signing algorithm for `musics.fcg` endpoint

qqmusic.py

class QQMusicBaseIE(InfoExtractor):
    def _get_musics_sign(self, payload: bytes):
        # This may not work for domains other than `y.qq.com` and browswer UA that contains `Headless`
        md5hex = hashlib.md5(payload).hexdigest().upper()
        hex_digits = [int(c, base=16) for c in md5hex]

        xor_digits = []
        for i, xor in enumerate([212, 45, 80, 68, 195, 163, 163, 203, 157, 220, 254, 91, 204, 79, 104, 6]):
            xor_digits.append((hex_digits[i * 2] * 16 + hex_digits[i * 2 + 1]) ^ xor)

        char_indicies = []
        for i in range(0, len(xor_digits) - 1, 3):
            char_indicies.extend([
                xor_digits[i] >> 2,
                ((xor_digits[i] & 3) << 4) | (xor_digits[i + 1] >> 4),
                ((xor_digits[i + 1] & 15) << 2) | (xor_digits[i + 2] >> 6),
                xor_digits[i + 2] & 63,
            ])
        char_indicies.extend([
            xor_digits[15] >> 2,
            (xor_digits[15] & 3) << 4,
        ])

        head = ''.join(md5hex[i] for i in [21, 4, 9, 26, 16, 20, 27, 30])
        tail = ''.join(md5hex[i] for i in [18, 11, 3, 2, 1, 7, 6, 25])
        body = ''.join('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='[i] for i in char_indicies)
        return re.sub(r'[\/+]', '', f'zzb{head}{body}{tail}'.lower())

    def make_fcu_req(self, mid, req_dict, **kwargs):
        payload = json.dumps({
            'comm': {
                'cv': 4747474,
                'ct': 24,
                'format': 'json',
                'inCharset': 'utf-8',
                'outCharset': 'utf-8',
                'notice': 0,
                'platform': 'yqq.json',
                'needNewCode': 1,
                'uin': self._get_uin(),
                'g_tk_new_20200303': self._get_g_tk(),
                'g_tk': self._get_g_tk(),
            },
            **req_dict
        }, separators=(',', ':')).encode('utf-8')

        return self._download_json(
            'https://u.y.qq.com/cgi-bin/musics.fcg', mid, data=payload,
            query={'_': int(time.time()), 'sign': self._get_sign(payload)}, **kwargs)