code: func (w *Writer) WriteThrough(p []byte) (n int, err error) {
  	if w.err != nil {
  		return 0, w.err
  	}
  	if w.Buffered() != 0 {
  		return 0, ErrNotEmpty
  	}
  
  	w.err = writeFrame(w.dest, w.state, w.opCode(), false, p)
  	if w.err == nil {
  		n = len(p)
  	}
  
  	w.dirty = true
  	w.fragmented = true
  
  	return n, w.err
  }
docs: // WriteThrough writes data bypassing the buffer.
  // Note that Writer's buffer must be empty before calling WriteThrough().