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

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')
+})