Follow redirects in the loader

packages/host/tests/helpers/index.gts

@@ -557,10 +557,6 @@ async function setupTestRealm({
     permissions,
     realmSecretSeed: testRealmSecretSeed,
   });
-  loader.prependURLHandlers([
-    (req) => sourceFetchRedirectHandle(req, adapter, realm),
-    (req) => sourceFetchReturnUrlHandle(req, realm.maybeHandle.bind(realm)),
-  ]);
 
   await realm.ready;
   return { realm, adapter };
@@ -890,87 +886,6 @@ export function diff(
   };
 }
 
-function isCardSourceFetch(request: Request) {
-  return (
-    request.method === 'GET' &&
-    request.headers.get('Accept') === SupportedMimeType.CardSource &&
-    request.url.includes(testRealmURL)
-  );
-}
-
-export async function sourceFetchReturnUrlHandle(
-  request: Request,
-  defaultHandle: (req: Request) => Promise<Response | null>,
-) {
-  if (isCardSourceFetch(request)) {
-    let r = await defaultHandle(request);
-    if (r) {
-      return new MockRedirectedResponse(r.body, r, request.url) as Response;
-    }
-  }
-  return null;
-}
-
-export async function sourceFetchRedirectHandle(
-  request: Request,
-  adapter: RealmAdapter,
-  realm: Realm,
-) {
-  let urlParts = new URL(request.url).pathname.split('.');
-  if (
-    isCardSourceFetch(request) &&
-    urlParts.length === 1 //has no extension
-  ) {
-    const realmPaths = new RealmPaths(realm.url);
-    const localPath = realmPaths.local(request.url);
-    const ref = await getFileWithFallbacks(
-      localPath,
-      adapter.openFile.bind(adapter),
-      executableExtensions,
-    );
-    let maybeExtension = ref?.path.split('.').pop();
-    let responseUrl = maybeExtension
-      ? `${request.url}.${maybeExtension}`
-      : request.url;
-
-    if (
-      ref &&
-      (ref.content instanceof ReadableStream ||
-        ref.content instanceof Uint8Array ||
-        typeof ref.content === 'string')
-    ) {
-      let r = createResponse(realm, ref.content, {
-        headers: {
-          'last-modified': formatRFC7231(ref.lastModified),
-        },
-      });
-      return new MockRedirectedResponse(r.body, r, responseUrl) as Response;
-    }
-  }
-  return null;
-}
-
-export class MockRedirectedResponse extends Response {
-  private _mockUrl: string;
-
-  constructor(
-    body?: BodyInit | null | undefined,
-    init?: ResponseInit,
-    url?: string,
-  ) {
-    super(body, init);
-    this._mockUrl = url || '';
-  }
-
-  get redirected() {
-    return true;
-  }
-
-  get url() {
-    return this._mockUrl;
-  }
-}
-
 export async function elementIsVisible(element: Element) {
   return new Promise((resolve) => {
     let intersectionObserver = new IntersectionObserver(function (entries) {

packages/realm-server/tests/loader-test.ts

@@ -178,4 +178,28 @@ module('loader', function (hooks) {
     let testingLoader = Loader.getLoaderFor(card);
     assert.strictEqual(testingLoader, loader, 'the loaders are the same');
   });
+
+  test('is able to follow redirects', async function (assert) {
+    loader.prependURLHandlers([
+      async (request) => {
+        if (request.url.includes('node-b.abc')) {
+          return new Response('final redirection url');
+        }
+        return null;
+      },
+      async (request) => {
+        if (!request.url.includes('node-a.abc')) {
+          return null;
+        }
+        return new Response('redirected', {
+          status: 301,
+          headers: new Headers({ Location: `http://node-b.abc` }),
+        });
+      },
+    ]);
+
+    let response = await loader.fetch(`http://node-a.abc`);
+    assert.strictEqual(response.url, 'http://node-b.abc/');
+    assert.true(response.redirected);
+  });
 });

packages/runtime-common/loader.ts

@@ -495,17 +495,50 @@ export class Loader {
     }
   }
 
+  // For following redirects of responses returned by loader's urlHandlers
+  async simulateFetch(request: Request, result: Response): Promise<Response> {
+    const urlString = request.url;
+    let redirectedHeaderKey = 'simulated-fetch-redirected'; // Temporary header to track if the request was redirected in the redirection chain
+
+    if (result.status >= 300 && result.status < 400) {
+      const location = result.headers.get('location');
+      if (location) {
+        request.headers.set(redirectedHeaderKey, 'true');
+        return await this.fetch(new URL(location, urlString), request);
+      }
+    }
+
+    // We are using Object.defineProperty because `url` and `redirected`
+    // response properties are read-only. We are overriding these properties to
+    // conform to the Fetch API specification where the `url` property is set to
+    // the final URL and the `redirected` property is set to true if the request
+    // was redirected. Normally, when using a native fetch, these properties are
+    // set automatically by the client, but in this case, we are simulating the
+    // fetch and need to set these properties manually.
+
+    if (request.url && !result.url) {
+      Object.defineProperty(result, 'url', { value: urlString });
+
+      if (request.headers.get(redirectedHeaderKey) === 'true') {
+        Object.defineProperty(result, 'redirected', { value: true });
+        request.headers.delete(redirectedHeaderKey);
+      }
+    }
+
+    return result;
+  }
+
   async fetch(
     urlOrRequest: string | URL | Request,
     init?: RequestInit,
   ): Promise<Response> {
     try {
       for (let handler of this.urlHandlers) {
-        let result = await handler(
-          this.asUnresolvedRequest(urlOrRequest, init),
-        );
+        let request = this.asUnresolvedRequest(urlOrRequest, init);
+
+        let result = await handler(request);
         if (result) {
-          return result;
+          return await this.simulateFetch(request, result);
         }
       }
       return await getNativeFetch()(this.asResolvedRequest(urlOrRequest, init));