Cake\Network\Response::cache PHP Method

    public function cache($since, $time = '+1 day')
    {
        if (!is_int($time)) {
            $time = strtotime($time);
        }
        $this->header(['Date' => gmdate("D, j M Y G:i:s ", time()) . 'GMT']);
        $this->modified($since);
        $this->expires($time);
        $this->sharable(true);
        $this->maxAge($time - time());
    }

 /**
  * Sends an asset file to the client
  *
  * @param \Cake\Network\Request $request The request object to use.
  * @param \Cake\Network\Response $response The response object to use.
  * @param string $assetFile Path to the asset file in the file system
  * @param string $ext The extension of the file to determine its mime type
  * @return void
  */
 protected function _deliverAsset(Request $request, Response $response, $assetFile, $ext)
 {
     $compressionEnabled = $response->compress();
     if ($response->type($ext) === $ext) {
         $contentType = 'application/octet-stream';
         $agent = $request->env('HTTP_USER_AGENT');
         if (preg_match('%Opera(/| )([0-9].[0-9]{1,2})%', $agent) || preg_match('/MSIE ([0-9].[0-9]{1,2})/', $agent)) {
             $contentType = 'application/octetstream';
         }
         $response->type($contentType);
     }
     if (!$compressionEnabled) {
         $response->header('Content-Length', filesize($assetFile));
     }
     $response->cache(filemtime($assetFile), $this->_cacheTime);
     $response->sendHeaders();
     readfile($assetFile);
     if ($compressionEnabled) {
         ob_end_flush();
     }
 }