feat(normalize): add normalize method compatible with the version from node:path

Sometimes used by us causing apps to rely on polyfilling node modules.
Instead we can also simply provide this method.

Added tests similar as the node package use to ensure compatibility.

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Author: susnux

lib/index.ts

@@ -131,3 +131,36 @@ export function isSamePath(path1: string, path2: string): boolean {
 
 	return path1 === path2
 }
+
+/**
+ * Normalizes the given path by removing leading, trailing and doubled slashes and also removing the dot sections.
+ *
+ * @param path - The path to normalize
+ */
+export function normalize(path: string): string {
+	const sections = path.split('/')
+		.filter((p, index, arr) => p !== '' || index === 0 || index === (arr.length - 1)) // remove double // but keep leading and trailing slash
+		.filter((p) => p !== '.') // remove useless /./ sections
+
+	const sanitizedSections: string[] = []
+	for (const section of sections) {
+		const lastSection = sanitizedSections.at(-1)
+		if (section === '..' && lastSection !== '..') {
+			// if the current section is ".." for the parent, we remove the last section
+			// But only if the last section is not also ".." which means that we are in a relative path outside of the root
+			// Note that absolute paths like "/../../foo" are valid as they resolve to "/foo"
+			if (lastSection === undefined) {
+				// if there is no last section, we are at the root and we can't go up further
+				// so we keep the ".." section as this is a relative path outside of the root
+				sanitizedSections.push(section)
+			} else if (lastSection !== '') {
+				// only remove parent if its not the root (leading slash)
+				sanitizedSections.pop()
+			}
+		} else {
+			sanitizedSections.push(section)
+		}
+	}
+
+	return sanitizedSections.join('/')
+}

test/normalize.test.ts

@@ -0,0 +1,29 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+import { expect, test } from 'vitest'
+import { normalize } from '../lib/index.ts'
+
+test('normalize', () => {
+	expect(normalize('./fixtures///b/../b/c.js')).toBe('fixtures/b/c.js')
+	expect(normalize('/foo/../../../bar')).toBe('/bar')
+	expect(normalize('a//b//../b')).toBe('a/b')
+	expect(normalize('a//b//./c')).toBe('a/b/c')
+	expect(normalize('a//b//.')).toBe('a/b')
+	expect(normalize('/a/b/c/../../../x/y/z')).toBe('/x/y/z')
+	expect(normalize('///..//./foo/.//bar')).toBe('/foo/bar')
+	expect(normalize('bar/foo../../')).toBe('bar/')
+	expect(normalize('bar/foo../..')).toBe('bar')
+	expect(normalize('bar/foo../../baz')).toBe('bar/baz')
+	expect(normalize('bar/foo../')).toBe('bar/foo../')
+	expect(normalize('bar/foo..')).toBe('bar/foo..')
+	expect(normalize('../foo../../../bar')).toBe('../../bar')
+	expect(normalize('../../.././../../../bar')).toBe('../../../../../../bar')
+	expect(normalize('../../../foo/../../../bar')).toBe('../../../../../bar')
+	expect(normalize('../../../foo/../../../bar/../../')).toBe('../../../../../../')
+	expect(normalize('../foobar/barfoo/foo/../../../bar/../../')).toBe('../../')
+	expect(normalize('../../../foobar/../../../bar/../../baz')).toBe('../../../../../../baz')
+	expect(normalize('/../../../foobar/../../../bar/../../baz')).toBe('/baz')
+})