web/src/decrypt/qmc.ts

import { QmcMapCipher, QmcRC4Cipher, QmcStaticCipher, QmcStreamCipher } from './qmc_cipher';
import {
  AudioMimeType,
  GetArrayBuffer,
  GetCoverFromFile,
  GetImageFromURL,
  GetMetaFromFile,
  SniffAudioExt,
  WriteMetaToFlac,
  WriteMetaToMp3,
} from '@/decrypt/utils';
import { parseBlob as metaParseBlob } from 'music-metadata-browser';
import { DecryptQMCWasm } from './qmc_wasm';

import iconv from 'iconv-lite';
import { DecryptResult } from '@/decrypt/entity';
import { queryAlbumCover } from '@/utils/api';
import { QmcDeriveKey } from '@/decrypt/qmc_key';

interface Handler {
  ext: string;
  version: number;
}

export const HandlerMap: { [key: string]: Handler } = {
  mgg: { ext: 'ogg', version: 2 },
  mgg1: { ext: 'ogg', version: 2 },
  mflac: { ext: 'flac', version: 2 },
  mflac0: { ext: 'flac', version: 2 },

  // qmcflac / qmcogg:
  // 有可能是 v2 加密但混用同一个后缀名。
  qmcflac: { ext: 'flac', version: 2 },
  qmcogg: { ext: 'ogg', version: 2 },

  qmc0: { ext: 'mp3', version: 1 },
  qmc2: { ext: 'ogg', version: 1 },
  qmc3: { ext: 'mp3', version: 1 },
  bkcmp3: { ext: 'mp3', version: 1 },
  bkcflac: { ext: 'flac', version: 1 },
  tkm: { ext: 'm4a', version: 1 },
  '666c6163': { ext: 'flac', version: 1 },
  '6d7033': { ext: 'mp3', version: 1 },
  '6f6767': { ext: 'ogg', version: 1 },
  '6d3461': { ext: 'm4a', version: 1 },
  '776176': { ext: 'wav', version: 1 },
};

export async function Decrypt(file: Blob, raw_filename: string, raw_ext: string): Promise<DecryptResult> {
  if (!(raw_ext in HandlerMap)) throw `Qmc cannot handle type: ${raw_ext}`;
  const handler = HandlerMap[raw_ext];
  let { version } = handler;

  const fileBuffer = await GetArrayBuffer(file);
  let musicDecoded: Uint8Array | undefined;

  if (version === 2 && globalThis.WebAssembly) {
    console.log('qmc: using wasm decoder');
    const v2Decrypted = await DecryptQMCWasm(fileBuffer);
    // 如果 v2 检测失败，降级到 v1 再尝试一次
    if (v2Decrypted) {
      musicDecoded = v2Decrypted;
    }
  }
  if (!musicDecoded) {
    // may throw error
    console.log('qmc: using js decoder');
    const d = new QmcDecoder(new Uint8Array(fileBuffer));
    musicDecoded = d.decrypt();
  }

  const ext = SniffAudioExt(musicDecoded, handler.ext);
  const mime = AudioMimeType[ext];

  let musicBlob = new Blob([musicDecoded], { type: mime });

  const musicMeta = await metaParseBlob(musicBlob);
  for (let metaIdx in musicMeta.native) {
    if (!musicMeta.native.hasOwnProperty(metaIdx)) continue;
    if (musicMeta.native[metaIdx].some((item) => item.id === 'TCON' && item.value === '(12)')) {
      console.warn('try using gbk encoding to decode meta');
      musicMeta.common.artist = iconv.decode(new Buffer(musicMeta.common.artist ?? ''), 'gbk');
      musicMeta.common.title = iconv.decode(new Buffer(musicMeta.common.title ?? ''), 'gbk');
      musicMeta.common.album = iconv.decode(new Buffer(musicMeta.common.album ?? ''), 'gbk');
    }
  }

  const info = GetMetaFromFile(raw_filename, musicMeta.common.title, musicMeta.common.artist);

