code: func (s *StreamArchive) StreamReader(relPath string, fi os.FileInfo, r io.Reader) (err error) {
  	fh, err := tar.FileInfoHeader(fi, "")
  	if err != nil {
  		return err
  	}
  	fh.Name = filepath.Join(relPath, fi.Name())
  	if err = s.Writer.WriteHeader(fh); err != nil {
  		return err
  	}
  	_, err = io.Copy(s.Writer, r)
  	return err
  }
docs: // StreamReader streams data from io.Reader to StreamArchive.