IoT Platform：裝置影子

操作步驟

1. 裝置C-SDK提供介面IOT_Shadow_Construct ，建立裝置影子。函式宣告如下：

   /**
   * @brief Construct the Device Shadow.
   * This function initialize the data structures, establish MQTT connection.
   * and subscribe the topic: "/shadow/get/${YourProduct_key}/${YourDevice_name}".
   *
   * @param [in] pparam: The specific initial parameter.
   * @retval NULL : Construct shadow failed.
   * @retval NOT_NULL : Construct success.
   * @see None.
   */
   void *IOT_Shadow_Construct(iotx_shadow_para_pt pparam);
                       

2. 使用IOT_Shadow_RegisterAttribute介面，註冊裝置影子的屬性。函式宣告如下：

   /**
   * @brief Create a data type registered to the server.
   *
   * @param [in] handle: The handle of device shadow.
   * @param [in] pattr: The parameter which registered to the server.
   * @retval SUCCESS_RETURN : Success.
   * @retval other : See iotx_err_t.
   * @see None.
   */
   iotx_err_t IOT_Shadow_RegisterAttribute(void *handle, iotx_shadow_attr_pt pattr);
                       

3. 裝置影子在每次開機時，裝置C-SDK提供IOT_Shadow_Pull介面，從雲端同步裝置狀態。函式宣告如下：

   /**
   * @brief Synchronize device shadow data from cloud.
   * It is a synchronous interface.
   * @param [in] handle: The handle of device shadow.
   * @retval SUCCESS_RETURN : Success.
   * @retval other : See iotx_err_t.
   * @see None.
   */
   iotx_err_t IOT_Shadow_Pull(void *handle);
                       

4. 當裝置端狀態發生變化時，裝置C-SDK提供介面IOT_Shadow_PushFormat_Init、IOT_Shadow_PushFormat_Add和IOT_Shadow_PushFormat_Finalize介面更新狀態，通過介面IOT_Shadow_Push將狀態同步到雲端。函式宣告如下：

   /**
   * @brief Start a process the structure of the data type format.
   *
   * @param [in] handle: The handle of device shadow.
   * @param [out] pformat: The format struct of device shadow.
   * @param [in] buf: The buf which store device shadow.
   * @param [in] size: Maximum length of device shadow attribute.
   * @retval SUCCESS_RETURN : Success.
   * @retval other : See iotx_err_t.
   * @see None.
   */
   iotx_err_t IOT_Shadow_PushFormat_Init(
                       void *handle,
                       format_data_pt pformat,
                       char *buf,
                       uint16_t size);
   
   
   /**
   * @brief Format the attribute name and value for update.
   *
   * @param [in] handle: The handle of device shadow.
   * @param [in] pformat: The format struct of device shadow.
   * @param [in] pattr: To have created the data type of the format in the add member attributes.
   * @retval SUCCESS_RETURN : Success.
   * @retval other : See iotx_err_t.
   * @see None.
   */
   iotx_err_t IOT_Shadow_PushFormat_Add(
                       void *handle,
                       format_data_pt pformat,
                       iotx_shadow_attr_pt pattr);
   
   
   /**
   * @brief Complete a process the structure of the data type format.
   *
   * @param [in] handle: The handle of device shadow.
   * @param [in] pformat: The format struct of device shadow.
   * @retval SUCCESS_RETURN : Success.
   * @retval other : See iotx_err_t.
   * @see None.
   */
   iotx_err_t IOT_Shadow_PushFormat_Finalize(void *handle, format_data_pt pformat);
                       

5. 當裝置需要與雲端中斷連線時，裝置C-SDK提供介面IOT_Shadow_DeleteAttribute和IOT_Shadow_Destroy，刪除雲端建立的屬性並釋放裝置影子。函式宣告如下：

   /**
   * @brief Deconstruct the specific device shadow.
   *
   * @param [in] handle: The handle of device shadow.
   * @retval SUCCESS_RETURN : Success.
   * @retval other : See iotx_err_t.
   * @see None.
   */
   iotx_err_t IOT_Shadow_Destroy(void *handle);