VBulletin. Last-modified и If-modified-since. : Вопросы сервера

if (!$vbulletin->userinfo['userid']){ 
if((THIS_SCRIPT == 'showthread' AND !empty($threadinfo)) OR (THIS_SCRIPT == 'forumdisplay' AND !empty($foruminfo))) 
{ 
      if(THIS_SCRIPT == 'showthread' AND !empty($threadinfo)) 
      {  
            if($threadinfo['lastpost']) 
            {  
                  $LastModified_unix = $threadinfo['lastpost']; 
                  $LastModified = gmdate("D, d M Y H:i:s \G\M\T", $LastModified_unix); 
                  $IfModifiedSince = false; 
                  if(isset($_ENV['HTTP_IF_MODIFIED_SINCE'])) 
                  { 
                        $IfModifiedSince = strtotime(substr($_ENV['HTTP_IF_MODIFIED_SINCE'], 5)); 
                  } 
                  if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) 
                  { 
                        $IfModifiedSince = strtotime(substr($_SERVER['HTTP_IF_MODIFIED_SINCE'], 5)); 
                  } 
                  if($IfModifiedSince AND $IfModifiedSince >= $LastModified_unix) 
                  { 
                        @header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified'); 
                        exit; 
                  } 
                  @header('Last-Modified: '. $LastModified); 
            } 
      } 
      else if(THIS_SCRIPT == 'forumdisplay' AND !empty($foruminfo)) 
      { $lastposta=$vbulletin->db->query_first("select lastpost from vbforum where forumid=".$foruminfo['forumid']); 
                  $LastModified_unix = $lastposta['lastpost']; 
                  $LastModified = gmdate("D, d M Y H:i:s \G\M\T", $LastModified_unix); 
                  $IfModifiedSince = false; 
                  if(isset($_ENV['HTTP_IF_MODIFIED_SINCE'])) 
                  { 
                        $IfModifiedSince = strtotime(substr($_ENV['HTTP_IF_MODIFIED_SINCE'], 5)); 
                  } 
                  if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) 
                  { 
                        $IfModifiedSince = strtotime(substr($_SERVER['HTTP_IF_MODIFIED_SINCE'], 5)); 
                  } 
                  if($IfModifiedSince AND $IfModifiedSince >= $LastModified_unix) 
                  { 
                        @header($_SERVER['SERVER_PROTOCOL'] . ' 304 Not Modified'); 
                        exit; 
                  } 
                  @header('Last-Modified: '. $LastModified); 
      } 
} 
}