refactor: qmc musicex footer parser

algo/qmc/key_mmkv.go

@@ -1,11 +1,9 @@
 package qmc
 
 import (
-	"bytes"
 	"encoding/base64"
 	"errors"
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -99,21 +97,13 @@ func OpenMMKV(vaultPath string, vaultKey string, logger *zap.Logger) error {
 	return nil
 }
 
-func readKeyFromMMKVCustom(d *Decoder) ([]byte, error) {
+func readKeyFromMMKVCustom(mid string) ([]byte, error) {
 	if streamKeyVault == nil {
 		return nil, fmt.Errorf("mmkv vault not loaded")
 	}
-	// 获取mid即数据库键值
-	_, err := d.raw.Seek(-128, io.SeekEnd)
-	if err != nil {
-		return nil, fmt.Errorf("get mid error: %w", err)
-	}
-	mid, err := io.ReadAll(io.LimitReader(d.raw, 64))   // 取64字节确保完全取完
-	mid = bytes.ReplaceAll(mid, []byte{0x00}, []byte{}) // clean NUL
-	mid = bytes.Trim(mid, "\0000")                      // maybe a little stupid
 
-	// 从数据库获取eKey
-	eKey, err := streamKeyVault.GetBytes(string(mid))
+	// get ekey from mmkv vault
+	eKey, err := streamKeyVault.GetBytes(mid)
 	if err != nil {
 		return nil, fmt.Errorf("get eKey error: %w", err)
 	}

algo/qmc/qmc.go

@@ -5,13 +5,12 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"go.uber.org/zap"
 	"io"
 	"runtime"
 	"strconv"
 	"strings"
 
-	"go.uber.org/zap"
-
 	"unlock-music.dev/cli/algo/common"
 	"unlock-music.dev/cli/internal/sniff"
 )
@@ -41,6 +40,8 @@ type Decoder struct {
 
 	// provider
 	logger *zap.Logger
+
+	footer qqMusicTagMusicEx
 }
 
 // Read implements io.Reader, offer the decrypted audio data.
@@ -146,27 +147,16 @@ func (d *Decoder) searchKey() (err error) {
 	case "STag":
 		return errors.New("qmc: file with 'STag' suffix doesn't contains media key")
 	case "cex\x00":
-		d.decodedKey, err = readKeyFromMMKVCustom(d)
-		if err == nil {
-			suffix := []byte{0x63, 0x65, 0x78, 0x00} // cex
-			for i := 0; i <= 3; i++ {
-				// 末尾的信息数据每192字节出现一次，故只要循环判断末尾不为musicex时即为歌曲数据
-				musicexLen, err := d.raw.Seek(int64(-(192*i)-4), io.SeekEnd)
-				if err != nil {
-					return fmt.Errorf("get musicexLen error: %w", err)
-				}
-				buf, err := io.ReadAll(io.LimitReader(d.raw, 4))
-				if err != nil {
-					return fmt.Errorf("get musicex error: %w", err)
-				}
-				if !bytes.Equal(buf, suffix) {
-					d.audioLen = int(musicexLen) + 4
-					return nil
-				}
-			}
-
+		audioLen, err := d.footer.Read(d.raw)
+		if err != nil {
+			return err
 		}
-		return err
+		d.audioLen = int(audioLen)
+		d.decodedKey, err = readKeyFromMMKVCustom(d.footer.mediafile)
+		if err != nil {
+			return err
+		}
+		return nil
 	default:
 		size := binary.LittleEndian.Uint32(suffixBuf)
 

algo/qmc/qmc_footer.go

@@ -0,0 +1,63 @@
+package qmc
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+type qqMusicTagMusicEx struct {
+	songid        uint32 // Song ID
+	unknown_1     uint32 // unused & unknown
+	unknown_2     uint32 // unused & unknown
+	mid           string // Media ID
+	mediafile     string // real file name
+	unknown_3     uint32 // unused; uninitialized memory?
+	sizeof_struct uint32 // 19.57: fixed value: 0xC0
+	version       uint32 // 19.57: fixed value: 0x01
+	tag_magic     []byte // fixed value "musicex\0" (8 bytes)
+}
+
+func (tag *qqMusicTagMusicEx) Read(raw io.ReadSeeker) (int64, error) {
+	_, err := raw.Seek(-16, io.SeekEnd)
+	if err != nil {
+		return 0, fmt.Errorf("musicex seek error: %w", err)
+	}
+
+	footerBuf := make([]byte, 4)
+	footerBuf, err = io.ReadAll(io.LimitReader(raw, 4))
+	if err != nil {
+		return 0, fmt.Errorf("get musicex error: %w", err)
+	}
+	footerLen := int64(binary.LittleEndian.Uint32(footerBuf))
+
+	audioLen, err := raw.Seek(-footerLen, io.SeekEnd)
+	buf, err := io.ReadAll(io.LimitReader(raw, audioLen))
+	if err != nil {
+		return 0, err
+	}
+
+	tag.songid = binary.LittleEndian.Uint32(buf[0:4])
+	tag.unknown_1 = binary.LittleEndian.Uint32(buf[4:8])
+	tag.unknown_2 = binary.LittleEndian.Uint32(buf[8:12])
+
+	for i := 0; i < 30; i++ {
+		u := binary.LittleEndian.Uint16(buf[12+i*2 : 12+(i+1)*2])
+		if u != 0 {
+			tag.mid += string(u)
+		}
+	}
+	for i := 0; i < 50; i++ {
+		u := binary.LittleEndian.Uint16(buf[72+i*2 : 72+(i+1)*2])
+		if u != 0 {
+			tag.mediafile += string(u)
+		}
+	}
+
+	tag.unknown_3 = binary.LittleEndian.Uint32(buf[173:177])
+	tag.sizeof_struct = binary.LittleEndian.Uint32(buf[177:181])
+	tag.version = binary.LittleEndian.Uint32(buf[181:185])
+	tag.tag_magic = buf[185:193]
+
+	return audioLen, nil
+}