⬥ ID3 encoding/decoding library in Go ⬥
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package id3ed
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"strconv"
)
// https://id3.org/ID3v1 - documentation
const ID3V1SIZE int = 128
type ID3v1Tags struct {
SongName string
Artist string
Album string
Year int
Comment string
Genre string
}
// Retrieves ID3v1 field values of provided io.ReadSeeker (usually a file)
func GetID3v1Tags(rs io.ReadSeeker) (*ID3v1Tags, error) {
// 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)
}
tag, err := read(rs, 3)
if err != nil {
return nil, err
}
if !bytes.Equal(tag, []byte("TAG")) {
// no TAG, given file does not use ID3v1
return nil, fmt.Errorf("does not use ID3v1: expected %s; got %s", "TAG", tag)
}
songname, err := readToString(rs, 30)
if err != nil {
return nil, err
}
artist, err := readToString(rs, 30)
if err != nil {
return nil, err
}
album, err := readToString(rs, 30)
if err != nil {
return nil, err
}
yearStr, err := 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)
}
comment, err := readToString(rs, 30)
if err != nil {
return nil, err
}
genreByte, err := read(rs, 1)
if err != nil {
return nil, err
}
genreInt, err := binary.ReadVarint(bytes.NewBuffer(genreByte))
if err != nil {
return nil, err
}
genre, exists := id3v1genres[int(genreInt)]
if !exists {
genre = ""
}
return &ID3v1Tags{
SongName: songname,
Artist: artist,
Album: album,
Year: year,
Comment: comment,
Genre: genre,
}, nil
}
// Writes given ID3v1.0 tags to dst
func WriteID3v1Tags(dst io.WriteSeeker, tags ID3v1Tags) error {
dst.Seek(0, io.SeekEnd)
// TAG
_, err := dst.Write([]byte("TAG"))
if err != nil {
return err
}
// Song name
err = writeToExtent(dst, []byte(tags.SongName), 30)
if err != nil {
return err
}
// Artist
err = writeToExtent(dst, []byte(tags.Artist), 30)
if err != nil {
return err
}
// Album
err = writeToExtent(dst, []byte(tags.Album), 30)
if err != nil {
return err
}
// Year
err = writeToExtent(dst, []byte(fmt.Sprint(tags.Year)), 4)
if err != nil {
return err
}
// Comment
err = writeToExtent(dst, []byte(tags.Comment), 30)
if err != nil {
return err
}
// Genre
genreCode := getKey(id3v1genres, tags.Genre)
if genreCode == -1 {
// if no genre found - encode genre code as 255
genreCode = 255
}
genrebyte := make([]byte, 1)
binary.PutVarint(genrebyte, int64(genreCode))
_, err = dst.Write(genrebyte)
if err != nil {
return err
}
return nil
}