使用Mosquitto实现MQTT客户端C语言

谷谷小师妹

使用Mosquitto实现MQTT客户端C语言

  上一篇文章已经将mosquitto移植到了arm平台上，现在将使用mosquitto完成mqtt客服端的demo，了解过mqtt协议的小伙伴都知道，mqtt主要分为代理服务器、发布者、订阅者三部分。接下来通过mqtt发布者和订阅者两个demo了解mosquitto库函数的使用。

一、Mosquitto库函数的API

mosquitto的api说明文档：https://mosquitto.org/api/files/mosquitto-h.html
mosquitto库中常见的函数应用总结：https://blog.csdn.net/makunIT/article/details/107283260
上面这位博主总结的比较好，我就在这里引用一下，需要的小伙伴可以看看。

二、mqtt发布者源码

mqtt_pub_demo.c

1. #include <stdio.h>
   
2. #include <stdlib.h>
   
3. #include <mosquitto.h>
   
4. #include <string.h>
   
5. 
   
6. #define HOST "192.168.2.99"
   
7. #define PORT  1883
   
8. #define KEEP_ALIVE 60
   
9. #define MSG_MAX_SIZE  512
   
10. 
    
11. bool session = true;
    
12. 
    
13. int main(void)
    
14. {
    
15. 
    
16.     int err = 0;
    
17. 
    
18.     printf("mqtt publish init...\n");
    
19.     struct mosquitto *mosq = NULL;
    
20.     char buff[MSG_MAX_SIZE];
    
21. 
    
22.     //libmosquitto 库初始化
    
23.     err = mosquitto_lib_init();
    
24.     if (err < 0){
    
25.         printf("mosquitto lib int fail...");
    
26.         goto fail_mosquitto_lib;
    
27.     }
    
28. 
    
29.     //创建mosquitto客户端
    
30.     mosq = mosquitto_new(NULL,session,NULL);
    
31.     if (mosq == NULL){
    
32.         printf("create client failed...\n");
    
33.         err = -1;
    
34.         goto fail_mosquitto_new;
    
35.     }
    
36. 
    
37.     //客户端连接服务器
    
38.     err = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE);
    
39.     if (err < 0){
    
40.         printf("connect fail");   
    
41.         goto fail_mosq_conn;
    
42.     }
    
43. 
    
44.     //不阻塞，库函数中将自动创建线程实现
    
45.     err = mosquitto_loop_start(mosq);
    
46.     if(err != MOSQ_ERR_SUCCESS){
    
47.         printf("mosquitto loop error\n");
    
48.         goto fail_mosq_loop_start;
    
49.     }
    
50. 
    
51.     while(fgets(buff, MSG_MAX_SIZE, stdin) != NULL)
    
52.     {
    
53.         mosquitto_publish(mosq, NULL, "temp", strlen(buff)+1, buff, 0, 0);
    
54.         memset(buff, 0, sizeof(buff));
    
55.     }
    
56. 
    
57.     mosquitto_disconnect(mosq);
    
58.     mosquitto_loop_stop(mosq, true);
    
59.     mosquitto_destroy(mosq);
    
60.     mosquitto_lib_cleanup();
    
61. 
    
62.     return 0;
    
63. fail_mosq_loop_start:
    
64.     mosquitto_disconnect(mosq);
    
65. fail_mosq_conn:
    
66.     mosquitto_destroy(mosq);
    
67. fail_mosquitto_new:
    
68.     mosquitto_lib_cleanup();
    
69. fail_mosquitto_lib:
    
70.     return err;
    
71. }

复制代码

Makefile

1. INCLUDES = -lmosquitto -lpthread -ldl -lssl -lcrypto  \
   
2. -I/home/linux/arm-lib/mosquitto/include \
   
3. -L/home/linux/arm-lib/mosquitto/lib \
   
4. -L/homelinux/arm-lib/openssl/lib
   
5. 
   
6. SOURCE = $(wildcard ./*.c)
   
7. 
   
8. OBJ = $(patsubst ./%.c, ./%.0, $(SOURCE))
   
9. 
   
10. #INCLUDES = $(wildcard ./*.h)
    
11. 
    
12. TARGET = mqtt_pub_demo
    
13. CC = arm-linux-gnueabihf-gcc
    
14. 
    
15. $(TARGET):$(OBJ)
    
16.     $(CC) $(OBJ) -o $(TARGET) $(INCLUDES)
    
17. 
    
18. %.0:%.c
    
19.     $(CC) -c [        DISCUZ_CODE_15        ]lt; -o $[url=home.php?mod=space&uid=19945]@[/url] $(INCLUDES)
    
20. 
    
21. clean:
    
22.     rm -rf $(OBJ) $(TARGET)

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三、mqtt订阅者源码

mqtt_sub_demo.c

1. #include <stdio.h>
   
2. #include <stdlib.h>
   
3. #include <mosquitto.h>
   
4. #include <string.h>
   
5. 
   
6. #define HOST "192.168.2.99"
   
7. #define PORT  1883
   
8. #define KEEP_ALIVE 60
   
9. 
   
10. bool session = true;
    
11. 
    
12. void mqtt_subscribe_callback(struct mosquitto *mosq,
    
13.                 void *userdata, int mid, int qos_count, const int *granted_qos)
    
14. {
    
15.     int i;
    
16.     printf("subscribed (mid: %d): %d", mid, granted_qos[0]);
    
17.     for(i=1; i < qos_count; i++){
    
18.         printf(", %d", granted_qos[i]);
    
19.     }
    
20.     printf("\n");
    
21. }
    
22. 
    
