From 4c2d9d6dd1e8cf4a41da37826f3e9b84802ec8dd Mon Sep 17 00:00:00 2001
From: Richard Harris <richard.a.harris@gmail.com>
Date: Tue, 7 Mar 2023 10:55:44 -0500
Subject: [PATCH 1/2] redirect when previewing prerendered pages - closes #8839

---
 .changeset/happy-panthers-leave.md            |  5 ++++
 .../kit/src/exports/vite/preview/index.js     | 27 +++++++++++++++++--
 2 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/happy-panthers-leave.md

diff --git a/.changeset/happy-panthers-leave.md b/.changeset/happy-panthers-leave.md
new file mode 100644
index 000000000000..4c4f8b6dad9f
--- /dev/null
+++ b/.changeset/happy-panthers-leave.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: redirect to path with/without trailing slash when previewing prerendered pages
diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index f70024bce238..fbf08ffe7326 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -108,8 +108,31 @@ export async function preview(vite, vite_config, svelte_config) {
 				let prerendered = is_file(filename);
 
 				if (!prerendered) {
-					filename += filename.endsWith('/') ? 'index.html' : '.html';
-					prerendered = is_file(filename);
+					const has_trailing_slash = pathname.endsWith('/');
+					const html_filename = `${filename}${has_trailing_slash ? 'index.html' : '.html'}`;
+
+					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);
+						}
+					} else if (is_file(filename + '/index.html')) {
+						redirect = pathname + '/';
+					}
+
+					if (redirect) {
+						res.writeHead(308, {
+							location: redirect
+						});
+
+						res.end();
+
+						return;
+					}
 				}
 
 				if (prerendered) {

From 3cff8d654fbed4447d13592dda0fadced651f8ea Mon Sep 17 00:00:00 2001
From: Rich Harris <richard.a.harris@gmail.com>
Date: Wed, 8 Mar 2023 09:47:03 -0500
Subject: [PATCH 2/2] Update packages/kit/src/exports/vite/preview/index.js

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

diff --git a/packages/kit/src/exports/vite/preview/index.js b/packages/kit/src/exports/vite/preview/index.js
index fbf08ffe7326..326818c3b181 100644
--- a/packages/kit/src/exports/vite/preview/index.js
+++ b/packages/kit/src/exports/vite/preview/index.js
@@ -125,7 +125,7 @@ export async function preview(vite, vite_config, svelte_config) {
 					}
 
 					if (redirect) {
-						res.writeHead(308, {
+						res.writeHead(307, {
 							location: redirect
 						});