nb int64     // Number of remaining bytes to read
}

func (fr *regFileReader) Read(b []byte) (n int, err error) {
	if int64(len(b)) > fr.nb {
		b = b[:fr.nb]
	}
	if len(b) > 0 {
		n, err = fr.r.Read(b)
		fr.nb -= int64(n)
	}
	switch {
	case err == io.EOF && fr.nb > 0:
		return n, io.ErrUnexpectedEOF
	case err == nil && fr.nb == 0:
		return n, io.EOF
	default:
		return n, err
	}
}