Command Delivery

Overview

A product model defines commands that can be delivered to the devices. Applications can call platform APIs to deliver commands to the devices to effectively manage these devices.

IoTDA supports synchronous and asynchronous command delivery.

For details, see Synchronous Command Delivery and Asynchronous Command Delivery.

Scenarios

• Synchronous delivery applies to scenarios that require real-time command delivery. Asynchronous delivery is used for device control.
• Data needs to be forwarded to other Huawei Cloud services for storage and processing based on data forwarding rules.

Constraints

• Max. size of a single message: 256 KB.
• Product models are required.
• Devices need to respond to the synchronous command within 20 seconds.
• Up to 20 asynchronous commands can be cached at a time.
• Max. cache duration (configurable): 48 hours.

APIs

• APIs for the platform and applications
  • Deliver a Command to a Device
  • Deliver an Asynchronous Command
  • Query a Command with a Specific ID
• APIs for MQTT devices
  • Platform Delivering a Command
  • Platform Delivering a Message.
• APIs for devices using LwM2M over CoAP
  • Platform Delivering a Command

Synchronous Command Delivery

You can deliver synchronous commands to MQTT devices one by one or in batches.

Synchronous Command Delivery to an Individual MQTT Device

For details on how to set and query properties, see instructions of the APIs for querying device properties and modifying device properties.

Figure 1 Command delivery process

1. An application calls the API for delivering a command to a device to send a command to the platform. Example message:

   POST https://{Endpoint}/v5/iot/{project_id}/devices/{device_id}/commands
   Content-Type: application/json
   X-Auth-Token: ********
   
   {
     "service_id" : "WaterMeter",
     "command_name" : "ON_OFF",
     "paras" : {
       "value" : "ON"
     }
   }

2. The platform sends the command to the device according to the protocol specifications. Example message:

   Topic: $oc/devices/{device_id}/sys/commands/request_id={request_id} 
   Data format:
   {
     "object_device_id": "{object_device_id}",
     "command_name": "ON_OFF",
     "service_id": "WaterMeter",
     "paras": {
       "value": "ON"
     }
   }

3. After executing the command, the device returns the command execution result through the API for delivering a command. Example message:

   Topic: $oc/devices/{device_id}/sys/commands/response/request_id={request_id}
   Data format:
   {
       "result_code": 0,
       "response_name": "COMMAND_RESPONSE",
       "paras": {
           "result": "success"
       }
   }

4. The platform synchronously sends a response to the HTTP command. Example message:

   Status Code: 200 OK
   Content-Type: application/json
   
   {
     "command_id" : "b1224afb-e9f0-4916-8220-b6bab568e888",
     "response" : {
       "result_code" : 0,
       "response_name" : "COMMAND_RESPONSE",
       "paras" : {
         "result" : "success"
       }
     }
   }

Synchronous Command Delivery to a Batch of MQTT Devices

The API for creating a batch task can be used to deliver a command to multiple MQTT devices. The following describes how to call the API for creating a batch task to deliver commands in batches.

1. An application calls the API for creating a batch task to send a command to the platform. Example message:

   POST https://{Endpoint}/v5/iot/{project_id}/batchtasks 
   Content-Type: application/json
   X-Auth-Token: ********
   {
     "app_id": "********",
     "task_name": "task123",
     "task_type": "createCommands",
     "targets": [
       "********",
       "********"
     ],
     "document": {
       "service_id": "water",
       "command_name": "ON_OFF",
       "paras": {
         "value": "ON"
       }
     }
   }

   Table 3 Parameters for creating a batch task of command delivery

   Parameter	Mandatory	Description
   app_id	No	Resource space ID.
   task_name	Yes	Custom task name.
   task_type	Yes	Type of the batch task. For details, see Create a Batch Task. Options: createCommands: task for creating synchronous commands in batches createAsyncCommands: task for creating asynchronous commands in batches
   targets	No	Device ID array, which is the target for executing the batch task.
   document	No	Task execution data file, in JSON format (key-value pairs). For details, see Deliver a Command to a Device.

