说明：MQTT客户端源码种类比较多，可以根据具体需求进行选择，这里采用linux C 编程方式和HTTP方式。

Ubuntu客户端源码

地址：https://docs.emqx.io/en/broker/latest/development/resource.html
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选择该源码进行下载，自行解压到linux目录，解压后目录文件如下：

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直接进行make编译

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编译过程提示类型不匹配，需要将include/libemqtt.h 117行修改返回值类型
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修改完成后继续make，即可编译成功。
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代码编写流程

  1. //初始化mqtt，需要提供一个mqtt_broker_handle_t  链接参数结构体
  2. void mqtt_init(mqtt_broker_handle_t *broker,const char* clientid);
  3. //初始化认证信息，用户名，密码
  4. void mqtt_init_auth(mqtt_broker_handle_t* broker, const char* username, const char* password);
  5. //初始化socket，内部设置一些参数和方法给broker，主机IP,端口
  6. int init_socket(mqtt_broker_handle_t* broker, const char* hostname, short port);
  7. //连接服务器，将borker对象传进去
  8. int mqtt_connect(mqtt_broker_handle_t* broker);
  9. //接收数据，参数：超时时间，返回值：接收到的数据个数
  10. int read_packet(int timeout)
  11. //发布，brocker对象，topic地址，信息，0
  12. int mqtt_publish(mqtt_broker_handle_t* broker, const char* topic, const char* msg, uint8_t retain)
  13. //订阅函数
  14. int mqtt_subscribe(mqtt_broker_handle_t* broker, const char* topic, uint16_t* message_id)

