127 lines
2.4 KiB
Go
127 lines
2.4 KiB
Go
package kwm
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import (
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"bytes"
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"encoding/binary"
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"errors"
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"strconv"
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"strings"
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"unicode"
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"github.com/unlock-music/cli/algo/common"
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)
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var (
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magicHeader = []byte{
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0x79, 0x65, 0x65, 0x6C, 0x69, 0x6F, 0x6E, 0x2D,
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0x6B, 0x75, 0x77, 0x6F, 0x2D, 0x74, 0x6D, 0x65}
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ErrKwFileSize = errors.New("kwm invalid file size")
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ErrKwMagicHeader = errors.New("kwm magic header not matched")
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)
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const keyPreDefined = "MoOtOiTvINGwd2E6n0E1i7L5t2IoOoNk"
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type Decoder struct {
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file []byte
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key []byte
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outputExt string
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bitrate int
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mask []byte
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audio []byte
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}
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func (d *Decoder) GetAudioData() []byte {
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return d.audio
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}
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func (d *Decoder) GetAudioExt() string {
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return "." + d.outputExt
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}
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func (d *Decoder) GetMeta() common.Meta {
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return nil
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}
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func NewDecoder(data []byte) common.Decoder {
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//todo: Notice the input data will be changed for now
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return &Decoder{file: data}
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}
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func (d *Decoder) Validate() error {
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lenData := len(d.file)
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if lenData < 1024 {
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return ErrKwFileSize
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}
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if !bytes.Equal(magicHeader, d.file[:16]) {
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return ErrKwMagicHeader
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}
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return nil
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}
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func generateMask(key []byte) []byte {
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keyInt := binary.LittleEndian.Uint64(key)
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keyStr := strconv.FormatUint(keyInt, 10)
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keyStrTrim := padOrTruncate(keyStr, 32)
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mask := make([]byte, 32)
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for i := 0; i < 32; i++ {
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mask[i] = keyPreDefined[i] ^ keyStrTrim[i]
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}
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return mask
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}
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func (d *Decoder) parseBitrateAndType() {
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bitType := string(bytes.TrimRight(d.file[0x30:0x38], string(byte(0))))
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charPos := 0
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for charPos = range bitType {
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if !unicode.IsNumber(rune(bitType[charPos])) {
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break
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}
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}
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var err error
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d.bitrate, err = strconv.Atoi(bitType[:charPos])
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if err != nil {
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d.bitrate = 0
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}
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d.outputExt = strings.ToLower(bitType[charPos:])
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}
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func (d *Decoder) Decode() error {
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d.parseBitrateAndType()
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d.mask = generateMask(d.file[0x18:0x20])
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d.audio = d.file[1024:]
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dataLen := len(d.audio)
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for i := 0; i < dataLen; i++ {
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d.audio[i] ^= d.mask[i&0x1F] //equals: [i % 32]
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}
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return nil
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}
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func padOrTruncate(raw string, length int) string {
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lenRaw := len(raw)
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out := raw
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if lenRaw == 0 {
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out = string(make([]byte, length))
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} else if lenRaw > length {
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out = raw[:length]
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} else if lenRaw < length {
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_tmp := make([]byte, 32)
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for i := 0; i < 32; i++ {
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_tmp[i] = raw[i%lenRaw]
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}
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out = string(_tmp)
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}
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return out
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}
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func init() {
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// Kuwo Mp3/Flac
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common.RegisterDecoder("kwm", false, NewDecoder)
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common.RegisterDecoder("kwm", false, common.NewRawDecoder)
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}
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