fix(rewrite): copy body from the request

.changeset/swift-phones-rhyme.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue where `Astro.rewrite` wasn't carrying over the body of a `Request` in on-demand pages.

packages/astro/src/core/render-context.ts

@@ -32,6 +32,7 @@ import { callMiddleware } from './middleware/callMiddleware.js';
 import { sequence } from './middleware/index.js';
 import { renderRedirect } from './redirects/render.js';
 import { type Pipeline, Slots, getParams, getProps } from './render/index.js';
+import { copyRequest } from "./routing/index.js";
 
 /**
  * Each request is rendered using a `RenderContext`.
@@ -224,7 +225,7 @@ export class RenderContext {
 				if (reroutePayload instanceof Request) {
 					this.request = reroutePayload;
 				} else {
-					this.request = new Request(
+					this.request = await copyRequest(
 						new URL(routeData.pathname ?? routeData.route, this.url.origin),
 						this.request
 					);
@@ -416,7 +417,7 @@ export class RenderContext {
 				if (reroutePayload instanceof Request) {
 					this.request = reroutePayload;
 				} else {
-					this.request = new Request(
+					this.request = await copyRequest(
 						new URL(routeData.pathname ?? routeData.route, this.url.origin),
 						this.request
 					);

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

@@ -2,3 +2,4 @@ export { createRouteManifest } from './manifest/create.js';
 export { deserializeRouteData, serializeRouteData } from './manifest/serialization.js';
 export { matchAllRoutes, matchRoute } from './match.js';
 export { validateDynamicRouteModule, validateGetStaticPathsResult } from './validation.js';
+export { copyRequest } from "./request.js"

packages/astro/src/core/routing/request.ts

@@ -0,0 +1,27 @@
+/**
+ * Utility function that creates a new `Request` with a new URL from an old `Request`.
+ * 
+ * @param newUrl The new `URL`
+ * @param oldRequest The old `Request`
+ */
+export async function copyRequest(newUrl: URL, oldRequest: Request): Promise<Request> {
+	const body = oldRequest.headers.get('content-type') ? oldRequest.blob() : Promise.resolve(undefined);
+	return body.then((requestBody) => {
+		return new Request(newUrl, {
+			method: oldRequest.method,
+			headers: oldRequest.headers,
+			body: requestBody,
+			referrer: oldRequest.referrer,
+			referrerPolicy: oldRequest.referrerPolicy,
+			mode: oldRequest.mode,
+			credentials: oldRequest.credentials,
+			cache: oldRequest.cache,
+			redirect: oldRequest.redirect,
+			integrity: oldRequest.integrity,
+			signal: oldRequest.signal,
+			keepalive: oldRequest.keepalive,
+		})
+	}
+
+		);
+}

packages/astro/test/fixtures/reroute/src/pages/post/post-a.astro

@@ -0,0 +1,14 @@
+---
+let email = ''
+if (Astro.request.method === 'POST') {
+	try {
+		const data = await Astro.request.formData();
+		email = data.get('email')?.toString().trim();
+	} catch {}
+}
+return Astro.rewrite('/post/post-b')
+---
+
+<h1>Post A</h1>
+
+<h2>{email}</h2>

packages/astro/test/fixtures/reroute/src/pages/post/post-b.astro

@@ -0,0 +1,13 @@
+---
+let email = ''
+if (Astro.request.method === 'POST') {
+	try {
+		const data = await Astro.request.formData();
+		email = data.get('email')?.toString().trim();
+	} catch {}
+}
+---
+
+<h1>Post B</h1>
+
+<h2>{email}</h2>

packages/astro/test/rewrite.test.js

@@ -4,7 +4,7 @@ import { load as cheerioLoad } from 'cheerio';
 import testAdapter from './test-adapter.js';
 import { loadFixture } from './test-utils.js';
 
-describe('Dev reroute', () => {
+describe.only('Dev reroute', () => {
 	/** @type {import('./test-utils').Fixture} */
 	let fixture;
 	let devServer;
@@ -61,6 +61,7 @@ describe('Dev reroute', () => {
 
 		assert.equal($('h1').text(), '404:  Not found');
 	});
+
 });
 
 describe('Build reroute', () => {
@@ -112,7 +113,7 @@ describe('Build reroute', () => {
 
 	it('should render the 404 built-in page', async () => {
 		try {
-			const html = await fixture.readFile('/spread/oops/index.html');
+			await fixture.readFile('/spread/oops/index.html');
 			assert.fail('Not found');
 		} catch {
 			assert.ok;
@@ -187,6 +188,24 @@ describe('SSR reroute', () => {
 		const html = await response.text();
 		assert.equal(html, 'Not found');
 	});
+
+	it.only('should pass the POST data from one page to another', async () => {
+		const html = await fixture.fetch('/post/post-a', {
+			method: "POST",
+			body: JSON.stringify({
+				email: "[email protected]",
+				title: "Fix my bugs",
+				completed: false
+			}),
+			headers: {
+				"Content-type": "application/json; charset=UTF-8"
+			}
+		}).then((res) => res.text());
+		const $ = cheerioLoad(html);
+
+		assert.equal($('h1').text(), 'Post B');
+		assert.match($('h2').text(), /example@example.com/);
+	});
 });
 
 describe('Middleware', () => {