fix(@angular/ssr): return 302 when redirectTo is a function

Ensure the server returns a 302 status code and sets the correct 'Location' header when the redirectTo value is a function, aligning with expected HTTP redirect behavior.

Author: alan-agius4

packages/angular/ssr/src/app.ts

@@ -174,15 +174,7 @@ export class AngularServerApp {
 
     const { redirectTo, status, renderMode } = matchedRoute;
     if (redirectTo !== undefined) {
-      return new Response(null, {
-        // Note: The status code is validated during route extraction.
-        // 302 Found is used by default for redirections
-        // See: https://developer.mozilla.org/en-US/docs/Web/API/Response/redirect_static#status
-        status: status ?? 302,
-        headers: {
-          'Location': buildPathWithParams(redirectTo, url.pathname),
-        },
-      });
+      return createRedirectResponse(buildPathWithParams(redirectTo, url.pathname), status);
     }
 
     if (renderMode === RenderMode.Prerender) {
@@ -324,20 +316,28 @@ export class AngularServerApp {
     let html = await assets.getIndexServerHtml().text();
     html = await this.runTransformsOnHtml(html, url, preload);
 
-    const { content } = await renderAngular(
+    const result = await renderAngular(
       html,
       this.boostrap,
       url,
       platformProviders,
       SERVER_CONTEXT_VALUE[renderMode],
     );
 
+    if (result.hasNavigationError) {
+      return null;
+    }
+
+    if (result.redirectTo) {
+      return createRedirectResponse(result.redirectTo, status);
+    }
+
     const { inlineCriticalCssProcessor, criticalCssLRUCache, textDecoder } = this;
 
     // Use a stream to send the response before finishing rendering and inling critical CSS, improving performance via header flushing.
     const stream = new ReadableStream({
       async start(controller) {
-        const renderedHtml = await content();
+        const renderedHtml = await result.content();
 
         if (!inlineCriticalCssProcessor) {
           controller.enqueue(textDecoder.encode(renderedHtml));
@@ -484,3 +484,20 @@ function appendPreloadHintsToHtml(html: string, preload: readonly string[]): str
     html.slice(bodyCloseIdx),
   ].join('\n');
 }
+
+/**
+ * Creates an HTTP redirect response with a specified location and status code.
+ *
+ * @param location - The URL to which the response should redirect.
+ * @param status - The HTTP status code for the redirection. Defaults to 302 (Found).
+ *                 See: https://developer.mozilla.org/en-US/docs/Web/API/Response/redirect_static#status
+ * @returns A `Response` object representing the HTTP redirect.
+ */
+function createRedirectResponse(location: string, status = 302): Response {
+  return new Response(null, {
+    status,
+    headers: {
+      'Location': location,
+    },
+  });
+}

packages/angular/ssr/src/routes/ng-routes.ts

@@ -160,15 +160,20 @@ async function* handleRoute(options: {
         invokeGetPrerenderParams,
         includePrerenderFallbackRoutes,
       );
-    } else if (typeof redirectTo === 'string') {
+    } else if (redirectTo !== undefined) {
       if (metadata.status && !VALID_REDIRECT_RESPONSE_CODES.has(metadata.status)) {
         yield {
           error:
             `The '${metadata.status}' status code is not a valid redirect response code. ` +
             `Please use one of the following redirect response codes: ${[...VALID_REDIRECT_RESPONSE_CODES.values()].join(', ')}.`,
         };
+      } else if (typeof redirectTo === 'string') {
+        yield {
+          ...metadata,
+          redirectTo: resolveRedirectTo(metadata.route, redirectTo),
+        };
       } else {
-        yield { ...metadata, redirectTo: resolveRedirectTo(metadata.route, redirectTo) };
+        yield metadata;
       }
     } else {
       yield metadata;

packages/angular/ssr/src/utils/ng.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
+import { APP_BASE_HREF, PlatformLocation } from '@angular/common';
 import {
   ApplicationRef,
   type PlatformRef,
@@ -19,8 +20,9 @@ import {
   platformServer,
   ɵrenderInternal as renderInternal,
 } from '@angular/platform-server';
+import { Router } from '@angular/router';
 import { Console } from '../console';
-import { stripIndexHtmlFromURL } from './url';
+import { joinUrlParts, stripIndexHtmlFromURL } from './url';
 
