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API and Variable Parameter Description

Last updated: 2021-08-20 18:12:55

    The header files of the device SDK for C provided for you to call such as API function declarations, constants, and variable parameter definitions are in the include directory. This document describes the variable parameters and API functions in the directory.

    Variable Parameter Configuration

    You can configure corresponding parameters in the SDK for C based on the needs in specific scenarios to ensure the smooth operations of your businesses. Variable connection parameters include:

    1. Timeout period of blocking MQTT calls (including connection, subscribing, and publishing) in milliseconds. 5000 ms is recommended.
    2. Size of the buffer for message sending and receiving over the MQTT protocol, which is 2,048 bytes by default and can be up to 16 KB.
    3. Size of the buffer for message sending and receiving over the CoAP protocol, which is 512 bytes by default and can be up to 1 KB.
    4. MQTT heartbeat message sending interval in milliseconds, which can be up to 690s.
    5. Maximum waiting time for reconnection in milliseconds. When a device is reconnected after disconnection, the waiting time will double if reconnection fails, and reconnection will stop when the maximum waiting time is exceeded.

    You can modify the configuration of the corresponding connection parameters by modifying the following macro definitions in the include/qcloud_iot_export_variables.h file.
    You need to recompile the SDK after modification. Below is the sample code:

    /* default MQTT/CoAP timeout value when connect/pub/sub (unit: ms) */
    #define QCLOUD_IOT_MQTT_COMMAND_TIMEOUT                             (5 * 1000)
    /* default MQTT keep alive interval (unit: ms) */
    #define QCLOUD_IOT_MQTT_KEEP_ALIVE_INTERNAL                         (240 * 1000)
    /* default MQTT Tx buffer size, MAX: 16*1024 */
    #define QCLOUD_IOT_MQTT_TX_BUF_LEN                                  (2048)
    /* default MQTT Rx buffer size, MAX: 16*1024 */
    #define QCLOUD_IOT_MQTT_RX_BUF_LEN                                  (2048)
    /* default COAP Tx buffer size, MAX: 1*1024 */
    #define COAP_SENDMSG_MAX_BUFLEN                                     (512)
    /* default COAP Rx buffer size, MAX: 1*1024 */
    #define COAP_RECVMSG_MAX_BUFLEN                                     (512)
    /* MAX MQTT reconnect interval (unit: ms) */
    #define MAX_RECONNECT_WAIT_INTERVAL                                 (60 * 1000)
    

    API Function Description

    The following describes the main features and corresponding APIs provided by the SDK for C v3.1.0 for you to compile business logic. For more information on API parameters and returned values, please see the comments in the header files of the SDK code such as include/exports/qcloud_iot_export_*.h.

    MQTT APIs

    No. Function Description
    1 IOT_MQTT_Construct Constructs MQTTClient and connects to MQTT cloud service
    2 IOT_MQTT_Destroy Closes MQTT connection and terminates MQTTClient
    3 IOT_MQTT_Yield Performs tasks such as reading MQTT messages, processing messages, timing out requests, and managing heartbeat packets and reconnection status in the current thread context
    4 IOT_MQTT_Publish Publishes MQTT message
    5 IOT_MQTT_Subscribe Subscribes to MQTT topic
    6 IOT_MQTT_Unsubscribe Unsubscribes from subscribed MQTT topic
    7 IOT_MQTT_IsConnected Queries whether MQTT is currently connected to
    8 IOT_MQTT_GetErrCode Gets the error code of IOT_MQTT_Construct failure

    Notes on use in multithreaded environment

    To use MQTT APIs in a multithreaded environment, you need to pay attention to the following:

    • You cannot use multiple threads to call IOT_MQTT_Yield, IOT_MQTT_Construct, or IOT_MQTT_Destroy.
    • You can use multiple threads to call IOT_MQTT_Publish, IOT_MQTT_Subscribe, and IOT_MQTT_Unsubscribe.
    • As the function to read MQTT messages from socket and process them, IOT_MQTT_Yield should have a certain execution time to prevent it from being suspended or preempted for a long time.

    Device shadow APIs

    For more information on the device shadow feature, please see Device Shadow Details.