发布服务器代码

  2. #include <libemqtt.h>
  3. #include <stdio.h>
  4. #include <string.h>
  5. #include <stdlib.h>
  6. #include <unistd.h>
  7. #include <arpa/inet.h>
  8. #include <linux/tcp.h>
  9. #include <signal.h>
  10. #define MAXBUF 1024
  11. int socket_id;
  12. int keepalive = 30;
  13. uint8_t read_buf[MAXBUF];
  15. int send_packet(void* socket_info, const void* buf, unsigned int count)
  16. {
  17.     int fd = *((int*)socket_info);
  18.     return send(fd, buf, count, 0);
  19. }
  21. int init_socket(mqtt_broker_handle_t* broker, const char* hostname, short port, int keepalive)
  22. {
  23.     int flag = 1;
  25.     // Create the socket
  26.     if((socket_id = socket(PF_INET, SOCK_STREAM, 0)) < 0)
  27.         return -1;
  29.     // Disable Nagle Algorithm
  30.     if (setsockopt(socket_id, IPPROTO_TCP, TCP_NODELAY, (char*)&flag, sizeof(flag)) < 0)
  31.         return -2;
  33.     struct sockaddr_in socket_address;
  34.     // Create the stuff we need to connect
  35.     socket_address.sin_family = AF_INET;
  36.     socket_address.sin_port = htons(port);
  37.     socket_address.sin_addr.s_addr = inet_addr(hostname);
  39.     // Connect the socket
  40.     if((connect(socket_id, (struct sockaddr*)&socket_address, sizeof(socket_address))) < 0)
  41.         return -1;
  43.     // MQTT stuffs
  44.     mqtt_set_alive(broker, keepalive);
  45.     broker->socket_info = (void*)&socket_id;
  46.     broker->send = send_packet;
  48.     return 0;
  49. }
  51. int read_packet(int timeout)
  52. {
  53.     if(timeout > 0)
  54.     {
  55.         fd_set readfds;
  56.         struct timeval tmv;
  58.         // Initialize the file descriptor set
  59.         FD_ZERO (&readfds);
  60.         FD_SET (socket_id, &readfds);
  62.         // Initialize the timeout data structure
  63.         tmv.tv_sec = timeout;
  64.         tmv.tv_usec = 0;
  66.         // select returns 0 if timeout, 1 if input available, -1 if error
  67.         if(select(1, &readfds, NULL, NULL, &tmv))
  68.             return -2;
  69.     }
  70.     //定义临时变量
  71.     int total_bytes = 0, bytes_rcvd, packet_length;
  72.     //清理buf
  73.     memset(read_buf, 0, sizeof(read_buf));
  75.     if((bytes_rcvd = recv(socket_id, (read_buf+total_bytes), MAXBUF, 0)) <= 0) {
  76.         return -1;
  77.     }
  79.     total_bytes += bytes_rcvd; // 赋值全部长度数
  80.     if (total_bytes < 2)       //少于2则退出
  81.         return -1;
  83.     uint16_t rem_len = mqtt_parse_rem_len(read_buf);  //求剩余长度
  84.     uint8_t rem_len_bytes = mqtt_num_rem_len_bytes(read_buf); //求剩余长度占用字节数
  87.     packet_length = rem_len + rem_len_bytes + 1; //剩余长度 + 剩余长度本身 + 固定头
  89.     while(total_bytes < packet_length) // 读包，如果读到的内容和整体长度不一致则继续接收
  90.     {
  91.         if((bytes_rcvd = recv(socket_id, (read_buf+total_bytes), MAXBUF, 0)) <= 0)
  92.             return -1;
  93.         total_bytes += bytes_rcvd; // 重新赋值总长度
  94.     }
  95.     //返回读到的数据长度
  96.     return packet_length;
  97. }
  99. int connect_mqtt_check(int packet_length,char *buf)
  100. {
  101.     //连接过程有返回数据，接收判断书否成功
  102.     if(packet_length < 0)
  103.     {
  104.         fprintf(stderr, "Error(%d) on read packet!\n", packet_length);
  105.         return -1;
  106.     }
  107.     //判断是否连接MQTT的ACK
  108.     if(MQTTParseMessageType(buf) != MQTT_MSG_CONNACK)
  109.     {
  110.         fprintf(stderr, "CONNACK expected!\n");
  111.         return -2;
  112.     }
  113.     //判断是否连接MQTT成功
  114.     if(buf[3] != 0x00)
  115.     {
  116.         fprintf(stderr, "CONNACK failed!\n");
  117.         return -2;
  118.     }
  119.     return 0;
  120. }
  122. int main(int argc,const char *argv[])
  123. {
  124.     mqtt_broker_handle_t mqtt_info;
  125.     //初始化mqtt数据
  126.     mqtt_init(&mqtt_info,argv[1]);
  127.     //填充验证信息
  128.     mqtt_init_auth(&mqtt_info,"user","admin");
  129.     //创建socket
  130.     init_socket(&mqtt_info,"127.0.0.1",1883,keepalive);
  132.     if(mqtt_connect(&mqtt_info) == -1)
  133.     {
  134.         printf("mqtt_connect is fail\n");
  135.     }
  137.     int packet_length;
  138.     //连接有返回数据，接收一下，判断是否成功
  139.     packet_length = read_packet(1);
  140.     if(connect_mqtt_check(packet_length,read_buf))
  141.     {
  142.         printf("connect mqtt server is fail \n");
  143.         return -1;
  144.     }
  146.     char top[30];
  147.     char date[20];
  148.     int i;
  149.     for(i=0;i<10;i++)
  150.     {
  151.         sprintf(top,"public/test%d/topic",i);
  152.         sprintf(date,"data num = %d",i);
  153.         mqtt_publish(&mqtt_info,top , date, 0);
  154.         usleep(500);
  155.     }
  156. //    mqtt_disconnect(&mqtt_info);
  157.     //close_socket(&mqtt_info);
  158.     return 0;
  159. }

