Integration defined middleware (#8869)

* Rebase

* Use an empty module if there is no real middleware

* Add debug logging

* Use normalizePath

* Add a better example in the changesetp

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Bjorn Lu <bjornlu.dev@gmail.com>

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Bjorn Lu <bjornlu.dev@gmail.com>

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

* Update packages/astro/src/core/middleware/vite-plugin.ts

Co-authored-by: Emanuele Stoppa <my.burning@gmail.com>

* Review comments

* oops

* Update .changeset/khaki-glasses-raise.md

Co-authored-by: Bjorn Lu <bjornlu.dev@gmail.com>

---------

Co-authored-by: Bjorn Lu <bjornlu.dev@gmail.com>
Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>
Co-authored-by: Emanuele Stoppa <my.burning@gmail.com>

15 files changed, 268 insertions, 75 deletions

diff --git a/.changeset/khaki-glasses-raise.md b/.changeset/khaki-glasses-raise.md
new file mode 100644
index 000000000..4a0622a42
--- /dev/null
+++ b/.changeset/khaki-glasses-raise.md
@@ -0,0 +1,48 @@
+---
+'astro': minor
+---
+
+## Integration Hooks to add Middleware
+
+It's now possible in Astro for an integration to add middleware on behalf of the user. Previously when a third party wanted to provide middleware, the user would need to create a `src/middleware.ts` file themselves. Now, adding third-party middleware is as easy as adding a new integration.
+
+For integration authors, there is a new `addMiddleware` function in the `astro:config:setup` hook. This function allows you to specify a middleware module and the order in which it should be applied:
+
+```js
+// my-package/middleware.js
+import { defineMiddleware } from 'astro:middleware';
+
+export const onRequest = defineMiddleware(async (context, next) => {
+  const response = await next();
+
+  if(response.headers.get('content-type') === 'text/html') {
+    let html = await response.text();
+    html = minify(html);
+    return new Response(html, {
+      status: response.status,
+      headers: response.headers
+    });
+  }
+
+  return response;
+});
+```
+
+You can now add your integration's middleware and specify that it runs either before or after the application's own defined middleware (defined in `src/middleware.{js,ts}`)
+
+```js
+// my-package/integration.js
+export function myIntegration() {
+  return {
+    name: 'my-integration',
+    hooks: {
+      'astro:config:setup': ({ addMiddleware }) => {
+        addMiddleware({
+          entrypoint: 'my-package/middleware',
+          order: 'pre'
+        });
+      }
+    }
+  };
+}
+```
diff --git a/packages/astro/src/@types/astro.ts b/packages/astro/src/@types/astro.ts
index 47ed001f0..e1bf2cd8b 100644
--- a/packages/astro/src/@types/astro.ts
+++ b/packages/astro/src/@types/astro.ts
@@ -1701,6 +1701,7 @@ export interface AstroSettings {
 	 */
 	clientDirectives: Map<string, string>;
 	devOverlayPlugins: string[];
+	middlewares: { pre: string[]; post: string[]; };
 	tsConfig: TSConfig | undefined;
 	tsConfigPath: string | undefined;
 	watchFiles: string[];
@@ -2279,6 +2280,7 @@ export interface AstroIntegration {
 			injectRoute: (injectRoute: InjectedRoute) => void;
 			addClientDirective: (directive: ClientDirectiveConfig) => void;
 			addDevOverlayPlugin: (entrypoint: string) => void;
+			addMiddleware: (mid: AstroIntegrationMiddleware) => void;
 			logger: AstroIntegrationLogger;
 			// TODO: Add support for `injectElement()` for full HTML element injection, not just scripts.
 			// This may require some refactoring of `scripts`, `styles`, and `links` into something
@@ -2349,6 +2351,11 @@ export type AstroMiddlewareInstance<R> = {
 	onRequest?: MiddlewareHandler<R>;
 };
 
