fix(binding-coap): send error response if content negotiation fails

eclipse-thingweb · Oct 19, 2022 · f53965b · f53965b
1 parent 0e913be
commit f53965b
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Showing 2 changed files with 45 additions and 10 deletions.
diff --git a/packages/binding-coap/src/coap-server.ts b/packages/binding-coap/src/coap-server.ts
@@ -244,23 +244,52 @@ export default class CoapServer implements ProtocolServer {
         }
     }
 
+    /**
+     * Negotiates the Content-Format that should be used for a CoAP response.
+     *
+     * If a specific Content-Format is requested by a client, as indicated by
+     * an Accept option, it will be set for the outgoing response if it is supported
+     * for the resource in question.
+     * If no Accept option is set, the default Content-Format will be used as a fallback.
+     * In these cases, the function returns `true` to indicate a successful negotation.
+     *
+     * If an Accept option is present but the Content-Format is not supported, the response
+     * will be sent immediately with a status code `4.06` (Not Acceptable) and an error
+     * message as a diagnostic payload in accordance with RFC 7252, sections 5.10.4 and
+     * 5.5.2.
+     * In this case, the function returns `false` to indicate the failed negotiation.
+     *
+     * @param req The incoming request.
+     * @param res The outgoing response.
+     * @param availableContentFormats The Content-Formats available for this resource.
+     * @param defaultContentFormat The default Content-Format used as a fallback.
+     * @returns `true` if the negotiation did not encounter any error, `false` otherwise.
+     */
     private negotiateContentFormat(
         req: IncomingMessage,
         res: OutgoingMessage,
         availableContentFormats: string[],
         defaultContentFormat: string
-    ) {
+    ): boolean {
         const accept = req.headers.Accept;
 
         if (typeof accept === "string" && availableContentFormats.includes(accept)) {
             debug(`Received available Content-Format ${accept} in Accept option.`);
             res.setHeader("Content-Format", accept);
-            return;
+            return true;
+        }
+
+        if (accept == null) {
+            debug(`Request did not contain an accept option, using the default ${defaultContentFormat}.`);
+            res.setHeader("Content-Format", defaultContentFormat);
         }
 
-        debug("Request did not contain an accept option or Content-Format is not supported.");
+        debug(`Request contained an accept option whose Content-Format ${accept} is not supported.`);
 
-        res.setHeader("Content-Format", defaultContentFormat);
+        res.code = "4.06";
+        res.end(`Content-Format ${accept} is not supported by this resource.`);
+
+        return false;
     }
 
     private async handleRequest(req: IncomingMessage, res: OutgoingMessage) {
@@ -341,14 +370,17 @@ export default class CoapServer implements ProtocolServer {
                 if (segments.length === 2 || segments[2] === "") {
                     // Thing root -> send TD
                     if (req.method === "GET") {
-                        this.negotiateContentFormat(
+                        const negotiationSuccessful = this.negotiateContentFormat(
                             req,
                             res,
                             [ContentSerdes.DEFAULT, ContentSerdes.TD],
                             ContentSerdes.TD
                         );
-                        res.code = "2.05";
-                        res.end(JSON.stringify(thing.getThingDescription()));
+
+                        if (negotiationSuccessful) {
+                            res.code = "2.05";
+                            res.end(JSON.stringify(thing.getThingDescription()));
+                        }
                     } else {
                         res.code = "4.05";
                         res.end("Method Not Allowed");

diff --git a/packages/binding-coap/test/coap-server-test.ts b/packages/binding-coap/test/coap-server-test.ts
@@ -25,7 +25,7 @@ import * as TD from "@node-wot/td-tools";
 import CoapServer from "../src/coap-server";
 import { CoapClient } from "../src/coap";
 import { Readable } from "stream";
-import { request } from "coap";
+import { IncomingMessage, request } from "coap";
 
 // should must be called to augment all variables
 should();
@@ -299,11 +299,14 @@ class CoapServerTest {
         for (const contentFormat of contentFormats) {
             const req = request(uri);
             req.setHeader("Accept", contentFormat);
-            req.on("response", (res) => {
+            req.on("response", (res: IncomingMessage) => {
                 const requestContentFormat = res.headers["Content-Format"];
 
                 if (contentFormat === unsupportedContentFormat) {
-                    expect(requestContentFormat).to.equal(defaultContentFormat);
+                    expect(res.code).to.equal("4.06");
+                    expect(res.payload.toString()).to.equal(
+                        `Content-Format ${unsupportedContentFormat} is not supported by this resource.`
+                    );
                 } else {
                     expect(requestContentFormat).to.equal(contentFormat);
                 }