2. The platform returns a 201 Created message to the application.
3. The device receives the command and sends the command result to the platform through the upstream topic. For details, see Platform Delivering a Command.
4. Call the API for querying the batch task list to query the execution status of a batch command delivery task.

Asynchronous Command Delivery

Asynchronous command delivery is used for IoTDA or applications to deliver commands to devices using LwM2M over CoAP to access IoTDA. Two modes are available.

Immediate Delivery of Asynchronous Commands

Figure 2 Command delivery for devices using LwM2M over CoAP

An example of the corresponding steps is as follows:

1. An application calls the API for delivering an asynchronous command to send a command to the platform. The send_strategy parameter in the command request is set to immediately. Example message:

   POST https://{endpoint}/v5/iot/{project_id}/devices/{device_id}/async-commands
   Content-Type: application/json
   X-Auth-Token: ********
   
   {
     "service_id" : "WaterMeter",
     "command_name" : "ON_OFF",
     "paras" : {
       "value" : "ON"
     },
      "expire_time": 0,
      "send_strategy": "immediately"
   }

2. The platform uses the codec to encode the command request, and sends the command through the Execute operation of the device management and service implementation interface defined in the LwM2M protocol. The message body is in binary format.
3. The platform sends a 200 OK message carrying the command status SENT to the application. (If the device is offline or the device does not receive the command, the delivery fails and the command status is FAILED.)
4. The device returns an ACK message after receiving the command.
5. If the application has subscribed to command status change notifications, the platform pushes a message to the application by calling the API for pushing a command status change notification. The command status carried in the message is DELIVERED. Example message:

   Method: POST
   request:
   Body:
   {
       "resource": "device.command.status",
       "event": "update",
       "event_time": "20200811T080745Z",
       "notify_data": {
           "header": {
               "app_id": "********",
               "device_id": "********",
               "node_id": "test0001",
               "product_id": "********",
               "gateway_id": "********",
               "tags": []
           },
           "body": {
               "command_id": "********",
               "created_time": "20200811T080738Z",
               "sent_time": "20200811T080738Z",
               "delivered_time": "20200811T080745Z",
               "response_time": "",
               "status": "DELIVERED",
               "result": null
           }
       }
   }

6. After the command is executed, the device returns the command execution result in a 205 Content message.
7. If the application has subscribed to command status change notifications, the platform uses the codec to decode the command response and sends a push message to the application by calling the API for pushing a command status change notification. The command status carried in the message is SUCCESSFUL. Example message:

   Method: POST
   request:
   Body:
   {
       "resource": "device.command.status",
       "event": "update",
       "event_time": "20200811T080745Z",
       "notify_data": {
           "header": {
               "app_id": "********",
               "device_id": "********",
               "node_id": "test0001",
               "product_id": "********",
               "gateway_id": "********",
               "tags": []
           },
           "body": {
               "command_id": "********",
               "created_time": "20200811T080738Z",
               "sent_time": "20200811T080738Z",
               "delivered_time": "20200811T080745Z",
               "response_time": "20200811T081745Z",
               "status": "SUCCESSFUL",
               "result": {
                   "resultCode":"SUCCESSFUL",
                   "resultDetail": {
                       "value": "ON"
                   }
               }
           }
       }
   }

Delayed Delivery of Asynchronous Commands

Figure 3 Delayed command delivery for devices using LwM2M over CoAP

1. An application calls the API for delivering an asynchronous command to send a command to the platform. The send_strategy parameter in the command request is set to delay.
2. The platform adds the command to the cache queue and reports a 200 OK message. The command status is PENDING.
3. The device goes online or reports data to the platform.
4. The platform uses the codec to encode the command request and sends the command to the device according to the protocol specifications.
5. If the application has subscribed to command status change notifications, the platform pushes a message to the application by calling the API for pushing a command status change notification. The command status carried in the message is SENT.
6. The subsequent flow is the same as 4 to 7 described in the immediate delivery scenario.

