feat: implement reroute in dev (#10818)

* chore: implement reroute in dev

* chore: revert naming change

* chore: conditionally create the new request

* chore: handle error

* remove only

* remove only

* chore: add tests and remove logs

* chore: fix regression

* chore: fix regression route matching

* chore: remove unwanted test

packages/astro/src/@types/astro.ts

@@ -245,6 +245,10 @@ export interface AstroGlobal<
 	 * [Astro reference](https://docs.astro.build/en/guides/server-side-rendering/)
 	 */
 	redirect: AstroSharedContext['redirect'];
+	/**
+	 * TODO add documentation
+	 */
+	reroute: AstroSharedContext['reroute'];
 	/**
 	 * The <Astro.self /> element allows a component to reference itself recursively.
 	 *
@@ -1918,6 +1922,18 @@ export interface AstroUserConfig {
 				origin?: boolean;
 			};
 		};
+
+		/**
+		 * @docs
+		 * @name experimental.rerouting
+		 * @type {boolean}
+		 * @default `false`
+		 * @version 4.6.0
+		 * @description
+		 *
+		 * TODO
+		 */
+		rerouting: boolean;
 	};
 }
 
@@ -2479,6 +2495,11 @@ interface AstroSharedContext<
 	 */
 	redirect(path: string, status?: ValidRedirectStatus): Response;
 
+	/**
+	 * TODO: add documentation
+	 */
+	reroute(reroutePayload: ReroutePayload): Promise<Response>;
+
 	/**
 	 * Object accessed via Astro middleware
 	 */
@@ -2784,7 +2805,9 @@ export interface AstroIntegration {
 	};
 }
 
-export type MiddlewareNext = () => Promise<Response>;
+export type ReroutePayload = string | URL | Request;
+
+export type MiddlewareNext = (reroutePayload?: ReroutePayload) => Promise<Response>;
 export type MiddlewareHandler = (
 	context: APIContext,
 	next: MiddlewareNext

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

@@ -1,4 +1,10 @@
-import type { RouteData, SSRElement, SSRResult } from '../../@types/astro.js';
+import type {
+	ComponentInstance,
+	ReroutePayload,
+	RouteData,
+	SSRElement,
+	SSRResult,
+} from '../../@types/astro.js';
 import { Pipeline } from '../base-pipeline.js';
 import { createModuleScriptElement, createStylesheetElementSet } from '../render/ssr-element.js';
 
@@ -41,4 +47,11 @@ export class AppPipeline extends Pipeline {
 	}
 
 	componentMetadata() {}
+	getComponentByRoute(_routeData: RouteData): Promise<ComponentInstance> {
+		throw new Error('unimplemented');
+	}
+
+	tryReroute(_reroutePayload: ReroutePayload): Promise<[RouteData, ComponentInstance]> {
+		throw new Error('unimplemented');
+	}
 }

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

@@ -65,6 +65,8 @@ export type SSRManifest = {
 	i18n: SSRManifestI18n | undefined;
 	middleware: MiddlewareHandler;
 	checkOrigin: boolean;
+	// TODO: remove once the experimental flag is removed
+	reroutingEnabled: boolean;
 };
 
 export type SSRManifestI18n = {

packages/astro/src/core/base-pipeline.ts

@@ -1,5 +1,7 @@
 import type {
+	ComponentInstance,
 	MiddlewareHandler,
+	ReroutePayload,
 	RouteData,
 	RuntimeMode,
 	SSRLoadedRenderer,
@@ -59,6 +61,23 @@ export abstract class Pipeline {
 
 	abstract headElements(routeData: RouteData): Promise<HeadElements> | HeadElements;
 	abstract componentMetadata(routeData: RouteData): Promise<SSRResult['componentMetadata']> | void;
+
+	/**
+	 * It attempts to retrieve the `RouteData` that matches the input `url`, and the component that belongs to the `RouteData`.
+	 *
+	 * ## Errors
+	 *
+	 * - if not `RouteData` is found
+	 *
+	 * @param {ReroutePayload} reroutePayload
+	 */
+	abstract tryReroute(reroutePayload: ReroutePayload): Promise<[RouteData, ComponentInstance]>;
+
+	/**
+	 * Tells the pipeline how to retrieve a component give a `RouteData`
+	 * @param routeData
+	 */
+	abstract getComponentByRoute(routeData: RouteData): Promise<ComponentInstance>;
 }
 
