vercel implementation

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

@@ -25,7 +25,7 @@ export type CreateContext = {
 	rerouteImpl?: RerouteImplementation;
 };
 
-const defaultRerouteImpl: RerouteImplementation = (path, context) => { throw new Error(`.reroute() has not been implemented for edge middleware.`) }
+const defaultRerouteImpl: RerouteImplementation = (path, context) => { throw new Error(`.reroute() has not been implemented for this edge middleware.`) }
 
 /**
  * Creates a context to be passed to Astro middleware `onRequest` function.

packages/integrations/vercel/src/serverless/adapter.ts

@@ -61,6 +61,7 @@ function getAdapter({
 			hybridOutput: 'stable',
 			staticOutput: 'stable',
 			serverOutput: 'stable',
+			reroute: 'experimental',
 			assets: {
 				supportKind: 'stable',
 				isSharpCompatible: true,

packages/integrations/vercel/src/serverless/entrypoint.ts

@@ -2,6 +2,7 @@ import type { SSRManifest } from 'astro';
 import { App } from 'astro/app';
 import { applyPolyfills } from 'astro/app/node';
 import type { IncomingMessage, ServerResponse } from 'node:http';
+import { rerouteImpl } from './reroute.js';
 
 import { ASTRO_LOCALS_HEADER } from './adapter.js';
 import { getRequest, setResponse } from './request-transform.js';
@@ -10,6 +11,7 @@ applyPolyfills();
 
 export const createExports = (manifest: SSRManifest) => {
 	const app = new App(manifest);
+	app.setReroute(rerouteImpl);
 
 	const handler = async (req: IncomingMessage, res: ServerResponse) => {
 		let request: Request;

packages/integrations/vercel/src/serverless/middleware.ts

@@ -60,11 +60,13 @@ function edgeMiddlewareTemplate(middlewarePath: string, vercelEdgeMiddlewareHand
 	${handlerTemplateImport}
 import { onRequest } from ${middlewarePath};
 import { createContext, trySerializeLocals } from 'astro/middleware';
+import { rerouteImpl } from "@astrojs/vercel/serverless/reroute.js"
 export default async function middleware(request, context) {
 	const url = new URL(request.url);
 	const ctx = createContext({
 		request,
-		params: {}
+		params: {},
+		rerouteImpl,
 	});
 	ctx.locals = ${handlerTemplateCall};
 	const next = async () => {

packages/integrations/vercel/src/serverless/reroute.ts

@@ -0,0 +1,10 @@
+import { trySerializeLocals } from 'astro/middleware';
+import { ASTRO_LOCALS_HEADER } from './adapter.js';
+
+export function rerouteImpl(path: string | URL, context: { request: Request, locals: Record<string, any> }) {
+	const newUrl = new URL(path, context.request.url);
+	const newHeaders = { ...context.request.headers, [ASTRO_LOCALS_HEADER]: trySerializeLocals(context.locals) };
+	const newRequest = new Request(newUrl, { ...context.request, headers: newHeaders });
+    // TODO: should not handle external requests
+	return fetch(newRequest);
+}