code: public function getResponse(Request $request) {
          $cacheFilename = $this->calculateRequestFilename($request);
  
          return $this->getCachedResponse($cacheFilename);
      }
docs: Returns an array caching HTTP headers that should be set for this request e.g.
  ['If-None-Match' => $matchValue, 'If-Modified-Since' => $modifiedValue]
  @param Request $request
  @return \Amp\Artax\Response