code: func (w *bufferedWriter) checkShrinkRequest() {
  	percentFilled := w.buf.Buffered() * 100 / w.bufSize
  	// If above the threshold, cancel the request.
  	if percentFilled > bufShrinkThreshold {
  		w.shrinkReq = false
  	}
  }
docs: // checkShrinkRequest checks how full the buffer is, and if is above a certain
  // threshold, cancels the shrink request