Allow components to return a Response (#2944)

* Allow components to return a Response

* Changeset

6 files changed, 80 insertions, 15 deletions

diff --git a/.changeset/chatty-cows-attack.md b/.changeset/chatty-cows-attack.md
new file mode 100644
index 000000000..7fe9fb8c2
--- /dev/null
+++ b/.changeset/chatty-cows-attack.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Allow components to return a Response
diff --git a/packages/astro/src/runtime/server/index.ts b/packages/astro/src/runtime/server/index.ts
index 7f314f721..b9970d59d 100644
--- a/packages/astro/src/runtime/server/index.ts
+++ b/packages/astro/src/runtime/server/index.ts
@@ -412,7 +412,8 @@ async function replaceHeadInjection(result: SSRResult, html: string): Promise<st
 export async function renderToString(result: SSRResult, componentFactory: AstroComponentFactory, props: any, children: any): Promise<string> {
 	const Component = await componentFactory(result, props, children);
 	if (!isAstroComponent(Component)) {
-		throw new Error('Cannot return a Response from a nested component.');
+		const response: Response = Component;
+		throw response;
 	}
 
 	let template = await renderAstroComponent(Component);
@@ -425,20 +426,31 @@ export async function renderPage(
 	props: any,
 	children: any
 ): Promise<{ type: 'html'; html: string } | { type: 'response'; response: Response }> {
-	const response = await componentFactory(result, props, children);
-
-	if (isAstroComponent(response)) {
-		let template = await renderAstroComponent(response);
-		const html = await replaceHeadInjection(result, template);
-		return {
-			type: 'html',
-			html,
-		};
-	} else {
-		return {
-			type: 'response',
-			response,
-		};
+	try {
+		const response = await componentFactory(result, props, children);
+
+		if (isAstroComponent(response)) {
+			let template = await renderAstroComponent(response);
+			const html = await replaceHeadInjection(result, template);
+			return {
+				type: 'html',
+				html,
+			};
+		} else {
+			return {
+				type: 'response',
+				response,
+			};
+		}
+	} catch(err) {
+		if(err instanceof Response) {
+			return {
+				type: 'response',
+				response: err
+			};
+		} else {
+			throw err;
+		}
 	}
 }
 
diff --git a/packages/astro/test/astro-response.test.js b/packages/astro/test/astro-response.test.js
new file mode 100644
index 000000000..719d14d30
--- /dev/null
+++ b/packages/astro/test/astro-response.test.js
@@ -0,0 +1,32 @@
+import { expect } from 'chai';
+import { load as cheerioLoad } from 'cheerio';
+import { loadFixture } from './test-utils.js';
+
+// Asset bundling
+describe('Returning responses', () => {
+	let fixture;
+	/** @type {import('./test-utils').DevServer} */
+	let devServer;
+
+	before(async () => {
+		fixture = await loadFixture({
+			projectRoot: './fixtures/astro-response/',
+		});
+
+		devServer = await fixture.startDevServer();
+	});
+
+	after(async () => {
+		await devServer.stop();
+	});
+
+	it('Works from a page', async () => {
+		let response = await fixture.fetch('/not-found');
+		expect(response.status).to.equal(404);
+	});
+
+	it('Works from a component', async () => {
+		let response = await fixture.fetch('/not-found-component');
+		expect(response.status).to.equal(404);
+	});
+});
diff --git a/packages/astro/test/fixtures/astro-response/src/components/not-found.astro b/packages/astro/test/fixtures/astro-response/src/components/not-found.astro
new file mode 100644
index 000000000..dd339e72b
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-response/src/components/not-found.astro
@@ -0,0 +1,6 @@
+---
+return new Response(null, {
+	status: 404,
+	statusText: `Not found`
+});
+---
diff --git a/packages/astro/test/fixtures/astro-response/src/pages/not-found-component.astro b/packages/astro/test/fixtures/astro-response/src/pages/not-found-component.astro
new file mode 100644
index 000000000..e1077e9c9
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-response/src/pages/not-found-component.astro
@@ -0,0 +1,4 @@
+---
+import NotFound from '../components/not-found.astro';
+---
+<NotFound />
diff --git a/packages/astro/test/fixtures/astro-response/src/pages/not-found.astro b/packages/astro/test/fixtures/astro-response/src/pages/not-found.astro
new file mode 100644
index 000000000..dd339e72b
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-response/src/pages/not-found.astro
@@ -0,0 +1,6 @@
+---
+return new Response(null, {
+	status: 404,
+	statusText: `Not found`
+});
+---