1 files changed, 38 insertions, 0 deletions
diff --git a/packages/astro/src/vite-plugin-astro-server/trailing-slash.ts b/packages/astro/src/vite-plugin-astro-server/trailing-slash.ts
new file mode 100644
index 000000000..00f71b784
--- /dev/null
+++ b/packages/astro/src/vite-plugin-astro-server/trailing-slash.ts
@@ -0,0 +1,38 @@
+import type * as vite from 'vite';
+import type { AstroSettings } from '../types/astro.js';
+
+import { collapseDuplicateTrailingSlashes, hasFileExtension } from '@astrojs/internal-helpers/path';
+import { trailingSlashMismatchTemplate } from '../template/4xx.js';
+import { writeHtmlResponse, writeRedirectResponse } from './response.js';
+
+export function trailingSlashMiddleware(settings: AstroSettings): vite.Connect.NextHandleFunction {
+	const { trailingSlash } = settings.config;
+
+	return function devTrailingSlash(req, res, next) {
+		const url = new URL(`http://localhost${req.url}`);
+		let pathname: string;
+		try {
+			pathname = decodeURI(url.pathname);
+		} catch (e) {
+			/* malformed uri */
+			return next(e);
+		}
+		if (pathname.startsWith('/_') || pathname.startsWith('/@')) {
+			return next();
+		}
+
+		const destination = collapseDuplicateTrailingSlashes(pathname, true);
+		if (pathname && destination !== pathname) {
+			return writeRedirectResponse(res, 301, `${destination}${url.search}`);
+		}
+
+		if (
+			(trailingSlash === 'never' && pathname.endsWith('/') && pathname !== '/') ||
+			(trailingSlash === 'always' && !pathname.endsWith('/') && !hasFileExtension(pathname))
+		) {
+			const html = trailingSlashMismatchTemplate(pathname, trailingSlash);
+			return writeHtmlResponse(res, 404, html);
+		}
+		return next();
+	};
+}