🐛 Fixed returning HTTP 500 response when recommendations check fails

ref ENG-737
ref https://linear.app/tryghost/issue/ENG-737/http-500-errors-from-recommendations-check-endpoint

- it's still possible for `this.#externalRequest.get` to throw, like if
  DNS resolution fails
- we want to try-catch this so we don't throw from this function and
  return a HTTP 500 to the user
- instead, we can just return `undefined`, which is the fallback
- adds a breaking test too

ghost/recommendations/src/RecommendationMetadataService.ts

@@ -40,25 +40,31 @@ export class RecommendationMetadataService {
     }
 
     async #fetchJSON(url: URL, options?: {timeout?: number}) {
-        // default content type is application/x-www-form-encoded which is what we need for the webmentions spec
-        const response = await this.#externalRequest.get(url.toString(), {
-            throwHttpErrors: false,
-            maxRedirects: 10,
-            followRedirect: true,
-            timeout: 15000,
-            retry: {
-                // Only retry on network issues, or specific HTTP status codes
-                limit: 3
-            },
-            ...options
-        });
+        // Even though we have throwHttpErrors: false, we still need to catch DNS errors
+        // that can arise from externalRequest, otherwise we'll return a HTTP 500 to the user
+        try {
+            // default content type is application/x-www-form-encoded which is what we need for the webmentions spec
+            const response = await this.#externalRequest.get(url.toString(), {
+                throwHttpErrors: false,
+                maxRedirects: 10,
+                followRedirect: true,
+                timeout: 15000,
+                retry: {
+                    // Only retry on network issues, or specific HTTP status codes
+                    limit: 3
+                },
+                ...options
+            });
 
-        if (response.statusCode >= 200 && response.statusCode < 300) {
-            try {
-                return JSON.parse(response.body);
-            } catch (e) {
-                return undefined;
+            if (response.statusCode >= 200 && response.statusCode < 300) {
+                try {
+                    return JSON.parse(response.body);
+                } catch (e) {
+                    return undefined;
+                }
             }
+        } catch (e) {
+            return undefined;
         }
     }
 

ghost/recommendations/test/RecommendationMetadataService.test.ts

@@ -32,6 +32,7 @@ describe('RecommendationMetadataService', function () {
 
     afterEach(function () {
         nock.cleanAll();
+        sinon.restore();
     });
 
     it('Returns metadata from the Ghost site', async function () {
@@ -181,6 +182,13 @@ describe('RecommendationMetadataService', function () {
         });
     });
 
+    it('does not throw an error even if fetching throws an error', async function () {
+        // TODO: simulate DNS resolution failures if possible
+        sinon.stub(got, 'get').rejects(new Error('Failed to fetch'));
+
+        await service.fetch(new URL('https://exampleghostsite.com/subdirectory'));
+    });
+
     it('Nullifies empty oembed data', async function () {
         nock('https://exampleghostsite.com')
             .get('/subdirectory/members/api/site')