 // eslint-disable-next-line @typescript-eslint/no-empty-interface

packages/astro/src/core/build/generate.ts

@@ -615,6 +615,7 @@ function createBuildManifest(
 		i18n: i18nManifest,
 		buildFormat: settings.config.build.format,
 		middleware,
+		reroutingEnabled: settings.config.experimental.rerouting,
 		checkOrigin: settings.config.experimental.security?.csrfProtection?.origin ?? false,
 	};
 }

packages/astro/src/core/build/pipeline.ts

@@ -1,4 +1,11 @@
-import type { RouteData, SSRLoadedRenderer, SSRResult } from '../../@types/astro.js';
+import type {
+	RouteData,
+	SSRLoadedRenderer,
+	SSRResult,
+	MiddlewareHandler,
+	ReroutePayload,
+	ComponentInstance,
+} from '../../@types/astro.js';
 import { getOutputDirectory, isServerLikeOutput } from '../../prerender/utils.js';
 import { BEFORE_HYDRATION_SCRIPT_ID, PAGE_SCRIPT_ID } from '../../vite-plugin-scripts/index.js';
 import type { SSRManifest } from '../app/types.js';
@@ -21,6 +28,8 @@ import { getVirtualModulePageNameFromPath } from './plugins/util.js';
 import { ASTRO_PAGE_EXTENSION_POST_PATTERN } from './plugins/util.js';
 import type { PageBuildData, StaticBuildOptions } from './types.js';
 import { i18nHasFallback } from './util.js';
+import { defineMiddleware } from '../middleware/index.js';
+import { undefined } from 'zod';
 
 /**
  * The build pipeline is responsible to gather the files emitted by the SSR build and generate the pages by executing these files.
@@ -225,4 +234,12 @@ export class BuildPipeline extends Pipeline {
 
 		return pages;
 	}
+
+	getComponentByRoute(_routeData: RouteData): Promise<ComponentInstance> {
+		throw new Error('unimplemented');
+	}
+
+	tryReroute(_reroutePayload: ReroutePayload): Promise<[RouteData, ComponentInstance]> {
+		throw new Error('unimplemented');
+	}
 }

packages/astro/src/core/build/plugins/plugin-manifest.ts

@@ -277,5 +277,6 @@ function buildManifest(
 		i18n: i18nManifest,
 		buildFormat: settings.config.build.format,
 		checkOrigin: settings.config.experimental.security?.csrfProtection?.origin ?? false,
+		reroutingEnabled: settings.config.experimental.rerouting,
 	};
 }

packages/astro/src/core/config/schema.ts

@@ -87,6 +87,7 @@ const ASTRO_CONFIG_DEFAULTS = {
 		globalRoutePriority: false,
 		i18nDomains: false,
 		security: {},
+		rerouting: false,
 	},
 } satisfies AstroUserConfig & { server: { open: boolean } };
 
@@ -525,6 +526,7 @@ export const AstroConfigSchema = z.object({
 				.optional()
 				.default(ASTRO_CONFIG_DEFAULTS.experimental.security),
 			i18nDomains: z.boolean().optional().default(ASTRO_CONFIG_DEFAULTS.experimental.i18nDomains),
+			rerouting: z.boolean().optional().default(ASTRO_CONFIG_DEFAULTS.experimental.rerouting),
 		})
 		.strict(
 			`Invalid or outdated experimental feature.\nCheck for incorrect spelling or outdated Astro version.\nSee https://docs.astro.build/en/reference/configuration-reference/#experimental-flags for a list of all current experiments.`

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

@@ -1,4 +1,9 @@
-import type { APIContext, MiddlewareHandler, MiddlewareNext } from '../../@types/astro.js';
+import type {
+	APIContext,
+	MiddlewareHandler,
+	MiddlewareNext,
+	ReroutePayload,
+} from '../../@types/astro.js';
 import { AstroError, AstroErrorData } from '../errors/index.js';
 
 /**
@@ -38,13 +43,13 @@ import { AstroError, AstroErrorData } from '../errors/index.js';
 export async function callMiddleware(
 	onRequest: MiddlewareHandler,
 	apiContext: APIContext,
-	responseFunction: () => Promise<Response> | Response
+	responseFunction: (reroutePayload?: ReroutePayload) => Promise<Response> | Response
 ): Promise<Response> {
 	let nextCalled = false;
 	let responseFunctionPromise: Promise<Response> | Response | undefined = undefined;
-	const next: MiddlewareNext = async () => {
+	const next: MiddlewareNext = async (payload) => {
 		nextCalled = true;
-		responseFunctionPromise = responseFunction();
+		responseFunctionPromise = responseFunction(payload);
 		return responseFunctionPromise;
 	};
 

