MQTT协议C语言实现的模块化设计

MQTT（Message Queuing Telemetry Transport）是一种轻量级的发布/订阅消息传输协议，广泛应用于物联网场景。在C语言中实现MQTT协议的模块化设计，可以提高代码的可读性、可维护性和可扩展性。以下是一个简单的模块化设计示例：

1. 首先，创建一个MQTT客户端的结构体，用于存储客户端的相关信息和状态：

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，实现一个初始化函数，用于创建并配置MQTT客户端实例：

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. 接下来，实现一个连接函数，用于连接到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. 实现一个发布消息函数，用于向MQTT代理发送消息：

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，实现一个解耦函数，用于处理MQTT客户端的关闭和清理工作：

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);
    }
}

通过以上模块化设计，可以将MQTT协议的实现分为不同的函数和结构体，便于后续的功能扩展和维护。