public function getResponseHeaders()
    {
        if (!is_array($this->responseHeaders)) {
            $this->responseHeaders = array();
            foreach (explode("\n", $this->responseHeader) as $line) {
                $line = explode(':', $line, 2);
                $name = strtoupper($line[0]);
                $value = isset($line[1]) ? trim($line[1]) : null;
                $this->responseHeaders[$name][] = $value;
            }
        }
        return $this->responseHeaders;
    }