT_URI;

        /* 产生随机的客户端 ID */
        rt_snprintf(cid, sizeof(cid), "rtthread%d", rt_tick_get());
        /* 配置连接参数 */
        rt_memcpy(&client.condata, &condata, sizeof(condata));
        client.condata.clientID.cstring = cid;
        client.condata.keepAliveInterval = 30;
        client.condata.cleansession = 1;
        client.condata.username.cstring = MQTT_USERNAME;
        client.condata.password.cstring = MQTT_PASSWORD;

        /* 配置 MQTT 遗言参数 */
        client.condata.willFlag = 1;
        client.condata.will.qos = 1;
        client.condata.will.retained = 0;
        client.condata.will.topicName.cstring = MQTT_PUBTOPIC;
        client.condata.will.message.cstring = MQTT_WILLMSG;

         /* 分配缓冲区 */
        client.buf_size = client.readbuf_size = 1024;
        client.buf = rt_calloc(1, client.buf_size);
        client.readbuf = rt_calloc(1, client.readbuf_size);
        if (!(client.buf && client.readbuf))
        {
            LOG_E("no memory for MQTT client buffer!");
            return -1;
        }

        /* 设置事件回调函数 */
        client.connect_callback = mqtt_connect_callback;
        client.online_callback = mqtt_online_callback;
        client.offline_callback = mqtt_offline_callback;

        /* 设置订阅表和事件回调函数*/
        client.messageHandlers[0].topicFilter = rt_strdup(MQTT_SUBTOPIC);
        client.messageHandlers[0].callback = mqtt_sub_callback;
        client.messageHandlers[0].qos = QOS1;

        /* 设置默认的订阅主题*/
        client.defaultMessageHandler = mqtt_sub_default_callback;
    }

    /* 运行 MQTT 客户端 */
    paho_mqtt_start(&client);
    is_started = 1;

    return 0;
}

/* 该函数用于停止 MQTT 客户端并释放内存空间 */
static int mqtt_stop(int argc, char **argv)
{
    if (argc != 1)
    {
        rt_kprintf("mqtt_stop    --stop mqtt worker thread and free mqtt client object.\n");
    }

    is_started = 0;

    return paho_mqtt_stop(&client);
}

/* 该函数用于发送数据到指定 topic */
static int mqtt_publish(int argc, char **argv)
{
    if (is_started == 0)
    {
        LOG_E("mqtt client is not connected.");
        return -1;
    }

    if (argc == 2)
    {
        paho_mqtt_publish(&client, QOS1, MQTT_PUBTOPIC, argv[1]);
    }
    else if (argc == 3)
    {
        paho_mqtt_publish(&client, QOS1, argv[1], argv[2]);
    }
    else
    {
        rt_kprintf("mqtt_publish <topic> [message]  --mqtt publish message to specified topic.\n");
        return -1;
    }

    return 0;
}

/* MQTT 新的订阅事件自定义回调函数 */
static void mqtt_new_sub_callback(MQTTClient *client, MessageData *msg_data)
{
    *((char *)msg_data->message->payload + msg_data->message->payloadlen) = '\0';
    LOG_D("mqtt new subscribe callback: %.*s %.*s",
               msg_data->topicName->lenstring.len,
               msg_data->topicName->lenstring.data,
               msg_data->message->payloadlen,
               (char *)msg_data->message->payload);
}

/* 该函数用于订阅新的 Topic */
static int mqtt_subscribe(int argc, char **argv)
{
    if (argc != 2)
    {
        rt_kprintf("mqtt_subscribe [topic]  --send an mqtt subscribe packet and wait for suback before returning.\n");
        return -1;
    }
	
	if (is_started == 0)
    {
        LOG_E("mqtt client is not connected.");
        return -1;
    }

    return paho_mqtt_subscribe(&client, QOS1, argv[1], mqtt_new_sub_callback);
}

/* 该函数用于取消订阅指定的 Topic */
static int mqtt_unsubscribe(int argc, char **argv)
{
    if (argc != 2)
    {
        rt_kprintf("mqtt_unsubscribe [topic]  --send an mqtt unsubscribe packet and wait for suback before returning.\n");
        return -1;
    }
	
	if (is_started == 0)
    {
        LOG_E("mqtt client is not connected.");
        return -1;
    }

    return paho_mqtt_unsubscribe(&client, argv[1]);
}

#ifdef FINSH_USING_MSH
MSH_CMD_EXPORT(mqtt_start, startup mqtt client);
MSH_CMD_EXPORT(mqtt_stop, stop mqtt client);
MSH_CMD_EXPORT(mqtt_publish, mqtt publish message to specified topic);
MSH_CMD_EXPORT(mqtt_subscribe,  mqtt subscribe topic);
MSH_CMD_EXPORT(mqtt_unsubscribe, mqtt unsubscribe topic);
#endif /* FINSH_USING_MSH */
```

## 运行示例

在 msh 中运行上述功能示例代码，可以实现向服务器订阅主题和向特定主题推送消息的功能，功能示例代码运行效果如下：

- 启动 MQTT 客户端，连接代理服务器并订阅主题：

```c
msh />mqtt_start                /* 启动 MQTT 客户端连接 Eclipse 服务器 */
inter mqtt_connect_callback!  /* 服务器连接成功，调用连接回调函数打印服务器信息 */
ipv4 address port: 1883
[MQTT] HOST =  'iot.eclipse.org'
msh />[MQTT] Subscribe #0 /mqtt/test  OK!  /* 订阅主题 /mqtt/test 成功 */
inter mqtt_online_callback!   /* MQTT 上线成功，调用上线回调函数 */
msh />
```
- 作为发布者向指定主题发布消息：

```c
msh />mqtt_pub  /mqtt/test hello-rtthread   /* 向指定主题发送  hello-rtthread 消息 */
msh />mqtt sub callback: /mqtt/test hello-rtthread /* 收到消息，执行回调函数 */
msh />
```

-  订阅新的 topic

```c
msh />mqtt_subscribe /test/topic          /* 订阅指定的 topic */
[I/MQTT:] Subscribe #1 /test/topic OK!
msh />
```

- 取消订阅 topic

```c
msh />mqtt_unsubscribe /test/topic       /* 取消订阅指定的 topic */
[561315] I/MQTT: Unsubscribe #1 /test/topic OK!
msh />
```

- 关闭 MQTT  客户端

```c
msh />mqtt_stop
[585107] D/MQTT: pub_sock recv 11 byte: DISCONNECT
[585110] I/MQTT: MQTT server is disconnected.
msh />
```