fix(dev): dont reroute endpoint responses (#9830)

* fix(dev): dont reroute endpoint responses

* factor out header name as a const

* add test case

* add changeset

.changeset/rotten-masks-rhyme.md

@@ -0,0 +1,5 @@
+---
+"astro": patch
+---
+
+Fixes an issue where 404 responses from endpoints were replaced with contents of 404.astro in dev mode.

packages/astro/src/core/app/index.ts

@@ -6,6 +6,7 @@ import type {
 	SSRManifest,
 } from '../../@types/astro.js';
 import { createI18nMiddleware, i18nPipelineHook } from '../../i18n/middleware.js';
+import { REROUTE_DIRECTIVE_HEADER } from '../../runtime/server/consts.js';
 import type { SinglePageBuiltModule } from '../build/types.js';
 import { getSetCookiesFromResponse } from '../cookies/index.js';
 import { consoleLogDestination } from '../logger/console.js';
@@ -278,7 +279,7 @@ export class App {
 
 		if (
 			REROUTABLE_STATUS_CODES.has(response.status) &&
-			response.headers.get('X-Astro-Reroute') !== 'no'
+			response.headers.get(REROUTE_DIRECTIVE_HEADER) !== 'no'
 		) {
 			return this.#renderError(request, {
 				response,
@@ -286,8 +287,8 @@ export class App {
 			});
 		}
 
-		if (response.headers.has('X-Astro-Reroute')) {
-			response.headers.delete('X-Astro-Reroute');
+		if (response.headers.has(REROUTE_DIRECTIVE_HEADER)) {
+			response.headers.delete(REROUTE_DIRECTIVE_HEADER);
 		}
 
 		if (addCookieHeader) {

packages/astro/src/runtime/server/consts.ts

@@ -0,0 +1 @@
+export const REROUTE_DIRECTIVE_HEADER = 'X-Astro-Reroute';

packages/astro/src/runtime/server/endpoint.ts

@@ -1,4 +1,5 @@
 import { bold } from 'kleur/colors';
+import { REROUTE_DIRECTIVE_HEADER } from './consts.js';
 import type { APIContext, EndpointHandler } from '../../@types/astro.js';
 import type { Logger } from '../../core/logger/core.js';
 
@@ -41,6 +42,6 @@ export async function renderEndpoint(
 	const response = await handler.call(mod, context);
 	// Endpoints explicitly returning 404 or 500 response status should
 	// NOT be subject to rerouting to 404.astro or 500.astro.
-	response.headers.set('X-Astro-Reroute', 'no');
+	response.headers.set(REROUTE_DIRECTIVE_HEADER, 'no');
 	return response;
 }

packages/astro/src/vite-plugin-astro-server/route.ts

@@ -35,6 +35,7 @@ import { preload } from './index.js';
 import { getComponentMetadata } from './metadata.js';
 import { handle404Response, writeSSRResult, writeWebResponse } from './response.js';
 import { getScriptsForURL } from './scripts.js';
+import { REROUTE_DIRECTIVE_HEADER } from '../runtime/server/consts.js';
 
 const clientLocalsSymbol = Symbol.for('astro.locals');
 
@@ -342,7 +343,7 @@ export async function handleRoute({
 			})
 		);
 	}
-	if (response.status === 404 && has404Route(manifestData)) {
+	if (response.status === 404 && has404Route(manifestData) && response.headers.get(REROUTE_DIRECTIVE_HEADER) !== "no") {
 		const fourOhFourRoute = await matchRoute('/404', manifestData, pipeline);
 		if (options && fourOhFourRoute?.route !== options.route)
 			return handleRoute({

packages/astro/test/dev-routing.test.js

@@ -246,6 +246,14 @@ describe('Development Routing', () => {
 			expect(body.title).to.equal('data [slug]');
 		});
 
+		it('error responses are served untouched', async () => {
+			const response = await fixture.fetch('/not-ok');
+			expect(response.status).to.equal(404);
+			expect(response.headers.get("Content-Type")).to.equal("text/plain;charset=UTF-8");
+			const body = await response.text();
+			expect(body).to.equal("Text from pages/not-ok.ts");
+		})
+
 		it('correct MIME type when loading /home.json (static route)', async () => {
 			const response = await fixture.fetch('/home.json');
 			expect(response.headers.get('content-type')).to.match(/application\/json/);

packages/astro/test/fixtures/with-endpoint-routes/src/pages/404.astro

@@ -0,0 +1 @@
+<h1>Text from pages/404.astro</h1>

packages/astro/test/fixtures/with-endpoint-routes/src/pages/not-ok.ts

@@ -0,0 +1,5 @@
+export async function GET() {
+    return new Response("Text from pages/not-ok.ts", {
+        status: 404,
+    });
+}