⬥ ID3 encoding/decoding library in Go ⬥
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package v1
import (
"bytes"
"fmt"
"io"
"strconv"
"github.com/Unbewohnte/id3ed/util"
)
// Retrieves ID3v1 field values of provided io.ReadSeeker (usually a file)
func Readv1Tag(rs io.ReadSeeker) (*ID3v1Tag, error) {
var tag ID3v1Tag
// set reader to the last 128 bytes
_, err := rs.Seek(-int64(ID3v1SIZE), io.SeekEnd)
if err != nil {
return nil, fmt.Errorf("could not seek: %s", err)
}
// ID
identifier, err := util.Read(rs, 3)
if err != nil {
return nil, err
}
if !bytes.Equal(identifier, []byte(ID3v1IDENTIFIER)) {
// no identifier, given file does not use ID3v1
return nil, fmt.Errorf("does not use ID3v1: expected %s; got %s", ID3v1IDENTIFIER, identifier)
}
// Songname
songname, err := util.ReadToString(rs, 30)
if err != nil {
return nil, err
}
tag.SongName = songname
// Artist
artist, err := util.ReadToString(rs, 30)
if err != nil {
return nil, err
}
tag.Artist = artist
// Album name
album, err := util.ReadToString(rs, 30)
if err != nil {
return nil, err
}
tag.Album = album
// Year
yearStr, err := util.ReadToString(rs, 4)
if err != nil {
return nil, err
}
year, err := strconv.Atoi(yearStr)
if err != nil {
return nil, fmt.Errorf("could not convert yearbytes into int: %s", err)
}
tag.Year = year
// Comment and Track
comment, err := util.Read(rs, 30)
if err != nil {
return nil, err
}
tag.Comment = util.ToStringLossy(comment)
tag.Track = 0
var track int = 0
// check if 29th byte is null byte (v1.0 or v1.1)
if comment[28] == 0 {
// it is v1.1, track number exists
track, err = util.ByteToInt(comment[29])
if err != nil {
return nil, fmt.Errorf("could not get int from byte: %s", err)
}
tag.Track = uint8(track)
comment = comment[0:28]
tag.Comment = util.ToStringLossy(comment)
}
// Genre
genreByte, err := util.Read(rs, 1)
if err != nil {
return nil, err
}
genreInt, err := util.ByteToInt(genreByte[0])
if err != nil {
return nil, fmt.Errorf("cannot convert bytes to int: %s", err)
}
genre, exists := id3v1genres[int(genreInt)]
if !exists {
genre = ""
}
tag.Genre = genre
if track == 0 {
tag.Version = V1_0
} else {
tag.Version = V1_1
}
return &tag, nil
}