code: func Wrap(w io.Writer) io.Writer {
  	fw := &flushWriter{
  		writer: w,
  	}
  	if flusher, ok := w.(http.Flusher); ok {
  		fw.flusher = flusher
  	}
  	return fw
  }
docs: // Wrap wraps an io.Writer into a writer that flushes after every write if
  // the writer implements the Flusher interface.