From 9bd5f6d6ce05adfd93c05004cbf6e9a68a30e072 Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Sun, 17 Dec 2023 20:23:07 -0800
Subject: [PATCH 1/6] fix: ensure assets are served gzip in preview

---
 .changeset/serious-pears-joke.md              |  5 +++
 packages/kit/src/exports/vite/index.js        | 25 -----------
 .../kit/src/exports/vite/preview/index.js     | 45 +++++++++++++++++++
 3 files changed, 50 insertions(+), 25 deletions(-)
 create mode 100644 .changeset/serious-pears-joke.md

diff --git a/.changeset/serious-pears-joke.md b/.changeset/serious-pears-joke.md
new file mode 100644
index 000000000000..209cd02a8d49
--- /dev/null
+++ b/.changeset/serious-pears-joke.md
@@ -0,0 +1,5 @@
+---
+"@sveltejs/kit": patch
+---
+
+fix: ensure assets are served gzip in preview
diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index dbd9c6c1c17a..0c944af5b407 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -626,31 +626,6 @@ function kit({ svelte_config }) {
 		 * @see https://vitejs.dev/guide/api-plugin.html#configurepreviewserver
 		 */
 		configurePreviewServer(vite) {
-			// generated client assets and the contents of `static`
-			// should we use Vite's built-in asset server for this?
-			// we would need to set the outDir to do so
-			const { paths } = svelte_config.kit;
-			const assets = paths.assets ? SVELTE_KIT_ASSETS : paths.base;
-			vite.middlewares.use(
-				scoped(
-					assets,
-					sirv(join(svelte_config.kit.outDir, 'output/client'), {
-						setHeaders: (res, pathname) => {
-							if (pathname.startsWith(`/${svelte_config.kit.appDir}/immutable`)) {
-								res.setHeader('cache-control', 'public,max-age=31536000,immutable');
-							}
-							if (vite_config.preview.cors) {
-								res.setHeader('Access-Control-Allow-Origin', '*');
-								res.setHeader(
-									'Access-Control-Allow-Headers',
-									'Origin, Content-Type, Accept, Range'
-								);
-							}
-						}
-					})
-				)
-			);
-
 			return preview(vite, vite_config, svelte_config);
 		},
 
diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index fe44e4524deb..b7cac4eedc9d 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -49,6 +49,29 @@ export async function preview(vite, vite_config, svelte_config) {
 	});
 
 	return () => {
+		// generated client assets and the contents of `static`
+		// should we use Vite's built-in asset server for this?
+		// we would need to set the outDir to do so
+		vite.middlewares.use(
+			scoped(
+				assets,
+				sirv(join(svelte_config.kit.outDir, 'output/client'), {
+					setHeaders: (res, pathname) => {
+						if (pathname.startsWith(`/${svelte_config.kit.appDir}/immutable`)) {
+							res.setHeader('cache-control', 'public,max-age=31536000,immutable');
+						}
+						if (vite_config.preview.cors) {
+							res.setHeader('Access-Control-Allow-Origin', '*');
+							res.setHeader(
+								'Access-Control-Allow-Headers',
+								'Origin, Content-Type, Accept, Range'
+							);
+						}
+					}
+				})
+			)
+		);
+
 		// prerendered dependencies
 		vite.middlewares.use(
 			mutable(join(svelte_config.kit.outDir, 'output/prerendered/dependencies'))
@@ -159,3 +182,25 @@ const mutable = (dir) =>
 function is_file(path) {
 	return fs.existsSync(path) && !fs.statSync(path).isDirectory();
 }
+
+/**
+ * @param {string} scope
+ * @param {(req: import('http').IncomingMessage, res: import('http').ServerResponse, next: () => void) => void} handler
+ * @returns {(req: import('http').IncomingMessage, res: import('http').ServerResponse, next: () => void) => void}
+ */
+function scoped(scope, handler) {
+	if (scope === '') return handler;
+
+	return (req, res, next) => {
+		if (req.url?.startsWith(scope)) {
+			const original_url = req.url;
+			req.url = req.url.slice(scope.length);
+			handler(req, res, () => {
+				req.url = original_url;
+				next();
+			});
+		} else {
+			next();
+		}
+	};
+}

From 4a894cb5aecb6763343bdadfedcdab74d1f8c972 Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Sun, 17 Dec 2023 20:36:04 -0800
Subject: [PATCH 2/6] format

