public function retrieveHeaders(): array
    {
        $this->setHeader('Connection', 'close');
        $this->setHeader('Accept', '');
        $this->setHeader('Accept-Language', '');
        $this->setHeader('User-Agent', '');
        
        $savedProto = $this->protocol;
        $this->protocol = 'HTTP/1.0';
        $this->request('HEAD');
        $this->protocol = $savedProto;
        
        return $this->getHeaders();
    }