/** * Return a sorted list of Vary headers. * * While headers are case-insensitive, header values are not. We can only * normalize the order of headers to combine cache entries. * * @param ResponseInterface $response The Response with Vary headers. * * @return array An array of sorted headers. */ private function normalizeVary(ResponseInterface $response) { $parts = AbstractMessage::normalizeHeader($response, 'vary'); sort($parts); return $parts; }