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unlock-music-cli/algo/qmc/qmc_footer_musicex.go

94 lines
2.6 KiB
Go

package qmc
import (
bytes "bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"strings"
)
type MusicExTagV1 struct {
SongID uint32 // Song ID
Unknown1 uint32 // unused & unknown
Unknown2 uint32 // unused & unknown
MediaID string // Media ID
MediaFileName string // real file name
Unknown3 uint32 // unused; uninitialized memory?
// 16 byte at the end of tag.
// TagSize should be respected when parsing.
TagSize uint32 // 19.57: fixed value: 0xC0
TagVersion uint32 // 19.57: fixed value: 0x01
TagMagic []byte // fixed value "musicex\0" (8 bytes)
}
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[0x04:0x0C],
}
if !bytes.Equal(tag.TagMagic, []byte("musicex\x00")) {
return nil, errors.New("MusicEx magic mismatch")
}
if tag.TagVersion != 1 {
return nil, errors.New(fmt.Sprintf("unsupported musicex tag version. expecting 1, got %d", tag.TagVersion))
}
if tag.TagSize < 0xC0 {
return nil, errors.New(fmt.Sprintf("unsupported musicex tag size. expecting at least 0xC0, got 0x%02x", 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()
}