---
 packages/kit/src/exports/vite/preview/index.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index b7cac4eedc9d..0bc2ee9354f0 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -62,10 +62,7 @@ export async function preview(vite, vite_config, svelte_config) {
 						}
 						if (vite_config.preview.cors) {
 							res.setHeader('Access-Control-Allow-Origin', '*');
-							res.setHeader(
-								'Access-Control-Allow-Headers',
-								'Origin, Content-Type, Accept, Range'
-							);
+							res.setHeader('Access-Control-Allow-Headers', 'Origin, Content-Type, Accept, Range');
 						}
 					}
 				})

From 51fea064e0abb138f23ec57076fb7cb3c326ad73 Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Sun, 17 Dec 2023 20:40:16 -0800
Subject: [PATCH 3/6] lint

---
 packages/kit/src/exports/vite/index.js | 26 +-------------------------
 1 file changed, 1 insertion(+), 25 deletions(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 0c944af5b407..7c0b8f5a4de9 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -1,5 +1,5 @@
 import fs from 'node:fs';
-import path, { join } from 'node:path';
+import path from 'node:path';
 
 import { svelte } from '@sveltejs/vite-plugin-svelte';
 import colors from 'kleur';
@@ -19,14 +19,12 @@ import { dev } from './dev/index.js';
 import { is_illegal, module_guard, normalize_id } from './graph_analysis/index.js';
 import { preview } from './preview/index.js';
 import { get_config_aliases, get_env, strip_virtual_prefix } from './utils.js';
-import { SVELTE_KIT_ASSETS } from '../../constants.js';
 import { write_client_manifest } from '../../core/sync/write_client_manifest.js';
 import prerender from '../../core/postbuild/prerender.js';
 import analyse from '../../core/postbuild/analyse.js';
 import { s } from '../../utils/misc.js';
 import { hash } from '../../runtime/hash.js';
 import { dedent, isSvelte5Plus } from '../../core/sync/utils.js';
-import sirv from 'sirv';
 import {
 	env_dynamic_private,
 	env_dynamic_public,
@@ -918,25 +916,3 @@ const create_service_worker_module = (config) => dedent`
 	export const prerendered = [];
 	export const version = ${s(config.kit.version.name)};
 `;
-
-/**
- * @param {string} scope
- * @param {(req: import('http').IncomingMessage, res: import('http').ServerResponse, next: () => void) => void} handler
- * @returns {(req: import('http').IncomingMessage, res: import('http').ServerResponse, next: () => void) => void}
- */
-function scoped(scope, handler) {
-	if (scope === '') return handler;
-
-	return (req, res, next) => {
-		if (req.url?.startsWith(scope)) {
-			const original_url = req.url;
-			req.url = req.url.slice(scope.length);
-			handler(req, res, () => {
-				req.url = original_url;
-				next();
-			});
-		} else {
-			next();
-		}
-	};
-}

From c46feb93c9d5ad4d26e56cb50c8dcf32e308b252 Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Sun, 17 Dec 2023 21:57:25 -0800
Subject: [PATCH 4/6] fix

---
 .../kit/src/exports/vite/preview/index.js     | 173 +++++++++++-------
 1 file changed, 107 insertions(+), 66 deletions(-)

diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index 0bc2ee9354f0..24a90790c060 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -7,6 +7,7 @@ import { loadEnv, normalizePath } from 'vite';
 import { getRequest, setResponse } from '../../../exports/node/index.js';
 import { installPolyfills } from '../../../exports/node/polyfills.js';
 import { SVELTE_KIT_ASSETS } from '../../../constants.js';
+import { not_found } from '../utils.js';
 
 /** @typedef {import('http').IncomingMessage} Req */
 /** @typedef {import('http').ServerResponse} Res */
@@ -21,6 +22,7 @@ export async function preview(vite, vite_config, svelte_config) {
 	installPolyfills();
 
 	const { paths } = svelte_config.kit;
+	const base = paths.base;
 	const assets = paths.assets ? SVELTE_KIT_ASSETS : paths.base;
 
 	const protocol = vite_config.preview.https ? 'https' : 'http';
@@ -49,104 +51,143 @@ export async function preview(vite, vite_config, svelte_config) {
 	});
 
