⬥ ID3 encoding/decoding library in Go ⬥
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package v1
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"os"
"github.com/Unbewohnte/id3ed/util"
)
// Writes given ID3v1.0 or ID3v1.1 tag to given io.WriteSeeker.
// NOTE: will not remove already existing ID3v1 tag if it`s present,
// use ⁕WriteToFile⁕ method if you`re working with REAL mp3 files !!!
func (tag *ID3v1Tag) write(dst io.WriteSeeker) error {
_, err := dst.Seek(0, io.SeekEnd)
if err != nil {
return fmt.Errorf("could not seek: %s", err)
}
// ID
_, err = dst.Write([]byte(ID3v1IDENTIFIER))
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// Song name
err = util.WriteToExtent(dst, []byte(tag.SongName), 30)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// Artist
err = util.WriteToExtent(dst, []byte(tag.Artist), 30)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// Album
err = util.WriteToExtent(dst, []byte(tag.Album), 30)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// Year
err = util.WriteToExtent(dst, []byte(fmt.Sprint(tag.Year)), 4)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// Comment and Track
// check for track number, if specified and valid - comment must be shrinked to 28 bytes and 29th
// byte must be 0 byte (use ID3v1.1 instead of v1.0)
if tag.Track == 0 {
// write only 30 bytes long comment without track
err = util.WriteToExtent(dst, []byte(tag.Comment), 30)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
} else {
// write 28 bytes long shrinked comment
err = util.WriteToExtent(dst, []byte(tag.Comment), 28)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// write 0 byte as padding
_, err = dst.Write([]byte{0})
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// write track byte
_, err = dst.Write([]byte{byte(tag.Track)})
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
}
// Genre
genreCode := util.GetKey(id3v1genres, tag.Genre)
if genreCode == -1 {
// if no genre found - encode genre code as 255
genreCode = ID3v1INVALIDGENRE
}
genrebyte := make([]byte, 1)
binary.PutVarint(genrebyte, int64(genreCode))
_, err = dst.Write(genrebyte)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
return nil
}
// Checks for existing ID3v1 or ID3v1.1 tag in file, if present - removes it and replaces with provided tag
func (tag *ID3v1Tag) WriteToFile(f *os.File) error {
defer f.Close()
// check for existing ID3v1 tag
f.Seek(-int64(ID3v1SIZE), io.SeekEnd)
identifier, err := util.Read(f, 3)
if err != nil {
return err
}
if !bytes.Equal(identifier, []byte(ID3v1IDENTIFIER)) {
// no existing identifier, just write given tag
err = tag.write(f)
if err != nil {
return err
}
return nil
}
// does contain ID3v1 tag. Removing it
fStats, err := f.Stat()
if err != nil {
return fmt.Errorf("cannot get file stats: %s", err)
}
err = f.Truncate(fStats.Size() - int64(ID3v1SIZE))
if err != nil {
return fmt.Errorf("could not truncate file %s", err)
}
// writing a new tag
err = tag.write(f)
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
return nil
}