LINUX--ubuntu移植MQTT並測試成功

1，MQTT簡介
MQTT 是一個輕量級協議，使用基於 TCP/IP 協議的發佈/訂閱消息轉發模式，在物聯網應用中大規模使用。 MQTT 協議的中心是 broker（ 服務器/代理） ，客戶端通過訂閱消息和發佈消息進行數據交互 ，如下圖所示：

2，Mosquitto安裝
（1）mosquitto下載
https://mosquitto.org/download/
進入下載頁面，選擇source中第一個下載mosquitto-1.5.8tar.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
//創建鏈接
$ sudo ln -s /usr/local/lib/libmosquitto.so.1 /usr/lib/libmosquitto.so.1
//更新鏈接
$ sudo ldconfig
3，mosquitto使用
進入命令行界面
（1）啓動mosquitto服務器
$ mosquitto -v
（2）訂閱消息（如topic）
$ mosquitto_sub -v -t topic
（3）發佈消息
$ mosquitto_pub -t topic -m good

4，libmosquitto客戶端編程（發佈消息，訂閱消息）
在安裝mosquitto成功後，可以在/usr/local/lib文件夾中有libmosquitto.so.1等文件，如下圖所示：

客戶端（訂閱消息）

1. #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();
//創建mosquitto客戶端
mosq = mosquitto_new(NULL,session,NULL);
if(!mosq){
printf(“create client failed…\n”);
mosquitto_lib_cleanup();
return 1;
}
//設置回調函數，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);
//客戶端連接服務器
if(mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE)){
fprintf(stderr, “Unable to connect.\n”);
return 1;
}
//循環處理網絡消息
mosquitto_loop_forever(mosq, -1, 1);

mosquitto_destroy(mosq);
mosquitto_lib_cleanup();

return 0;

}

客戶端（發佈消息）

1. #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();
//創建mosquitto客戶端
mosq = mosquitto_new(NULL,session,NULL);
if(!mosq){
printf(“create client failed…\n”);
mosquitto_lib_cleanup();
return 1;
}
//連接服務器
if(mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE)){
fprintf(stderr, “Unable to connect.\n”);
return 1;
}
//開啓一個線程，在線程裏不停的調用 mosquitto_loop() 來處理網絡信息
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)
{
/發佈消息/
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
在編譯程序時需加上-lmosquitto鏈接。如：

$ gcc -o mosquitto_client_sub mosquitto_client_sub.c -lmosquitto
5,客戶端使用
（1）開啓mosquitto服務
$ mosquitto -v
（2）啓動訂閱消息客戶端及發佈消息客戶端
$ ./mosquitto_client_sub
$ ./mosquitto_client_pub