decodeHex

1/**
2 * Decodes a hex-encoded string into a regular string.
3 *
4 * @param hex - The hex string to decode.
5 * @returns Decoded string or null if input is invalid.
6 */
7export function decodeHex(hex: string): string | null {
8  try {
9    if (hex.length % 2 !== 0 || /[^0-9a-f]/i.test(hex)) {
10      return null;
11    }
12
13    const bytes = new Uint8Array(hex.length / 2);
14    for (let i = 0; i < hex.length; i += 2) {
15      bytes[i / 2] = parseInt(hex.slice(i, i + 2), 16);
16    }
17
18    return new TextDecoder().decode(bytes);
19  } catch {
20    return null;
21  }
22}

1test('decodeHex - decodes ASCII string', () => {
2  expect(decodeHex('48656c6c6f')).toBe('Hello');
3});
4
5test('decodeHex - decodes Unicode string', () => {
6  expect(decodeHex('d09fd180d0b8d0b2d0b5d182')).toBe('Привет');
7});
8
9test('decodeHex - empty string returns empty', () => {
10  expect(decodeHex('')).toBe('');
11});
12
13test('decodeHex - invalid hex returns null (odd length)', () => {
14  expect(decodeHex('123')).toBeNull();
15});
16
17test('decodeHex - invalid hex returns null (bad chars)', () => {
18  expect(decodeHex('zzzz')).toBeNull();
19});