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

@@ -1,17 +1,14 @@
-import type { APIContext, MiddlewareHandler, Params } from '../../@types/astro.js';
+import type { APIContext, MiddlewareHandler, Params, ReroutePayload } from '../../@types/astro.js';
 import {
 	computeCurrentLocale,
 	computePreferredLocale,
 	computePreferredLocaleList,
 } from '../../i18n/utils.js';
-import { ASTRO_VERSION } from '../constants.js';
+import { ASTRO_VERSION, clientLocalsSymbol, clientAddressSymbol } from '../constants.js';
 import { AstroCookies } from '../cookies/index.js';
 import { AstroError, AstroErrorData } from '../errors/index.js';
 import { sequence } from './sequence.js';
 
-const clientAddressSymbol = Symbol.for('astro.clientAddress');
-const clientLocalsSymbol = Symbol.for('astro.locals');
-
 function defineMiddleware(fn: MiddlewareHandler) {
 	return fn;
 }
@@ -49,6 +46,12 @@ function createContext({
 	const url = new URL(request.url);
 	const route = url.pathname;
 
+	// TODO verify that this function works in an edge middleware environment
+	const reroute = (_reroutePayload: ReroutePayload) => {
+		// return dummy response
+		return Promise.resolve(new Response(null));
+	};
+
 	return {
 		cookies: new AstroCookies(request),
 		request,
@@ -56,6 +59,7 @@ function createContext({
 		site: undefined,
 		generator: `Astro v${ASTRO_VERSION}`,
 		props: {},
+		reroute,
 		redirect(path, status) {
 			return new Response(null, {
 				status: status || 302,

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

@@ -1,4 +1,4 @@
-import type { APIContext, MiddlewareHandler } from '../../@types/astro.js';
+import type { APIContext, MiddlewareHandler, ReroutePayload } from '../../@types/astro.js';
 import { defineMiddleware } from './index.js';
 
 // From SvelteKit: https://github.com/sveltejs/kit/blob/master/packages/kit/src/exports/hooks/sequence.js
@@ -10,10 +10,9 @@ export function sequence(...handlers: MiddlewareHandler[]): MiddlewareHandler {
 	const filtered = handlers.filter((h) => !!h);
 	const length = filtered.length;
 	if (!length) {
-		const handler: MiddlewareHandler = defineMiddleware((context, next) => {
+		return defineMiddleware((context, next) => {
 			return next();
 		});
-		return handler;
 	}
 
 	return defineMiddleware((context, next) => {
@@ -24,11 +23,11 @@ export function sequence(...handlers: MiddlewareHandler[]): MiddlewareHandler {
 			// @ts-expect-error
 			// SAFETY: Usually `next` always returns something in user land, but in `sequence` we are actually
 			// doing a loop over all the `next` functions, and eventually we call the last `next` that returns the `Response`.
-			const result = handle(handleContext, async () => {
+			const result = handle(handleContext, async (payload: ReroutePayload) => {
 				if (i < length - 1) {
 					return applyHandle(i + 1, handleContext);
 				} else {
-					return next();
+					return next(payload);
 				}
 			});
 			return result;

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

@@ -4,6 +4,8 @@ import type {
 	AstroGlobalPartial,
 	ComponentInstance,
 	MiddlewareHandler,
+	MiddlewareNext,
+	ReroutePayload,
 	RouteData,
 	SSRResult,
 } from '../@types/astro.js';
@@ -39,14 +41,23 @@ export class RenderContext {
 		public locals: App.Locals,
 		readonly middleware: MiddlewareHandler,
 		readonly pathname: string,
-		readonly request: Request,
-		readonly routeData: RouteData,
+		public request: Request,
+		public routeData: RouteData,
 		public status: number,
-		readonly cookies = new AstroCookies(request),
-		readonly params = getParams(routeData, pathname),
-		readonly url = new URL(request.url)
+		protected cookies = new AstroCookies(request),
+		public params = getParams(routeData, pathname),
+		protected url = new URL(request.url)
 	) {}
 
