package qmc import ( "bytes" "encoding/binary" "errors" "fmt" "io" "strconv" "strings" "unlock-music.dev/cli/algo/common" "unlock-music.dev/cli/internal/sniff" ) type Decoder struct { raw io.ReadSeeker // raw is the original file reader audio io.Reader // audio is the encrypted audio data audioLen int // audioLen is the audio data length offset int // offset is the current audio read position decodedKey []byte // decodedKey is the decoded key for cipher cipher common.StreamDecoder rawMetaExtra1 int rawMetaExtra2 int } // Read implements io.Reader, offer the decrypted audio data. // Validate should call before Read to check if the file is valid. func (d *Decoder) Read(p []byte) (int, error) { n, err := d.audio.Read(p) if n > 0 { d.cipher.Decrypt(p[:n], d.offset) d.offset += n } return n, err } func NewDecoder(r io.ReadSeeker) common.Decoder { return &Decoder{raw: r} } func (d *Decoder) Validate() error { // search & derive key err := d.searchKey() if err != nil { return err } // check cipher type and init decode cipher if len(d.decodedKey) > 300 { d.cipher, err = newRC4Cipher(d.decodedKey) if err != nil { return err } } else if len(d.decodedKey) != 0 { d.cipher, err = newMapCipher(d.decodedKey) if err != nil { return err } } else { d.cipher = newStaticCipher() } // test with first 16 bytes if err := d.validateDecode(); err != nil { return err } // reset position, limit to audio, prepare for Read if _, err := d.raw.Seek(0, io.SeekStart); err != nil { return err } d.audio = io.LimitReader(d.raw, int64(d.audioLen)) return nil } func (d *Decoder) validateDecode() error { _, err := d.raw.Seek(0, io.SeekStart) if err != nil { return fmt.Errorf("qmc seek to start: %w", err) } buf := make([]byte, 16) if _, err := io.ReadFull(d.raw, buf); err != nil { return fmt.Errorf("qmc read header: %w", err) } d.cipher.Decrypt(buf, 0) _, ok := sniff.AudioExtension(buf) if !ok { return errors.New("qmc: detect file type failed") } return nil } func (d *Decoder) searchKey() error { fileSizeM4, err := d.raw.Seek(-4, io.SeekEnd) if err != nil { return err } suffixBuf := make([]byte, 4) if _, err := io.ReadFull(d.raw, suffixBuf); err != nil { return err } switch string(suffixBuf) { case "QTag": return d.readRawMetaQTag() case "STag": return errors.New("qmc: file with 'STag' suffix doesn't contains media key") default: size := binary.LittleEndian.Uint32(suffixBuf) if size <= 0xFFFF && size != 0 { // assume size is key len return d.readRawKey(int64(size)) } // try to use default static cipher d.audioLen = int(fileSizeM4 + 4) return nil } } func (d *Decoder) readRawKey(rawKeyLen int64) error { audioLen, err := d.raw.Seek(-(4 + rawKeyLen), io.SeekEnd) if err != nil { return err } d.audioLen = int(audioLen) rawKeyData, err := io.ReadAll(io.LimitReader(d.raw, rawKeyLen)) if err != nil { return err } // clean suffix NULs rawKeyData = bytes.TrimRight(rawKeyData, "\x00") d.decodedKey, err = deriveKey(rawKeyData) if err != nil { return err } return nil } func (d *Decoder) readRawMetaQTag() error { // get raw meta data len if _, err := d.raw.Seek(-8, io.SeekEnd); err != nil { return err } buf, err := io.ReadAll(io.LimitReader(d.raw, 4)) if err != nil { return err } rawMetaLen := int64(binary.BigEndian.Uint32(buf)) // read raw meta data audioLen, err := d.raw.Seek(-(8 + rawMetaLen), io.SeekEnd) if err != nil { return err } d.audioLen = int(audioLen) rawMetaData, err := io.ReadAll(io.LimitReader(d.raw, rawMetaLen)) if err != nil { return err } items := strings.Split(string(rawMetaData), ",") if len(items) != 3 { return errors.New("invalid raw meta data") } d.decodedKey, err = deriveKey([]byte(items[0])) if err != nil { return err } d.rawMetaExtra1, err = strconv.Atoi(items[1]) if err != nil { return err } d.rawMetaExtra2, err = strconv.Atoi(items[2]) if err != nil { return err } return nil } //goland:noinspection SpellCheckingInspection func init() { supportedExts := []string{ "qmc0", "qmc3", //QQ Music MP3 "qmc2", "qmc4", "qmc6", "qmc8", //QQ Music M4A "qmcflac", //QQ Music FLAC "qmcogg", //QQ Music OGG "tkm", //QQ Music Accompaniment M4A "bkcmp3", "bkcm4a", "bkcflac", "bkcwav", "bkcape", "bkcogg", "bkcwma", //Moo Music "666c6163", //QQ Music Weiyun Flac "6d7033", //QQ Music Weiyun Mp3 "6f6767", //QQ Music Weiyun Ogg "6d3461", //QQ Music Weiyun M4a "776176", //QQ Music Weiyun Wav "mgg", "mgg1", "mggl", //QQ Music New Ogg "mflac", "mflac0", //QQ Music New Flac } for _, ext := range supportedExts { common.RegisterDecoder(ext, false, NewDecoder) } }