126 lines
2.4 KiB
Go
126 lines
2.4 KiB
Go
package kwm
|
|
|
|
import (
|
|
"bytes"
|
|
"encoding/binary"
|
|
"errors"
|
|
"github.com/davecgh/go-spew/spew"
|
|
"github.com/umlock-music/cli/algo/common"
|
|
"strconv"
|
|
"strings"
|
|
"unicode"
|
|
)
|
|
|
|
var (
|
|
magicHeader = []byte{
|
|
0x79, 0x65, 0x65, 0x6C, 0x69, 0x6F, 0x6E, 0x2D,
|
|
0x6B, 0x75, 0x77, 0x6F, 0x2D, 0x74, 0x6D, 0x65}
|
|
ErrKwFileSize = errors.New("kwm invalid file size")
|
|
ErrKwMagicHeader = errors.New("kwm magic header not matched")
|
|
)
|
|
|
|
const keyPreDefined = "MoOtOiTvINGwd2E6n0E1i7L5t2IoOoNk"
|
|
|
|
type Decoder struct {
|
|
file []byte
|
|
|
|
key []byte
|
|
outputExt string
|
|
bitrate int
|
|
mask []byte
|
|
|
|
audio []byte
|
|
}
|
|
|
|
func (d *Decoder) GetCoverImage() []byte {
|
|
return nil
|
|
}
|
|
|
|
func (d *Decoder) GetAudioData() []byte {
|
|
return d.audio
|
|
}
|
|
|
|
func (d *Decoder) GetAudioExt() string {
|
|
return d.outputExt
|
|
}
|
|
|
|
func (d *Decoder) GetMeta() common.Meta {
|
|
return nil
|
|
}
|
|
|
|
func NewDecoder(data []byte) *Decoder {
|
|
//todo: Notice the input data will be changed for now
|
|
return &Decoder{file: data}
|
|
}
|
|
|
|
func (d *Decoder) Validate() error {
|
|
lenData := len(d.file)
|
|
if lenData < 1024 {
|
|
return ErrKwFileSize
|
|
}
|
|
if !bytes.Equal(magicHeader, d.file[:16]) {
|
|
return ErrKwMagicHeader
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
func generateMask(key []byte) []byte {
|
|
keyInt := binary.LittleEndian.Uint64(key)
|
|
keyStr := strconv.FormatUint(keyInt, 10)
|
|
keyStrTrim := padOrTruncate(keyStr, 32)
|
|
mask := make([]byte, 32)
|
|
for i := 0; i < 32; i++ {
|
|
mask[i] = keyPreDefined[i] ^ keyStrTrim[i]
|
|
}
|
|
return mask
|
|
}
|
|
|
|
func (d *Decoder) parseBitrateAndType() {
|
|
bitType := string(bytes.TrimRight(d.file[0x30:0x38], string(byte(0))))
|
|
charPos := 0
|
|
for charPos = range bitType {
|
|
if !unicode.IsNumber(rune(bitType[charPos])) {
|
|
break
|
|
}
|
|
}
|
|
var err error
|
|
d.bitrate, err = strconv.Atoi(bitType[:charPos])
|
|
if err != nil {
|
|
d.bitrate = 0
|
|
}
|
|
d.outputExt = strings.ToLower(bitType[charPos:])
|
|
|
|
}
|
|
|
|
func (d *Decoder) Decode() error {
|
|
d.parseBitrateAndType()
|
|
|
|
d.mask = generateMask(d.file[0x18:0x20])
|
|
|
|
d.audio = d.file[1024:]
|
|
dataLen := len(d.audio)
|
|
spew.Dump(d.audio[:1024])
|
|
for i := 0; i < dataLen; i++ {
|
|
d.audio[i] ^= d.mask[i&0x1F] //equals: [i % 32]
|
|
}
|
|
return nil
|
|
}
|
|
|
|
func padOrTruncate(raw string, length int) string {
|
|
lenRaw := len(raw)
|
|
out := raw
|
|
if lenRaw == 0 {
|
|
out = string(make([]byte, length))
|
|
} else if lenRaw > length {
|
|
out = raw[:length]
|
|
} else if lenRaw < length {
|
|
_tmp := make([]byte, 32)
|
|
for i := 0; i < 32; i++ {
|
|
_tmp[i] = raw[i%lenRaw]
|
|
}
|
|
out = string(_tmp)
|
|
}
|
|
return out
|
|
}
|