+	/**
+	 * A flag that tells the render content if the rerouting was triggered
+	 */
+	isRerouting = false;
+	/**
+	 * A safety net in case of loops
+	 */
+	counter = 0;
+
 	static create({
 		locals = {},
 		middleware,
@@ -56,7 +67,7 @@ export class RenderContext {
 		routeData,
 		status = 200,
 	}: Pick<RenderContext, 'pathname' | 'pipeline' | 'request' | 'routeData'> &
-		Partial<Pick<RenderContext, 'locals' | 'middleware' | 'status'>>) {
+		Partial<Pick<RenderContext, 'locals' | 'middleware' | 'status'>>): RenderContext {
 		return new RenderContext(
 			pipeline,
 			locals,
@@ -80,11 +91,11 @@ export class RenderContext {
 	 * - fallback
 	 */
 	async render(componentInstance: ComponentInstance | undefined): Promise<Response> {
-		const { cookies, middleware, pathname, pipeline, routeData } = this;
+		const { cookies, middleware, pathname, pipeline } = this;
 		const { logger, routeCache, serverLike, streaming } = pipeline;
 		const props = await getProps({
 			mod: componentInstance,
-			routeData,
+			routeData: this.routeData,
 			routeCache,
 			pathname,
 			logger,
@@ -92,8 +103,37 @@ export class RenderContext {
 		});
 		const apiContext = this.createAPIContext(props);
 
-		const lastNext = async () => {
-			switch (routeData.type) {
+		this.counter++;
+		if (this.counter == 4) {
+			return new Response('Loop Detected', {
+				// https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/508
+				status: 508,
+				statusText: 'Loop Detected',
+			});
+		}
+		const lastNext: MiddlewareNext = async (payload) => {
+			if (payload) {
+				if (this.pipeline.manifest.reroutingEnabled) {
+					try {
+						const [routeData, component] = await pipeline.tryReroute(payload);
+						this.routeData = routeData;
+						componentInstance = component;
+					} catch (e) {
+						return new Response('Not found', {
+							status: 404,
+							statusText: 'Not found',
+						});
+					} finally {
+						this.isRerouting = true;
+					}
+				} else {
+					this.pipeline.logger.warn(
+						'router',
+						'You tried to use the routing feature without enabling it via experimental flag. This is not allowed.'
+					);
+				}
+			}
+			switch (this.routeData.type) {
 				case 'endpoint':
 					return renderEndpoint(componentInstance as any, apiContext, serverLike, logger);
 				case 'redirect':
@@ -108,7 +148,7 @@ export class RenderContext {
 							props,
 							{},
 							streaming,
-							routeData
+							this.routeData
 						);
 					} catch (e) {
 						// If there is an error in the page's frontmatter or instantiation of the RenderTemplate fails midway,
@@ -119,7 +159,11 @@ export class RenderContext {
 					// Signal to the i18n middleware to maybe act on this response
 					response.headers.set(ROUTE_TYPE_HEADER, 'page');
 					// Signal to the error-page-rerouting infra to let this response pass through to avoid loops
-					if (routeData.route === '/404' || routeData.route === '/500') {
+					if (
+						this.routeData.route === '/404' ||
+						this.routeData.route === '/500' ||
+						this.isRerouting
+					) {
 						response.headers.set(REROUTE_DIRECTIVE_HEADER, 'no');
 					}
 					return response;
@@ -130,7 +174,9 @@ export class RenderContext {
 			}
 		};
 
-		const response = await callMiddleware(middleware, apiContext, lastNext);
+		const response = this.isRerouting
+			? await lastNext()
+			: await callMiddleware(middleware, apiContext, lastNext);
 		if (response.headers.get(ROUTE_TYPE_HEADER)) {
 			response.headers.delete(ROUTE_TYPE_HEADER);
 		}
@@ -143,10 +189,36 @@ export class RenderContext {
 
