feat: implement reroute in dev

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;
 }
@@ -49,13 +46,20 @@ 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,
 		params,
 		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;