NeteaseMusicLyricDownloader/modules/utils/dump.py

import binascii
import json
import os
import struct
import base64

from Cryptodome.Cipher import AES
from Cryptodome.Util.Padding import unpad
from Cryptodome.Util.strxor import strxor as xor
from mutagen import mp3, flac, id3
from modules.utils.wrappers import escape_file_not_found, escape_permission_error


def regular_filename(filename):
    """处理替换非法字符"""
    replaces = {  # 处理非法字符所用的替换字典(根据网易云下载的文件分析得到)
        "|": "｜",
        ":": "：",
        "<": "＜",
        ">": "＞",
        "?": "？",
        "/": "／",
        "\\": "＼",
        "*": "＊",
        '"': "＂"
    }
    for k, v in replaces.items():
        filename = filename.replace(k, v)
    return filename


@escape_file_not_found
@escape_permission_error
def load_and_decrypt_from_ncm(file_path, target_dir, out_format, return_output_path=False) -> dict | str | tuple:
    # Original author: Nzix Repo: nondanee
    """解锁指定文件并按照规则保存在指定位置
    ``file_path`` 源文件路径
    ``target_dir`` 解锁后文件保存路径
    ``out_format`` 输出文件格式，使用“字典”格式字符串，若使用源文件名仅替换后缀则传入\"original\""""

    core_key = binascii.a2b_hex('687A4852416D736F356B496E62617857')
    meta_key = binascii.a2b_hex('2331346C6A6B5F215C5D2630553C2728')

    f = open(file_path, 'rb')

    # magic header
    header = f.read(8)
    assert binascii.b2a_hex(header) == b'4354454e4644414d'

    f.seek(2, 1)

    # key data
    key_length = f.read(4)
    key_length = struct.unpack('<I', bytes(key_length))[0]

    key_data = bytearray(f.read(key_length))
    key_data = bytes(bytearray([byte ^ 0x64 for byte in key_data]))

    cryptor = AES.new(core_key, AES.MODE_ECB)
    key_data = unpad(cryptor.decrypt(key_data), 16)[17:]
    key_length = len(key_data)

    # S-box (standard RC4 Key-scheduling algorithm)
    key = bytearray(key_data)
    S = bytearray(range(256))
    j = 0

    for i in range(256):
        j = (j + S[i] + key[i % key_length]) & 0xFF
        S[i], S[j] = S[j], S[i]

    # meta data
    meta_length = f.read(4)
    meta_length = struct.unpack('<I', bytes(meta_length))[0]

    if meta_length:
        meta_data = bytearray(f.read(meta_length))
        meta_data = bytes(bytearray([byte ^ 0x63 for byte in meta_data]))
        identifier = meta_data.decode('utf-8')
        meta_data = base64.b64decode(meta_data[22:])

        cryptor = AES.new(meta_key, AES.MODE_ECB)
        meta_data = unpad(cryptor.decrypt(meta_data), 16).decode('utf-8')
        meta_data = json.loads(meta_data[6:])
    else:
        meta_data = {'format': 'flac' if os.fstat(f.fileno()).st_size > 1024 ** 2 * 16 else 'mp3'}

    f.seek(5, 1)

    # album cover
    image_space = f.read(4)
    image_space = struct.unpack('<I', bytes(image_space))[0]
    image_size = f.read(4)
    image_size = struct.unpack('<I', bytes(image_size))[0]
    image_data = f.read(image_size) if image_size else None

    f.seek(image_space - image_size, 1)

    # media data
    if out_format == "original":
        output_path = f"{os.path.splitext(file_path)[0]}.{meta_data['format']}"
    elif meta_length:
        output_path = os.path.join(target_dir, regular_filename(out_format % {"name": meta_data["musicName"],
                                                                              "artists": "".join(
            [x[0]+"," for x in meta_data["artist"]]
        )[:-1]} + "." + meta_data["format"]))
    else:
        output_path = os.path.join(target_dir, "Unnamed." + meta_data["format"])

    data = f.read()
    f.close()

    # stream cipher (modified RC4 Pseudo-random generation algorithm)
    stream = [S[(S[i] + S[(i + S[i]) & 0xFF]) & 0xFF] for i in range(256)]
    stream = bytes(bytearray(stream * (len(data) // 256 + 1))[1:1 + len(data)])
    data = xor(data, stream)

    m = open(output_path, 'wb')
    m.write(data)
    m.close()

    # media tag
    if meta_length:
        def embed(item, content, t):
            item.encoding = 0
            item.type = t
            item.mime = 'image/png' if content[0:4] == binascii.a2b_hex('89504E47') else 'image/jpeg'
            item.data = content

        if image_data:
            if meta_data['format'] == 'flac':
                audio = flac.FLAC(output_path)
                image = flac.Picture()
                embed(image, image_data, 3)
                audio.clear_pictures()
                audio.add_picture(image)
                audio.save()
            elif meta_data['format'] == 'mp3':
                audio = mp3.MP3(output_path)
                image = id3.APIC()
                embed(image, image_data, 6)
                audio.tags.add(image)
                audio.save()

        if meta_length:
            if meta_data['format'] == 'flac':
                audio = flac.FLAC(output_path)
                audio['description'] = identifier
            else:
                audio = mp3.EasyMP3(output_path)
                audio['title'] = 'placeholder'
                audio.tags.RegisterTextKey('comment', 'COMM')
                audio['comment'] = identifier
            audio['title'] = meta_data['musicName']
            audio['album'] = meta_data['album']
            audio['artist'] = '/'.join([artist[0] for artist in meta_data['artist']])
            audio.save()
        if return_output_path:
            return meta_data, output_path
        else:
            return meta_data
    else:
        if return_output_path:
            return "no_meta_data", output_path
        else:
            return "no_meta_data"