STM32 基于LwIP - MQTT

以STM32F407x为例，首先进行网卡的基本配置：

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使能FREERTOS，是为了更方便的进行使用。

代码部分：

  1. //注意，提前修改MEMP_NUM_SYS_TIMEOUT 宏为128
  2. void StartDefaultTask(void const * argument)
  3. {
  4.       /* init code for LWIP */
  5.       MX_LWIP_Init();
  6.       /* USER CODE BEGIN StartDefaultTask */
  7.         ip_addr_t ppp;
  8.         uint8_t user_data;
  9.         struct mqtt_connect_client_info_t cloent_info;
  10.         ppp.addr = inet_addr("192.168.1.178");
  11.         mqtt_client_t *client_my = mqtt_client_new();
  12.         cloent_info.client_user = "admin";
  13.         cloent_info.client_pass = "admin";
  14.         cloent_info.keep_alive = 30;
  15.         cloent_info.client_id = "STM32";
  16.         mqtt_client_connect(client_my,&ppp,LWIP_IANA_PORT_MQTT,NULL,&user_data,&cloent_info);
  17.         uint8_t temp[] = "hello";
  18.         /* Infinite loop */
  19.          for(;;)
  20.          {
  21.             //发布
  22.             mqtt_publish(client_my,"/sys/temp", (void *)&temp, sizeof(temp), 0,0,
  23.                                    NULL, client_my);
  25.              //5s发布一次数据
  26.              osDelay(5000);
  27.            }
  28.   /* USER CODE END StartDefaultTask */
  29. }

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ESP8266_RTOS_SDK

环境：ubuntu20
开发工具：IDF Python2 pip

1.环境搭建

SDK下载地:https://www.espressif.com/zh-hans/support/download/sdks-demos?keys=&field_type_tid%5B%5D=14
编译工具链下载：https://dl.espressif.com/dl/xtensa-lx106-elf-gcc8_4_0-esp-2020r3-linux-amd64.tar.gz
云盘连接：链接：https://pan.baidu.com/s/1sOaOx2mMgfvso7N80slfIQ
提取码：xkxg
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①创建一个目录（mkdir exp8266）
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②安装python2及pip

  1. sudo apt update   #更新库
  2. sudo apt install python2  #安装python2
  3. sudo apt install curl #安装curl工具，方便下载其他内容
  4. sudo update-alternatives --install /usr/bin/python python /usr/bin/python2 1 #配置python2为默认python工具
  5. curl https://bootstrap.pypa.io/pip/2.7/get-pip.py --output get-pip.py  #下载pip2包
  6. sudo python get-pip.py  #安装pip

③拷贝及解压SDK、工具链

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#进入ESP8266目录，执行安装依赖包
python -m pip install -r requirements.txt
git submodule add https://github.com/espressif/esp-mqtt.git components/espmqtt  #获取mqtt子模块

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④添加环境变量

#终端输入如下命令，并将相应代码填入其中
#pwd获取当前目录位置
mqtt@mqtt-virtual-machine:~/esp8266/ESP8266_RTOS_SDK$ pwd
/home/mqtt/esp8266/ESP8266_RTOS_SDK  #这里应该与自己的路径对应，复制下来

mqtt@mqtt-virtual-machine:~/esp8266/ESP8266_RTOS_SDK$ gedit ~/.bashrc   #打开后在最后一行填写

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#进入到编译工具链根目录，获取路径复制
mqtt@mqtt-virtual-machine:~/esp8266/xtensa-lx106-elf/bin$ pwd

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添加完成后保存退出，关闭终端重新打开，输入xt 按两下tab键看到如下画面说明成功：
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⑤编译测试

#进入到SDK中
cd examples/get-started/hello_world/   #进入helloworld工程当中

make menuconfig #配置工程

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⑥配置工程

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⑦编译工程

make all #编译工程，等待结束
#连接开发板到虚拟机，检查ls /dev/ttyUSB0 是否存在
make flash #烧写代码，如果遇到权限问题，sudo chmod 777 /dev/ttyUSB0 即可
make monitor  #打开串口监听数据
#结束监听 Ctrl + ] 即可

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2.手册获取

SDK手册:https://docs.espressif.com/projects/esp8266-rtos-sdk/en/latest/get-started/index.html