微消息队列MQTT（3）（实现一个简单Mqtt客户端）

相关文档

阿里云（C语言接入 阿里云Mqtt微消息队列）：
https://help.aliyun.com/document_detail/146611.html?spm=a2c4g.11186623.6.1007.5c5725932sKjsl
https://www.eclipse.org/paho/files/mqttdoc/MQTTClient/html/index.html?spm=a2c4g.11186623.2.8.72a8379bBBeLUj
CSDN：
https://blog.csdn.net/qq_43260665/article/details/88370100

1：下载一个Paho C库

1：先进入一个文件夹 
    cd /opt/iot
2：使用git命令下载库    
    git clone https://github.com.cnpmjs.org/eclipse/paho.mqtt.c.git
3：进行编译安装：
        1：cd paho.mqtt.c
        //编译
        2：make
        //安装
        3：sudo make install

2：查看动态库

cd build/output
存在以下文件
paho-mqtt3a ： 一般实际开发中就是使用这个，a表示的是异步消息推送（asynchronous）。
paho-mqtt3as ： as表示的是 异步+加密（asynchronous+OpenSSL）。
paho-mqtt3c ： c 表示的应该是同步（Synchronize），一般性能较差，是发送+等待模式。
paho-mqtt3cs ： cs表示的是 同步+加密（Synchronize+OpenSSL）。
在samples中还会有一些示例代码；
MQTTAsync_publish   MQTTAsync_subscribe
MQTTClient_publish   MQTTClient_subscribe   MQTTClient_publish_async        
paho_c_pub      paho_cs_sub
paho_cs_pub     paho_c_sub

3：编写 发布端（客户端）代码 mqtt_publish.c

vim

////引用相关库
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
//定义常量
#define ADDRESS     "tcp://post-cn-nif23a2s52f.mqtt.aliyuncs.com:1883"
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "topic_mqtt"
//#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000
//以下为    发布者客户端
int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    MQTTClient_deliveryToken token;
    //临时参数
    int rc;
    //创建一个发布者 客服端
    MQTTClient_create(&client, ADDRESS, CLIENTID,MQTTCLIENT_PERSISTENCE_NONE, NULL);
    //设置相关的连接参数
    conn_opts.keepAliveInterval = 60;
    conn_opts.cleansession = 1;
    //使用客户端连接服务端
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }
    //设置发送的消息
    pubmsg.qos = QOS;
    pubmsg.retained = 0;
    char buf[1024];
    while(1){
        printf("enter the message you want to send\n");
        fgets(buf,sizeof(buf),stdin);
        pubmsg.payload = (void *)buf;
        pubmsg.payloadlen = strlen(buf);
        MQTTClient_publishMessage(client,TOPIC,&pubmsg,&token);
        printf("waiting for %d seconds for publication of %s on topic %s for client with CLIENTID :%s\n",TIMEOUT/1000,buf,TOPIC,CLIENTID);
        int rv=MQTTClient_waitForCompletion(client,token,TIMEOUT);
        printf("Message with delivery token %d delivered\n",rv);
        //用于测试
        printf("%s\n",buf);
        sleep(3);
    }
}

4：进行编译 运行 mqtt_publish.c

编译：gcc mqtt_publish.c 
-L（大写的L） -I（大写的I）
查找对应的包：-o mqtt_publish -lpaho-mqtt3c -L ./opt/iot/paho.mqtt.c/ -I ./opt/iot/paho.mqtt.c/src/ 
说明 ：如果没有将头文件和动态库放到编译器默认寻找的位置 需要在编译时指定包
进行编译：
gcc mqtt_publish.c -o mqtt_publish -lpaho-mqtt3c -L ./opt/iot/paho.mqtt.c/ -I ./opt/iot/paho.mqtt.c/src/
进行运行
./mqtt_publish
返回：   mqtt的客户端还没运行
MQTTClient_connect failure:Transport endpoint is not connected

5：编写 订阅端（客户端）代码 mqtt_subscribe.c

////引用相关库
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTClient.h"
//定义常量
#define ADDRESS     "tcp://post-cn-nif23a2s52f.mqtt.aliyuncs.com:1883"
#define CLIENTID    "ExampleClientSub"
#define TOPIC       "topic_mqtt"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L
volatile MQTTClient_deliveryToken token;
void delivered(void *context, MQTTClient_deliveryToken dt)
{
    printf("Message with token value %d delivery confirmed\n", dt);
    token = dt;
}
int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
    //进行打印
    int i;
    char* payloadptr;
    printf("Message arrived\n");
    printf("     topic: %s\n", topicName);
    printf("   message: ");
    payloadptr = message->payload;
    for(i=0; i<message->payloadlen; i++)
    {
        putchar(*payloadptr++);
    }
    putchar('\n');
    MQTTClient_freeMessage(&message);
    MQTTClient_free(topicName);
    return 1;
}
void connlost(void *context, char *cause)
{
    printf("\nConnection lost\n");
    printf("     cause: %s\n", cause);
}
int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    //临时参数
    int rc;
    int ch;
    //创建一个订阅者 客服端
    MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    //设置相关的连接参数
    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;
    //设置为订阅者 客服端 异步消费消息
    MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }
    printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
           "Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
    //订阅者 客服端订阅消息
    MQTTClient_subscribe(client, TOPIC, QOS);
    do
    {
        q = getchar();
    } while(ch!='Q' && ch != 'q');
    //断开客户端连接
    MQTTClient_disconnect(client, 10000);
    //销毁客户端连接
    MQTTClient_destroy(&client);
    return rc;
}

6：进行编译 运行 mqtt_subscribe.c

先打开另一个客户端
然后进入该文件夹 /opt/iot/paho.mqtt.c/build/code
进行编译：
 gcc mqtt_subscribe.c -o mqtt_subscribe -lpaho-mqtt3c -L ./opt/iot/paho.mqtt.c/build/output/
进行运行：
./mqtt_subscribe
报错：
MQTTClient_connect failure:Transport endpoint is not connected
先去阿里云服务器管理  放开1883端口

7：测试

在发布端（客户端）进行消息的发送
在订阅端（客户端） 进行消息的接收
查看相关的打印 并查看阿里云平台的mqtt