 /**
  * Represents the bootstrap mechanism for an Angular application.
@@ -35,28 +37,25 @@ export type AngularBootstrap = Type<unknown> | (() => Promise<ApplicationRef>);
  * Renders an Angular application or module to an HTML string.
  *
  * This function determines whether the provided `bootstrap` value is an Angular module
- * or a bootstrap function and calls the appropriate rendering method (`renderModule` or
- * `renderApplication`) based on that determination.
+ * or a bootstrap function and invokes the appropriate rendering method (`renderModule` or `renderApplication`).
  *
- * @param html - The HTML string to be used as the initial document content.
- * @param bootstrap - Either an Angular module type or a function that returns a promise
- *                    resolving to an `ApplicationRef`.
- * @param url - The URL of the application. This is used for server-side rendering to
- *              correctly handle route-based rendering.
- * @param platformProviders - An array of platform providers to be used during the
- *                             rendering process.
- * @param serverContext - A string representing the server context, used to provide additional
- *                        context or metadata during server-side rendering.
- * @returns A promise resolving to an object containing a `content` method, which returns a
- *          promise that resolves to the rendered HTML string.
+ * @param html - The initial HTML document content.
+ * @param bootstrap - An Angular module type or a function returning a promise that resolves to an `ApplicationRef`.
+ * @param url - The application URL, used for route-based rendering in SSR.
+ * @param platformProviders - An array of platform providers for the rendering process.
+ * @param serverContext - A string representing the server context, providing additional metadata for SSR.
+ * @returns A promise resolving to an object containing:
+ *          - `hasNavigationError`: Indicates if a navigation error occurred.
+ *          - `redirectTo`: (Optional) The redirect URL if a navigation redirect occurred.
+ *          - `content`: A function returning a promise that resolves to the rendered HTML string.
  */
 export async function renderAngular(
   html: string,
   bootstrap: AngularBootstrap,
   url: URL,
   platformProviders: StaticProvider[],
   serverContext: string,
-): Promise<{ content: () => Promise<string> }> {
+): Promise<{ hasNavigationError: boolean; redirectTo?: string; content: () => Promise<string> }> {
   // A request to `http://www.example.com/page/index.html` will render the Angular route corresponding to `http://www.example.com/page`.
   const urlToRender = stripIndexHtmlFromURL(url).toString();
   const platformRef = platformServer([
@@ -82,6 +81,9 @@ export async function renderAngular(
     ...platformProviders,
   ]);
 
+  let redirectTo: string | undefined;
+  let hasNavigationError = true;
+
   try {
     let applicationRef: ApplicationRef;
     if (isNgModule(bootstrap)) {
@@ -94,7 +96,29 @@ export async function renderAngular(
     // Block until application is stable.
     await applicationRef.whenStable();
 
+    // TODO(alanagius): Find a way to avoid rendering here especially for redirects as any output will be discarded.
+    const envInjector = applicationRef.injector;
+    const router = envInjector.get(Router);
+    const lastSuccessfulNavigation = router.lastSuccessfulNavigation;
+
+    if (lastSuccessfulNavigation?.finalUrl) {
+      hasNavigationError = false;
+
+      const { finalUrl, initialUrl } = lastSuccessfulNavigation;
+      const finalUrlStringified = finalUrl.toString();
+
+      if (initialUrl.toString() !== finalUrlStringified) {
+        const baseHref =
+          envInjector.get(APP_BASE_HREF, null, { optional: true }) ??
+          envInjector.get(PlatformLocation).getBaseHrefFromDOM();
+
+        redirectTo = joinUrlParts(baseHref, finalUrlStringified);
+      }
+    }
+
     return {
+      hasNavigationError,
+      redirectTo,
       content: () =>
         new Promise<string>((resolve, reject) => {
           // Defer rendering to the next event loop iteration to avoid blocking, as most operations in `renderInternal` are synchronous.
@@ -110,6 +134,10 @@ export async function renderAngular(
     await asyncDestroyPlatform(platformRef);
 
     throw error;
+  } finally {
+    if (hasNavigationError || redirectTo) {
+      void asyncDestroyPlatform(platformRef);
+    }
   }
 }
 
