利用EMQX建立MQTT服务器通讯

使用EMQX搭建MQTT服务，可参考另一个博客https://editor.csdn.net/md/?articleId=121849144
一、建立连接

	MQTTPacket_connectData condata = MQTTPacket_connectData_initializer;
    client.isconnected = 0;
    client.uri = flash_db_syscfg_ptr()->mqtt_uri;
    
    static char cid[20] = { 0 };

    /* generate the random client ID */
    rt_snprintf(cid, sizeof(cid), "FRYER_%s", sys_info_ptr()->dev_str);
    /* config connect param */
    memcpy(&client.condata, &condata, sizeof(condata));
    client.condata.clientID.cstring = cid;
    client.condata.keepAliveInterval = 30;
    client.condata.cleansession = 1;
    client.condata.username.cstring = MQTT_USERNAME;
    client.condata.password.cstring = MQTT_PASSWORD;

    /* config MQTT will param. */
    static char will_pubtopic[MQTT_TOPIC_LEN]={0};
    rt_snprintf(will_pubtopic,MQTT_TOPIC_LEN,MQTT_PUBTOPIC,sys_info_ptr()->dev_str,"will");
    client.condata.willFlag = 1;
    client.condata.will.qos = 1;
    client.condata.will.retained = 0;
    client.condata.will.topicName.cstring = will_pubtopic;
    client.condata.will.message.cstring = MQTT_WILLMSG;

    /* malloc buffer. */
    client.buf_size = client.readbuf_size = 1024;
    client.buf = rt_calloc(1, client.buf_size);
    client.readbuf = rt_calloc(1, client.readbuf_size);
    if (!(client.buf && client.readbuf))
    {
        LOG_E("no memory for MQTT client buffer!");
    }

    /* set event callback function */
    client.connect_callback = mqtt_connect_callback;
    client.online_callback = mqtt_online_callback;
    client.offline_callback = mqtt_offline_callback;

    /* set subscribe table and event callback */
    static char subtopic[MQTT_TOPIC_LEN]={0};
    rt_snprintf(subtopic,MQTT_TOPIC_LEN,MQTT_SUBTOPIC,sys_info_ptr()->dev_str,"ctrl");
    client.messageHandlers[0].topicFilter = subtopic;
    client.messageHandlers[0].callback = mqtt_sub_callback;
    client.messageHandlers[0].qos = QOS1;

    /* set default subscribe event callback */
    client.defaultMessageHandler = mqtt_sub_default_callback;
    
    //断开连接后重连时间
    client.reconnect_interval = 60000;
    //连接超时时间
    client.connect_timeout = 10000;

    /* run mqtt client */
    paho_mqtt_start(&client);
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    client.connect_callback = mqtt_connect_callback;
    client.online_callback = mqtt_online_callback;
    client.offline_callback = mqtt_offline_callback;
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连接、在线、离线回调函数配置

client.messageHandlers[0].callback = mqtt_sub_callback;
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订阅消息回调函数配置

二、消息处理函数

client_cmd_t    client_cmd[]={
    "run",  cmd_run,
    "pid",  cmd_pid,
    "para", cmd_para,
    "menu", cmd_menu,
};

static void mqtt_sub_callback(MQTTClient *c, MessageData *msg_data)
{
    *((char *)msg_data->message->payload + msg_data->message->payloadlen) = '\0';
//    LOG_D("mqtt sub callback: %.*s %.*s",
//               msg_data->topicName->lenstring.len,
//               msg_data->topicName->lenstring.data,
//               msg_data->message->payloadlen,
//               (char *)msg_data->message->payload);
    
