.. vim: syntax=rst

.. highlight:: sh

C/C++
============================

本文主要介绍如何在 C 项目中使用 `Eclipse Paho C` ，实现 ST200TH 设备与 MQTT 服务器的连接、订阅、收发消息等功能。

[Eclipse Paho C](https://www.eclipse.org/paho/index.php?page=clients/c/index.php) 与 Eclipse Paho
Embedded C 均为 Eclipse Paho 项目下的 C 语言客户端库（MQTT C Client），均为使用 ANSI C 编写的功能齐全的 MQTT 客户端。


前提条件
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

安装依赖包
------------------

.. code-block:: bash
   :linenos:

   sudo apt-get update
   sudo apt-get -y install build-essential git cmake openssl libssl-dev


编译 Paho MQTT 库
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Linux/Mac
------------------

.. code-block:: bash
   :linenos:

   git clone https://github.com/eclipse/paho.mqtt.c.git
   cd paho.mqtt.c
   make
   sudo make install


Windows
------------------

.. code-block:: bash
   :linenos:
   
   mkdir build.paho
   cd build.paho
   call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64
   cmake -G "NMake Makefiles" -DPAHO_WITH_SSL=TRUE -DPAHO_BUILD_DOCUMENTATION=FALSE -DPAHO_BUILD_SAMPLES=TRUE -DCMAKE_BUILD_TYPE=Release -DCMAKE_VERBOSE_MAKEFILE=TRUE ..
   nmake


连接使用
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
连接设置
------------------

本文将使用自定义的接入认证方式，服务器接入信息如下：

- Broker: **mqtt.geek-smart.cn**
- TCP Port: **1883**
- WebSocket Port: **8083**

导入依赖包
------------------
.. code-block:: c
   :linenos:

   #include "stdlib.h"
   #include "string.h"
   #include "unistd.h"
   #include "MQTTClient.h"


定义连接地址、认证信息以及消息发布主题
------------------
.. code-block:: c
   :linenos:

   #define ADDRESS     "tcp://mqtt.geek-smart.cn:1883"
   #define USERNAME    "************"  // 用户名
   #define PASSWORD    "************"  // 密码
   #define CLIENTID    "c-client"
   #define QOS         0
   #define SUB_TOPIC       "/HYUGHV/lVtAcHuor***/4cebd60bf***/subscribe" // 订阅主题
   #define PUB_TOPIC       "/HYUGHV/lVtAcHuor***/4cebd60bf***/publish"   // 发布主题
   #define TIMEOUT     10000L


定义消息发布函数
------------------
.. code-block:: c
   :linenos:

   void publish(MQTTClient client, char *topic, char *payload) {
       MQTTClient_message message = MQTTClient_message_initializer;
       message.payload = payload;
       message.payloadlen = strlen(payload);
       message.qos = QOS;
       message.retained = 0;
       MQTTClient_deliveryToken token;
       MQTTClient_publishMessage(client, topic, &message, &token);
       MQTTClient_waitForCompletion(client, token, TIMEOUT);
       printf("Send `%s` to topic `%s` \n", payload, PUB_TOPIC);
   }


定义 on_message 回调函数，用于打印订阅主题接收的消息内容
------------------------------------------------------------------------
.. code-block:: c
   :linenos:

   int on_message(void *context, char *topicName, int topicLen, MQTTClient_message *message) {
       char *payload = message->payload;
       printf("Received `%s` from `%s` topic \n", payload, topicName);
       MQTTClient_freeMessage(&message);
       MQTTClient_free(topicName);
       return 1;
   }


初始化 MQTT 客户端并订阅主题
------------------------------------------------------------------------
.. code-block:: c
   :linenos:

   int rc;
   MQTTClient client;