LwM2M/CoAP Device Command Execution Status

The figure below illustrates the command execution status and the table below describes the status change mechanism.

Figure 4 LwM2M/CoAP command delivery status

Platform Command Delivery Example

1. Access the IoTDA service page and click Access Console. Click the target instance card.
2. In the navigation pane, choose Devices > All Devices. On the device list, click a device to access its details page.
3. The Cloud Delivery tab page varies according to the device protocol.
   • Devices using MQTT support only synchronous command delivery. Click Command Delivery on the right. In the displayed dialog box, select the command to be delivered and set command parameters.
     Figure 5 Command delivery - Synchronous command delivery
     
   • Devices using LwM2M over CoAP support only asynchronous command delivery. Click Deliver Command on the right. In the displayed dialog box, select the command to be delivered and set command parameters. You can choose to send the command immediately or after a delay.
     Figure 6 Command delivery - Asynchronous command delivery
     

• On the Message Trace tab page, you can view the creation time, sending time, delivered time, and the delivery status of a command delivery task. This information helps you learn the command execution status.
• In addition, you can call the API for querying a command with a specific ID to query the status and content of delivered commands on the platform.

The application uses the Java SDK for the development of synchronous command delivery. The development environment used in the example is JDK 1.8 or later. Download an SDK.

1. Configure the Maven dependency.

   <dependency>
       <groupId>com.huaweicloud.sdk</groupId>
       <artifactId>huaweicloud-sdk-core</artifactId>
       <version>[3.0.40-rc, 3.2.0)</version>
   </dependency>
   <dependency>
       <groupId>com.huaweicloud.sdk</groupId>
       <artifactId>huaweicloud-sdk-iotda</artifactId>
       <version>[3.0.40-rc, 3.2.0)</version>
   </dependency>

2. The following is an example of delivering a synchronous command:

   public class CommandSolution {
       // REGION_ID: If CN East-Shanghai1 is used, enter cn-east-3. If CN North-Beijing4 is used, enter cn-north-4. If CN South-Guangzhou is used, enter cn-south-4.
       private static final String REGION_ID = "<YOUR REGION ID>";
       // ENDPOINT: On the console, choose Overview and click Access Addresses to view the HTTPS application access address.
       private static final String ENDPOINT = "<YOUR ENDPOINT>";
       // For the standard or enterprise edition, create a region object.
       public static final Region REGION_CN_NORTH_4 = new Region(REGION_ID, ENDPOINT);
       public static void main(String[] args) {
           String ak = "<YOUR AK>";
           String sk = "<YOUR SK>";
           String projectId = "<YOUR PROJECTID>";
           // Create a credential.
           ICredential auth = new BasicCredentials().withDerivedPredicate(AbstractCredentials.DEFAULT_DERIVED_PREDICATE)
               .withAk(ak)
               .withSk(sk)
               .withProjectId(projectId);
           // Create and initialize an IoTDAClient instance.
           IoTDAClient client = IoTDAClient.newBuilder().withCredential(auth)
               // For the basic edition, select the region object in IoTDARegion.
               //.withRegion(IoTDARegion.CN_NORTH_4)
               // For the standard or enterprise edition, create a region object.
               .withRegion(REGION_CN_NORTH_4).build();
           // Instantiate a request object.
           CreateCommandRequest request = new CreateCommandRequest();
           request.withDeviceId("<YOUR DEVICE_ID>");
           DeviceCommandRequest body = new DeviceCommandRequest();
           body.withParas("{\"value\":\"1\"}");
           request.withBody(body);
           try {
               CreateCommandResponse response = client.createCommand(request);
               System.out.println(response.toString());
           } catch (ConnectionException e) {
               e.printStackTrace();
           } catch (RequestTimeoutException e) {
               e.printStackTrace();
           } catch (ServiceResponseException e) {
               e.printStackTrace();
               System.out.println(e.getHttpStatusCode());
               System.out.println(e.getRequestId());
               System.out.println(e.getErrorCode());
               System.out.println(e.getErrorMsg());
           }
       }
   }