 	return () => {
+		// Remove the base middleware. It screws with the URL.
+		// It also only lets through requests beginning with the base path, so that requests beginning
+		// with the assets URL never reach us. We could serve assets separately before the base
+		// middleware, but we'd need that to occur after the compression middleware, so would need to
+		// insert it manually into the stack, which would be at least as bad as doing this.
+		for (let i = vite.middlewares.stack.length - 1; i > 0; i--) {
+			// @ts-expect-error using internals
+			if (vite.middlewares.stack[i].handle.name === 'viteBaseMiddleware') {
+				vite.middlewares.stack.splice(i, 1);
+			}
+		}
+
 		// generated client assets and the contents of `static`
-		// should we use Vite's built-in asset server for this?
-		// we would need to set the outDir to do so
 		vite.middlewares.use(
 			scoped(
 				assets,
 				sirv(join(svelte_config.kit.outDir, 'output/client'), {
 					setHeaders: (res, pathname) => {
+						// only apply to immutable directory, not e.g. version.json
 						if (pathname.startsWith(`/${svelte_config.kit.appDir}/immutable`)) {
 							res.setHeader('cache-control', 'public,max-age=31536000,immutable');
 						}
-						if (vite_config.preview.cors) {
-							res.setHeader('Access-Control-Allow-Origin', '*');
-							res.setHeader('Access-Control-Allow-Headers', 'Origin, Content-Type, Accept, Range');
-						}
 					}
 				})
 			)
 		);
 
+		vite.middlewares.use((req, res, next) => {
+			const original_url = /** @type {string} */ (req.url);
+			const { pathname, search } = new URL(original_url, 'http://dummy');
+
+			// if `paths.base === '/a/b/c`, then the root route is `/a/b/c/`,
+			// regardless of the `trailingSlash` route option
+			if (base.length > 1 && pathname === base) {
+				let location = base + '/';
+				if (search) location += search;
+				res.writeHead(307, {
+					location
+				});
+				res.end();
+				return;
+			}
+
+			if (pathname.startsWith(base)) {
+				next();
+			} else {
+				res.statusCode = 404;
+				not_found(req, res, base);
+			}
+		});
+
 		// prerendered dependencies
 		vite.middlewares.use(
-			mutable(join(svelte_config.kit.outDir, 'output/prerendered/dependencies'))
+			scoped(base, mutable(join(svelte_config.kit.outDir, 'output/prerendered/dependencies')))
 		);
 
 		// prerendered pages (we can't just use sirv because we need to
 		// preserve the correct trailingSlash behaviour)
-		vite.middlewares.use((req, res, next) => {
-			let if_none_match_value = req.headers['if-none-match'];
+		vite.middlewares.use(
+			scoped(base, (req, res, next) => {
+				let if_none_match_value = req.headers['if-none-match'];
 
-			if (if_none_match_value?.startsWith('W/"')) {
-				if_none_match_value = if_none_match_value.substring(2);
-			}
+				if (if_none_match_value?.startsWith('W/"')) {
+					if_none_match_value = if_none_match_value.substring(2);
+				}
 
-			if (if_none_match_value === etag) {
-				res.statusCode = 304;
-				res.end();
-				return;
-			}
+				if (if_none_match_value === etag) {
+					res.statusCode = 304;
+					res.end();
+					return;
+				}
 
-			const { pathname, search } = new URL(/** @type {string} */ (req.url), 'http://dummy');
+				const { pathname, search } = new URL(/** @type {string} */ (req.url), 'http://dummy');
 
-			let filename = normalizePath(
-				join(svelte_config.kit.outDir, 'output/prerendered/pages' + pathname)
-			);
-			let prerendered = is_file(filename);
+				let filename = normalizePath(
+					join(svelte_config.kit.outDir, 'output/prerendered/pages' + pathname)
+				);
+				let prerendered = is_file(filename);
 
-			if (!prerendered) {
-				const has_trailing_slash = pathname.endsWith('/');
-				const html_filename = `${filename}${has_trailing_slash ? 'index.html' : '.html'}`;
+				if (!prerendered) {
+					const has_trailing_slash = pathname.endsWith('/');
+					const html_filename = `${filename}${has_trailing_slash ? 'index.html' : '.html'}`;
 
-				/** @type {string | undefined} */
-				let redirect;
+					/** @type {string | undefined} */
+					let redirect;
 
-				if (is_file(html_filename)) {
-					filename = html_filename;
-					prerendered = true;
-				} else if (has_trailing_slash) {
-					if (is_file(filename.slice(0, -1) + '.html')) {
-						redirect = pathname.slice(0, -1);
+					if (is_file(html_filename)) {
+						filename = html_filename;
+						prerendered = true;
+					} else if (has_trailing_slash) {
+						if (is_file(filename.slice(0, -1) + '.html')) {
+							redirect = pathname.slice(0, -1);
+						}
+					} else if (is_file(filename + '/index.html')) {
+						redirect = pathname + '/';
 					}
-				} else if (is_file(filename + '/index.html')) {
-					redirect = pathname + '/';
-				}
 
