}

func (fw *regFileWriter) Write(b []byte) (n int, err error) {
	overwrite := int64(len(b)) > fw.nb
	if overwrite {
		b = b[:fw.nb]
	}
	if len(b) > 0 {
		n, err = fw.w.Write(b)
		fw.nb -= int64(n)
	}
	switch {
	case err != nil:
		return n, err
	case overwrite:
		return n, ErrWriteTooLong
	default:
		return n, nil
	}
}