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0.8.6 • Public • Published

OPC UA Client Protocol Binding

W3C Web of Things (WoT) Protocol Binding for OPC UA. This package uses nodep-opcua as a low-level client for OPCUA over TCP.

Protocol specifier

The protocol prefix handled by this binding is opc.tcp. This is the standard prefix used by OPC-UA connection endpoint.

Getting Started

You can define an OPCUA property in a thing description, by using an "opc.tcp://" href.

const thingDescription = {
    "@context": "https://www.w3.org/2019/wot/td/v1",
    "@type": ["Thing"],
    securityDefinitions: { nosec_sc: { scheme: "nosec" } },
    security: "nosec_sc",
    title: "servient",
    description: "node-wot CLI Servient",
    properties: {
        pumpSpeed: {
            description: "the pump speed",
            type: "number",
            forms: [
                    href: "opc.tcp://opcuademo.sterfive.com:26543", // endpoint,
                    op: ["readproperty", "observeproperty"],
                    "opcua:nodeId": "ns=1;s=PumpSpeed",
// examples/src/opcua/dempo-opcua1.ts
import { Servient } from "@node-wot/core";
import { OPCUAClientFactory } from "@node-wot/binding-opcua";

(async () => {
    const servient = new Servient();
    servient.addClientFactory(new OPCUAClientFactory());

    const wot = await servient.start();
    const thing = await wot.consume(thingDescription);

    const content = await thing.readProperty("pumpSpeed");
    const json = (await content.value()).valueOf();

    console.log("Pump Speed is", json);

    await servient.shutdown();

Run the Example App

The examples/src/opcua folder contains a set of typescript demo that shows you how to define a thing description containing OPCUA Variables and methods.

  • demo-opcua1.ts shows how to define and read an OPC-UA variable in WoT.
  • demo-opcua2.ts shows how to subscribe to an OPC-UA variable in WoT.
  • opcua-coffee-machine-demo.ts demonstrates how to define and invoke OPCUA methods as WoT actions.

Form extensions


the href property must contains a OPCUA endpoint url in the form opc.tcp://MACHINE:PORT/Application such as for instance: opc.tcp://opcuademo.sterfive.com:26543 or opc.tcp://localhost:48010


The form must contain an opcua:nodeId property that describes the nodeId of the OPCUA Variable to read/write/subscribe or the nodeId of the OPCUA Object related to the action.

The opcua:nodeId can have 2 forms:

  • a NodeId as a string, such as "ns=1;i=1234" , for instance:
"opcua:nodeId": "ns=1;s=\"Machine\".\"Component\""
  • or browsePath: The browse path will be converted into the corresponding nodeId at runtime when first encountered.
"opcua:nodeId": { root: "i=84", path: "/Objects/2:DeviceSet/1:CoffeeMachine" },


for example:

const thingDescription = {
    // ...
    actions: {
        brewCoffee: {
            forms: [
                    href: "opc.tcp://opcuademo.sterfive.com:26543",
                    op: ["invokeaction"],
                    "opcua:nodeId": { root: "i=84", path: "/Objects/2:DeviceSet/1:CoffeeMachine" },
                    "opcua:method": { root: "i=84", path: "/Objects/2:DeviceSet/1:CoffeeMachine/2:MethodSet/9:Start" },

defining a property

const thingDescription = {
    // ...
    properties: {
        temperature: {
            description: "the temperature",
            observable: true,
            readOnly: true,
            unit: "m/s",
            type: "number",
            forms: [
                    href: "opc.tcp://opcuademo.sterfive.com:26543",
                    op: ["readproperty", "observeproperty"],
                    "opcua:nodeId": "ns=1;s=Temperature",


The OPC-UA binding for node-wot offers additionals feature to allow you to interact with OPCUA Variant and DataValue in OPCUA JSON encoded form. For an example of use, you can dive into the unit test of the binding-opcua library.

Exploring the unit tests

A set of examples can be found in this unit test: packages\binding-opcua\test\full-opcua-thing-test.ts

Additional tools

basic OPC-UA demo server

A basic demo OPC-UA server can be started using the following command.

thingweb.node-wot> ts-node packages/binding-opcua/test/fixture/basic-opcua-server.ts
Server started opc.tcp://<YOURMACHINENAME>:7890

awesome WoT - OPCUA tools

the node-wot-opcua-tools project provides some useful applications built on top of thingweb.node-wob and the OPCUA binding.




npm i @node-wot/binding-opcua

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