php下获取客户端IP

/**
	 * 获取客户端IP, 可能被伪造
	 * @return string
	 */
	public function ip(){
		
		if(getenv('HTTP_CLIENT_IP') && strcasecmp(getenv('HTTP_CLIENT_IP'), 'unknown')){
			$ip = getenv('HTTP_CLIENT_IP');
		}elseif(getenv('HTTP_X_FORWARDED_FOR') && strcasecmp(getenv('HTTP_X_FORWARDED_FOR'), 'unknown')){
			$ip = getenv('HTTP_X_FORWARDED_FOR');
		}elseif(getenv('REMOTE_ADDR') && strcasecmp(getenv('REMOTE_ADDR'), 'unknown')){
			$ip = getenv('REMOTE_ADDR');
		}elseif(isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], 'unknown')){
			$ip = $_SERVER['REMOTE_ADDR'];
		}
		return preg_match("/[\d\.]{7,15}/", $ip, $matches) ? $matches[0] : 'unknown';
	}