code: func (l *Handler) Upload(ctx context.Context, sessionID session.ID, reader io.Reader) (string, error) {
  	path := l.path(sessionID)
  	f, err := os.Create(path)
  	if err != nil {
  		return "", trace.ConvertSystemError(err)
  	}
  	defer f.Close()
  	_, err = io.Copy(f, reader)
  	if err != nil {
  		return "", trace.Wrap(err)
  	}
  	return fmt.Sprintf("%v://%v", teleport.SchemeFile, path), nil
  }
docs: // Upload uploads session recording to file storage, in case of file handler,
  // writes the file to local directory