   Table 6 Parameters

   Parameter	Description
   ak	Access key ID (AK) of your Huawei Cloud account. You can create and check your AK/SK on the My Credentials > Access Keys page of the Huawei Cloud console. For details, see Access Keys.
   sk	Secret access key (SK) of your Huawei Cloud account.
   projectId	Project ID. For details on how to obtain a project ID, see Obtaining a Project ID.
   IoTDARegion.CN_NORTH_4	Region where the platform to be accessed is located. The available regions of the platform have been defined in the SDK code IoTDARegion.java. On the console, you can view the region name of the current service and the mapping between regions and endpoints. For details, see Platform Connection Information.
   REGION_ID	If CN East-Shanghai1 is used, enter cn-east-3. If CN North-Beijing4 is used, enter cn-north-4. If CN South-Guangzhou is used, enter cn-south-4.
   ENDPOINT	On the console, choose Overview and click Access Addresses to view the HTTPS application access address.
   DEVICE_ID	Unique ID of the device that a message is delivered to. The value of this parameter is allocated by the platform during device registration. The value is a string of no more than 128 characters. Only letters, digits, underscores (_), and hyphens (-) are allowed.

To configure the device to use the Java SDK to deliver synchronous commands, perform the following steps. In this example, JDK 1.8 or a later version is used.

1. Configure the Maven dependency of the SDK on devices.

   <dependency>
   	<groupId>com.huaweicloud</groupId>
   	<artifactId>iot-device-sdk-java</artifactId>
   	<version>1.1.4</version>
   </dependency>

2. Configure the SDK and device connection parameters on devices.

   // Load the CA certificate of the IoT platform. For details about how to obtain the certificate, visit https://support.huaweicloud.com/intl/en-us/devg-iothub/iot_02_1004.html.
   URL resource = BroadcastMessageSample.class.getClassLoader().getResource("ca.jks");
   File file = new File(resource.getPath());
   
   // The format is ssl://Domain name:Port number.
   // To obtain the domain name, log in to the Huawei Cloud IoTDA console. In the navigation pane, choose Overview and click Access Details in the Instance Information area. Select the access domain name corresponding to port 8883.
   String serverUrl = "ssl://localhost:8883";
   // Device ID created on the platform
   String deviceId = "deviceId";
   // Secret corresponding to the device ID
   String deviceSecret = "secret";
   // Create a device.
   IoTDevice device = new IoTDevice(serverUrl, deviceId, deviceSecret, file);
   if (device.init() != 0) {
       return;
   }

3. Set the command delivery callback function and send a response.

    client.setCommandListener(new CommandListener() {
       @Override
       public void onCommand(String requestId, String serviceId, String commandName, Map<String, Object> paras) {
           log.info("onCommand, serviceId = " +serviceId);
           log.info("onCommand , name = " + commandName);
           log.info("onCommand, paras =  " + paras.toString());
   
           // Define the processing command.
   
           // Send a command response.
           device.getClient().respondCommand(requestId, new CommandRsp(0));
       }   
   });

Verify the setting:

1. On the IoTDA console, click the target instance card. In the navigation pane, choose Devices > All Devices. On the displayed page, locate the target device, and click View in the Operation column to access its details page. Click the Message Trace tab, and click Start Trace.
   Figure 7 Message tracing - Starting message tracing
   

2. Run the SDK code on the device to bring the device online.
3. Run the application code. After receiving a command, the device processes and responds to the command. The following is an example of a command received by the device.
   Figure 8 Successful command delivery result on the device
   

4. Check the result on the Message Trace tab page.
   Figure 9 Message tracing - Delivering commands