decodeBase64Url

1/**
2 * Decodes a base64url-encoded string into its original form.
3 * Replaces base64url-safe characters with base64 ones and adds padding if needed.
4 *
5 * @param input - The base64url-encoded string.
6 * @returns The decoded UTF-8 string.
7 */
8export function decodeBase64Url(input: string): string {
9  const base64 = input
10    .replace(/-/g, '+')
11    .replace(/_/g, '/')
12    .padEnd(Math.ceil(input.length / 4) * 4, '=');
13
14  return Buffer.from(base64, 'base64').toString('utf-8');
15}

1test('decodeBase64Url - decodes simple text', () => {
2  expect(decodeBase64Url('aGVsbG8')).toBe('hello');
3});
4
5test('decodeBase64Url - decodes text with special characters', () => {
6  expect(decodeBase64Url('aGVsbG8rd29ybGQv')).toBe('hello+world/');
7});
8
9test('decodeBase64Url - adds padding as needed', () => {
10  expect(decodeBase64Url('Zm9v')).toBe('foo'); // 'foo' is 'Zm9v'
11});
12
13test('decodeBase64Url - handles unicode characters', () => {
14  expect(decodeBase64Url('4pyTIMOgY2hlY2s')).toBe('✓ check');
15});
16
17test('decodeBase64Url - empty string', () => {
18  expect(decodeBase64Url('')).toBe('');
19});