-				if (redirect) {
-					if (search) redirect += search;
-					res.writeHead(307, {
-						location: redirect
-					});
+					if (redirect) {
+						if (search) redirect += search;
+						res.writeHead(307, {
+							location: redirect
+						});
 
-					res.end();
+						res.end();
 
-					return;
+						return;
+					}
 				}
-			}
 
-			if (prerendered) {
-				res.writeHead(200, {
-					'content-type': lookup(pathname) || 'text/html',
-					etag
-				});
+				if (prerendered) {
+					res.writeHead(200, {
+						'content-type': lookup(pathname) || 'text/html',
+						etag
+					});
 
-				fs.createReadStream(filename).pipe(res);
-			} else {
-				next();
-			}
-		});
+					fs.createReadStream(filename).pipe(res);
+				} else {
+					next();
+				}
+			})
+		);
 
 		// SSR
 		vite.middlewares.use(async (req, res) => {
 			const host = req.headers['host'];
-			req.url = req.originalUrl;
 
-			const request = await getRequest({
-				base: `${protocol}://${host}`,
-				request: req
-			});
+			let request;
+
+			try {
+				request = await getRequest({
+					base: `${protocol}://${host}`,
+					request: req
+				});
+			} catch (/** @type {any} */ err) {
+				res.statusCode = err.status || 400;
+				return res.end('Invalid request body');
+			}
 
 			setResponse(
 				res,
@@ -175,15 +216,10 @@ const mutable = (dir) =>
 			})
 		: (_req, _res, next) => next();
 
-/** @param {string} path */
-function is_file(path) {
-	return fs.existsSync(path) && !fs.statSync(path).isDirectory();
-}
-
 /**
  * @param {string} scope
- * @param {(req: import('http').IncomingMessage, res: import('http').ServerResponse, next: () => void) => void} handler
- * @returns {(req: import('http').IncomingMessage, res: import('http').ServerResponse, next: () => void) => void}
+ * @param {Handler} handler
+ * @returns {Handler}
  */
 function scoped(scope, handler) {
 	if (scope === '') return handler;
@@ -201,3 +237,8 @@ function scoped(scope, handler) {
 		}
 	};
 }
+
+/** @param {string} path */
+function is_file(path) {
+	return fs.existsSync(path) && !fs.statSync(path).isDirectory();
+}

From 18a6806691f8c7db9d2b96951a6b7fcd88b32dfd Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Mon, 18 Dec 2023 11:16:31 -0800
Subject: [PATCH 5/6] sync other changes

---
 packages/kit/src/exports/vite/preview/index.js | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index 24a90790c060..7552257651cf 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -177,17 +177,10 @@ export async function preview(vite, vite_config, svelte_config) {
 		vite.middlewares.use(async (req, res) => {
 			const host = req.headers['host'];
 
-			let request;
-
-			try {
-				request = await getRequest({
-					base: `${protocol}://${host}`,
-					request: req
-				});
-			} catch (/** @type {any} */ err) {
-				res.statusCode = err.status || 400;
-				return res.end('Invalid request body');
-			}
+			const request = await getRequest({
+				base: `${protocol}://${host}`,
+				request: req
+			});
 
 			setResponse(
 				res,

From 38592124d7a0a2d0cb6ff99d0bfa0bb255c354d4 Mon Sep 17 00:00:00 2001
From: Ben McCann <322311+benmccann@users.noreply.github.com>
Date: Mon, 18 Dec 2023 11:18:18 -0800
Subject: [PATCH 6/6] update comment

---
 packages/kit/src/exports/vite/preview/index.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index 7552257651cf..997922bb5272 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -54,8 +54,8 @@ export async function preview(vite, vite_config, svelte_config) {
 		// Remove the base middleware. It screws with the URL.
 		// It also only lets through requests beginning with the base path, so that requests beginning
 		// with the assets URL never reach us. We could serve assets separately before the base
-		// middleware, but we'd need that to occur after the compression middleware, so would need to
-		// insert it manually into the stack, which would be at least as bad as doing this.
+		// middleware, but we'd need that to occur after the compression and cors middlewares, so would
+		// need to insert it manually into the stack, which would be at least as bad as doing this.
 		for (let i = vite.middlewares.stack.length - 1; i > 0; i--) {
 			// @ts-expect-error using internals
 			if (vite.middlewares.stack[i].handle.name === 'viteBaseMiddleware') {