Fix truncated basepath (#3345)

* Fix svelte-kit dev/preview when config.kit.paths.base is set

* add test of truncated base

* changeset

* handle edge cases

* actually i guess this belongs here

* decode then check

* fix newly failing test

Co-authored-by: Andrew Soutar <andrew@andrewsoutar.com>

.changeset/curly-pets-vanish.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Handle requests for /basepath

packages/kit/src/core/adapt/prerender/prerender.js

@@ -229,7 +229,13 @@ export async function prerender({ cwd, out, log, config, build_data, fallback, a
 					if (!is_root_relative(resolved)) continue;
 
 					const parsed = new URL(resolved, 'http://localhost');
-					const pathname = decodeURI(parsed.pathname).replace(config.kit.paths.base, '');
+
+					let pathname = decodeURI(parsed.pathname);
+
+					if (config.kit.paths.base) {
+						if (!pathname.startsWith(config.kit.paths.base)) continue;
+						pathname = pathname.slice(config.kit.paths.base.length) || '/';
+					}
 
 					const file = pathname.slice(1);
 					if (files.has(file)) continue;

packages/kit/src/runtime/server/index.js

@@ -105,7 +105,12 @@ export async function respond(incoming, options, state = {}) {
 					});
 				}
 
-				const decoded = decodeURI(request.url.pathname).replace(options.paths.base, '');
+				let decoded = decodeURI(request.url.pathname);
+
+				if (options.paths.base) {
+					if (!decoded.startsWith(options.paths.base)) return;
+					decoded = decoded.slice(options.paths.base.length) || '/';
+				}
 
 				for (const route of options.manifest._.routes) {
 					const match = route.pattern.exec(decoded);

packages/kit/test/apps/options-2/svelte.config.js

@@ -3,6 +3,9 @@ import path from 'path';
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
 	kit: {
+		paths: {
+			base: '/basepath'
+		},
 		serviceWorker: {
 			register: false
 		},

packages/kit/test/apps/options-2/test/test.js

@@ -3,22 +3,24 @@ import { test } from '../../../utils.js';
 
 /** @typedef {import('@playwright/test').Response} Response */
 
-test.describe.parallel('Service worker', () => {
-	test('serves /', async ({ page }) => {
-		await page.goto('/');
+test.describe.parallel('paths.base', () => {
+	test('serves /basepath', async ({ page }) => {
+		await page.goto('/basepath');
 		expect(await page.textContent('h1')).toBe('Hello');
 	});
+});
 
+test.describe.parallel('Service worker', () => {
 	if (!process.env.DEV) {
-		test('build /service-worker.js', async ({ request }) => {
-			const response = await request.get('/service-worker.js');
+		test('build /basepath/service-worker.js', async ({ request }) => {
+			const response = await request.get('/basepath/service-worker.js');
 			const content = await response.text();
 
 			expect(content).toMatch(/\/_app\/start-[a-z0-9]+\.js/);
 		});
 
-		test('does not register /service-worker.js', async ({ page }) => {
-			await page.goto('/');
+		test('does not register /basepath/service-worker.js', async ({ page }) => {
+			await page.goto('/basepath');
 			expect(await page.content()).not.toMatch(/navigator\.serviceWorker/);
 		});
 	}

packages/kit/test/apps/options/source/pages/origin/index.svelte

@@ -1,7 +1,9 @@
 <script context="module">
+	import { base } from '$app/paths';
+
 	/** @type {import('@sveltejs/kit').Load} */
 	export async function load({ url, fetch }) {
-		const res = await fetch('/origin.json');
+		const res = await fetch(`${base}/origin.json`);
 		const data = await res.json();
 
 		return {