 	createAPIContext(props: APIContext['props']): APIContext {
 		const renderContext = this;
-		const { cookies, params, pipeline, request, url } = this;
+		const { cookies, params, pipeline, url } = this;
 		const generator = `Astro v${ASTRO_VERSION}`;
 		const redirect = (path: string, status = 302) =>
 			new Response(null, { status, headers: { Location: path } });
+
+		const reroute = async (reroutePayload: ReroutePayload) => {
+			try {
+				const [routeData, component] = await pipeline.tryReroute(reroutePayload);
+				this.routeData = routeData;
+				if (reroutePayload instanceof Request) {
+					this.request = reroutePayload;
+				} else {
+					this.request = new Request(
+						new URL(routeData.pathname ?? routeData.route, this.url.origin),
+						this.request
+					);
+				}
+				this.url = new URL(this.request.url);
+				this.cookies = new AstroCookies(this.request);
+				this.params = getParams(routeData, url.toString());
+				this.isRerouting = true;
+				return await this.render(component);
+			} catch (e) {
+				return new Response('Not found', {
+					status: 404,
+					statusText: 'Not found',
+				});
+			}
+		};
+
 		return {
 			cookies,
 			get clientAddress() {
@@ -167,7 +239,7 @@ export class RenderContext {
 					renderContext.locals = val;
 					// we also put it on the original Request object,
 					// where the adapter might be expecting to read it after the response.
-					Reflect.set(request, clientLocalsSymbol, val);
+					Reflect.set(this.request, clientLocalsSymbol, val);
 				}
 			},
 			params,
@@ -179,7 +251,8 @@ export class RenderContext {
 			},
 			props,
 			redirect,
-			request,
+			reroute,
+			request: this.request,
 			site: pipeline.site,
 			url,
 		};
@@ -249,17 +322,43 @@ export class RenderContext {
 		slotValues: Record<string, any> | null
 	): AstroGlobal {
 		const renderContext = this;
-		const { cookies, locals, params, pipeline, request, url } = this;
+		const { cookies, locals, params, pipeline, url } = this;
 		const { response } = result;
 		const redirect = (path: string, status = 302) => {
 			// If the response is already sent, error as we cannot proceed with the redirect.
-			if ((request as any)[responseSentSymbol]) {
+			if ((this.request as any)[responseSentSymbol]) {
 				throw new AstroError({
 					...AstroErrorData.ResponseSentError,
 				});
 			}
 			return new Response(null, { status, headers: { Location: path } });
 		};
+
+		const reroute = async (reroutePayload: ReroutePayload) => {
+			try {
+				const [routeData, component] = await pipeline.tryReroute(reroutePayload);
+				this.routeData = routeData;
+				if (reroutePayload instanceof Request) {
+					this.request = reroutePayload;
+				} else {
+					this.request = new Request(
+						new URL(routeData.pathname ?? routeData.route, this.url.origin),
+						this.request
+					);
+				}
+				this.url = new URL(this.request.url);
+				this.cookies = new AstroCookies(this.request);
+				this.params = getParams(routeData, url.toString());
+				this.isRerouting = true;
+				return await this.render(component);
+			} catch (e) {
+				return new Response('Not found', {
+					status: 404,
+					statusText: 'Not found',
+				});
+			}
+		};
+
 		const slots = new Slots(result, slotValues, pipeline.logger) as unknown as AstroGlobal['slots'];
 
 		// `Astro.self` is added by the compiler
@@ -283,7 +382,8 @@ export class RenderContext {
 			props,
 			locals,
 			redirect,
-			request,
+			reroute,
+			request: this.request,
 			response,
 			slots,
 			site: pipeline.site,

packages/astro/src/prerender/routing.ts

@@ -54,7 +54,7 @@ async function preloadAndSetPrerenderStatus({
 			continue;
 		}
 
-		const preloadedComponent = await pipeline.preload(filePath);
+		const preloadedComponent = await pipeline.preload(route, filePath);
 
 		// gets the prerender metadata set by the `astro:scanner` vite plugin
 		const prerenderStatus = getPrerenderStatus({

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

@@ -1,8 +1,10 @@
-import url from 'node:url';
+import { fileURLToPath } from 'node:url';
 import type {
 	AstroSettings,
 	ComponentInstance,
 	DevToolbarMetadata,
+	ManifestData,
+	ReroutePayload,
 	RouteData,
 	SSRElement,
 	SSRLoadedRenderer,
@@ -15,7 +17,7 @@ import { enhanceViteSSRError } from '../core/errors/dev/index.js';
 import { AggregateError, CSSError, MarkdownError } from '../core/errors/index.js';
 import type { Logger } from '../core/logger/core.js';
 import type { ModuleLoader } from '../core/module-loader/index.js';
-import { Pipeline, loadRenderer } from '../core/render/index.js';
+import { loadRenderer, Pipeline } from '../core/render/index.js';
 import { isPage, resolveIdToUrl, viteID } from '../core/util.js';
 import { isServerLikeOutput } from '../prerender/utils.js';
 import { PAGE_SCRIPT_ID } from '../vite-plugin-scripts/index.js';
@@ -30,6 +32,13 @@ export class DevPipeline extends Pipeline {
 	// so it needs to be mutable here unlike in other environments
 	override renderers = new Array<SSRLoadedRenderer>();
 
+	manifestData: ManifestData | undefined;
+
+	componentInterner: WeakMap<RouteData, ComponentInstance> = new WeakMap<
+		RouteData,
+		ComponentInstance
+	>();
+
 	private constructor(
 		readonly loader: ModuleLoader,
 		readonly logger: Logger,
@@ -44,13 +53,18 @@ export class DevPipeline extends Pipeline {
 		super(logger, manifest, mode, [], resolve, serverLike, streaming);
 	}
 