+export type AstroIntegrationMiddleware = {
+	order: 'pre' | 'post';
+	entrypoint: string;
+};
+
 export interface AstroPluginOptions {
 	settings: AstroSettings;
 	logger: Logger;
diff --git a/packages/astro/src/core/build/plugins/plugin-middleware.ts b/packages/astro/src/core/build/plugins/plugin-middleware.ts
index 628a1cb70..7f3760612 100644
--- a/packages/astro/src/core/build/plugins/plugin-middleware.ts
+++ b/packages/astro/src/core/build/plugins/plugin-middleware.ts
@@ -1,70 +1,8 @@
-import type { Plugin as VitePlugin } from 'vite';
-import { getOutputDirectory } from '../../../prerender/utils.js';
-import { MIDDLEWARE_PATH_SEGMENT_NAME } from '../../constants.js';
-import { addRollupInput } from '../add-rollup-input.js';
 import type { BuildInternals } from '../internal.js';
 import type { AstroBuildPlugin } from '../plugin.js';
 import type { StaticBuildOptions } from '../types.js';
-
-export const MIDDLEWARE_MODULE_ID = '@astro-middleware';
-
-const EMPTY_MIDDLEWARE = '\0empty-middleware';
-
-export function vitePluginMiddleware(
-	opts: StaticBuildOptions,
-	internals: BuildInternals
-): VitePlugin {
-	let resolvedMiddlewareId: string;
-	return {
-		name: '@astro/plugin-middleware',
-		enforce: 'post',
-		options(options) {
-			return addRollupInput(options, [MIDDLEWARE_MODULE_ID]);
-		},
-
-		async resolveId(id) {
-			if (id === MIDDLEWARE_MODULE_ID) {
-				const middlewareId = await this.resolve(
-					`${decodeURI(opts.settings.config.srcDir.pathname)}${MIDDLEWARE_PATH_SEGMENT_NAME}`
-				);
-				if (middlewareId) {
-					resolvedMiddlewareId = middlewareId.id;
-					return middlewareId.id;
-				} else {
-					return EMPTY_MIDDLEWARE;
-				}
-			}
-			if (id === EMPTY_MIDDLEWARE) {
-				return EMPTY_MIDDLEWARE;
-			}
-		},
-
-		load(id) {
-			if (id === EMPTY_MIDDLEWARE) {
-				return 'export const onRequest = undefined';
-			} else if (id === resolvedMiddlewareId) {
-				this.emitFile({
-					type: 'chunk',
-					preserveSignature: 'strict',
-					fileName: 'middleware.mjs',
-					id,
-				});
-			}
-		},
-
-		writeBundle(_, bundle) {
-			for (const [chunkName, chunk] of Object.entries(bundle)) {
-				if (chunk.type === 'asset') {
-					continue;
-				}
-				if (chunk.fileName === 'middleware.mjs') {
-					const outputDirectory = getOutputDirectory(opts.settings.config);
-					internals.middlewareEntryPoint = new URL(chunkName, outputDirectory);
-				}
-			}
-		},
-	};
-}
+import { vitePluginMiddlewareBuild } from '../../middleware/vite-plugin.js';
+export { MIDDLEWARE_MODULE_ID } from '../../middleware/vite-plugin.js';
 
 export function pluginMiddleware(
 	opts: StaticBuildOptions,
@@ -75,7 +13,7 @@ export function pluginMiddleware(
 		hooks: {
 			'build:before': () => {
 				return {
-					vitePlugin: vitePluginMiddleware(opts, internals),
+					vitePlugin: vitePluginMiddlewareBuild(opts, internals),
 				};
 			},
 		},
diff --git a/packages/astro/src/core/config/settings.ts b/packages/astro/src/core/config/settings.ts
index cf4db7598..fca392c97 100644
--- a/packages/astro/src/core/config/settings.ts
+++ b/packages/astro/src/core/config/settings.ts
@@ -97,6 +97,7 @@ export function createBaseSettings(config: AstroConfig): AstroSettings {
 		renderers: [],
 		scripts: [],
 		clientDirectives: getDefaultClientDirectives(),
+		middlewares: { pre: [], post: [] },
 		watchFiles: [],
 		devOverlayPlugins: [],
 		timer: new AstroTimer(),
diff --git a/packages/astro/src/core/create-vite.ts b/packages/astro/src/core/create-vite.ts
index be62de671..fda837209 100644
--- a/packages/astro/src/core/create-vite.ts
+++ b/packages/astro/src/core/create-vite.ts
@@ -31,6 +31,7 @@ import astroScannerPlugin from '../vite-plugin-scanner/index.js';
 import astroScriptsPlugin from '../vite-plugin-scripts/index.js';
 import astroScriptsPageSSRPlugin from '../vite-plugin-scripts/page-ssr.js';
 import { vitePluginSSRManifest } from '../vite-plugin-ssr-manifest/index.js';
+import { vitePluginMiddleware } from './middleware/vite-plugin.js';
 import { joinPaths } from './path.js';
 