    cJSON * root = NULL;
    cJSON * item = NULL;//cjson对象
    
    root = cJSON_Parse(msg_data->message->payload);   
    if (root) 
    {
        item = cJSON_GetObjectItem(root, "cmd");
        if( item ){
            for( uint8_t i=0; ivaluestring,client_cmd[i].cmd) ){
                    LOG_D("receive the %s command",client_cmd[i].cmd);
                    client_cmd[i].cmd_func(root);
                    break;
                }
            }
        }
        cJSON_Delete(root);
    }
    else{
        LOG_D("can not parse the mqtt message payload");
    }
}
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if( rt_strstr(item->valuestring,client_cmd[i].cmd) ){
	LOG_D("receive the %s command",client_cmd[i].cmd);
	client_cmd[i].cmd_func(root);
	break;
}

client_cmd_t    client_cmd[]={
    "run",  cmd_run,
    "pid",  cmd_pid,
    "para", cmd_para,
    "menu", cmd_menu,
};
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利用消息数据结构处理不同分支消息，rt_strstr比较下发topic中是否带有run、pid、para、menu等的字符串进行函数跳转

三、消息发送

void client_send_msg(char *fryer)
{

    if( sys_info_ptr()->net_connect == NET_SERVER ){
        char *cjson_str = NULL;
        cJSON * root =  cJSON_CreateObject();
        cJSON * slot =  cJSON_CreateObject();
        
        cJSON_AddItemToObject(root, "voltage",      cJSON_CreateNumber(sys_info_ptr()->voltage));
        cJSON_AddItemToObject(root, "current",      cJSON_CreateNumber(sys_info_ptr()->current));
        cJSON_AddItemToObject(root, "temperature",  cJSON_CreateNumber(sys_info_ptr()->temp));
        cJSON_AddItemToObject(root, "slot",         cJSON_CreateString(fryer));
        cJSON_AddItemToObject(root, "work",         slot);
        
        cJSON_AddItemToObject(slot, "curr_temp",    cJSON_CreateNumber((((fryer_state_t*)fryer_get_handle(fryer))->temp)));
        cJSON_AddItemToObject(slot, "target_temp",  cJSON_CreateNumber((((fryer_state_t*)fryer_get_handle(fryer))->target_temp)));
        cJSON_AddItemToObject(slot, "mode",         cJSON_CreateNumber((int)(((fryer_state_t*)fryer_get_handle(fryer))->mlcd_status->cooking_mode)));
        cJSON_AddItemToObject(slot, "menu",         cJSON_CreateNumber((int)(((fryer_state_t*)fryer_get_handle(fryer))->mlcd_ctrl->menu_sel)));
        cJSON_AddItemToObject(slot, "run",          cJSON_CreateNumber((int)(((fryer_state_t*)fryer_get_handle(fryer))->mlcd_ctrl->cooking_run)));
        cJSON_AddItemToObject(slot, "seg",          cJSON_CreateNumber((int)(((fryer_state_t*)fryer_get_handle(fryer))->mlcd_status->cooking_seg)));
        cJSON_AddItemToObject(slot, "P",            cJSON_CreateNumber((((fryer_state_t*)fryer_get_handle(fryer))->pid.uKP_Coe)));
        cJSON_AddItemToObject(slot, "I",            cJSON_CreateNumber((((fryer_state_t*)fryer_get_handle(fryer))->pid.uKI_Coe)));
        cJSON_AddItemToObject(slot, "D",            cJSON_CreateNumber((((fryer_state_t*)fryer_get_handle(fryer))->pid.uKD_Coe)));

        cjson_str = cJSON_Print(root);
    //    LOG_D("json:\n%s\n", cjson_str);
        
        client_publish("work",cjson_str);
        
        free(cjson_str);
        cJSON_Delete(root);
    }
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使用JSON结构组织成上传数据，最后需要使用cJSON_Delete删除的动态生成JSON结构，不然发生内存泄露。

四、topic说明

#define MQTT_SUBTOPIC           "sub/%s/%s"
#define MQTT_PUBTOPIC           "pub/%s/%s"
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sub为订阅topic，pub为发布topic，第一个%s为设备ID，可利用通配符过滤只接收指定ID的消息避免资源浪费，第二个%s为命令字符串，即控制设备或请求设备数据命令