    No. Function Description
    1 IOT_Shadow_Construct Constructs device shadow client ShadowClient and connects to MQTT cloud service
    2 IOT_Shadow_Publish The shadow client publishes an MQTT message
    3 IOT_Shadow_Subscribe The shadow client subscribes to an MQTT topic
    4 IOT_Shadow_Unsubscribe The shadow client unsubscribes from a subscribed MQTT topic
    5 IOT_Shadow_IsConnected Queries whether MQTT of the shadow client is currently connected to
    6 IOT_Shadow_Destroy Closes shadow MQTT connection and terminates ShadowClient
    7 IOT_Shadow_Yield Performs tasks such as reading MQTT messages, processing messages, timing out requests, and managing heartbeat packets and reconnection status in the current thread context
    8 IOT_Shadow_Update Updates device shadow document asynchronously
    9 IOT_Shadow_Update_Sync Updates device shadow document synchronously
    10 IOT_Shadow_Get Gets device shadow document asynchronously
    11 IOT_Shadow_Get_Sync Gets device shadow document synchronously
    12 IOT_Shadow_Register_Property Registers the attribute of the current device
    13 IOT_Shadow_UnRegister_Property Deletes registered device attribute
    14 IOT_Shadow_JSON_ConstructReport Adds reported field to JSON document for update in a non-overwriting manner
    15 IOT_Shadow_JSON_Construct_OverwriteReport Adds reported field to JSON document for update in an overwriting manner
    16 IOT_Shadow_JSON_ConstructReportAndDesireAllNull Adds reported field to JSON document and empties desired field
    17 IOT_Shadow_JSON_ConstructDesireAllNull Adds "desired": null field to JSON document

    CoAP APIs

    No. Function Description
    1 IOT_COAP_Construct Constructs CoAPClient and completes CoAP connection
    2 IOT_COAP_Destroy Closes CoAP connection and terminates CoAPClient
    3 IOT_COAP_Yield Performs tasks such as reading CoAP messages and processing messages in the current thread context
    4 IOT_COAP_SendMessage Publishes CoAP message
    5 IOT_COAP_GetMessageId Gets msgId in CoAP Response message
    6 IOT_COAP_GetMessagePayload Gets the content of CoAP Response message
    7 IOT_COAP_GetMessageCode Gets the error code of CoAP Response message

    OTA APIs

    For more information on the OTA firmware download feature, please see Device Firmware Update.

    No. Function Description
    1 IOT_OTA_Init Initializes OTA module. The client needs to initialize MQTT/CoAP before calling this API
    2 IOT_OTA_Destroy Releases resources related to OTA module
    3 IOT_OTA_ReportVersion Reports local firmware version information to OTA server
    4 IOT_OTA_IsFetching Checks whether the firmware is being downloaded
    5 IOT_OTA_IsFetchFinish Checks whether the firmware has been downloaded
    6 IOT_OTA_FetchYield Gets firmware from remote server with specific timeout value
    7 IOT_OTA_Ioctl Gets specified OTA information
    8 IOT_OTA_GetLastError Gets the last error code
    9 IOT_OTA_StartDownload Establishes HTTP connection with firmware server according to obtained firmware update address and local firmware information offset (whether to support checkpoint restart)
    10 IOT_OTA_UpdateClientMd5 Calculates the MD5 of local firmware before checkpoint restart
    11 IOT_OTA_ReportUpgradeBegin Reports the status of impending update to server before firmware update
    12 IOT_OTA_ReportUpgradeSuccess Reports the status of update success to server after successful firmware update
    13 IOT_OTA_ReportUpgradeFail Reports the status of update failure to server after failed firmware update

    Log APIs

    For more information on the device log reporting feature, please see the log reporting section of the IoT Hub documentation in the SDK docs directory.

    No. Function Description
    1 IOT_Log_Set_Level Sets the printout level of SDK logs
    2 IOT_Log_Get_Level Returns the printout level of SDK logs
    3 IOT_Log_Set_MessageHandler Sets log callback function to redirect SDK logs to another output method
    4 IOT_Log_Init_Uploader Enables SDK log reporting to the cloud and initializes resources
    5 IOT_Log_Fini_Uploader Disables SDK log reporting to the cloud and releases resources
    6 IOT_Log_Upload Reports SDK execution logs to the cloud
    7 IOT_Log_Set_Upload_Level Sets the reporting level of SDK logs
    8 IOT_Log_Get_Upload_Level Returns the reporting level of SDK logs
    9 Log_d/i/w/e Prints SDK logs by level

    System time APIs

    No. Function Description
    1 IOT_Get_SysTime Gets IoT Hub's backend time. Currently, the time sync feature is supported only for the MQTT channel

    Gateway feature APIs

    Fore more information on the gateway feature, please see the gateway product section of the IoT Hub documentation in the SDK docs directory.

    No. Function Description
    1 IOT_Gateway_Construct Constructs gateway client and completes MQTT connection
    2 IOT_Gateway_Destroy Closes MQTT connection and terminates gateway client
    3 IOT_Gateway_Subdev_Online Connects subdevice
    4 IOT_Gateway_Subdev_Offline Disconnects subdevice
    5 IOT_Gateway_Yield Performs tasks such as reading MQTT messages, processing messages, timing out requests, and managing heartbeat packets and reconnection status in the current thread context
    6 IOT_Gateway_Publish Publishes MQTT message
    7 IOT_Gateway_Subscribe Subscribes to MQTT topic
    8 IOT_Gateway_Unsubscribe Unsubscribes from subscribed MQTT topic
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