feat: rerouting

.changeset/pink-ligers-share.md

@@ -0,0 +1,49 @@
+---
+"astro": minor
+---
+
+Add experimental rerouting in Astro, via `reroute()` function and `next()` function. 
+
+The feature is available via experimental flag:
+
+```js
+export default defineConfig({
+  experimental: {
+    rerouting: true
+  }
+})
+```
+
+When enabled, you can use `reroute()` to **render** another page without changing the URL of the browser in Astro pages and endpoints.
+
+```astro
+---
+// src/pages/dashboard.astro
+if (!Astro.props.allowed) {
+	return Astro.reroute("/")
+}
+---
+```
+
+```js
+// src/pages/api.js
+export function GET(ctx) {
+	if (!ctx.locals.allowed) {
+		return ctx.reroute("/")
+	}
+}
+```
+
+The middleware `next()` function now accepts the same payload of the `reroute()` function. For example, with `next("/")`, you can call the next middleware function with a new `Request`.
+
+```js
+// src/middleware.js
+export function onRequest(ctx, next) {
+	if (!ctx.cookies.get("allowed")) {
+		return next("/") // new signature
+	}
+	return next();
+}
+```
+
+> **NOTE**: please [read the RFC](https://github.com/withastro/roadmap/blob/feat/reroute/proposals/0047-rerouting.md) to understand the current expectations of the new APIs.

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

@@ -246,7 +246,16 @@ export interface AstroGlobal<
 	 */
 	redirect: AstroSharedContext['redirect'];
 	/**
-	 * TODO add documentation
+	 * It reroutes to another page. As opposed to redirects, the URL won't change, and Astro will render the HTML emitted
+	 * by the rerouted URL passed as argument.
+	 *
+	 * ## Example
+	 *
+	 * ```js
+	 * if (pageIsNotEnabled) {
+	 * 	return Astro.reroute('/fallback-page')
+	 * }
+	 * ```
 	 */
 	reroute: AstroSharedContext['reroute'];
 	/**
@@ -1640,7 +1649,7 @@ export interface AstroUserConfig {
 		domains?: Record<string, string>;
 	};
 
-	/** ⚠️ WARNING: SUBJECT TO CHANGE */
+	/** ! WARNING: SUBJECT TO CHANGE */
 	db?: Config.Database;
 
 	/**
@@ -1927,10 +1936,38 @@ export interface AstroUserConfig {
 		 * @name experimental.rerouting
 		 * @type {boolean}
 		 * @default `false`
-		 * @version 4.6.0
+		 * @version 4.7.0
 		 * @description
 		 *
-		 * TODO
+		 * Enables the use of rerouting features in Astro pages, Endpoints and Astro middleware:
+		 * 
+		 * ```astro
+		 * ---
+		 * // src/pages/dashboard.astro
+		 * if (!Astro.props.allowed) {
+		 * 	return Astro.reroute("/")
+		 * }
+		 * ---
+		 * ```
+		 * 
+		 * ```js
+		 * // src/pages/api.js
+		 * export function GET(ctx) {
+		 * 	if (!ctx.locals.allowed) {
+		 * 		return ctx.reroute("/")
+		 * 	}
+		 * }
+		 * ```
+		 * 
+		 * ```js
+		 * // src/middleware.js
+		 * export function onRequest(ctx, next) {
+		 * 	if (!ctx.cookies.get("allowed")) {
+		 * 		return next("/") // new signature
+		 * 	}
+		 * 	return next();
+		 * }
+		 * ```
 		 */
 		rerouting: boolean;
 	};
@@ -2495,7 +2532,16 @@ interface AstroSharedContext<
 	redirect(path: string, status?: ValidRedirectStatus): Response;
 
 	/**
-	 * TODO: add documentation
+	 * It reroutes to another page. As opposed to redirects, the URL won't change, and Astro will render the HTML emitted
+	 * by the rerouted URL passed as argument.
+	 *
+	 * ## Example
+	 *
+	 * ```js
+	 * if (pageIsNotEnabled) {
+	 * 	return Astro.reroute('/fallback-page')
+	 * }
+	 * ```
 	 */
 	reroute(reroutePayload: ReroutePayload): Promise<Response>;
 
@@ -2614,7 +2660,17 @@ export interface APIContext<
 	redirect: AstroSharedContext['redirect'];
 
 	/**
-	 * TODO: docs
+	 * It reroutes to another page. As opposed to redirects, the URL won't change, and Astro will render the HTML emitted
+	 * by the rerouted URL passed as argument.
+	 *
+	 * ## Example
+	 *
+	 * ```ts
+	 * // src/pages/secret.ts
+	 * export function GET(ctx) {
+	 *   return ctx.reroute(new URL("../"), ctx.url);
+	 * }
+	 * ```
 	 */
 	reroute: AstroSharedContext['reroute'];
 

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

@@ -98,7 +98,6 @@ export class AppPipeline extends Pipeline {
 			const componentInstance = await this.getComponentByRoute(foundRoute);
 			return [foundRoute, componentInstance];
 		} else {
-			// TODO: handle error properly
 			throw new Error('Route not found');
 		}
 	}

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

@@ -5,6 +5,7 @@ import type {
 	ReroutePayload,
 } from '../../@types/astro.js';
 import { AstroError, AstroErrorData } from '../errors/index.js';
+import type { Logger } from '../logger/core.js';
 
 /**
  * Utility function that is in charge of calling the middleware.
@@ -46,14 +47,25 @@ export async function callMiddleware(
 	responseFunction: (
 		apiContext: APIContext,
 		reroutePayload?: ReroutePayload
-	) => Promise<Response> | Response
+	) => Promise<Response> | Response,
+	// TODO: remove these two arguments once rerouting goes out of experimental
+	enableRerouting: boolean,
+	logger: Logger
 ): Promise<Response> {
 	let nextCalled = false;
 	let responseFunctionPromise: Promise<Response> | Response | undefined = undefined;
 	const next: MiddlewareNext = async (payload) => {
 		nextCalled = true;
+		if (enableRerouting) {
+			responseFunctionPromise = responseFunction(apiContext, payload);
+		} else {
+			logger.warn(
+				'router',
+				'You tried to use the routing feature without enabling it via experimental flag. This is not allowed.'
+			);
+			responseFunctionPromise = responseFunction(apiContext);
+		}
 		// We need to pass the APIContext pass to `callMiddleware` because it can be mutated across middleware functions
-		responseFunctionPromise = responseFunction(apiContext, payload);
 		return responseFunctionPromise;
 	};
 

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

@@ -174,7 +174,13 @@ export class RenderContext {
 			}
 		};
 
-		const response = await callMiddleware(middleware, apiContext, lastNext);
+		const response = await callMiddleware(
+			middleware,
+			apiContext,
+			lastNext,
+			this.pipeline.manifest.reroutingEnabled,
+			this.pipeline.logger
+		);
 		if (response.headers.get(ROUTE_TYPE_HEADER)) {
 			response.headers.delete(ROUTE_TYPE_HEADER);
 		}

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

@@ -220,7 +220,6 @@ export class DevPipeline extends Pipeline {
 			const componentInstance = await this.getComponentByRoute(foundRoute);
 			return [foundRoute, componentInstance];
 		} else {
-			// TODO: handle error properly
 			throw new Error('Route not found');
 		}
 	}