   MQTTClient_create(&client, ADDRESS, CLIENTID, 0, NULL);
   MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
   conn_opts.username = USERNAME;
   conn_opts.password = PASSWORD;
   MQTTClient_setCallbacks(client, NULL, NULL, on_message, NULL);
   if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
       printf("Failed to connect, return code %d\n", rc);
       exit(-1);
   } else {
       printf("Connected to MQTT Broker!\n");
   }
   // subscribe topic
   MQTTClient_subscribe(client, SUB_TOPIC, QOS);


循环调用 `publish` 函数，完成消息发布
------------------------------------------------------------------------
.. code-block:: c
   :linenos:

   char payload[64];
   for (int i = 0; i < 100; i += 1) {
       // 获取设备基本信息 每隔两秒获取一次
       snprintf(payload, 64, "\{\"type\":\"info\"\}");
       publish(client, PUB_TOPIC, payload);
       sleep(2);
   }


完整代码
------------------------------------------------------------------------
.. code-block:: c
   :linenos:

   #include "stdlib.h"
   #include "string.h"
   #include "unistd.h"
   #include "MQTTClient.h"

   #define ADDRESS     "tcp://mqtt.geek-smart.cn:1883"
   #define USERNAME    "************"  // username
   #define PASSWORD    "************" // password
   #define CLIENTID    "c-client"
   #define QOS         0
   #define SUB_TOPIC       "/HYUGHV/lVtAcHuor***/4cebd60bf***/subscribe" // subscribe
   #define PUB_TOPIC       "/HYUGHV/lVtAcHuor***/4cebd60bf***/publish"   // publish
   #define TIMEOUT     10000L


   void publish(MQTTClient client, char *topic, char *payload) {
       MQTTClient_message message = MQTTClient_message_initializer;
       message.payload = payload;
       message.payloadlen = strlen(payload);
       message.qos = QOS;
       message.retained = 0;
       MQTTClient_deliveryToken token;
       MQTTClient_publishMessage(client, topic, &message, &token);
       MQTTClient_waitForCompletion(client, token, TIMEOUT);
       printf("Send `%s` to topic `%s` \n", payload, PUB_TOPIC);
   }

   int on_message(void *context, char *topicName, int topicLen, MQTTClient_message *message) {
       char *payload = message->payload;
       printf("Received `%s` from `%s` topic \n", payload, topicName);
       MQTTClient_freeMessage(&message);
       MQTTClient_free(topicName);
       return 1;
   }

   int main(int argc, char *argv[]) {
       int rc;
       MQTTClient client;

       MQTTClient_create(&client, ADDRESS, CLIENTID, 0, NULL);
       MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
       conn_opts.username = USERNAME;
       conn_opts.password = PASSWORD;
       MQTTClient_setCallbacks(client, NULL, NULL, on_message, NULL);
       if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
           printf("Failed to connect, return code %d\n", rc);
           exit(-1);
       } else {
           printf("Connected to MQTT Broker!\n");
       }
       // 订阅获取到的内容
       MQTTClient_subscribe(client, SUB_TOPIC, QOS);
       char payload[64];
       for (int i = 0; i < 100; i += 1) {
           // 获取设备基本信息 每隔两秒获取一次
           snprintf(payload, 64, "\{\"type\":\"info\"\}");
           publish(client, PUB_TOPIC, payload);
           sleep(2);
       }
       MQTTClient_disconnect(client, TIMEOUT);
       MQTTClient_destroy(&client);
       return rc;
   }


测试验证
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
编写 CMakeLists.txt
------------------------------------------------------------------------
.. code-block:: cmake
   :linenos:

   cmake_minimum_required(VERSION 3.17)
   project(mqtt_c C)
   include_directories(/usr/local/include)
   link_directories(/usr/local/lib)
   set(CMAKE_C_STANDARD 99)
   add_executable(mqtt_c main.c)
   target_link_libraries(mqtt_c paho-mqtt3c)
   
编译
------------------------------------------------------------------------
.. code-block:: bash
   :linenos:

   cmake .
   make

运行
------------------------------------------------------------------------
.. code-block:: bash
   :linenos:

   ./mqtt_c