internal/bufio/bufio.go
func (w *Writer) Flush() error {
	if w.err != nil {
		return w.err
	}
	return w.wr.Flush()
}
func (w *Writer) Flush() error {
	if w.err != nil {
		return w.err
	}
	return w.wr.Flush()
}
// Flush writes any buffered data to the underlying io.Writer.