func (w *Writer) Copy(r *Reader) error {
	for {
		n, err := r.Read()
		if err != nil {
			if err == io.EOF {
				return nil
			}
			return err
		}
		if err := w.Write(n); err != nil {
			return err
		}
	}
}
func (w *Writer) Copy(r *Reader) error {
	for {
		n, err := r.Read()
		if err != nil {
			if err == io.EOF {
				return nil
			}
			return err
		}
		if err := w.Write(n); err != nil {
			return err
		}
	}
}
// Copy copies a hashtree reader in a writer.