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Azure IoT Hub direct methods (Node) | Microsoft Docs
How to use Azure IoT Hub direct methods. You use the Azure IoT SDKs for Node.js to implement a simulated device app that includes a direct method and a service app that invokes the direct method.
iot-hub
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iot-hub
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08/25/2017
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H1Hack27Feb2017

Use direct methods on your IoT device with Node.js

[!INCLUDE iot-hub-selector-c2d-methods]

At the end of this tutorial, you have two Node.js console apps:

  • CallMethodOnDevice.js, which calls a method in the simulated device app and displays the response.
  • SimulatedDevice.js, which connects to your IoT hub with the device identity created earlier, and responds to the method called by the cloud.

Note

The article Azure IoT SDKs provides information about the Azure IoT SDKs that you can use to build both applications to run on devices and your solution back end.

To complete this tutorial, you need the following:

  • Node.js version 4.0.x or later.
  • An active Azure account. (If you don't have an account, you can create a free account in just a couple of minutes.)

[!INCLUDE iot-hub-get-started-create-hub]

[!INCLUDE iot-hub-get-started-create-device-identity]

Create a simulated device app

In this section, you create a Node.js console app that responds to a method called by the cloud.

  1. Create a new empty folder called simulateddevice. In the simulateddevice folder, create a package.json file using the following command at your command prompt. Accept all the defaults:

    npm init

  2. At your command prompt in the simulateddevice folder, run the following command to install the azure-iot-device Device SDK package and azure-iot-device-mqtt package:

    npm install azure-iot-device azure-iot-device-mqtt --save

  3. Using a text editor, create a new SimulatedDevice.js file in the simulateddevice folder.

  4. Add the following require statements at the start of the SimulatedDevice.js file:

    'use strict';

var Mqtt = require('azure-iot-device-mqtt').Mqtt;
var DeviceClient = require('azure-iot-device').Client;

  5. Add a connectionString variable and use it to create a DeviceClient instance. Replace {device connection string} with the device connection string you generated in the Create a device identity section:

    var connectionString = '{device connection string}';
var client = DeviceClient.fromConnectionString(connectionString, Mqtt);

  6. Add the following function to implement the method on the device:

    function onWriteLine(request, response) {
    console.log(request.payload);

    response.send(200, 'Input was written to log.', function(err) {
        if(err) {
            console.error('An error ocurred when sending a method response:\n' + err.toString());
        } else {
            console.log('Response to method \'' + request.methodName + '\' sent successfully.' );
        }
    });
}

  7. Open the connection to your IoT hub and start initialize the method listener:

    client.open(function(err) {
    if (err) {
        console.error('could not open IotHub client');
    }  else {
        console.log('client opened');
        client.onDeviceMethod('writeLine', onWriteLine);
    }
});

  8. Save and close the SimulatedDevice.js file.

Note

To keep things simple, this tutorial does not implement any retry policy. In production code, you should implement retry policies (such as connection retry), as suggested in the MSDN article Transient Fault Handling.

Call a method on a device

In this section, you create a Node.js console app that calls a method in the simulated device app and then displays the response.

  1. Create a new empty folder called callmethodondevice. In the callmethodondevice folder, create a package.json file using the following command at your command prompt. Accept all the defaults:

    npm init

  2. At your command prompt in the callmethodondevice folder, run the following command to install the azure-iothub package:

    npm install azure-iothub --save

  3. Using a text editor, create a CallMethodOnDevice.js file in the callmethodondevice folder.

  4. Add the following require statements at the start of the CallMethodOnDevice.js file:

    'use strict';

var Client = require('azure-iothub').Client;

  5. Add the following variable declaration and replace the placeholder value with the IoT Hub connection string for your hub:

    var connectionString = '{iothub connection string}';
var methodName = 'writeLine';
var deviceId = 'myDeviceId';

  6. Create the client to open the connection to your IoT hub.

    var client = Client.fromConnectionString(connectionString);

  7. Add the following function to invoke the device method and print the device response to the console:

    var methodParams = {
    methodName: methodName,
    payload: 'hello world',
    timeoutInSeconds: 30
};

client.invokeDeviceMethod(deviceId, methodParams, function (err, result) {
    if (err) {
        console.error('Failed to invoke method \'' + methodName + '\': ' + err.message);
    } else {
        console.log(methodName + ' on ' + deviceId + ':');
        console.log(JSON.stringify(result, null, 2));
    }
});

  8. Save and close the CallMethodOnDevice.js file.

Run the apps

You are now ready to run the apps.

  1. At a command prompt in the simulateddevice folder, run the following command to start listening for method calls from your IoT Hub:

    node SimulatedDevice.js

  2. At a command prompt in the callmethodondevice folder, run the following command to begin monitoring your IoT hub:

    node CallMethodOnDevice.js

  3. You will see the device react to the method by printing out the message and the application which called the method display the response from the device:

Next steps

In this tutorial, you configured a new IoT hub in the Azure portal, and then created a device identity in the IoT hub's identity registry. You used this device identity to enable the simulated device app to react to methods invoked by the cloud. You also created an app that invokes methods on the device and displays the response from the device.

To continue getting started with IoT Hub and to explore other IoT scenarios, see:

To learn how to extend your IoT solution and schedule method calls on multiple devices, see the Schedule and broadcast jobs tutorial.