-	static create({
-		loader,
-		logger,
-		manifest,
-		settings,
-	}: Pick<DevPipeline, 'loader' | 'logger' | 'manifest' | 'settings'>) {
-		return new DevPipeline(loader, logger, manifest, settings);
+	static create(
+		manifestData: ManifestData,
+		{
+			loader,
+			logger,
+			manifest,
+			settings,
+		}: Pick<DevPipeline, 'loader' | 'logger' | 'manifest' | 'settings'>
+	) {
+		const pipeline = new DevPipeline(loader, logger, manifest, settings);
+		pipeline.manifestData = manifestData;
+		return pipeline;
 	}
 
 	async headElements(routeData: RouteData): Promise<HeadElements> {
@@ -81,7 +95,7 @@ export class DevPipeline extends Pipeline {
 				scripts.add({ props: { type: 'module', src }, children: '' });
 
 				const additionalMetadata: DevToolbarMetadata['__astro_dev_toolbar__'] = {
-					root: url.fileURLToPath(settings.config.root),
+					root: fileURLToPath(settings.config.root),
 					version: ASTRO_VERSION,
 					debugInfo: await getInfoOutput({ userConfig: settings.config, print: false }),
 				};
@@ -135,7 +149,7 @@ export class DevPipeline extends Pipeline {
 		return getComponentMetadata(filePath, loader);
 	}
 
-	async preload(filePath: URL) {
+	async preload(routeData: RouteData, filePath: URL) {
 		const { loader } = this;
 		if (filePath.href === new URL(DEFAULT_404_COMPONENT, this.config.root).href) {
 			return { default: default404Page } as any as ComponentInstance;
@@ -148,7 +162,9 @@ export class DevPipeline extends Pipeline {
 
 		try {
 			// Load the module from the Vite SSR Runtime.
-			return (await loader.import(viteID(filePath))) as ComponentInstance;
+			const componentInstance = (await loader.import(viteID(filePath))) as ComponentInstance;
+			this.componentInterner.set(routeData, componentInstance);
+			return componentInstance;
 		} catch (error) {
 			// If the error came from Markdown or CSS, we already handled it and there's no need to enhance it
 			if (MarkdownError.is(error) || CSSError.is(error) || AggregateError.is(error)) {
@@ -161,5 +177,51 @@ export class DevPipeline extends Pipeline {
 
 	clearRouteCache() {
 		this.routeCache.clearAll();
+		this.componentInterner = new WeakMap<RouteData, ComponentInstance>();
+	}
+
+	async getComponentByRoute(routeData: RouteData): Promise<ComponentInstance> {
+		const component = this.componentInterner.get(routeData);
+		if (component) {
+			return component;
+		} else {
+			const filePath = new URL(`./${routeData.component}`, this.config.root);
+			return await this.preload(routeData, filePath);
+		}
+	}
+
+	async tryReroute(payload: ReroutePayload): Promise<[RouteData, ComponentInstance]> {
+		let foundRoute;
+		if (!this.manifestData) {
+			throw new Error('Missing manifest data');
+		}
+
+		for (const route of this.manifestData.routes) {
+			if (payload instanceof URL) {
+				if (route.pattern.test(payload.pathname)) {
+					foundRoute = route;
+					break;
+				}
+			} else if (payload instanceof Request) {
+				// TODO: handle request, if needed
+			} else {
+				if (route.pattern.test(decodeURI(payload))) {
+					foundRoute = route;
+					break;
+				}
+			}
+		}
+
+		if (foundRoute) {
+			const componentInstance = await this.getComponentByRoute(foundRoute);
+			return [foundRoute, componentInstance];
+		} else {
+			// TODO: handle error properly
+			throw new Error('Route not found');
+		}
+	}
+
+	setManifestData(manifestData: ManifestData) {
+		this.manifestData = manifestData;
 	}
 }

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

@@ -35,10 +35,10 @@ export default function createVitePluginAstroServer({
 		configureServer(viteServer) {
 			const loader = createViteLoader(viteServer);
 			const manifest = createDevelopmentManifest(settings);
-			const pipeline = DevPipeline.create({ loader, logger, manifest, settings });
 			let manifestData: ManifestData = ensure404Route(
 				createRouteManifest({ settings, fsMod }, logger)
 			);
+			const pipeline = DevPipeline.create(manifestData, { loader, logger, manifest, settings });
 			const controller = createController({ loader });
 			const localStorage = new AsyncLocalStorage();
 
