func (w *metacacheBlockWriter) Close() error {
	w.wg.Wait()
	return w.streamErr
}

type metacacheBlock struct {
	data  []byte
	n     int
	First string `json:"f"`
	Last  string `json:"l"`
	EOS   bool   `json:"eos,omitempty"`
}

func (b metacacheBlock) headerKV() map[string]string {
	json := jsoniter.ConfigCompatibleWithStandardLibrary
	v, err := json.Marshal(b)
	if err != nil {

			return -1, err
		}
		if tmp.First == "" && tmp.Last == "" && tmp.EOS {
			return 0, errFileNotFound
		}
		if tmp.First >= search {
			o.debugln("First >= search", v)
			return i, nil
		}
		if tmp.Last >= search {
			o.debugln("Last >= search", v)
			return i, nil
		}
		if tmp.EOS {
			o.debugln("no match, at EOS", v)
			return -3, io.EOF
		}