23. //消息回调函数，收到订阅的消息后调用
    
24. void mqtt_message_callback(struct mosquitto *mosq, void *userdata, const struct mosquitto_message *message)
    
25. {
    
26.     if (message->payloadlen){
    
27.         printf("%s %s \n", message->topic, (char *)message->payload);
    
28.     }else{
    
29.         printf("%s (null)\n",message->topic);
    
30.     }
    
31. }
    
32. 
    
33. //mqtt连接回调
    
34. void mqtt_connect_callback(struct mosquitto *mosq, void *userdata, int result)
    
35. {
    
36.     int ret;
    
37.     if (!result){
    
38.         ret = mosquitto_subscribe(mosq, NULL, "temp", 2);
    
39.         if(ret < 0){
    
40.             printf("Subscription failed\n");
    
41.         }else{
    
42.             printf("Subscription succeeded\n");
    
43.         }
    
44.     }else{
    
45.         printf("connect failed\n");
    
46.     }
    
47. }
    
48. 
    
49. //日志回调函数
    
50. void mqtt_log_callback(struct mosquitto *mosq, void *userdata, int level, const char *str)
    
51. {
    
52.     printf("log__   %s\n", str);   
    
53. }
    
54. 
    
55. int main(void)
    
56. {
    
57. 
    
58.     int err = 0;
    
59.     printf("mqtt client init...\n");
    
60. 
    
61.     struct mosquitto *mosq = NULL;
    
62. 
    
63.     //libmosquitto 库初始化
    
64.     err = mosquitto_lib_init();
    
65.     if (err < 0){
    
66.         printf("mosquitto lib int fail...");
    
67.         goto fail_mosquitto_lib;
    
68.     }
    
69. 
    
70.     //创建mosquitto客户端
    
71.     mosq = mosquitto_new(NULL,session,NULL);
    
72.     if (mosq == NULL){
    
73.         printf("create client failed...\n");
    
74.         err = -1;
    
75.         goto fail_mosquitto_new;
    
76.     }
    
77. 
    
78.     //设置回调函数
    
79.     mosquitto_log_callback_set(mosq, mqtt_log_callback);
    
80.     mosquitto_connect_callback_set(mosq, mqtt_connect_callback);
    
81.     mosquitto_message_callback_set(mosq, mqtt_message_callback);
    
82.     mosquitto_subscribe_callback_set(mosq, mqtt_subscribe_callback);
    
83. 
    
84.     //客户端连接服务器
    
85.     err = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE);
    
86.     if (err < 0){
    
87.         printf("connect fail");   
    
88.         goto fail_mosq_conn;
    
89.     }
    
90.    
    
91.     //主线成将被阻塞至此
    
92.     err = mosquitto_loop_forever(mosq, -1, 1);
    
93.     if (err < 0){
    
94.         printf("mosquitto loop fail");
    
95.         goto fail_mosq_loop_stop;
    
96.     }
    
97. 
    
98.     mosquitto_disconnect(mosq);
    
99.     mosquitto_loop_stop(mosq, false);
    
100.     mosquitto_destroy(mosq);
     
101.     mosquitto_lib_cleanup();
     
102. 
     
103.     return 0;
     
104. 
     
105. fail_mosq_loop_stop:
     
106.     mosquitto_disconnect(mosq);
     
107. fail_mosq_conn:
     
108.     mosquitto_destroy(mosq);
     
109. fail_mosquitto_new:
     
110.     mosquitto_lib_cleanup();
     
111. fail_mosquitto_lib:
     
112.     return err;
     
113. }

复制代码

Makefile

1. INCLUDES = -lmosquitto -lpthread -ldl -lssl -lcrypto  \
   
2. -I/home/xfg/linux/arm-lib/mosquitto/include \
   
3. -L/home/xfg/linux/arm-lib/mosquitto/lib \
   
4. -L/home/xfg/linux/arm-lib/openssl/lib
   
5. 
   
6. SOURCE = mqtt_sub_demo.c
   
7. 
   
8. TARGET = mqtt_sub_demo
   
9. CC = arm-linux-gnueabihf-gcc
   
10. 
    
11. $(TARGET):$(SOURCE)
    
12.     $(CC) $(SOURCE) -o $(TARGET) $(INCLUDES)
    
13. 
    
14. clean:
    
15.     rm -rf $(TARGET)
    

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四、测试

• 在虚拟机上打开代理服务器，并将编译生成的mqtt_sub_demo和mqtt_pub_demo移动到ARM开发版上
  
• 打开mqqt订阅者
  
• 打开mqtt发布者，发布信息
  
  完成后，可以看订阅者接受的信息是否正确
  
  由此可以看出编写的测试程序没问题。
  

五、参考文献

mosquitto库中常见的函数应用总结：https://blog.csdn.net/makunIT/article/details/107283260
基于MQTT协议的Mosquitto的使用及libmosquitto客户端编程:https://blog.csdn.net/danwuxie/article/details/86517568
基于mosquitto的MQTT客户端实现C语言:https://www.cnblogs.com/y-c-y/p/11686916.html
Qt官方MQTT库的使用，附一个MqttClient例子:https://www.cnblogs.com/yexiaopeng/p/8542894.html
mosquitto的api说明文档：https://mosquitto.org/api/files/mosquitto-h.html