opts = append([]s2.WriterOption{s2.WriterPadding(compPadEncrypted), s2.WriterPaddingSrc(rng)}, compressOpts...)
	}
	comp := s2.NewWriter(pw, opts...)
	indexCh := make(chan []byte, 1)
	go func() {
		defer xioutil.SafeClose(indexCh)
		cn, err := io.Copy(comp, r)
		if err != nil {
			comp.Close()
			pw.CloseWithError(err)
			return
		}
		if on > 0 && on != cn {
			// if client didn't sent all data