func (b *Writer) ReadFrom(r io.Reader) (n int64, err error) {
	if b.err != nil {
		return 0, b.err
	}
	readerFrom, readerFromOK := b.wr.(io.ReaderFrom)
	var m int
	for {
		if b.Available() == 0 {
			if err1 := b.Flush(); err1 != nil {
				return n, err1
			}
		}
		if readerFromOK && b.Buffered() == 0 {
			nn, err := readerFrom.ReadFrom(r)
			b.err = err
			n += nn
			return n, err
		}
		nr := 0