log error and ignore for external redirects

packages/astro/src/core/logger/core.ts

@@ -26,6 +26,7 @@ export type LoggerLabel =
 	| 'watch'
 	| 'middleware'
 	| 'preferences'
+	| 'redirects'
 	// SKIP_FORMAT: A special label that tells the logger not to apply any formatting.
 	// Useful for messages that are already formatted, like the server start message.
 	| 'SKIP_FORMAT';

packages/astro/src/core/routing/manifest/create.ts

@@ -451,6 +451,19 @@ export function createRouteManifest(
 			.map(([{ dynamic, content }]) => (dynamic ? `[${content}]` : content))
 			.join('/')}`.toLowerCase();
 
+		{
+			let destination: string
+			if (typeof to === "string") {
+				destination = to
+			}
+			else {
+				destination = to.destination
+			}
+			if (destination.startsWith("http")) {
+				return logger.error('redirects', `Redirecting to an external URLs is not supported: ${from} -> ${to}`);
+			}
+		}
+
 		const routeData: RouteData = {
 			type: 'redirect',
 			route,

packages/astro/test/redirects.test.js

@@ -14,6 +14,7 @@ describe('Astro.redirect', () => {
 				adapter: testAdapter(),
 				redirects: {
 					'/api/redirect': '/test',
+					'/external/redirect': 'https://example.com/',
 				},
 			});
 			await fixture.build();
@@ -27,6 +28,14 @@ describe('Astro.redirect', () => {
 			expect(response.headers.get('location')).to.equal('/login');
 		});
 
+		it('Ignores external redirect', async () => {
+			const app = await fixture.loadTestAdapterApp();
+			const request = new Request('http://example.com/external/redirect');
+			const response = await app.render(request);
+			expect(response.status).to.equal(404);
+			expect(response.headers.get('location')).to.equal(null);
+		});
+
 		it('Warns when used inside a component', async () => {
 			const app = await fixture.loadTestAdapterApp();
 			const request = new Request('http://example.com/late');