code: func LogOf(req *http.Request, w http.ResponseWriter) logger {
  	if rl, ok := w.(*respLogger); ok {
  		return rl
  	}
  
  	return &passthroughLogger{}
  }
docs: // LogOf returns the logger hiding in w. If there is not an existing logger
  // then a passthroughLogger will be created which will log to stdout immediately
  // when Addf is called.