Read from Quix with Node.js

Quix supports real-time data streaming over WebSockets. JavaScript clients can receive updates on parameter and event definition updates, parameter data and event data as they happen. Following examples use SignalR client library to connect to Quix over WebSockets.

Setting up SignalR

If you are using a package manager like npm, you can install SignalR using npm install @microsoft/signalr. For other installation options that don’t depend on a platform like Node.js such as consuming SignalR from a CDN please refer to SignalR documentation.

Following code snippet shows how you can connect to Quix after SignalR has been setup.

var signalR = require("@microsoft/signalr");

const options = {
    accessTokenFactory: () => 'your_access_token'
};

const connection = new signalR.HubConnectionBuilder()
    .withUrl("https://reader-your-workspace-id.portal.quix.ai/hub", options)
    .build();

connection.start().then(() => console.log("SignalR connected."));

If the connection is successful, you should see the console log "SignalR connected".

Reading data from a stream

Before you can read data from a stream, you need to subscribe to an event like parameter definition, event definition, parameter data or event data.

Following is an example of establishing a connection to Quix, subscribing to a parameter data stream, reading data from that stream, and unsubscribing from the event using a SignalR client.

var signalR = require("@microsoft/signalr");

const options = {
    accessTokenFactory: () => 'your_access_token'
};

const connection = new signalR.HubConnectionBuilder()
    .withUrl("https://reader-your-workspace-id.portal.quix.ai/hub", options)
    .build();

// Establish connection
connection.start().then(() => {
    console.log("Connected to Quix.");

    // Subscribe to parameter data stream.
    connection.invoke("SubscribeToParameter", "your-topic-name", "your-stream-id", "your-parameter-id");

    // Read data from the stream.
    connection.on("ParameterDataReceived", data => {
        let model = JSON.stringify(data);
        console.log("Received data from stream: " + model);

        // Unsubscribe from stream.
        connection.invoke("UnsubscribeFromParameter", "your-topic-name", "your-stream-id", "your-parameter-id");
    });
});

Following is a list of subscriptions available for SignalR clients.

• SubscribeToParameter(topicName, streamId, parameterId): Subscribes to a parameter data stream. Use UnsubscribeFromParameter(topicname, streamId, parameterId) to unsubscribe.

• SubscribeToParameterDefinitions(topicName, streamId): Subscribes to parameter definition updates.

• SubscribeToEvent(topicName, streamId, eventId): Subscribes to an event data stream. Use UnsubscribeFromEvent(topicName, streamId, eventId) to unsubscribe.

• SubscribeToEventDefinitions(topicName, streamId): Subscribes to event definition updates.

• UnsubscribeFromStream(topicName, streamId): Unsubscribes from all subscriptions of the specified stream.

Following is a list of SignalR events supported by Quix and their payloads.

• ParameterDataReceived: Add a listener to this event to receive parameter data from a stream. Following is a sample payload for this event.

{
  topicName: 'topic-1',
  streamId: 'b45969d2-4624-4ab7-9779-c8f90ce79420',
  timestamps: [ 1591733989000000000, 1591733990000000000, 1591733991000000000 ],
  numericValues: { ParameterA: [ 1, 2, 3 ] },
  stringValues: {},
  tagValues: { ParameterA: [ null, null, 'tag-1' ] }
}

• ParameterDefinitionsUpdated: Add a listener to this event to receive data from SubscribeToParameterDefinitions subscription. Following is a sample payload of this event.

{
    topicName: 'topic-1',
    streamId: 'b45969d2-4624-4ab7-9779-c8f90ce79420',
    definitions: [
        {
            Id: 'ParameterA',
            Name: 'Parameter A',
            Description: 'Description of parameter A',
            MinimumValue: null,
            MaximumValue: 100.0,
            Unit: 'kmh',
            CustomProperties: null,
            Localtion: '/car/general'
        }
    ]
}

• EventDataReceived: Add a listener to this event to receive data from SubscribeToEvent subscription. Following is a sample payload of this event.

{
    topicName: 'topic-1',
    streamId: 'b45969d2-4624-4ab7-9779-c8f90ce79420'
    id: 'EventA',
    timestamp: 1591733990000000000,
    value: 'val-a',
    tags: {
        tag1: 'val1'
    }
}