protected function formatter(ServerRequestInterface $request) { $accept = $request->getHeaderLine('Accept'); $priorities = $this->priorities(); if (!empty($accept)) { $preferred = $this->negotiator->getBest($accept, array_keys($priorities)); } if (!empty($preferred)) { $formatter = $priorities[$preferred->getValue()]; } else { $formatter = array_shift($priorities); } return $this->resolve($formatter); }