php 获取顶级域名

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/**      * 获取顶级域名      * @param $url      * @return string      */     public static function getDoMain($url){         if(empty($url)){             return '';         }         if(strpos($url,'http://') !== false){             $url = str_replace('http://','',$url);         }         if(strpos($url,'https://') !== false){             $url = str_replace('https://','',$url);         }         $n = 0;         for($i = 1;$i <= 3;$i++) {             $n = strpos($url, '/', $n);             $i != 3 && $n++;         }           $nn = strpos($url, '?');         $mix_num =  min($n,$nn);         if($mix_num > 0 || !empty($mix_num)){             //防止链接带有点 （.） 导致出错             $url = mb_substr($url,0,$mix_num);         }         $data = explode('.', $url);           $co_ta = count($data);         //判断是否是双后缀         $no_tow = true;         $host_cn = 'com.cn,net.cn,org.cn,gov.cn';         $host_cn = explode(',', $host_cn);         foreach($host_cn as $val){             if(strpos($url,$val)){                 $no_tow = false;             }         }         //截取域名后的目录         $del = strpos($data[$co_ta-1], '/');         if($del > 0 || !empty($del)){             $data[$co_ta-1] = mb_substr($data[$co_ta-1],0,$del);         }         //如果是返回FALSE ，如果不是返回true         if($no_tow == true){             $host = $data[$co_ta-2].'.'.$data[$co_ta-1];         }else{             $host = $data[$co_ta-3].'.'.$data[$co_ta-2].'.'.$data[$co_ta-1];         }           return $host;     }