C language implements mosquitto publish and subscribe messages
1. Install mosquitto
1.1, compile and install
- Installation dependencies
sudo apt-get install libssl-dev
sudo apt-get install uuid-dev
sudo apt-get install cmake
- Download resource package
Download link: https://mosquitto.org/download/
wget https://mosquitto.org/files/source/mosquitto-1.6.12.tar.gz
- Unzip
tar -zxvf mosquitto-1.6.12.tar.gz
- Enter the source directory
cd mosquitto-1.6.12/
- Compile and install
make
sudo make install
- Linking
When we are using mosquitto, the library asks us to link it ourselves.
$(CC) mqtt_sub.c -I ./mosq/mosquitto-1.6.12/lib -L ./mosq/mosquitto-1.6.12/lib -lmosquitto
1.2, direct installation
- Install the server side
sudo apt-get install mosquitto
- Install the client
sudo apt install mosquitto-clients
2. Release
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include "mosquitto.h"
#define HOST "xxxxxx"
#define PORT 1883
#define KEEP_ALIVE 60
#define MSG_MAX_SIZE 512
static int running = 1;
void my_connect_callback(struct mosquitto *mosq, void *obj, int rc)
{
printf("Call the function: my_connect_callback\n");
}
void my_disconnect_callback(struct mosquitto *mosq, void *obj, int rc)
{
printf("Call the function: my_disconnect_callback\n");
running = 0;
}
void my_publish_callback(struct mosquitto *mosq, void *obj, int mid)
{
printf("Call the function: my_publish_callback\n");
}
int main()
{
int ret;
struct mosquitto *mosq;
char buff[MSG_MAX_SIZE];
//初始化libmosquitto库
ret = mosquitto_lib_init();
if(ret){
printf("Init lib error!\n");
return -1;
}
//创建一个发布端实例
mosq = mosquitto_new("pub_test", true, NULL);
if(mosq == NULL){
printf("New pub_test error!\n");
mosquitto_lib_cleanup();
return -1;
}
//设置回调函数
mosquitto_connect_callback_set(mosq, my_connect_callback);
mosquitto_disconnect_callback_set(mosq, my_disconnect_callback);
mosquitto_publish_callback_set(mosq, my_publish_callback);
// 连接至服务器
// 参数：句柄、ip（host）、端口、心跳
ret = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE);
if(ret){
printf("Connect server error!\n");
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();
return -1;
}
printf("Start!\n");
//mosquitto_loop_start作用是开启一个线程，在线程里不停的调用 mosquitto_loop() 来处理网络信息
int loop = mosquitto_loop_start(mosq);
if(loop != MOSQ_ERR_SUCCESS)
{
printf("mosquitto loop error\n");
return 1;
}
while(fgets(buff, MSG_MAX_SIZE, stdin) != NULL)
{
/*发布消息*/
mosquitto_publish(mosq,NULL,"test",strlen(buff)+1,buff,0,0);
memset(buff,0,sizeof(buff));
}
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();
printf("End!\n");
return 0;
}
3. Subscription
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "mosquitto.h"
#define HOST "xxxxxxx"
#define PORT 1883
#define KEEP_ALIVE 60
#define MSG_MAX_SIZE 512
// 定义运行标志决定是否需要结束
static int running = 1;
void my_connect_callback(struct mosquitto *mosq, void *obj, int rc)
{
printf("Call the function: on_connect\n");
if(rc){
// 连接错误，退出程序
printf("on_connect error!\n");
exit(1);
}else{
// 订阅主题
// 参数：句柄、id、订阅的主题、qos
if(mosquitto_subscribe(mosq, NULL, "test", 2)){
printf("Set the topic error!\n");
exit(1);
}
}
}
void my_disconnect_callback(struct mosquitto *mosq, void *obj, int rc)
{
printf("Call the function: my_disconnect_callback\n");
running = 0;
}
void my_subscribe_callback(struct mosquitto *mosq, void *obj, int mid, int qos_count, const int *granted_qos)
{
printf("Call the function: on_subscribe\n");
}
void my_message_callback(struct mosquitto *mosq, void *obj, const struct mosquitto_message *msg)
{
printf("Call the function: on_message\n");
printf("Recieve a message of %s : %s\n", (char *)msg->topic, (char *)msg->payload);
if(0 == strcmp(msg->payload, "quit")){
mosquitto_disconnect(mosq);
}
}
int main()
{
int ret;
struct mosquitto *mosq;
// 初始化mosquitto库
ret = mosquitto_lib_init();
if(ret){
printf("Init lib error!\n");
return -1;
}
// 创建一个订阅端实例
// 参数：id（不需要则为NULL）、clean_start、用户数据
mosq = mosquitto_new("sub_test", true, NULL);
if(mosq == NULL){
printf("New sub_test error!\n");
mosquitto_lib_cleanup();
return -1;
}
// 设置回调函数
// 参数：句柄、回调函数
mosquitto_connect_callback_set(mosq, my_connect_callback);
mosquitto_disconnect_callback_set(mosq, my_disconnect_callback);
mosquitto_subscribe_callback_set(mosq, my_subscribe_callback);
mosquitto_message_callback_set(mosq, my_message_callback);
// 连接至服务器
// 参数：句柄、ip（host）、端口、心跳
ret = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE);
if(ret){
printf("Connect server error!\n");
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();
return -1;
}
// 开始通信：循环执行、直到运行标志running被改变
printf("Start!\n");
while(running)
{
mosquitto_loop(mosq, -1, 1);
}
// 结束后的清理工作
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();
printf("End!\n");
return 0;
}
Here I will talk about the callback function separately, there are several callback functions, as follows
mosquitto_connect_callback_set(mosq, my_connect_callback);
mosquitto_disconnect_callback_set(mosq, my_disconnect_callback);
mosquitto_subscribe_callback_set(mosq, my_subscribe_callback);
mosquitto_message_callback_set(mosq, my_message_callback);
- mosquitto_subscribe_callback_set()
这个函数叫做【中间函数】或者【登记回调函数】，他的职能是监控事件的发生。
- my_subscribe_callback
相应的这个函数就是回调函数，他是事件发生后实现的方法。
- The execution of the callback function is mainly divided into the following steps:
1、主函数需要调用回调函数
2、中间函数登记回调函数
3、触发回调函数事件
4、调用回调函数
5、响应回调事件
For example, one day you go to a supermarket to buy something, and the thing you want to buy is gone, and then you tell the clerk that the thing you bought has arrived and call you. After a few days, the clerk will call you and then you Go to the supermarket to buy something.
In this example, the clerk is registering 回调函数, the phone number is 回调函数, if the item arrives 触发回调事件, if the clerk calls 调用回调函数you, if you go to pick up the item相应回调事件