 interface CreateViteOptions {
@@ -134,6 +135,7 @@ export async function createVite(
 			astroContentVirtualModPlugin({ settings }),
 			astroContentImportPlugin({ fs, settings }),
 			astroContentAssetPropagationPlugin({ mode, settings }),
+			vitePluginMiddleware({ settings }),
 			vitePluginSSRManifest(),
 			astroAssetsPlugin({ settings, logger, mode }),
 			astroPrefetch({ settings }),
diff --git a/packages/astro/src/core/middleware/loadMiddleware.ts b/packages/astro/src/core/middleware/loadMiddleware.ts
index b8528eb4b..46e1e32e2 100644
--- a/packages/astro/src/core/middleware/loadMiddleware.ts
+++ b/packages/astro/src/core/middleware/loadMiddleware.ts
@@ -1,6 +1,5 @@
-import type { AstroSettings } from '../../@types/astro.js';
-import { MIDDLEWARE_PATH_SEGMENT_NAME } from '../constants.js';
 import type { ModuleLoader } from '../module-loader/index.js';
+import { MIDDLEWARE_MODULE_ID } from './vite-plugin.js';
 
 /**
  * It accepts a module loader and the astro settings, and it attempts to load the middlewares defined in the configuration.
@@ -9,12 +8,9 @@ import type { ModuleLoader } from '../module-loader/index.js';
  */
 export async function loadMiddleware(
 	moduleLoader: ModuleLoader,
-	srcDir: AstroSettings['config']['srcDir']
 ) {
-	// can't use node Node.js builtins
-	let middlewarePath = `${decodeURI(srcDir.pathname)}${MIDDLEWARE_PATH_SEGMENT_NAME}`;
 	try {
-		const module = await moduleLoader.import(middlewarePath);
+		const module = await moduleLoader.import(MIDDLEWARE_MODULE_ID);
 		return module;
 	} catch {
 		return void 0;
diff --git a/packages/astro/src/core/middleware/sequence.ts b/packages/astro/src/core/middleware/sequence.ts
index d8d71c66b..ca3dc90a0 100644
--- a/packages/astro/src/core/middleware/sequence.ts
+++ b/packages/astro/src/core/middleware/sequence.ts
@@ -7,7 +7,8 @@ import { defineMiddleware } from './index.js';
  * It accepts one or more middleware handlers and makes sure that they are run in sequence.
  */
 export function sequence(...handlers: MiddlewareEndpointHandler[]): MiddlewareEndpointHandler {
-	const length = handlers.length;
+	const filtered = handlers.filter(h => !!h);
+	const length = filtered.length;
 	if (!length) {
 		const handler: MiddlewareEndpointHandler = defineMiddleware((context, next) => {
 			return next();
@@ -19,7 +20,7 @@ export function sequence(...handlers: MiddlewareEndpointHandler[]): MiddlewareEn
 		return applyHandle(0, context);
 
