code: func CachableResponse(req *http.Request,
  	resp *http.Response,
  	opts Options) ([]cacheobject.Reason, time.Time, error) {
  	return cacheobject.UsingRequestResponse(req, resp.StatusCode, resp.Header, opts.PrivateCache)
  }
docs: // Given an HTTP Request and Response, determine the possible reasons a response SHOULD NOT
  // be cached.