func LimitWriter(w io.Writer, limit int64, err error) io.Writer {
	return &limitedWriter{w, limit, err}
}

type limitedWriter struct {
	w io.Writer
	n int64
	e error
}

func (lw *limitedWriter) Write(p []byte) (int, error) {
	if lw.n < 1 {
		return 0, lw.e
	}
	if lw.n < int64(len(p)) {
		p = p[:lw.n]
	}
	n, err := lw.w.Write(p)
	lw.n -= int64(n)
	return n, err
}