解析php 版获取重定向后的地址(代码)

//取重定向的地址 
 class RedirectUrl{ 
     //地址 
     var $url; 
     //初始化地址 
     function RedirectUrl($url){ 
         $this->url = $url; 
     } 
     /** 
      * get_redirect_url() 
      * 取重定向的地址 
      * 
      * @param string $url 
      * @return string 
      */ 
     private function get_redirect_url($url){ 
         $redirect_url = null; 

         $url_parts = @parse_url($url); 
         if (!$url_parts) return false; 
         if (!isset($url_parts['host'])) return false; //can't process relative URLs 
         if (!isset($url_parts['path'])) $url_parts['path'] = '/'; 

         $sock = fsockopen($url_parts['host'], (isset($url_parts['port']) ? (int)$url_parts['port'] : 80), $errno, $errstr, 30); 
         if (!$sock) return false; 

         $request = "HEAD " . $url_parts['path'] . (isset($url_parts['query']) ?'?'.$url_parts['query'] : '') . " HTTP/1.1\r\n"; 
         $request .= 'Host: ' . $url_parts['host'] . "\r\n"; 
         $request .= "Connection: Close\r\n\r\n"; 
         fwrite($sock, $request); 
         $response = ''; 
         while(!feof($sock)) $response .= fread($sock, 8192); 
         fclose($sock); 

         if (preg_match('/^Location: (.+?)$/m', $response, $matches)){ 
             return trim($matches[1]); 
         } else { 
             return false; 
         } 
     } 

     /** 
      * get_all_redirects() 
      * 取所有重定向地址 
      * 
      * @param string $url 
      * @return array 
      */ 
     private function get_all_redirects($url){ 
         $redirects = array(); 
         while ($newurl = $this->get_redirect_url($url)){ 
             if (in_array($newurl, $redirects)){ 
                 break; 
             } 
             $redirects[] = $newurl; 
             $url = $newurl; 
         } 
         return $redirects; 
     } 

     /** 
      * get_final_url() 
      * 取实际地址 
      * 
      * @param string $url 
      * @return string 
      */ 
     function get_final_url(){ 
         $redirects = $this->get_all_redirects($this->url); 

         if (count($redirects)>0){ 
             return array_pop($redirects); 
         } else { 
             return $this->url; 
         } 
     } 
 } 

 /** 
  * get_show_pic 
  * 取最终要显示的图片地址 
  * 
  * @param string $url 
  * @return  string 
  */ 
 function get_show_pic($url,$noimg ='noimg.gif',$newimg="http://special.ku6img.com/projects/2010/d-color/images/slt-1.jpg"){ 
     $obj = new RedirectUrl($url); 

     $realurl = $obj->get_final_url(); 

     if(strpos($realurl,$noimg)>0){ 
         return $newimg; 
     } 
     return $url; 
 } 
 //参考 
 echo "<img src='".get_show_pic("http://i2.ku6img.com/encode/picpath/2010/12/9/14/1294948410019/5.jpg")."'/>"; 
 ?>