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

		if err != nil {
			return nil, err
		}

		// Pick output column names
		if expr.As != "" {
			output, err = output.Set(expr.As, v)
		} else if comp, ok := getLastKeypathComponent(expr.Expression); ok {
			output, err = output.Set(comp, v)
		} else {
			output, err = output.Set(fmt.Sprintf("_%d", i+1), v)
		}
		if err != nil {
			return nil, err
		}
	}

	// Update count of records output.