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Getting Started with MQTT

Last updated: 2021-08-31 12:20:24

    This document describes how to create devices and permissions in the IoT Hub console and quickly try out device connection to IoT Hub over the MQTT protocol for message sending and receiving based on the mqtt_sample of the C-SDK.

    Operations in Console

    Creating product and device

    1. Log in to the IoT Hub console and click Products on the left sidebar.
    2. On the product list page, click Create Product.
    3. On the pop-up product adding page, select the node type and product type, enter the product name, select the authentication method and data format, and enter the product description.
      Then, click Confirm (select as shown below for directly connected general devices).
    4. After the product is created, click Devices at the bottom of the generated product page.
    5. On the device list page, click Add Device.
      • If the authentication method is certificate authentication, after the device name is entered, be sure to click Download in the pop-up window. The device key and device certificate in the downloaded package are used for authenticating the device during connection to IoT Hub.
      • If the authentication method is key authentication, after the device name is entered, the key of the added device will be displayed in the pop-up window.

    Creating topic

    1. On the generated product page, click Permissions.
    2. On the permission list page, click Add Topic Permission.
    3. In the topic permission pop-up window, enter data, set the operation permission to Subscribe and Publish, and click Confirm.
    4. Then, the productID/\${deviceName}/data topic will be created, and you can view all permissions of the product in the permission list on the product page.

    Compiling and Running Demo

    The following describes how to compile and run the mqtt_sample demo in the Linux environment (with a key-authenticated device as example).

    1. Compile the SDK

    (1) Modify CMakeLists.txt to ensure that the following options exist:

    set(BUILD_TYPE                   "release")
    set(COMPILE_TOOLS                "gcc") 
    set(PLATFORM                     "linux")

    (2) Run the following script for compilation.


    (3) The demo output is in the output/release/bin folder.

    2. Enter the device information

    Enter the information of the device created above on the IoT Hub platform in device_info.json.


    3. Run the mqtt_sample demo

    INF|2019-09-12 21:28:20|device.c|iot_device_info_set(67): SDK_Ver: 3.1.0, Product_ID: S3EUVBRJLB, Device_Name: test_device
    DBG|2019-09-12 21:28:20|HAL_TLS_mbedtls.c|HAL_TLS_Connect(204): Setting up the SSL/TLS structure...
    DBG|2019-09-12 21:28:20|HAL_TLS_mbedtls.c|HAL_TLS_Connect(246): Performing the SSL/TLS handshake...
    DBG|2019-09-12 21:28:20|HAL_TLS_mbedtls.c|HAL_TLS_Connect(247): Connecting to /S3EUVBRJLB.iotcloud.tencentdevices.com/8883...
    INF|2019-09-12 21:28:20|HAL_TLS_mbedtls.c|HAL_TLS_Connect(269): connected with /S3EUVBRJLB.iotcloud.tencentdevices.com/8883...
    INF|2019-09-12 21:28:20|mqtt_client.c|IOT_MQTT_Construct(125): mqtt connect with id: p8t0W success
    INF|2019-09-12 21:28:20|mqtt_sample.c|main(303): Cloud Device Construct Success
    DBG|2019-09-12 21:28:20|mqtt_client_subscribe.c|qcloud_iot_mqtt_subscribe(138): topicName=$sys/operation/result/S3EUVBRJLB/test_device|packet_id=1932
    INF|2019-09-12 21:28:20|mqtt_sample.c|_mqtt_event_handler(71): subscribe success, packet-id=1932
    DBG|2019-09-12 21:28:20|system_mqtt.c|_system_mqtt_sub_event_handler(80): mqtt sys topic subscribe success
    DBG|2019-09-12 21:28:20|mqtt_client_publish.c|qcloud_iot_mqtt_publish(337): publish packetID=0|topicName=$sys/operation/S3EUVBRJLB/test_device|payload={"type": "get", "resource": ["time"]}
    DBG|2019-09-12 21:28:20|system_mqtt.c|_system_mqtt_message_callback(63): Recv Msg Topic:$sys/operation/result/S3EUVBRJLB/test_device, payload:{"type":"get","time":1568294900}
    INF|2019-09-12 21:28:21|mqtt_sample.c|main(316): system time is 1568294900
    DBG|2019-09-12 21:28:21|mqtt_client_subscribe.c|qcloud_iot_mqtt_subscribe(138): topicName=S3EUVBRJLB/test_device/data|packet_id=1933
    INF|2019-09-12 21:28:21|mqtt_sample.c|_mqtt_event_handler(71): subscribe success, packet-id=1933
    DBG|2019-09-12 21:28:21|mqtt_client_publish.c|qcloud_iot_mqtt_publish(329): publish topic seq=1934|topicName=S3EUVBRJLB/test_device/data|payload={"action": "publish_test", "count": "0"}
    INF|2019-09-12 21:28:21|mqtt_sample.c|_mqtt_event_handler(98): publish success, packet-id=1934
    INF|2019-09-12 21:28:21|mqtt_sample.c|on_message_callback(195): Receive Message With topicName:S3EUVBRJLB/test_device/data, payload:{"action": "publish_test", "count": "0"}
    INF|2019-09-12 21:28:22|mqtt_client_connect.c|qcloud_iot_mqtt_disconnect(437): mqtt disconnect!
    INF|2019-09-12 21:28:22|system_mqtt.c|_system_mqtt_sub_event_handler(98): mqtt client has been destroyed
    INF|2019-09-12 21:28:22|mqtt_client.c|IOT_MQTT_Destroy(186): mqtt release!

    4. Observe message sending

    The following log information shows that the demo reported data to /{productID}/{deviceName}/data through the Publish message type of MQTT, and that the server received and successfully processed the message.

    INF|2019-09-12 21:28:21|mqtt_sample.c|_mqtt_event_handler(98): publish success, packet-id=1934

    5. Observe message receiving

    The following log information shows that as the message reached the subscribed topic, it was pushed to the demo as-is by the server and entered the corresponding callback function.

    INF|2019-09-12 21:28:21|mqtt_sample.c|on_message_callback(195): Receive Message With topicName:S3EUVBRJLB/test_device/data, payload:{"action": "publish_test", "count": "0"}

    6. Observe logs in the console

    Log in to the IoT Hub console, click the product name, and click Cloud Log on the top to view the message just reported.

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