@@ -47,6 +47,7 @@ export default function createVitePluginAstroServer({
 				pipeline.clearRouteCache();
 				if (needsManifestRebuild) {
 					manifestData = ensure404Route(createRouteManifest({ settings }, logger));
+					pipeline.setManifestData(manifestData);
 				}
 			}
 			// Rebuild route manifest on file change, if needed.
@@ -144,6 +145,7 @@ export function createDevelopmentManifest(settings: AstroSettings): SSRManifest
 		inlinedScripts: new Map(),
 		i18n: i18nManifest,
 		checkOrigin: settings.config.experimental.security?.csrfProtection?.origin ?? false,
+		reroutingEnabled: settings.config.experimental.rerouting,
 		middleware(_, next) {
 			return next();
 		},

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

@@ -114,7 +114,7 @@ export async function matchRoute(
 
 	if (custom404) {
 		const filePath = new URL(`./${custom404.component}`, config.root);
-		const preloadedComponent = await pipeline.preload(filePath);
+		const preloadedComponent = await pipeline.preload(custom404, filePath);
 
 		return {
 			route: custom404,
@@ -197,40 +197,38 @@ export async function handleRoute({
 			if (!pathNameHasLocale && pathname !== '/') {
 				return handle404Response(origin, incomingRequest, incomingResponse);
 			}
-			request = createRequest({
-				base: config.base,
-				url,
-				headers: incomingRequest.headers,
-				logger,
-				// no route found, so we assume the default for rendering the 404 page
-				staticLike: config.output === 'static' || config.output === 'hybrid',
-			});
-			route = {
-				component: '',
-				generate(_data: any): string {
-					return '';
-				},
-				params: [],
-				// Disable eslint as we only want to generate an empty RegExp
-				// eslint-disable-next-line prefer-regex-literals
-				pattern: new RegExp(''),
-				prerender: false,
-				segments: [],
-				type: 'fallback',
-				route: '',
-				fallbackRoutes: [],
-				isIndex: false,
-			};
-			renderContext = RenderContext.create({
-				pipeline: pipeline,
-				pathname,
-				middleware,
-				request,
-				routeData: route,
-			});
-		} else {
-			return handle404Response(origin, incomingRequest, incomingResponse);
 		}
+		request = createRequest({
+			base: config.base,
+			url,
+			headers: incomingRequest.headers,
+			logger,
+			// no route found, so we assume the default for rendering the 404 page
+			staticLike: config.output === 'static' || config.output === 'hybrid',
+		});
+		route = {
+			component: '',
+			generate(_data: any): string {
+				return '';
+			},
+			params: [],
+			// Disable eslint as we only want to generate an empty RegExp
+			// eslint-disable-next-line prefer-regex-literals
+			pattern: new RegExp(''),
+			prerender: false,
+			segments: [],
+			type: 'fallback',
+			route: '',
+			fallbackRoutes: [],
+			isIndex: false,
+		};
+		renderContext = RenderContext.create({
+			pipeline: pipeline,
+			pathname,
+			middleware,
+			request,
+			routeData: route,
+		});
 	} else {
 		const filePath: URL | undefined = matchedRoute.filePath;
 		const { preloadedComponent } = matchedRoute;

packages/astro/test/fixtures/middleware-virtual/astro.config.mjs

@@ -0,0 +1,3 @@
+import { defineConfig } from "astro/config";
+
+export default defineConfig({})

packages/astro/test/fixtures/middleware-virtual/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "@test/middleware-virtual",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}

packages/astro/test/fixtures/middleware-virtual/src/middleware.js

@@ -0,0 +1,6 @@
+import { defineMiddleware } from 'astro:middleware';
+
+export const onRequest = defineMiddleware(async (context, next) => {
+	console.log('[MIDDLEWARE] in ' + context.url.toString());
+	return next();
+});

packages/astro/test/fixtures/middleware-virtual/src/pages/index.astro

@@ -0,0 +1,13 @@
+---
+const data = Astro.locals;
+---
+
+<html>
+<head>
+	<title>Index</title>
+</head>
+<body>
+
+<span>Index</span>
+</body>
+</html>

packages/astro/test/fixtures/reroute/astro.config.mjs

@@ -0,0 +1,8 @@
+import { defineConfig } from 'astro/config';
+
+// https://astro.build/config
+export default defineConfig({
+	experimental: {
+		rerouting: true
+	}
+});

