public function getResponseHeaders($headerKey = null)
    {
        $headers = array();
        $headerKey = strtolower($headerKey);
        
        foreach ($this->response_headers as $header) {
            $parts = explode(":", $header, 2);
            
            $key = isset($parts[0]) ? $parts[0] : null;
            $value = isset($parts[1]) ? $parts[1] : null;
            
            $headers[trim(strtolower($key))] = trim($value);
        }
        
        if ($headerKey) {
            return isset($headers[$headerKey]) ? $headers[$headerKey] : false;
        }
        
        return $headers;
    }