Sulu\Bundle\MediaBundle\Media\FormatManager\FormatManager::getResponseHeaders PHP Method

    protected function getResponseHeaders($mimeType = '', $setExpireHeaders = false)
    {
        $headers = [];
        if (!empty($mimeType)) {
            $headers['Content-Type'] = $mimeType;
        }
        if (empty($this->responseHeaders)) {
            return $headers;
        }
        $headers = array_merge($headers, $this->responseHeaders);
        if (isset($this->responseHeaders['Expires']) && $setExpireHeaders) {
            $date = new \DateTime();
            $date->modify($this->responseHeaders['Expires']);
            $headers['Expires'] = $date->format('D, d M Y H:i:s \\G\\M\\T');
        } else {
            // will remove exist set expire header
            $headers['Expires'] = null;
            $headers['Cache-Control'] = 'no-cache';
            $headers['Pragma'] = null;
        }
        return $headers;
    }