⬥ ID3 encoding/decoding library in Go ⬥
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package v2
import (
"fmt"
"io"
"os"
"path/filepath"
"github.com/Unbewohnte/id3ed/util"
)
// Writes ID3v2Tag to ws
func (tag *ID3v2Tag) write(ws io.WriteSeeker) error {
_, err := ws.Seek(0, io.SeekStart)
if err != nil {
return fmt.Errorf("could not seek: %s", err)
}
// write header
_, err = ws.Write(tag.Header.toBytes())
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
// write frames
for _, frame := range tag.Frames {
_, err = ws.Write(frame.toBytes())
if err != nil {
return fmt.Errorf("could not write to writer: %s", err)
}
}
// write padding if has any
if tag.Padding != 0 {
util.WriteToExtent(ws, []byte{0}, int(tag.Padding))
}
return nil
}
// Writes ID3v2Tag to file, removing already existing tag if found
func (tag *ID3v2Tag) WriteToFile(f *os.File) error {
defer f.Close()
_, err := f.Seek(0, io.SeekStart)
if err != nil {
return fmt.Errorf("could not seek: %s", err)
}
// check if there`s content at all
fStats, err := f.Stat()
if err != nil {
return err
}
if fStats.Size() < 3 {
// there`s no way that the file can contain TAG,
// just write and exit
// `write` for some reason removes all contents if there`s no tag, so
// we need forcefully store already existing data and
// write it again afterwards
_, err := f.Seek(0, io.SeekStart)
if err != nil {
return fmt.Errorf("could not seek: %s", err)
}
contents, err := util.Read(f, uint64(fStats.Size()))
if err != nil {
return err
}
err = tag.write(f)
if err != nil {
return err
}
_, err = f.Write(contents)
if err != nil {
return err
}
// apparently, there are 3 zerobytes
// that appear after writing the contents for some
// alien-like reason so we need to remove them.
fStats, err = f.Stat()
if err != nil {
return err
}
err = f.Truncate(fStats.Size() - 3)
if err != nil {
return err
}
return nil
}
// check for an existing tag
possibleHeaderID, err := util.ReadToString(f, 3)
if err != nil {
return err
}
if possibleHeaderID != HEADERIDENTIFIER {
// No existing tag, just write what we have
// and exit
// `write` for some reason removes all contents if there`s no tag, so
// we need forcefully store already existing data and
// write it again afterwards
_, err := f.Seek(0, io.SeekStart)
if err != nil {
return fmt.Errorf("could not seek: %s", err)
}
contents, err := util.Read(f, uint64(fStats.Size()))
if err != nil {
return err
}
err = tag.write(f)
if err != nil {
return err
}
_, err = f.Write(contents)
if err != nil {
return err
}
// apparently, there are 3 zerobytes
// that appear after writing the contents for some
// alien-like reason so we need to remove them.
fStats, err = f.Stat()
if err != nil {
return err
}
err = f.Truncate(fStats.Size() - 3)
if err != nil {
return err
}
return nil
}
// there is an existing tag, remove it
// and write a new one
// get size of the existing tag
existingHeader, err := readHeader(f)
if err != nil {
return err
}
existingHeaderSize := existingHeader.Size()
// cannot truncate just the existing tag with f.Truncate(),
// so we need to improvise and have a temporary copy of the mp3,
// wipe the original file, write our tag and place the actual
// music without the old tag from the temporary copy.
// create a temporary file
temporaryDir := os.TempDir()
tmpF, err := os.CreateTemp(temporaryDir, fmt.Sprintf("%s_TEMP", filepath.Base(f.Name())))
if err != nil {
return err
}
defer tmpF.Close()
// remove it afterwards
defer os.Remove(filepath.Join(temporaryDir, tmpF.Name()))
// copy contents of the original mp3 to a temporary one
_, err = io.Copy(tmpF, f)
if err != nil {
return err
}
// fully remove contents of the original file
err = f.Truncate(0)
if err != nil {
return err
}
// write our tag to the original file, which is at that moment is
// empty
err = tag.write(f)
if err != nil {
return err
}
tmpFStats, err := tmpF.Stat()
if err != nil {
return err
}
// read all contents of the temporary file, except the existing tag
musicDataSize := int64(tmpFStats.Size() - int64(existingHeaderSize))
_, err = tmpF.Seek(int64(existingHeaderSize), io.SeekStart)
if err != nil {
return fmt.Errorf("could not seek: %s", err)
}
musicData, err := util.Read(tmpF, uint64(musicDataSize))
if err != nil {
return err
}
// and write them into the original file, which
// contains only the new tag
_, err = f.Write(musicData)
if err != nil {
return err
}
return nil
}