README.md

CoAP Protocol Binding of node-wot

W3C WoT Binding Template specification for CoAP can be found here.

Current Maintainer(s): @JKRhb

Protocol specifier

The protocol prefix handled by this binding is coap:// or coaps://.

Getting Started

In the following examples, how to use the CoAP binding of node-wot is shown.

Prerequisites

• npm install @node-wot/core
• npm install @node-wot/binding-coap

Client Example

The client example tries to connect to a TestThing via CoAP and read the string property. The Thing Description is located under the following CoAP URI coap://plugfest.thingweb.io:5683/testthing.

node example-client.js

// example-client.js
const { Servient } = require("@node-wot/core");
const { CoapClientFactory } = require("@node-wot/binding-coap");

// create Servient and add CoAP binding
const servient = new Servient();
servient.addClientFactory(new CoapClientFactory());

servient
    .start()
    .then(async (WoT) => {
        try {
            const td = await WoT.requestThingDescription("coap://plugfest.thingweb.io:5683/testthing");
            const thing = await WoT.consume(td);

            // read property
            const read1 = await thing.readProperty("string");
            console.log("string value is: ", await read1.value());
        } catch (err) {
            console.error("Script error:", err);
        }
    })
    .catch((err) => {
        console.error("Start error:", err);
    });

Using PSK with CoAPs (DTLS)

The CoAP binding also supports secure communication over coaps:// using DTLS with Pre-Shared Keys (PSK).

To use PSK security, define a psk security scheme in the Thing Description and provide the credentials when consuming the Thing.

Thing Description Example (PSK)

{
    "title": "SecureThing",
    "securityDefinitions": {
        "psk_sc": {
            "scheme": "psk"
        }
    },
    "security": ["psk_sc"],
    "properties": {
        "count": {
            "type": "integer",
            "forms": [
                {
                    "href": "coaps://localhost:5684/count"
                }
            ]
        }
    }
}

Client Example with PSK

const { Servient } = require("@node-wot/core");
const { CoapClientFactory } = require("@node-wot/binding-coap");

const servient = new Servient();
servient.addClientFactory(new CoapClientFactory());

servient
    .start()
    .then(async (WoT) => {
        try {
            const td = await WoT.requestThingDescription("coaps://localhost:5684/secureThing");
            const thing = await WoT.consume(td);

            // configure PSK security
            thing.setSecurity(td.securityDefinitions, {
                identity: "Client_identity",
                psk: "secretPSK",
            });

            const value = await thing.readProperty("count");
            console.log("count value is:", await value.value());
        } catch (err) {
            console.error("Script error:", err);
        }
    })
    .catch((err) => {
        console.error("Start error:", err);
    });

Notes

• The identity must match the server configuration.
• The psk must match the server's configured secret.
• Currently, only the psk security scheme is supported for coaps:// in this binding.

Server Example

The server example produces a thing that allows for setting a property count. The thing is reachable through CoAP.

node example-server.js

// example-server.js
const { Servient } = require("@node-wot/core");
const { CoapServer } = require("@node-wot/binding-coap");

// create Servient add HTTP binding
const servient = new Servient();
servient.addServer(new CoapServer());

servient.start().then((WoT) => {
    WoT.produce({
        title: "MyCounter",
        properties: {
            count: {
                type: "integer",
            },
        },
    }).then((thing) => {
        console.log("Produced " + thing.getThingDescription().title);

        let count = 0;

        // set property handlers (using async-await)
        thing.setPropertyReadHandler("count", async () => count);
        thing.setPropertyWriteHandler("count", async (intOutput) => {
            count = await intOutput.value();
        });

        thing.expose().then(() => {
            console.info(thing.getThingDescription().title + " ready");
            console.info("TD : " + JSON.stringify(thing.getThingDescription()));
        });
    });
});

More Details

See https://github.com/eclipse-thingweb/node-wot/