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cli/algo/qmc/qmc.go

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package qmc
import (
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"bytes"
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"encoding/binary"
"errors"
"fmt"
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"io"
"strconv"
"strings"
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"unlock-music.dev/cli/algo/common"
"unlock-music.dev/cli/internal/sniff"
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)
type Decoder struct {
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raw io.ReadSeeker // raw is the original file reader
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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
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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
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}
return n, err
}
func NewDecoder(r io.ReadSeeker) common.Decoder {
return &Decoder{raw: r}
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}
func (d *Decoder) Validate() error {
// search & derive key
err := d.searchKey()
if err != nil {
return err
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}
// check cipher type and init decode cipher
if len(d.decodedKey) > 300 {
d.cipher, err = newRC4Cipher(d.decodedKey)
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if err != nil {
return err
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}
} else if len(d.decodedKey) != 0 {
d.cipher, err = newMapCipher(d.decodedKey)
if err != nil {
return err
}
} else {
d.cipher = newStaticCipher()
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}
// test with first 16 bytes
if err := d.validateDecode(); err != nil {
return err
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}
// 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 {
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return err
}
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suffixBuf := make([]byte, 4)
if _, err := io.ReadFull(d.raw, suffixBuf); err != nil {
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return err
}
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switch string(suffixBuf) {
case "QTag":
return d.readRawMetaQTag()
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case "STag":
return errors.New("qmc: file with 'STag' suffix doesn't contains media key")
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default:
size := binary.LittleEndian.Uint32(suffixBuf)
if size <= 0xFFFF && size != 0 { // assume size is key len
return d.readRawKey(int64(size))
}
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// try to use default static cipher
d.audioLen = int(fileSizeM4 + 4)
return nil
}
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}
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
}
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// clean suffix NULs
rawKeyData = bytes.TrimRight(rawKeyData, "\x00")
d.decodedKey, err = deriveKey(rawKeyData)
if err != nil {
return err
}
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return nil
}
func (d *Decoder) readRawMetaQTag() error {
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// get raw meta data len
if _, err := d.raw.Seek(-8, io.SeekEnd); err != nil {
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return err
}
buf, err := io.ReadAll(io.LimitReader(d.raw, 4))
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if err != nil {
return err
}
rawMetaLen := int64(binary.BigEndian.Uint32(buf))
// read raw meta data
audioLen, err := d.raw.Seek(-(8 + rawMetaLen), io.SeekEnd)
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if err != nil {
return err
}
d.audioLen = int(audioLen)
rawMetaData, err := io.ReadAll(io.LimitReader(d.raw, rawMetaLen))
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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
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}
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
}
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//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
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"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
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"mflac", "mflac0", //QQ Music New Flac
}
for _, ext := range supportedExts {
common.RegisterDecoder(ext, false, NewDecoder)
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}
}