@@ -134,7 +162,10 @@ export function isNgModule(value: AngularBootstrap): value is Type<unknown> {
 function asyncDestroyPlatform(platformRef: PlatformRef): Promise<void> {
   return new Promise((resolve) => {
     setTimeout(() => {
-      platformRef.destroy();
+      if (!platformRef.destroyed) {
+        platformRef.destroy();
+      }
+
       resolve();
     }, 0);
   });

packages/angular/ssr/test/app_spec.ts

@@ -38,6 +38,11 @@ describe('AngularServerApp', () => {
         { path: 'redirect/relative', redirectTo: 'home' },
         { path: 'redirect/:param/relative', redirectTo: 'home' },
         { path: 'redirect/absolute', redirectTo: '/home' },
+        {
+          path: 'redirect-to-function',
+          redirectTo: () => 'home',
+          pathMatch: 'full',
+        },
       ],
       [
         {
@@ -106,25 +111,25 @@ describe('AngularServerApp', () => {
 
       it('should correctly handle top level redirects', async () => {
         const response = await app.handle(new Request('http://localhost/redirect'));
-        expect(response?.headers.get('location')).toContain('/home');
+        expect(response?.headers.get('location')).toBe('/home');
         expect(response?.status).toBe(302);
       });
 
       it('should correctly handle relative nested redirects', async () => {
         const response = await app.handle(new Request('http://localhost/redirect/relative'));
-        expect(response?.headers.get('location')).toContain('/redirect/home');
+        expect(response?.headers.get('location')).toBe('/redirect/home');
         expect(response?.status).toBe(302);
       });
 
       it('should correctly handle relative nested redirects with parameter', async () => {
         const response = await app.handle(new Request('http://localhost/redirect/param/relative'));
-        expect(response?.headers.get('location')).toContain('/redirect/param/home');
+        expect(response?.headers.get('location')).toBe('/redirect/param/home');
         expect(response?.status).toBe(302);
       });
 
       it('should correctly handle absolute nested redirects', async () => {
         const response = await app.handle(new Request('http://localhost/redirect/absolute'));
-        expect(response?.headers.get('location')).toContain('/home');
+        expect(response?.headers.get('location')).toBe('/home');
         expect(response?.status).toBe(302);
       });
 
@@ -253,5 +258,13 @@ describe('AngularServerApp', () => {
         expect(response).toBeNull();
       });
     });
+
+    describe('SSR pages', () => {
+      it('returns a 302 status and redirects to the correct location when redirectTo is a function', async () => {
+        const response = await app.handle(new Request('http://localhost/redirect-to-function'));
+        expect(response?.headers.get('location')).toBe('/home');
+        expect(response?.status).toBe(302);
+      });
+    });
   });
 });

packages/angular/ssr/test/routes/ng-routes_spec.ts

@@ -53,6 +53,16 @@ describe('extractRoutesAndCreateRouteTree', () => {
   });
 
   describe('route configuration validation', () => {
+    it('should error when a redirect uses an invalid status code', async () => {
+      setAngularAppTestingManifest(
+        [{ path: '', redirectTo: () => 'home', pathMatch: 'full' }],
+        [{ path: '', renderMode: RenderMode.Server, status: 404 }],
+      );
+
+      const { errors } = await extractRoutesAndCreateRouteTree({ url });
+      expect(errors[0]).toContain(`The '404' status code is not a valid redirect response code.`);
+    });
+
     it(`should error when a route starts with a '/'`, async () => {
       setAngularAppTestingManifest(
         [{ path: 'home', component: DummyComponent }],
@@ -88,7 +98,7 @@ describe('extractRoutesAndCreateRouteTree', () => {
       );
     });
 
-    it(`should not error when a catch-all route didn't match any Angular route.`, async () => {
+    it(`should not error when a catch-all route didn't match any Angular route`, async () => {
       setAngularAppTestingManifest(
         [{ path: 'home', component: DummyComponent }],
         [