  let imgUrl = GetCoverFromFile(musicMeta);
  if (!imgUrl) {
    imgUrl = await getCoverImage(info.title, info.artist, musicMeta.common.album);
    if (imgUrl) {
      const imageInfo = await GetImageFromURL(imgUrl);
      if (imageInfo) {
        imgUrl = imageInfo.url;
        try {
          const newMeta = { picture: imageInfo.buffer, title: info.title, artists: info.artist?.split(' _ ') };
          if (ext === 'mp3') {
            musicDecoded = WriteMetaToMp3(Buffer.from(musicDecoded), newMeta, musicMeta);
            musicBlob = new Blob([musicDecoded], { type: mime });
          } else if (ext === 'flac') {
            musicDecoded = WriteMetaToFlac(Buffer.from(musicDecoded), newMeta, musicMeta);
            musicBlob = new Blob([musicDecoded], { type: mime });
          } else {
            console.info('writing metadata for ' + ext + ' is not being supported for now');
          }
        } catch (e) {
          console.warn('Error while appending cover image to file ' + e);
        }
      }
    }
  }
  return {
    title: info.title,
    artist: info.artist,
    ext: ext,
    album: musicMeta.common.album,
    picture: imgUrl,
    file: URL.createObjectURL(musicBlob),
    blob: musicBlob,
    mime: mime,
  };
}

async function getCoverImage(title: string, artist?: string, album?: string): Promise<string> {
  const song_query_url = 'https://stats.ixarea.com/apis' + '/music/qq-cover';
  try {
    const data = await queryAlbumCover(title, artist, album);
    return `${song_query_url}/${data.Type}/${data.Id}`;
  } catch (e) {
    console.warn(e);
  }
  return '';
}

export class QmcDecoder {
  private static readonly BYTE_COMMA = ','.charCodeAt(0);
  file: Uint8Array;
  size: number;
  decoded: boolean = false;
  audioSize?: number;
  cipher?: QmcStreamCipher;

  constructor(file: Uint8Array) {
    this.file = file;
    this.size = file.length;
    this.searchKey();
  }

  decrypt(): Uint8Array {
    if (!this.cipher) {
      throw new Error('no cipher found');
    }
    if (!this.audioSize || this.audioSize <= 0) {
      throw new Error('invalid audio size');
    }
    const audioBuf = this.file.subarray(0, this.audioSize);

    if (!this.decoded) {
      this.cipher.decrypt(audioBuf, 0);
      this.decoded = true;
    }

    return audioBuf;
  }

  private searchKey() {
    const last4Byte = this.file.slice(-4);
    const textEnc = new TextDecoder();
    if (textEnc.decode(last4Byte) === 'QTag') {
      const sizeBuf = this.file.slice(-8, -4);
      const sizeView = new DataView(sizeBuf.buffer, sizeBuf.byteOffset);
      const keySize = sizeView.getUint32(0, false);
      this.audioSize = this.size - keySize - 8;
      const rawKey = this.file.subarray(this.audioSize, this.size - 8);
      const keyEnd = rawKey.findIndex((v) => v == QmcDecoder.BYTE_COMMA);
      this.setCipher(rawKey.subarray(0, keyEnd));
    } else {
      const sizeView = new DataView(last4Byte.buffer, last4Byte.byteOffset);
      const keySize = sizeView.getUint32(0, true);
      if (keySize < 0x300) {
        this.audioSize = this.size - keySize - 4;
        const rawKey = this.file.subarray(this.audioSize, this.size - 4);
        this.setCipher(rawKey);
      } else {
        this.audioSize = this.size;
        this.cipher = new QmcStaticCipher();
      }
    }
  }

  private setCipher(keyRaw: Uint8Array) {
    const keyDec = QmcDeriveKey(keyRaw);
    if (keyDec.length > 300) {
      this.cipher = new QmcRC4Cipher(keyDec);
    } else {
      this.cipher = new QmcMapCipher(keyDec);
    }
  }
}