public function post($request)
	{
		if ($request instanceof Request) {
			$request = $request->xml();
		}

		$ch = curl_init();
		curl_setopt($ch, CURLOPT_URL, $this->url);
		if ($this->user_agent != null) {
			curl_setopt($ch, CURLOPT_USERAGENT, $this->user_agent);
		}
		curl_setopt($ch, CURLOPT_HEADER, 0); // no headers in the output
		curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); // return instead of output
		curl_setopt($ch, CURLOPT_POST, 1);
		curl_setopt($ch, CURLOPT_POSTFIELDS, $request);
		curl_setopt($ch, CURLOPT_HTTPHEADER, array(
			'Content-type: application/xml; charset=utf-8',
			));
		$response = curl_exec($ch);
		curl_close($ch);

		if (empty($response)) {
			return null;
		}

		return $response;
	}