 		function applyHandle(i: number, handleContext: APIContext) {
-			const handle = handlers[i];
+			const handle = filtered[i];
 			// @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`.
diff --git a/packages/astro/src/core/middleware/vite-plugin.ts b/packages/astro/src/core/middleware/vite-plugin.ts
new file mode 100644
index 000000000..d25012516
--- /dev/null
+++ b/packages/astro/src/core/middleware/vite-plugin.ts
@@ -0,0 +1,124 @@
+import type { Plugin as VitePlugin } from 'vite';
+import { normalizePath } from 'vite';
+import { getOutputDirectory } from '../../prerender/utils.js';
+import { MIDDLEWARE_PATH_SEGMENT_NAME } from '../constants.js';
+import { addRollupInput } from '../build/add-rollup-input.js';
+import type { BuildInternals } from '../build/internal.js';
+import type { StaticBuildOptions } from '../build/types.js';
+import type { AstroSettings } from '../../@types/astro.js';
+
+export const MIDDLEWARE_MODULE_ID = '@astro-middleware';
+const EMPTY_MIDDLEWARE = '\0empty-middleware';
+
+export function vitePluginMiddleware({
+	settings
+}: {
+	settings: AstroSettings
+}): VitePlugin {
+	let isCommandBuild = false;
+	let resolvedMiddlewareId: string | undefined = undefined;
+	const hasIntegrationMiddleware = settings.middlewares.pre.length > 0 || settings.middlewares.post.length > 0;
+
+	return {
+		name: '@astro/plugin-middleware',
+
+		config(opts, { command }) {
+			isCommandBuild = command === 'build';
+			return opts;
+		},
+
+		async resolveId(id) {
+			if (id === MIDDLEWARE_MODULE_ID) {
+				const middlewareId = await this.resolve(
+					`${decodeURI(settings.config.srcDir.pathname)}${MIDDLEWARE_PATH_SEGMENT_NAME}`
+				);
+				if (middlewareId) {
+					resolvedMiddlewareId = middlewareId.id;
+					return MIDDLEWARE_MODULE_ID;
+				} else if(hasIntegrationMiddleware) {
+					return MIDDLEWARE_MODULE_ID;
+				} else {
+					return EMPTY_MIDDLEWARE;
+				}
+			}
+			if (id === EMPTY_MIDDLEWARE) {
+				return EMPTY_MIDDLEWARE;
+			}
+		},
+
+		async load(id) {
+			if (id === EMPTY_MIDDLEWARE) {
+				return 'export const onRequest = undefined';
+			} else if (id === MIDDLEWARE_MODULE_ID) {
+				// In the build, tell Vite to emit this file
+				if(isCommandBuild) {
+					this.emitFile({
+						type: 'chunk',
+						preserveSignature: 'strict',
+						fileName: 'middleware.mjs',
+						id,
+					});
+				}
+
+				const preMiddleware = createMiddlewareImports(settings.middlewares.pre, 'pre');
+				const postMiddleware = createMiddlewareImports(settings.middlewares.post, 'post');
+
+				const source = `
+import { onRequest as userOnRequest } from '${resolvedMiddlewareId}';
+import { sequence } from 'astro:middleware';
+${preMiddleware.importsCode}${postMiddleware.importsCode}
+
+export const onRequest = sequence(
+	${preMiddleware.sequenceCode}${preMiddleware.sequenceCode ? ',' : ''}
+	userOnRequest${postMiddleware.sequenceCode ? ',' : ''}
+	${postMiddleware.sequenceCode}
+);
+`.trim();
+
+				return source;
+			}
+		},
+	};
+}
+
+function createMiddlewareImports(entrypoints: string[], prefix: string): {
+	importsCode: string
+	sequenceCode: string
+} {
+	let importsRaw = '';
+	let sequenceRaw = '';
+	let index = 0;
+	for(const entrypoint of entrypoints) {
+		const name = `_${prefix}_${index}`;
+		importsRaw += `import { onRequest as ${name} } from '${normalizePath(entrypoint)}';\n`;
+		sequenceRaw += `${index > 0 ? ',' : ''}${name}`
+		index++;
+	}
+
+	return {
+		importsCode: importsRaw,
+		sequenceCode: sequenceRaw
+	};
+}
+
+export function vitePluginMiddlewareBuild(
+	opts: StaticBuildOptions,
+	internals: BuildInternals
+): VitePlugin {
+	return {
+		name: '@astro/plugin-middleware-build',
+
+		options(options) {
+			return addRollupInput(options, [MIDDLEWARE_MODULE_ID]);
+		},
+
+		writeBundle(_, bundle) {
+			for (const [chunkName, chunk] of Object.entries(bundle)) {
+				if (chunk.type !== 'asset' && chunk.fileName === 'middleware.mjs') {
+					const outputDirectory = getOutputDirectory(opts.settings.config);
+					internals.middlewareEntryPoint = new URL(chunkName, outputDirectory);
+				}
+			}
+		},
+	};
+}
diff --git a/packages/astro/src/integrations/index.ts b/packages/astro/src/integrations/index.ts
index 4c527cea3..23d2160a4 100644
--- a/packages/astro/src/integrations/index.ts
+++ b/packages/astro/src/integrations/index.ts
@@ -136,6 +136,17 @@ export async function runHookConfigSetup({
 					}
 					addedClientDirectives.set(name, buildClientDirectiveEntrypoint(name, entrypoint));
 				},
+				addMiddleware: ({ order, entrypoint }) => {
+					if(typeof updatedSettings.middlewares[order] === 'undefined') {
+						throw new Error(
+							`The "${integration.name}" integration is trying to add middleware but did not specify an order.`
+						);
+					}
+					logger.debug('middleware', `The integration ${integration.name} has added middleware that runs ${
+						order === 'pre' ? 'before' : 'after'
+					} any application middleware you define.`);
+					updatedSettings.middlewares[order].push(entrypoint);
+				},
 				logger: integrationLogger,
 			};
 
