cli/algo/qmc/qmc.go

186 lines
3.4 KiB
Go
Raw Normal View History

2021-12-13 12:42:07 +00:00
package qmc
import (
"encoding/binary"
"errors"
"io"
"strconv"
"strings"
"github.com/unlock-music/cli/algo/common"
2021-12-13 12:42:07 +00:00
)
type Decoder struct {
r io.ReadSeeker
fileExt string
2021-12-13 12:42:07 +00:00
audioLen int
decodedKey []byte
cipher streamCipher
2021-12-13 12:42:07 +00:00
offset int
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) {
2021-12-13 12:42:07 +00:00
n := len(p)
if d.audioLen-d.offset <= 0 {
return 0, io.EOF
} else if d.audioLen-d.offset < n {
n = d.audioLen - d.offset
}
m, err := d.r.Read(p[:n])
if m == 0 {
return 0, err
}
d.cipher.Decrypt(p[:m], d.offset)
2021-12-13 12:42:07 +00:00
d.offset += m
return m, err
}
func NewDecoder(r io.ReadSeeker) (*Decoder, error) {
d := &Decoder{r: r}
err := d.searchKey()
if err != nil {
2021-12-13 12:42:07 +00:00
return nil, err
}
if len(d.decodedKey) > 300 {
d.cipher, err = NewRC4Cipher(d.decodedKey)
2021-12-13 12:42:07 +00:00
if err != nil {
return nil, err
}
} else if len(d.decodedKey) != 0 {
d.cipher, err = NewMapCipher(d.decodedKey)
if err != nil {
return nil, err
}
} else {
d.cipher = NewStaticCipher()
2021-12-13 12:42:07 +00:00
}
_, err = d.r.Seek(0, io.SeekStart)
2021-12-13 12:42:07 +00:00
if err != nil {
return nil, err
}
2021-12-13 12:42:07 +00:00
return d, nil
}
func (d *Decoder) Validate() error {
buf := make([]byte, 16)
if _, err := io.ReadFull(d.r, buf); err != nil {
return err
}
_, err := d.r.Seek(0, io.SeekStart)
if err != nil {
return err
}
d.cipher.Decrypt(buf, 0)
fileExt, ok := common.SniffAll(buf)
if !ok {
return errors.New("detect file type failed")
}
d.fileExt = fileExt
return nil
}
func (d Decoder) GetFileExt() string {
return d.fileExt
}
func (d *Decoder) searchKey() error {
fileSizeM4, err := d.r.Seek(-4, io.SeekEnd)
if err != nil {
2021-12-13 12:42:07 +00:00
return err
}
buf, err := io.ReadAll(io.LimitReader(d.r, 4))
if err != nil {
return err
}
if string(buf) == "QTag" {
if err := d.readRawMetaQTag(); err != nil {
return err
}
} else {
size := binary.LittleEndian.Uint32(buf)
if size < 0x300 && size != 0 {
return d.readRawKey(int64(size))
} else {
// try to use default static cipher
d.audioLen = int(fileSizeM4 + 4)
return nil
}
}
return nil
}
func (d *Decoder) readRawKey(rawKeyLen int64) error {
audioLen, err := d.r.Seek(-(4 + rawKeyLen), io.SeekEnd)
if err != nil {
return err
}
d.audioLen = int(audioLen)
rawKeyData, err := io.ReadAll(io.LimitReader(d.r, rawKeyLen))
if err != nil {
return err
}
d.decodedKey, err = DecryptKey(rawKeyData)
if err != nil {
return err
}
2021-12-13 12:42:07 +00:00
return nil
}
func (d *Decoder) readRawMetaQTag() error {
2021-12-13 12:42:07 +00:00
// get raw meta data len
if _, err := d.r.Seek(-8, io.SeekEnd); err != nil {
return err
}
buf, err := io.ReadAll(io.LimitReader(d.r, 4))
if err != nil {
return err
}
rawMetaLen := int64(binary.BigEndian.Uint32(buf))
// read raw meta data
audioLen, err := d.r.Seek(-(8 + rawMetaLen), io.SeekEnd)
if err != nil {
return err
}
d.audioLen = int(audioLen)
rawMetaData, err := io.ReadAll(io.LimitReader(d.r, 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 = DecryptKey([]byte(items[0]))
if err != nil {
return err
2021-12-13 12:42:07 +00:00
}
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
}