packages/astro/test/fixtures/reroute/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "@test/reroute",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}

packages/astro/test/fixtures/reroute/src/pages/blog/hello/index.astro

@@ -0,0 +1,11 @@
+---
+return Astro.reroute(new URL("../../", Astro.url))
+---
+<html>
+<head>
+	<title>Blog hello</title>
+</head>
+<body>
+<h1>Blog hello</h1>
+</body>
+</html>

packages/astro/test/fixtures/reroute/src/pages/blog/salut/index.astro

@@ -0,0 +1,11 @@
+---
+return Astro.reroute(new Request(new URL("../../", Astro.url)))
+---
+<html>
+<head>
+	<title>Blog hello</title>
+</head>
+<body>
+<h1>Blog hello</h1>
+</body>
+</html>

packages/astro/test/fixtures/reroute/src/pages/index.astro

@@ -0,0 +1,10 @@
+---
+---
+<html>
+	<head>
+		<title>Index</title>
+	</head>
+	<body>
+		<h1>Index</h1>
+	</body>
+</html>

packages/astro/test/fixtures/reroute/src/pages/reroute.astro

@@ -0,0 +1,11 @@
+---
+return Astro.reroute("/")
+---
+<html>
+	<head>
+		<title>Reroute</title>
+	</head>
+	<body>
+		<h1>Reroute</h1>
+	</body>
+</html>

packages/astro/test/reroute.test.js

@@ -0,0 +1,42 @@
+import { describe, it, before, after } from 'node:test';
+import { loadFixture } from './test-utils.js';
+import { load as cheerioLoad } from 'cheerio';
+import assert from 'node:assert/strict';
+
+describe('Dev reroute', () => {
+	/** @type {import('./test-utils').Fixture} */
+	let fixture;
+	let devServer;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/reroute/',
+		});
+		devServer = await fixture.startDevServer();
+	});
+
+	after(async () => {
+		await devServer.stop();
+	});
+
+	it('the render the index page when navigating /reroute ', async () => {
+		const html = await fixture.fetch('/reroute').then((res) => res.text());
+		const $ = cheerioLoad(html);
+
+		assert.equal($('h1').text(), 'Index');
+	});
+
+	it('the render the index page when navigating /blog/hello ', async () => {
+		const html = await fixture.fetch('/blog/hello').then((res) => res.text());
+		const $ = cheerioLoad(html);
+
+		assert.equal($('h1').text(), 'Index');
+	});
+
+	it('the render the index page when navigating /blog/salut ', async () => {
+		const html = await fixture.fetch('/blog/hello').then((res) => res.text());
+		const $ = cheerioLoad(html);
+
+		assert.equal($('h1').text(), 'Index');
+	});
+});

packages/astro/test/units/routing/route-matching.test.js

@@ -146,7 +146,7 @@ describe('Route matching', () => {
 
 		const loader = createViteLoader(container.viteServer);
 		const manifest = createDevelopmentManifest(container.settings);
-		pipeline = DevPipeline.create({ loader, logger: defaultLogger, manifest, settings });
+		pipeline = DevPipeline.create(undefined, { loader, logger: defaultLogger, manifest, settings });
 		manifestData = createRouteManifest(
 			{
 				cwd: fileURLToPath(root),

packages/astro/test/units/vite-plugin-astro-server/request.test.js

@@ -22,7 +22,7 @@ async function createDevPipeline(overrides = {}) {
 	const loader = overrides.loader ?? createLoader();
 	const manifest = createDevelopmentManifest(settings);
 
-	return DevPipeline.create({ loader, logger: defaultLogger, manifest, settings });
+	return DevPipeline.create(undefined, { loader, logger: defaultLogger, manifest, settings });
 }
 
 describe('vite-plugin-astro-server', () => {

pnpm-lock.yaml

@@ -3102,6 +3102,12 @@ importers:
         specifier: workspace:*
         version: link:../../..
 
+  packages/astro/test/fixtures/middleware-virtual:
+    dependencies:
+      astro:
+        specifier: workspace:*
+        version: link:../../..
+
   packages/astro/test/fixtures/minification-html:
     dependencies:
       astro:
@@ -3300,6 +3306,12 @@ importers:
         specifier: workspace:*
         version: link:../../..
 
+  packages/astro/test/fixtures/reroute:
+    dependencies:
+      astro:
+        specifier: workspace:*
+        version: link:../../..
+
   packages/astro/test/fixtures/root-srcdir-css:
     dependencies:
       astro: