feat(core): add helper function to fetch a TD

packages/binding-http/test/http-client-test.ts

@@ -22,12 +22,20 @@ import chai, { expect, should } from "chai";
 
 import * as http from "http";
 
-import { Content, DefaultContent, ContentSerdes, createLoggers, ProtocolServer } from "@node-wot/core";
+import {
+    Content,
+    DefaultContent,
+    ContentSerdes,
+    createLoggers,
+    ProtocolServer,
+    Servient,
+    Helpers,
+} from "@node-wot/core";
 
 import { Readable } from "stream";
 
 import HttpClient from "../src/http-client";
-import { HttpForm } from "../src/http";
+import { HttpForm, HttpClientFactory } from "../src/http";
 
 import express from "express";
 import serveStatic from "serve-static";
@@ -518,4 +526,24 @@ class HttpClientTest2 {
             );
         });
     }
+
+    @test async "should fetchTD successfully"() {
+        const servient = new Servient();
+        servient.addClientFactory(new HttpClientFactory());
+        const helpers = new Helpers(servient);
+        const td = await helpers.fetchTD("http://plugfest.thingweb.io:8083/counter");
+        expect(td).to.contains.keys("@context", "title");
+    }
+
+    @test async "should fail fetching a non TD resource"() {
+        const servient = new Servient();
+        servient.addClientFactory(new HttpClientFactory());
+        const helpers = new Helpers(servient);
+        try {
+            await helpers.fetchTD("http://plugfest.thingweb.io:8083/"); // reports array
+            expect(1).to.equal(0, "Does not report that we do not deal with a proper TD");
+        } catch (err) {
+            // correct since it is not a proper TD
+        }
+    }
 }

packages/core/src/helpers.ts

@@ -34,7 +34,7 @@ import * as TDT from "wot-thing-description-types";
 import { ContentSerdes } from "./content-serdes";
 import Ajv, { ValidateFunction, ErrorObject } from "ajv";
 import TDSchema from "wot-thing-description-types/schema/td-json-schema-validation.json";
-import { DataSchemaValue, ExposedThingInit } from "wot-typescript-definitions";
+import { DataSchemaValue, ExposedThingInit, ThingDescription } from "wot-typescript-definitions";
 import { SomeJSONSchema } from "ajv/dist/types/json-schema";
 import { ThingInteraction, ThingModelHelpers } from "@node-wot/td-tools";
 import { Resolver } from "@node-wot/td-tools/src/resolver-interface";
@@ -152,8 +152,28 @@ export default class Helpers implements Resolver {
         }
     }
 
-    // TODO: specialize fetch to retrieve just thing descriptions
-    // see https://github.com/eclipse-thingweb/node-wot/issues/1055
+    /**
+     * Fetches a resource with additionally checking TD conformance
+     *
+     * @param uri The URI of a TD resource
+     * @returns A ThingDescription
+     */
+    public async fetchTD(uri: string): Promise<ThingDescription> {
+        const data = await this.fetch(uri);
+        const isValid = Helpers.tsSchemaValidator(data);
+        if (!isValid) {
+            const errors = Helpers.tsSchemaValidator.errors?.map((o: ErrorObject) => o.message).join("\n");
+            throw new Error(errors);
+        }
+        return data as ThingDescription;
+    }
+
+    /**
+     * Fetches a resource
+     *
+     * @param uri The URI of a resource
+     * @returns An object
+     */
     public fetch(uri: string): Promise<unknown> {
         return new Promise<unknown>((resolve, reject) => {
             const client = this.srv.getClientFor(Helpers.extractScheme(uri));

packages/examples/src/bindings/coap/example-client.ts

@@ -15,18 +15,16 @@
 
 import { Servient, Helpers } from "@node-wot/core";
 import { CoapClientFactory } from "@node-wot/binding-coap";
-import { ThingDescription } from "wot-typescript-definitions";
 
 // create Servient and add CoAP binding
 const servient = new Servient();
 servient.addClientFactory(new CoapClientFactory());
 
 const wotHelper = new Helpers(servient);
 wotHelper
-    .fetch("coap://plugfest.thingweb.io:5683/testthing")
-    .then(async (fetched) => {
-        const td: ThingDescription = fetched as ThingDescription;
-        // using await for serial execution (note 'async' in then() of fetch())
+    .fetchTD("coap://plugfest.thingweb.io:5683/testthing")
+    .then(async (td) => {
+        // using await for serial execution (note 'async' in then() of fetchTD())
         try {
             const WoT = await servient.start();
             const thing = await WoT.consume(td);

packages/examples/src/bindings/http/example-client.ts

@@ -15,18 +15,16 @@
 
 import { Servient, Helpers } from "@node-wot/core";
 import { HttpClientFactory } from "@node-wot/binding-http";
-import { ThingDescription } from "wot-typescript-definitions";
 
 // create Servient and add HTTP  binding
 const servient = new Servient();
 servient.addClientFactory(new HttpClientFactory());
 
 const wotHelper = new Helpers(servient);
 wotHelper
-    .fetch("http://plugfest.thingweb.io:8083/testthing")
-    .then(async (fetched) => {
-        const td: ThingDescription = fetched as ThingDescription;
-        // using await for serial execution (note 'async' in then() of fetch())
+    .fetchTD("http://plugfest.thingweb.io:8083/testthing")
+    .then(async (td) => {
+        // using await for serial execution (note 'async' in then() of fetchTD())
         try {
             const WoT = await servient.start();
             const thing = await WoT.consume(td);

packages/examples/src/scripts/counter-client.ts

@@ -14,7 +14,6 @@
  ********************************************************************************/
 
 import { Helpers } from "@node-wot/core";
-import { ThingDescription } from "wot-typescript-definitions";
 
 let WoTHelpers!: Helpers;
 
@@ -31,11 +30,11 @@ function getFormIndexForDecrementWithCoAP(thing: WoT.ConsumedThing): number {
     return 0;
 }
 
-WoTHelpers.fetch("coap://localhost:5683/counter")
+WoTHelpers.fetchTD("coap://localhost:5683/counter")
     .then(async (td) => {
-        // using await for serial execution (note 'async' in then() of fetch())
+        // using await for serial execution (note 'async' in then() of fetchTD())
         try {
-            const thing = await WoT.consume(td as ThingDescription);
+            const thing = await WoT.consume(td);
             console.info("=== TD ===");
             console.info(td);
             console.info("==========");

packages/examples/src/scripts/smart-coffee-machine-client.ts

@@ -17,7 +17,6 @@
 // It considers a fictional smart coffee machine in order to demonstrate the capabilities of Web of Things.
 // An accompanying tutorial is available at http://www.thingweb.io/smart-coffee-machine.html.
 
-import { ThingDescription } from "wot-typescript-definitions";
 import { Helpers } from "@node-wot/core";
 let WoTHelpers!: Helpers;
 
@@ -29,9 +28,9 @@ function log(msg: string, data: unknown) {
     console.info("======================");
 }
 
-WoTHelpers.fetch("http://127.0.0.1:8080/smart-coffee-machine").then(async (td) => {
+WoTHelpers.fetchTD("http://127.0.0.1:8080/smart-coffee-machine").then(async (td) => {
     try {
-        const thing = await WoT.consume(td as ThingDescription);
+        const thing = await WoT.consume(td);
         log("Thing Description:", td);
 
         // Read property allAvailableResources

packages/examples/src/security/oauth/consumer.ts

@@ -13,12 +13,11 @@
  * SPDX-License-Identifier: EPL-2.0 OR W3C-20150513
  ********************************************************************************/
 import { Helpers } from "@node-wot/core";
-import { ThingDescription } from "wot-typescript-definitions";
 
 let WoTHelpers!: Helpers;
 
-WoTHelpers.fetch("https://localhost:8080/oauth").then((td) => {
-    WoT.consume(td as ThingDescription).then(async (thing) => {
+WoTHelpers.fetchTD("https://localhost:8080/oauth").then((td) => {
+    WoT.consume(td).then(async (thing) => {
         try {
             const resp = await thing.invokeAction("sayOk");
             const result = await resp?.value();

packages/examples/src/testthing/testclient.ts

@@ -14,7 +14,6 @@
  ********************************************************************************/
 
 import { Helpers } from "@node-wot/core";
-import { ThingDescription } from "wot-typescript-definitions";
 let WoTHelpers!: Helpers;
 
 console.log = () => {
@@ -51,11 +50,11 @@ async function testPropertyWrite(
     }
 }
 
-WoTHelpers.fetch("http://localhost:8080/testthing")
+WoTHelpers.fetchTD("http://localhost:8080/testthing")
     .then(async (td) => {
-        // using await for serial execution (note 'async' in then() of fetch())
+        // using await for serial execution (note 'async' in then() of fetchTD())
         try {
-            const thing = await WoT.consume(td as ThingDescription);
+            const thing = await WoT.consume(td);
             console.info("=== TD ===");
             console.info(td);
             console.info("==========");