c++ - Libmosquitto 发布不会将所有消息传递到 Azure IoT 中心

Question

我尝试每秒向 Azure Iot Hub 内置事件中心发布超过 100 条消息。我正在使用 libmosquitto 1.6.8 库。我正在使用 Azure Iot Hub 的免费套餐，我知道每秒有 100 条消息的限制。但这与该问题无关。我什至无法将一半的消息发布到 AZ Iot Hub。

基本上，我在 multimap 中有一个需要发送的多个值的列表。指标列表:

std::multimap< const std::string, std::tuple< const std::string, const std::string, float> > calculatedMetricList;

我将迭代多重映射并将每个值构建到对象有效负载中并将其发送。这意味着 mosquitto_publish 方法将被多次调用。

以下是发布消息的代码:

void MosquittoClient::sendDataToUpstreamSystem(){

StatisticalMethod statisticalMethod;
int rc;

MosquittoClient pub_mosq(
    "<IoT Hub Name>.azure-devices.net",
    "<deviceID>", 
    "<username>", 
    "<Password>", 
    "devices/<deviceID>/messages/events/");

printf("Using MQTT to get data payload from host: %s and on port: %d.\r\n", pub_mosq.get_host(), pub_mosq.get_port());
// init the mosquitto lib
mosquitto_lib_init();

// create the mosquito object
struct mosquitto* mosq = mosquitto_new(pub_mosq.get_deviceID(), false, NULL);

// add callback functions
mosquitto_connect_callback_set(mosq, MosquittoClient::connect_callback);
mosquitto_publish_callback_set(mosq, MosquittoClient::publish_callback);
mosquitto_message_callback_set(mosq, MosquittoClient::on_message);
mosquitto_disconnect_callback_set(mosq, MosquittoClient::on_disconnect_callback);

// set mosquitto username, password and options
mosquitto_username_pw_set(mosq, pub_mosq.get_userName(), pub_mosq.get_password());

// specify the certificate to use
std::ifstream infile(pub_mosq.get_certificate());
bool certExists = infile.good();
infile.close();

if (!certExists)
{
    printf("Warning: Could not find file '%s'! The mosquitto loop may fail.\r\n", pub_mosq.get_certificate());
}

printf("Using certificate: %s\r\n", pub_mosq.get_certificate());
mosquitto_tls_set(mosq, pub_mosq.get_certificate(), NULL, NULL, NULL, NULL);

// specify the mqtt version to use
int* option = new int(MQTT_PROTOCOL_V311);
rc = mosquitto_opts_set(mosq, MOSQ_OPT_PROTOCOL_VERSION, option);
if (rc != MOSQ_ERR_SUCCESS)
{
    rc = pub_mosq.mosquitto_error(rc, "Error: opts_set protocol version");
}
else
{
    printf("Setting up options OK\r\n");
}

// connect
printf("Connecting...\r\n");
rc = mosquitto_connect_async(mosq, pub_mosq.get_host(), pub_mosq.get_port(), 4);
if (rc != MOSQ_ERR_SUCCESS)
{
    rc = pub_mosq.mosquitto_error(rc, NULL);
}
else
{
    printf("Connect returned OK\r\n");

    rc = mosquitto_loop_start(mosq);

    if (rc != MOSQ_ERR_SUCCESS)
    {
        rc = pub_mosq.mosquitto_error(rc, NULL);
    }
    else
    {
        do
        {
            for (auto itr = Metrics::calculatedMetricList.begin(); itr != Metrics::calculatedMetricList.end(); itr++) { 
                int msgId = rand();

                std::string test1= itr->first;
                std::string test2 = std::get<0>(itr->second);
                std::string test3= std::get<1>(itr->second); // metric type 
                float value = std::get<2>(itr->second); // value

                DataPayload objectPayload(
                    75162345,
                    496523,
                    test3,
                    value,
                    "test",
                    test1,
                    "test",
                    "test",
                    123,
                    213,
                    23
                );

                objectPayload.setPayload();
                std::string dataPayload = objectPayload.getPayload();

                //DEBUG
                std::cout << "dataPayload: " << dataPayload << std::endl;
                //DEBUG
                std::cout << "dataPayload Size: " << dataPayload.size() << std::endl;

                // once connected, we can publish (send) a Telemetry message
                printf("Publishing to topic: %s\r\n", pub_mosq.get_topic());

                rc = pub_mosq.publishToTopic(mosq, &msgId, dataPayload.size(), (char *)dataPayload.c_str());

                if (rc == MOSQ_ERR_SUCCESS)
                {
                    printf("Publish returned OK\r\n");
                }
                else 
                {               
                    rc = pub_mosq.mosquitto_error(rc, NULL);
                }
            } 

        } while (rc != MOSQ_ERR_SUCCESS);   
    }
}

mosquitto_loop_stop(mosq, true);
mosquitto_destroy(mosq);

mosquitto_lib_cleanup();}

发布方式:

    int MosquittoClient::publishToTopic(struct mosquitto *mosq, int *msgId, int sizeOfData, char *data)
{
    return mosquitto_publish(mosq, msgId, p_topic, sizeOfData, data, 1, true);
}

运行程序时，根据控制台，所有发布的消息都返回正常。但 Azure IoT 中心一侧仅显示一两条消息。

下图是IoT Hub的监控，当时只有一条消息通过。 Device Explorer Twin Monitoring

我尝试了很多不同的解决方案，但程序无法发布所有消息。看起来发布方法正在等待完成第一条消息，但迭代正在移动到下一条消息，导致它被删除。如果这是消息丢失的原因，那么按顺序发送消息的最佳方法是什么？否则，还有什么可能导致消息被丢弃？

更新

问题是程序没有等到消息成功发布到代理(Azure IoT 中心)。如果返回publish_callback，就知道消息是否成功发布到broker。

void MosquittoClient::publish_callback(struct mosquitto* mosq, void* userdata, int mid)
{
    printf("Publish OK.\r\n");
}

解决方案是在销毁之前休眠线程，清理调用并在建立连接之前启动 Mosquitto 循环。

sleep(30);
mosquitto_loop_stop(mosq, true);
mosquitto_destroy(mosq);
mosquitto_lib_cleanup();

Answer 1

mosquitto_publish() 是异步的:让它返回 MOSQ_ERR_SUCCESS 仅意味着消息的发布已正确传递到 Mosquitto 线程。因此，目前您正在排队大量消息，然后让您的程序在有机会实际发送数据包之前终止。

您可以使用 MosquittoClient::publish_callback 回调来检查在停止循环并终止程序之前所有消息是否已有效发送。