init: dec-music 项目初始化

decrypt/qmc/qmc_footer_musicex.go

@@ -0,0 +1,90 @@
+package qmc
+
+import (
+	bytes "bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+)
+
+type musicExTagV1 struct {
+	songID        uint32
+	unknown1      uint32
+	unknown2      uint32
+	mediaID       string
+	mediaFileName string
+	unknown3      uint32
+	tagSize       uint32
+	tagVersion    uint32
+	tagMagic      []byte
+}
+
+func newMusicExTag(f io.ReadSeeker) (*musicExTagV1, error) {
+	_, err := f.Seek(-16, io.SeekEnd)
+	if err != nil {
+		return nil, fmt.Errorf("musicex seek error: %w", err)
+	}
+
+	buffer := make([]byte, 16)
+	bytesRead, err := f.Read(buffer)
+	if err != nil {
+		return nil, fmt.Errorf("get musicex error: %w", err)
+	}
+	if bytesRead != 16 {
+		return nil, fmt.Errorf("MusicExV1: read %d bytes (expected %d)", bytesRead, 16)
+	}
+
+	tag := &musicExTagV1{
+		tagSize:    binary.LittleEndian.Uint32(buffer[0x00:0x04]),
+		tagVersion: binary.LittleEndian.Uint32(buffer[0x04:0x08]),
+		tagMagic:   buffer[0x08:0x10],
+	}
+
+	if !bytes.Equal(tag.tagMagic, []byte("musicex\x00")) {
+		return nil, errors.New("MusicEx magic mismatch")
+	}
+	if tag.tagVersion != 1 {
+		return nil, fmt.Errorf("unsupported musicex tag version: %d", tag.tagVersion)
+	}
+
+	if tag.tagSize < 0xC0 {
+		return nil, fmt.Errorf("unsupported musicex tag size: 0x%x", tag.tagSize)
+	}
+
+	buffer = make([]byte, tag.tagSize)
+	bytesRead, err = f.Read(buffer)
+	if err != nil {
+		return nil, err
+	}
+	if uint32(bytesRead) != tag.tagSize {
+		return nil, fmt.Errorf("MusicExV1: read %d bytes (expected %d)", bytesRead, tag.tagSize)
+	}
+
+	tag.songID = binary.LittleEndian.Uint32(buffer[0x00:0x04])
+	tag.unknown1 = binary.LittleEndian.Uint32(buffer[0x04:0x08])
+	tag.unknown2 = binary.LittleEndian.Uint32(buffer[0x08:0x0C])
+	tag.mediaID = readUnicodeTagName(buffer[0x0C:], 30*2)
+	tag.mediaFileName = readUnicodeTagName(buffer[0x48:], 50*2)
+	tag.unknown3 = binary.LittleEndian.Uint32(buffer[0xAC:0xB0])
+	return tag, nil
+}
+
+// readUnicodeTagName reads a buffer to maxLen.
+// reconstruct text by skipping alternate char (ascii chars encoded in UTF-16-LE),
+// until finding a zero or reaching maxLen.
+func readUnicodeTagName(buffer []byte, maxLen int) string {
+	builder := strings.Builder{}
+
+	for i := 0; i < maxLen; i += 2 {
+		chr := buffer[i]
+		if chr != 0 {
+			builder.WriteByte(chr)
+		} else {
+			break
+		}
+	}
+
+	return builder.String()
+}