基於MQTT協議的Mosquitto的使用及libmosquitto客戶端程式設計
概述:工作之餘學習mqtt,使用開源的Mosquitto實現mqtt的使用。如:broker(伺服器/代理),訊息訂閱及釋出。
系統環境:ubuntu14.04
1,MQTT簡介
MQTT 是一個輕量級協議,使用基於 TCP/IP 協議的釋出/訂閱訊息轉發模式,在物聯網應用中大規模使用。 MQTT 協議的中心是 broker( 伺服器/代理) ,客戶端通過訂閱訊息和釋出訊息進行資料互動 ,如下圖所示:
2,Mosquitto安裝
(1)mosquitto下載
下載地址,進入下載頁面,選擇source中第一個下載mosquitto-1.4.9.tar.gz
(2)mosquitto依賴庫安裝
$ sudo apt-get install libssl-dev
$ sudo apt-get install libc-ares-dev
$ sudo apt-get install uuid-dev
(3)mosquitto的安裝
//解壓
$ tar zxvf mosquitto-1.4.9.tar.gz
$ cd mosquitto-1.4.9
$ make
$ sudo make install
(4)編譯問題解決
如果出現error while loading shared libraries: libmosquitto.so.1: cannot open shared object file: No such file or directory
//建立連結
$ sudo ln -s /usr/local/lib/libmosquitto.so.1 /usr/lib/libmosquitto.so.1
//更新連結
$ sudo ldconfig
3,mosquitto使用
進入命令列介面
(1)啟動mosquitto伺服器
$ mosquitto -v
(2)訂閱訊息(如topic)
$ mosquitto_sub -v -t topic
(3)釋出訊息
$ mosquitto_pub -t topic -m good
效果如下圖所示:
4,libmosquitto客戶端程式設計(釋出訊息,訂閱訊息)
在安裝mosquitto成功後,可以在/usr/local/lib資料夾中有libmosquitto.so.1等檔案,如下圖所示:
這裡貼一個demo
客戶端(訂閱訊息)
#include <stdio.h>
#include <stdlib.h>
#include <mosquitto.h>
#include <string.h>
#define HOST "localhost"
#define PORT 1883
#define KEEP_ALIVE 60
bool session = true;
void my_message_callback(struct mosquitto *mosq, void *userdata, const struct mosquitto_message *message)
{
if(message->payloadlen){
printf("%s %s", message->topic, message->payload);
}else{
printf("%s (null)\n", message->topic);
}
fflush(stdout);
}
void my_connect_callback(struct mosquitto *mosq, void *userdata, int result)
{
int i;
if(!result){
/* Subscribe to broker information topics on successful connect. */
mosquitto_subscribe(mosq, NULL, "Gai爺:", 2);
}else{
fprintf(stderr, "Connect failed\n");
}
}
void my_subscribe_callback(struct mosquitto *mosq, void *userdata, int mid, int qos_count, const int *granted_qos)
{
int i;
printf("Subscribed (mid: %d): %d", mid, granted_qos[0]);
for(i=1; i<qos_count; i++){
printf(", %d", granted_qos[i]);
}
printf("\n");
}
void my_log_callback(struct mosquitto *mosq, void *userdata, int level, const char *str)
{
/* Pring all log messages regardless of level. */
printf("%s\n", str);
}
int main()
{
struct mosquitto *mosq = NULL;
//libmosquitto 庫初始化
mosquitto_lib_init();
//建立mosquitto客戶端
mosq = mosquitto_new(NULL,session,NULL);
if(!mosq){
printf("create client failed..\n");
mosquitto_lib_cleanup();
return 1;
}
//設定回撥函式,需要時可使用
//mosquitto_log_callback_set(mosq, my_log_callback);
mosquitto_connect_callback_set(mosq, my_connect_callback);
mosquitto_message_callback_set(mosq, my_message_callback);
//mosquitto_subscribe_callback_set(mosq, my_subscribe_callback);
//客戶端連線伺服器
if(mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE)){
fprintf(stderr, "Unable to connect.\n");
return 1;
}
//迴圈處理網路訊息
mosquitto_loop_forever(mosq, -1, 1);
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();
return 0;
}
客戶端(釋出訊息)
#include <stdio.h>
#include <stdlib.h>
#include <mosquitto.h>
#include <string.h>
#define HOST "localhost"
#define PORT 1883
#define KEEP_ALIVE 60
#define MSG_MAX_SIZE 512
bool session = true;
int main()
{
char buff[MSG_MAX_SIZE];
struct mosquitto *mosq = NULL;
//libmosquitto 庫初始化
mosquitto_lib_init();
//建立mosquitto客戶端
mosq = mosquitto_new(NULL,session,NULL);
if(!mosq){
printf("create client failed..\n");
mosquitto_lib_cleanup();
return 1;
}
//連線伺服器
if(mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE)){
fprintf(stderr, "Unable to connect.\n");
return 1;
}
//開啟一個執行緒,線上程裡不停的呼叫 mosquitto_loop() 來處理網路資訊
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)
{
/*釋出訊息*/
mosquitto_publish(mosq,NULL,"Gai爺:",strlen(buff)+1,buff,0,0);
memset(buff,0,sizeof(buff));
}
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();
return 0;
}
注意
在編譯程式時需加上-lmosquitto連結。如:
$ gcc -o mosquitto_client_sub mosquitto_client_sub.c -lmosquitto
5,客戶端使用
(1)開啟mosquitto服務
$ mosquitto -v
(2)啟動訂閱訊息客戶端及釋出訊息客戶端
$ ./mosquitto_client_sub
$ ./mosquitto_client_pub
(3)效果
參考資料:
如果想詳細瞭解mqtt中libmosquitto的使用可以看一下這篇文章。