MQTT協議C語言實現的模塊化設計

MQTT（Message Queuing Telemetry Transport）是一種輕量級的發布/訂閱消息傳輸協議，廣泛應用于物聯網場景。在C語言中實現MQTT協議的模塊化設計，可以提高代碼的可讀性、可維護性和可擴展性。以下是一個簡單的模塊化設計示例：

1. 首先，創建一個MQTT客戶端的結構體，用于存儲客戶端的相關信息和狀態：

typedef struct {
    MQTTClient client;
    char *broker_address;
    int broker_port;
    char *client_id;
    char *username;
    char *password;
    MQTTMessage *message;
    int message_count;
} MQTTClientModule;

2. 然后，實現一個初始化函數，用于創建并配置MQTT客戶端實例：

int mqtt_client_init(MQTTClientModule *module, const char *broker_address, int broker_port, const char *client_id, const char *username, const char *password) {
    module->client = mqtt_client_new(client_id, broker_address, broker_port, username, password);
    if (!module->client) {
        return -1;
    }
    module->broker_address = strdup(broker_address);
    module->broker_port = broker_port;
    module->client_id = strdup(client_id);
    module->username = strdup(username);
    module->password = strdup(password);
    module->message_count = 0;
    return 0;
}

3. 接下來，實現一個連接函數，用于連接到MQTT代理：

int mqtt_client_connect(MQTTClientModule *module) {
    if (mqtt_client_connect_async(module->client, NULL, NULL) != MQTTCLIENT_SUCCESS) {
        return -1;
    }
    while (mqtt_client_is_connected(module->client) == MQTTCLIENT_DISCONNECTED) {
        usleep(10000);
    }
    return 0;
}

4. 實現一個發布消息函數，用于向MQTT代理發送消息：

int mqtt_client_publish(MQTTClientModule *module, const char *topic, const char *payload, int payload_len) {
    MQTTMessage message;
    memset(&message, 0, sizeof(message));
    message.topic = strdup(topic);
    message.payload = (unsigned char *)malloc(payload_len + 1);
    memcpy(message.payload, payload, payload_len);
    message.payload[payload_len] = '\0';
    message.payload_len = payload_len;

    int result = mqtt_client_publish_message(module->client, &message);
    if (result != MQTTCLIENT_SUCCESS) {
        return -1;
    }
    module->message_count++;
    return 0;
}

5. 最后，實現一個解耦函數，用于處理MQTT客戶端的關閉和清理工作：

void mqtt_client_destroy(MQTTClientModule *module) {
    if (module->client) {
        mqtt_client_disconnect(module->client);
        mqtt_client_free(module->client);
    }
    if (module->broker_address) {
        free(module->broker_address);
    }
    if (module->client_id) {
        free(module->client_id);
    }
    if (module->username) {
        free(module->username);
    }
    if (module->password) {
        free(module->password);
    }
    if (module->message) {
        for (int i = 0; i < module->message_count; i++) {
            MQTTMessage *msg = &module->message[i];
            if (msg->topic) {
                free(msg->topic);
            }
            if (msg->payload) {
                free(msg->payload);
            }
        }
        free(module->message);
    }
}

通過以上模塊化設計，可以將MQTT協議的實現分為不同的函數和結構體，便于后續的功能擴展和維護。