refactor: improve mmkv logic

algo/qmc/qmc.go

@@ -6,7 +6,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"runtime"
 	"strconv"
 	"strings"
 
@@ -133,14 +132,15 @@ func (d *Decoder) searchKey() (err error) {
 	}
 	fileSize := int(fileSizeM4) + 4
 
-	//goland:noinspection GoBoolExpressions
-	if runtime.GOOS == "darwin" && !strings.HasPrefix(d.params.Extension, ".qmc") {
-		d.decodedKey, err = readKeyFromMMKV(d.params.FilePath, d.logger)
+	if key, ok := d.params.CryptoParams.QmcKeys.Get(d.params.FilePath); ok {
+		d.logger.Debug("QQMusic Mac Legacy file", zap.String("file", d.params.FilePath), zap.String("key", key))
+		d.decodedKey, err = deriveKey([]byte(key))
 		if err == nil {
 			d.audioLen = fileSize
-			return
+			return nil
 		}
-		d.logger.Warn("read key from mmkv failed", zap.Error(err))
+		d.decodedKey = nil
+		d.logger.Warn("could not derive key, skip", zap.Error(err))
 	}
 
 	suffixBuf := make([]byte, 4)
@@ -153,17 +153,17 @@ func (d *Decoder) searchKey() (err error) {
 		return d.readRawMetaQTag()
 	case "STag":
 		return errors.New("qmc: file with 'STag' suffix doesn't contains media key")
+	// MusicEx\0
 	case "cex\x00":
 		footer, err := NewMusicExTag(d.raw)
 		if err != nil {
 			return err
 		}
 		d.audioLen = fileSize - int(footer.TagSize)
-		d.decodedKey, err = readKeyFromMMKVCustom(footer.MediaFileName)
-		if err != nil {
-			return err
+		if key, ok := d.params.CryptoParams.QmcKeys.Get(footer.MediaFileName); ok {
+			d.decodedKey, err = deriveKey([]byte(key))
 		}
-		return nil
+		return err
 	default:
 		size := binary.LittleEndian.Uint32(suffixBuf)