使用Mosquitto实现MQTT客服端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

#include <stdio.h>#include <stdlib.h>#include <mosquitto.h>#include <string.h>#define HOST \"192.168.2.99\"#define PORT  1883#define KEEP_ALIVE 60#define MSG_MAX_SIZE  512bool session = true;int main(void){int err = 0;printf(\"mqtt publish init...\\n\");struct mosquitto *mosq = NULL;char buff[MSG_MAX_SIZE];//libmosquitto 库初始化err = mosquitto_lib_init();if (err < 0){printf(\"mosquitto lib int fail...\");goto fail_mosquitto_lib;}//创建mosquitto客户端mosq = mosquitto_new(NULL,session,NULL);if (mosq == NULL){printf(\"create client failed...\\n\");err = -1;goto fail_mosquitto_new;}//客户端连接服务器err = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE);if (err < 0){printf(\"connect fail\");goto fail_mosq_conn;}//不阻塞，库函数中将自动创建线程实现err = mosquitto_loop_start(mosq);if(err != MOSQ_ERR_SUCCESS){printf(\"mosquitto loop error\\n\");goto fail_mosq_loop_start;}while(fgets(buff, MSG_MAX_SIZE, stdin) != NULL){mosquitto_publish(mosq, NULL, \"temp\", strlen(buff)+1, buff, 0, 0);memset(buff, 0, sizeof(buff));}mosquitto_disconnect(mosq);mosquitto_loop_stop(mosq, true);mosquitto_destroy(mosq);mosquitto_lib_cleanup();return 0;fail_mosq_loop_start:mosquitto_disconnect(mosq);fail_mosq_conn:mosquitto_destroy(mosq);fail_mosquitto_new:mosquitto_lib_cleanup();fail_mosquitto_lib:return err;}

Makefile

INCLUDES = -lmosquitto -lpthread -ldl -lssl -lcrypto  \\-I/home/linux/arm-lib/mosquitto/include \\-L/home/linux/arm-lib/mosquitto/lib \\-L/homelinux/arm-lib/openssl/libSOURCE = $(wildcard ./*.c)OBJ = $(patsubst ./%.c, ./%.0, $(SOURCE))#INCLUDES = $(wildcard ./*.h)TARGET = mqtt_pub_demoCC = arm-linux-gnueabihf-gcc$(TARGET):$(OBJ)$(CC) $(OBJ) -o $(TARGET) $(INCLUDES)%.0:%.c$(CC) -c $< -o $@ $(INCLUDES)clean:rm -rf $(OBJ) $(TARGET)

三、mqtt订阅者源码

mqtt_sub_demo.c

#include <stdio.h>#include <stdlib.h>#include <mosquitto.h>#include <string.h>#define HOST \"192.168.2.99\"#define PORT  1883#define KEEP_ALIVE 60bool session = true;void mqtt_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]);ad8}printf(\"\\n\");}//消息回调函数，收到订阅的消息后调用void mqtt_message_callback(struct mosquitto *mosq, void *userdata, const struct mosquitto_message *message){if (message->payloadlen){printf(\"%s %s \\n\", message->topic, (char *)message->payload);}else{printf(\"%s (null)\\n\",message->topic);}}//mqtt连接回调void mqtt_connect_callback(struct mosquitto *mosq, void *userdata, int result){int ret;if (!result){ret = mosquitto_subscribe(mosq, NULL, \"temp\", 2);if(ret < 0){printf(\"Subscription failed\\n\");}else{printf(\"Subscription succeeded\\n\");}}else{printf(\"connect failed\\n\");}}//日志回调函数void mqtt_log_callback(struct mosquitto *mosq, void *userdata, int level, const char *str){printf(\"log__   %s\\n\", str);}int main(void){int err = 0;printf(\"mqtt client init...\\n\");struct mosquitto *mosq = NULL;//libmosquitto 库初始化err = mosquitto_lib_init();if (err < 0){printf(\"mosquitto lib int fail...\");goto fail_mosquitto_lib;}//创建mosquitto客户端mosq = mosquitto_new(NULL,session,NULL);if (mosq == NULL){printf(\"create client failed...\\n\");err = -1;goto fail_mosquitto_new;}//设置回调函数mosquitto_log_callback_set(mosq, mqtt_log_callback);mosquitto_connect_callback_set(mosq, mqtt_connect_callback);mosquitto_message_callback_set(mosq, mqtt_message_callback);mosquitto_subscribe_callback_set(mosq, mqtt_subscribe_callback);//客户端连接服务器err = mosquitto_connect(mosq, HOST, PORT, KEEP_ALIVE);if (err < 0){printf(\"connect fail\");goto fail_mosq_conn;}//主线成将被阻塞至此err = mosquitto_loop_forever(mosq, -1, 1);if (err < 0){printf(\"mosquitto loop fail\");goto fail_mosq_loop_stop;}mosquitto_disconnect(mosq);mosquitto_loop_stop(mosq, false);mosquitto_destroy(mosq);mosquitto_lib_cleanup();return 0;fail_mosq_loop_stop:mosquitto_disconnect(mosq);fail_mosq_conn:mosquitto_destroy(mosq);fail_mosquitto_new:mosquitto_lib_cleanup();fail_mosquitto_lib:return err;}

Makefile

INCLUDES = -lmosquitto -lpthread -ldl -lssl -lcrypto  \\-I/home/xfg/linux/arm-lib/mosquitto/include \\-L/home/xfg/linux/arm-lib/mosquitto/lib \\-L/home/xfg/linux/arm-lib/openssl/libSOURCE = mqtt_sub_demo.cTARGET = mqtt_sub_demoCC = arm-linux-gnueabihf-gcc$(TARGET):$(SOURCE)$(CC) $(SOURCE) -o $(TARGET) $(INCLUDES)clean:rm -rf $(TARGET)
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