5 files changed, 80 insertions, 10 deletions

diff --git a/.changeset/good-frogs-report.md b/.changeset/good-frogs-report.md
new file mode 100644
index 000000000..fdac3299e
--- /dev/null
+++ b/.changeset/good-frogs-report.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Emit middleware as an entrypoint during build
diff --git a/packages/astro/src/core/build/plugins/index.ts b/packages/astro/src/core/build/plugins/index.ts
index 982a90ce3..235879c0e 100644
--- a/packages/astro/src/core/build/plugins/index.ts
+++ b/packages/astro/src/core/build/plugins/index.ts
@@ -10,12 +10,14 @@ import { pluginInternals } from './plugin-internals.js';
 import { pluginPages } from './plugin-pages.js';
 import { pluginPrerender } from './plugin-prerender.js';
 import { pluginSSR } from './plugin-ssr.js';
+import { pluginMiddleware } from './plugin-middleware.js';
 
 export function registerAllPlugins({ internals, options, register }: AstroBuildPluginContainer) {
 	register(pluginComponentEntry(internals));
 	register(pluginAliasResolve(internals));
 	register(pluginAnalyzer(internals));
 	register(pluginInternals(internals));
+	register(pluginMiddleware(options, internals));
 	register(pluginPages(options, internals));
 	register(pluginCSS(options, internals));
 	register(astroHeadBuildPlugin(options, internals));
diff --git a/packages/astro/src/core/build/plugins/plugin-middleware.ts b/packages/astro/src/core/build/plugins/plugin-middleware.ts
new file mode 100644
index 000000000..507c4ae71
--- /dev/null
+++ b/packages/astro/src/core/build/plugins/plugin-middleware.ts
@@ -0,0 +1,63 @@
+import type { Plugin as VitePlugin } from 'vite';
+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';
+import type { StaticBuildOptions } from '../types';
+
+export const MIDDLEWARE_MODULE_ID = '@astro-middleware';
+export const RESOLVED_MIDDLEWARE_MODULE_ID = '\0@astro-middleware';
+
+let inputs: Set<string> = new Set();
+export function vitePluginMiddleware(
+	opts: StaticBuildOptions,
+	_internals: BuildInternals
+): VitePlugin {
+	return {
+		name: '@astro/plugin-middleware',
+		options(options) {
+			if (opts.settings.config.experimental.middleware) {
+				return addRollupInput(options, [MIDDLEWARE_MODULE_ID]);
+			}
+		},
+
+		resolveId(id) {
+			if (id === MIDDLEWARE_MODULE_ID && opts.settings.config.experimental.middleware) {
+				return RESOLVED_MIDDLEWARE_MODULE_ID;
+			}
+		},
+
+		async load(id) {
+			if (id === RESOLVED_MIDDLEWARE_MODULE_ID && opts.settings.config.experimental.middleware) {
+				const imports: string[] = [];
+				const exports: string[] = [];
+				let middlewareId = await this.resolve(
+					`${opts.settings.config.srcDir.pathname}/${MIDDLEWARE_PATH_SEGMENT_NAME}`
+				);
+				if (middlewareId) {
+					imports.push(`import { onRequest } from "${middlewareId.id}"`);
+					exports.push(`export { onRequest }`);
+				}
+				const result = [imports.join('\n'), exports.join('\n')];
+
+				return result.join('\n');
+			}
+		},
+	};
+}
+
+export function pluginMiddleware(
+	opts: StaticBuildOptions,
+	internals: BuildInternals
+): AstroBuildPlugin {
+	return {
+		build: 'ssr',
+		hooks: {
+			'build:before': () => {
+				return {
+					vitePlugin: vitePluginMiddleware(opts, internals),
+				};
+			},
+		},
+	};
+}
diff --git a/packages/astro/src/core/build/plugins/plugin-pages.ts b/packages/astro/src/core/build/plugins/plugin-pages.ts
index ba4f0df32..68967c390 100644
--- a/packages/astro/src/core/build/plugins/plugin-pages.ts
+++ b/packages/astro/src/core/build/plugins/plugin-pages.ts
@@ -1,10 +1,10 @@
 import type { Plugin as VitePlugin } from 'vite';
 import { pagesVirtualModuleId, resolvedPagesVirtualModuleId } from '../../app/index.js';
-import { MIDDLEWARE_PATH_SEGMENT_NAME } from '../../constants.js';
 import { addRollupInput } from '../add-rollup-input.js';
 import { eachPageData, type BuildInternals } from '../internal.js';
 import type { AstroBuildPlugin } from '../plugin';
 import type { StaticBuildOptions } from '../types';
+import { MIDDLEWARE_MODULE_ID } from './plugin-middleware.js';
 
 function vitePluginPages(opts: StaticBuildOptions, internals: BuildInternals): VitePlugin {
 	return {
@@ -24,13 +24,6 @@ function vitePluginPages(opts: StaticBuildOptions, internals: BuildInternals): V
 
 		async load(id) {
 			if (id === resolvedPagesVirtualModuleId) {
-				let middlewareId = null;
-				if (opts.settings.config.experimental.middleware) {
-					middlewareId = await this.resolve(
-						`${opts.settings.config.srcDir.pathname}/${MIDDLEWARE_PATH_SEGMENT_NAME}`
-					);
-				}
-
 				let importMap = '';
 				let imports = [];
 				let i = 0;
@@ -54,11 +47,15 @@ function vitePluginPages(opts: StaticBuildOptions, internals: BuildInternals): V
 
 				const def = `${imports.join('\n')}
 
-${middlewareId ? `import * as _middleware from "${middlewareId.id}";` : ''}
+${
+	opts.settings.config.experimental.middleware
+		? `import * as _middleware from "${MIDDLEWARE_MODULE_ID}";`
+		: ''
+}
 
 export const pageMap = new Map([${importMap}]);
 export const renderers = [${rendererItems}];
-${middlewareId ? `export const middleware = _middleware;` : ''}
+${opts.settings.config.experimental.middleware ? `export const middleware = _middleware;` : ''}
 `;
 
 				return def;
diff --git a/packages/astro/src/core/build/static-build.ts b/packages/astro/src/core/build/static-build.ts
index 7d5424eb4..fbb0f431d 100644
--- a/packages/astro/src/core/build/static-build.ts
+++ b/packages/astro/src/core/build/static-build.ts
@@ -27,6 +27,7 @@ import { createPluginContainer, type AstroBuildPluginContainer } from './plugin.
 import { registerAllPlugins } from './plugins/index.js';
 import type { PageBuildData, StaticBuildOptions } from './types';
 import { getTimeStat } from './util.js';
+import { RESOLVED_MIDDLEWARE_MODULE_ID } from './plugins/plugin-middleware.js';
 
 export async function viteBuild(opts: StaticBuildOptions) {
 	const { allPages, settings } = opts;
@@ -172,6 +173,8 @@ async function ssrBuild(
 					entryFileNames(chunkInfo) {
 						if (chunkInfo.facadeModuleId === resolvedPagesVirtualModuleId) {
 							return opts.buildConfig.serverEntry;
+						} else if (chunkInfo.facadeModuleId === RESOLVED_MIDDLEWARE_MODULE_ID) {
+							return 'middleware.mjs';
 						} else {
 							return '[name].mjs';
 						}