feat: provide normalizeUrl helper

.changeset/tough-mangos-develop.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': minor
+---
+
+feat: provide `normalizeUrl` helper

packages/kit/src/exports/index.js

@@ -1,5 +1,13 @@
 import { HttpError, Redirect, ActionFailure } from '../runtime/control.js';
 import { BROWSER, DEV } from 'esm-env';
+import {
+	add_data_suffix,
+	add_resolution_suffix,
+	has_data_suffix,
+	has_resolution_suffix,
+	strip_data_suffix,
+	strip_resolution_suffix
+} from '../runtime/pathname.js';
 
 export { VERSION } from '../version.js';
 
@@ -207,3 +215,49 @@ export function fail(status, data) {
 export function isActionFailure(e) {
 	return e instanceof ActionFailure;
 }
+
+/**
+ * Strips possible SvelteKit-internal suffixes and trailing slashes from the URL pathname.
+ * Returns the normalized URL as well as a method for adding the potential suffix back
+ * based on a new pathname (possibly including search) or URL.
+ * ```js
+ * import { normalizeUrl } from '@sveltejs/kit';
+ *
+ * const { url, denormalize } = normalizeUrl('/blog/post/__data.json');
+ * console.log(url.pathname); // /blog/post
+ * console.log(denormalize('/blog/post/a')); // /blog/post/a/__data.json
+ * ```
+ * @param {URL | string} url
+ * @returns {{ url: URL, wasNormalized: boolean, denormalize: (url?: string | URL) => URL }}
+ */
+export function normalizeUrl(url) {
+	url = new URL(url, 'http://internal');
+
+	const is_route_resolution = has_resolution_suffix(url.pathname);
+	const is_data_request = has_data_suffix(url.pathname);
+	const has_trailing_slash = url.pathname !== '/' && url.pathname.endsWith('/');
+
+	if (is_route_resolution) {
+		url.pathname = strip_resolution_suffix(url.pathname);
+	} else if (is_data_request) {
+		url.pathname = strip_data_suffix(url.pathname);
+	} else if (has_trailing_slash) {
+		url.pathname = url.pathname.slice(0, -1);
+	}
+
+	return {
+		url,
+		wasNormalized: is_data_request || is_route_resolution || has_trailing_slash,
+		denormalize: (new_url = url) => {
+			new_url = new URL(new_url, url);
+			if (is_route_resolution) {
+				new_url.pathname = add_resolution_suffix(new_url.pathname);
+			} else if (is_data_request) {
+				new_url.pathname = add_data_suffix(new_url.pathname);
+			} else if (has_trailing_slash && !new_url.pathname.endsWith('/')) {
+				new_url.pathname += '/';
+			}
+			return new_url;
+		}
+	};
+}

packages/kit/src/exports/index.spec.js

@@ -0,0 +1,53 @@
+import { normalizeUrl } from './index.js';
+import { assert, describe, it } from 'vitest';
+
+describe('normalizeUrl', () => {
+	it('noop for regular url', () => {
+		const original = new URL('http://example.com/foo/bar');
+		const { url, wasNormalized, denormalize } = normalizeUrl(original);
+
+		assert.equal(wasNormalized, false);
+		assert.equal(url.href, original.href);
+		assert.equal(denormalize().href, original.href);
+		assert.equal(denormalize('/baz').href, 'http://example.com/baz');
+		assert.equal(
+			denormalize('?some=query#hash').href,
+			'http://example.com/foo/bar?some=query#hash'
+		);
+		assert.equal(denormalize('http://somethingelse.com/').href, 'http://somethingelse.com/');
+		assert.equal(
+			denormalize(new URL('http://somethingelse.com/')).href,
+			'http://somethingelse.com/'
+		);
+	});
+
+	it('should normalize trailing slash', () => {
+		const original = new URL('http://example.com/foo/bar/');
+		const { url, wasNormalized, denormalize } = normalizeUrl(original);
+
+		assert.equal(wasNormalized, true);
+		assert.equal(url.href, original.href.slice(0, -1));
+		assert.equal(denormalize().href, original.href);
+		assert.equal(denormalize('/baz').href, 'http://example.com/baz/');
+	});
+
+	it('should normalize data request route', () => {
+		const original = new URL('http://example.com/foo/__data.json');
+		const { url, wasNormalized, denormalize } = normalizeUrl(original);
+
+		assert.equal(wasNormalized, true);
+		assert.equal(url.href, 'http://example.com/foo');
+		assert.equal(denormalize().href, original.href);
+		assert.equal(denormalize('/baz').href, 'http://example.com/baz/__data.json');
+	});
+
+	it('should normalize route request route', () => {
+		const original = new URL('http://example.com/foo/__route.js');
+		const { url, wasNormalized, denormalize } = normalizeUrl(original);
+
+		assert.equal(wasNormalized, true);
+		assert.equal(url.href, 'http://example.com/foo');
+		assert.equal(denormalize().href, original.href);
+		assert.equal(denormalize('/baz').href, 'http://example.com/baz/__route.js');
+	});
+});

packages/kit/types/index.d.ts

@@ -2005,6 +2005,23 @@ declare module '@sveltejs/kit' {
 	 * @param e The object to check.
 	 * */
 	export function isActionFailure(e: unknown): e is ActionFailure;
+	/**
+	 * Strips possible SvelteKit-internal suffixes and trailing slashes from the URL pathname.
+	 * Returns the normalized URL as well as a method for adding the potential suffix back
+	 * based on a new pathname (possibly including search) or URL.
+	 * ```js
+	 * import { normalizeUrl } from '@sveltejs/kit';
+	 *
+	 * const { url, denormalize } = normalizeUrl('/blog/post/__data.json');
+	 * console.log(url.pathname); // /blog/post
+	 * console.log(denormalize('/blog/post/a')); // /blog/post/a/__data.json
+	 * ```
+	 * */
+	export function normalizeUrl(url: URL | string): {
+		url: URL;
+		wasNormalized: boolean;
+		denormalize: (url?: string | URL) => URL;
+	};
 	export type LessThan<TNumber extends number, TArray extends any[] = []> = TNumber extends TArray["length"] ? TArray[number] : LessThan<TNumber, [...TArray, TArray["length"]]>;
 	export type NumericRange<TStart extends number, TEnd extends number> = Exclude<TEnd | LessThan<TEnd>, LessThan<TStart>>;
 	export const VERSION: string;