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AzureTwins Library

AzureTwins is a library, that helps you work with Azure Twins API. It supports full set of operations provided by the service.

NOTE: The library tries to maintain permanent MQTT connection to Azure Twin to receive any asynchronous updates. However it case of connection failure it doesn't restore connection automatically. This should be taken care of by the application.

Prerequisites

AzureTwins library requires AzureIotHub to be included as well. This is needed for authentication procedure with Device Connection String as credentials.

This dependency between the libraries can easily be resolved as needed.

How to create AzureTwin client

The client requires Device Connection String, connection status listener, a listener for desired properties updates and method invocation listener as constructor parameters.

#require "AzureIoTHub.agent.lib.nut:2.1.0"
@include "../AzureTwins.agent.lib.nut"

function onUpdated(version, body) {
}

function onMethod(method, data) {
    return "200";
}

function onConnect(status) {
}

twin <- AzureTwin(connectionString, onConnect, onUpdate, onMethod);

onConnect callback

onConnect callback receives AzureTwins connection status.

Status Description
AT_DISCONNECTED The connection was lost. To reconnect call reconnect() method.
AT_CONNECTING The library tries to establish connection
AT_CONNECTED MQTT connection established
AT_SUBSCRIBING The library tries to subscribe to specific topic to receive
notifications
AT_SUBSCRIBED The library is up and ready

onUpdate callback

onUpdate receives updates to the desired properties when they happen. It accepts desired properties document version and body.

The library follows this document for this functionality implementation.

NOTE: body is provided in a form of string as it receives from the server. No validation and parsing are performed.

onMethod

onMethod is called in response to 3d party request. The function accepts method name and set of parameters in form of unparsed string.

NOTE The callback MUST return status code from the set of HTTP status codes

How to get latest version of Azure Twin document

getCurrentStatus method may be used to retrieve latest state of the twin document in JSON format. Its implementation follows the spec

The function accepts single callback function that is executed when a response is received or an error happens.

function onStatusReceived(err, body) {

}

twin.getCurrentStatus(onStatusReceived);

The signature of the callback function is the following

Parameter Description
error If not null indicates error condition.
body Unparsed JSON document. May be null in case of error

How to update device twin's reported properties

updateStatus method may be used to patch twin's reported properties. Its implementation follows the spec

The function accepts new set of properties in a form serialized JSON document and a callback function that is executed when document is updated or in case of communication issues.

The signature of the callback function is the following

Parameter Description
error If not null indicates error condition.
body Unparsed JSON document. Contains the new ETag value for the reported properties collection