diff --git a/packages/astro/src/vite-plugin-astro-server/route.ts b/packages/astro/src/vite-plugin-astro-server/route.ts
index de1910227..2b0bcbea7 100644
--- a/packages/astro/src/vite-plugin-astro-server/route.ts
+++ b/packages/astro/src/vite-plugin-astro-server/route.ts
@@ -162,7 +162,6 @@ export async function handleRoute({
 	manifest,
 }: HandleRoute): Promise<void> {
 	const env = pipeline.getEnvironment();
-	const settings = pipeline.getSettings();
 	const config = pipeline.getConfig();
 	const moduleLoader = pipeline.getModuleLoader();
 	const { logger } = env;
@@ -177,7 +176,7 @@ export async function handleRoute({
 	let mod: ComponentInstance | undefined = undefined;
 	let options: SSROptions | undefined = undefined;
 	let route: RouteData;
-	const middleware = await loadMiddleware(moduleLoader, settings.config.srcDir);
+	const middleware = await loadMiddleware(moduleLoader);
 
 	if (!matchedRoute) {
 		if (config.experimental.i18n) {
diff --git a/packages/astro/test/fixtures/middleware space/astro.config.mjs b/packages/astro/test/fixtures/middleware space/astro.config.mjs
new file mode 100644
index 000000000..3fee066cd
--- /dev/null
+++ b/packages/astro/test/fixtures/middleware space/astro.config.mjs
@@ -0,0 +1,23 @@
+import { defineConfig } from 'astro/config';
+import { fileURLToPath } from 'node:url';
+
+export default defineConfig({
+	integrations: [
+		{
+			name: 'my-middleware',
+			hooks: {
+				'astro:config:setup':({ addMiddleware }) => {
+					addMiddleware({
+						entrypoint: fileURLToPath(new URL('./integration-middleware-pre.js', import.meta.url)),
+						order: 'pre'
+					});
+
+					addMiddleware({
+						entrypoint: fileURLToPath(new URL('./integration-middleware-post.js', import.meta.url)),
+						order: 'post'
+					});
+				}
+			}
+		}
+	]
+});
diff --git a/packages/astro/test/fixtures/middleware space/integration-middleware-post.js b/packages/astro/test/fixtures/middleware space/integration-middleware-post.js
new file mode 100644
index 000000000..4cc63c6b7
--- /dev/null
+++ b/packages/astro/test/fixtures/middleware space/integration-middleware-post.js
@@ -0,0 +1,13 @@
+import { sequence, defineMiddleware } from 'astro:middleware';
+
+export const onRequest = defineMiddleware((context, next) => {
+	if(context.url.pathname === '/integration-post') {
+		return new Response(JSON.stringify({ post: 'works' }), {
+			headers: {
+				'content-type': 'application/json'
+			}
+		});
+	}
+
+	return next();
+});
diff --git a/packages/astro/test/fixtures/middleware space/integration-middleware-pre.js b/packages/astro/test/fixtures/middleware space/integration-middleware-pre.js
new file mode 100644
index 000000000..3bf484b2b
--- /dev/null
+++ b/packages/astro/test/fixtures/middleware space/integration-middleware-pre.js
@@ -0,0 +1,13 @@
+import { sequence, defineMiddleware } from 'astro:middleware';
+
+export const onRequest = defineMiddleware((context, next) => {
+	if(context.url.pathname === '/integration-pre') {
+		return new Response(JSON.stringify({ pre: 'works' }), {
+			headers: {
+				'content-type': 'application/json'
+			}
+		});
+	}
+
+	return next();
+});
diff --git a/packages/astro/test/fixtures/middleware space/package.json b/packages/astro/test/fixtures/middleware space/package.json
index bc889aa63..91d4a344c 100644
--- a/packages/astro/test/fixtures/middleware space/package.json
+++ b/packages/astro/test/fixtures/middleware space/package.json
@@ -4,5 +4,8 @@
   "private": true,
   "dependencies": {
     "astro": "workspace:*"
+  },
+  "exports": {
+    "./integration-middleware.js": "./integration-middleware.js"
   }
 }
diff --git a/packages/astro/test/middleware.test.js b/packages/astro/test/middleware.test.js
index ac3054620..a9487950e 100644
--- a/packages/astro/test/middleware.test.js
+++ b/packages/astro/test/middleware.test.js
@@ -85,6 +85,20 @@ describe('Middleware in DEV mode', () => {
 		let headers = res.headers;
 		expect(headers.get('set-cookie')).to.not.equal(null);
 	});
+
+	describe('Integration hooks', () => {
+		it('Integration middleware marked as "pre" runs', async () => {
+			let res = await fixture.fetch('/integration-pre');
+			let json = await res.json();
+			expect(json.pre).to.equal('works');
+		});
+
+		it('Integration middleware marked as "post" runs', async () => {
+			let res = await fixture.fetch('/integration-post');
+			let json = await res.json();
+			expect(json.post).to.equal('works');
+		});
+	});
 });
 
 describe('Middleware in PROD mode, SSG', () => {