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 }