Add KGM Decoder

algo/kgm/kgm.go

@@ -0,0 +1,91 @@
+package kgm
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"github.com/umlock-music/cli/algo/common"
+	"github.com/umlock-music/cli/internal/logging"
+)
+
+var (
+	vprHeader = []byte{
+		0x05, 0x28, 0xBC, 0x96, 0xE9, 0xE4, 0x5A, 0x43,
+		0x91, 0xAA, 0xBD, 0xD0, 0x7A, 0xF5, 0x36, 0x31}
+	kgmHeader = []byte{
+		0x7C, 0xD5, 0x32, 0xEB, 0x86, 0x02, 0x7F, 0x4B,
+		0xA8, 0xAF, 0xA6, 0x8E, 0x0F, 0xFF, 0x99, 0x14}
+	ErrKgmMagicHeader = errors.New("kgm/vpr magic header not matched")
+)
+
+type Decoder struct {
+	file  []byte
+	key   []byte
+	isVpr bool
+	audio []byte
+}
+
+func NewDecoder(file []byte) *Decoder {
+	return &Decoder{
+		file: file,
+	}
+}
+
+func (d Decoder) GetCoverImage() []byte {
+	return nil
+}
+
+func (d Decoder) GetAudioData() []byte {
+	return d.audio
+}
+
+func (d Decoder) GetAudioExt() string {
+	return ""
+}
+
+func (d Decoder) GetMeta() common.Meta {
+	return nil
+}
+
+func (d *Decoder) Validate() error {
+	if bytes.Equal(kgmHeader, d.file[:len(kgmHeader)]) {
+		d.isVpr = false
+	} else if bytes.Equal(vprHeader, d.file[:len(vprHeader)]) {
+		d.isVpr = true
+	} else {
+		return ErrKgmMagicHeader
+	}
+
+	d.key = d.file[0x1c:0x2c]
+	d.key = append(d.key, 0x00)
+	_ = d.file[0x2c:0x3c] //key2
+	return nil
+
+}
+
+func (d *Decoder) Decode() error {
+	headerLen := binary.LittleEndian.Uint32(d.file[0x10:0x14])
+	dataEncrypted := d.file[headerLen:]
+	lenData := len(dataEncrypted)
+	initMask()
+	if fullMaskLen < lenData {
+		logging.Log().Warn("文件过大，处理后的音频不完整,请向我们报告此文件的信息")
+		lenData = fullMaskLen
+	}
+	d.audio = make([]byte, lenData)
+
+	for i := 0; i < lenData; i++ {
+		med8 := d.key[i%17] ^ dataEncrypted[i]
+		med8 ^= (med8 & 0xf) << 4
+
+		msk8 := maskV2PreDef[i%272] ^ maskV2[i>>4]
+		msk8 ^= (msk8 & 0xf) << 4
+		d.audio[i] = med8 ^ msk8
+	}
+	if d.isVpr {
+		for i := 0; i < lenData; i++ {
+			d.audio[i] ^= maskDiffVpr[i%17]
+		}
+	}
+	return nil
+}