谁能说明一下discuzX2.5upload/index.php文件思路

<br>
<!--?php<br /-->
<br>
/**<br>
 *      [Discuz!] (C)2001-2099 Comsenz Inc.<br>
 *      This is NOT a freeware, use is subject to license terms<br>
 *<br>
 *      $Id: index.php 27617 2012-02-07 08:24:14Z monkey $<br>
 */<br>
<br>
if(!empty($_SERVER['QUERY_STRING']) && is_numeric($_SERVER['QUERY_STRING'])) {<br>
$_ENV['curapp'] = 'home';<br>
$_GET = array('mod'=>'space', 'uid'=>$_SERVER['QUERY_STRING']);<br>
} else {<br>
<br>
$url = '';<br>
$domain = $_ENV = array();<br>
$jump = false;<br>
@include_once './data/sysdata/cache_domain.php';<br>
$_ENV['domain'] = $domain;<br>
if(empty($_ENV['domain'])) {<br>
$_ENV['curapp'] = 'forum';<br>
} else {<br>
$_ENV['defaultapp'] = array('portal.php' => 'portal', 'forum.php' => 'forum', 'group.php' => 'group', 'home.php' => 'home');<br>
$_ENV['hostarr'] = explode('.', $_SERVER['HTTP_HOST']);<br>
$_ENV['domainroot'] = substr($_SERVER['HTTP_HOST'], strpos($_SERVER['HTTP_HOST'], '.')+1);<br>
if(!empty($_ENV['domain']['app']) && is_array($_ENV['domain']['app']) && in_array($_SERVER['HTTP_HOST'], $_ENV['domain']['app'])) {<br>
$_ENV['curapp'] = array_search($_SERVER['HTTP_HOST'], $_ENV['domain']['app']);<br>
if($_ENV['curapp'] == 'mobile') {<br>
$_ENV['curapp'] = 'forum';<br>
if(@$_GET['mobile'] != 'no') {<br>
@$_GET['mobile'] = 'yes';<br>
}<br>
}<br>
if($_ENV['curapp'] == 'default' || !isset($_ENV['defaultapp'][$_ENV['curapp'].'.php'])) {<br>
$_ENV['curapp'] = '';<br>
}<br>
} elseif(!empty($_ENV['domain']['root']) && is_array($_ENV['domain']['root']) && in_array($_ENV['domainroot'], $_ENV['domain']['root'])) {<br>
<br>
$_G['setting']['holddomain'] = $_ENV['domain']['holddomain'] ? $_ENV['domain']['holddomain'] : array('www');<br>
$list = $_ENV['domain']['list'];<br>
if(isset($list[$_SERVER['HTTP_HOST']])) {<br>
$domain = $list[$_SERVER['HTTP_HOST']];<br>
$id = intval($domain['id']);<br>
switch($domain['idtype']) {<br>
case 'subarea':<br>
$_ENV['curapp'] = 'forum';<br>
$_GET['gid'] = $id;<br>
break;<br>
case 'forum':<br>
$_ENV['curapp'] = 'forum';<br>
$_GET['mod'] = 'forumdisplay';<br>
$_GET['fid'] = $id;<br>
break;<br>
case 'topic':<br>
$_ENV['curapp'] = 'portal';<br>
$_GET['mod'] = 'topic';<br>
$_GET['topicid'] = $id;<br>
break;<br>
case 'channel':<br>
$_ENV['curapp'] = 'portal';<br>
$_GET['mod'] = 'list';<br>
$_GET['catid'] = $id;<br>
break;<br>
}<br>
} elseif(count($_ENV['hostarr']) > 2 && $_ENV['hostarr'][0] != 'www' && !checkholddomain($_ENV['hostarr'][0])) {<br>
$_ENV['prefixdomain'] = addslashes($_ENV['hostarr'][0]);<br>
$_ENV['domainroot'] = addslashes($_ENV['domainroot']);<br>
require_once './source/class/class_core.php';<br>
C::app()->init_setting = true;<br>
C::app()->init_user = false;<br>
C::app()->init_session = false;<br>
C::app()->init_cron = false;<br>
C::app()->init_misc = false;<br>
C::app()->init();<br>
$jump = true;<br>
$domain = C::t('common_domain')->fetch_by_domain_domainroot($_ENV['prefixdomain'], $_ENV['domainroot']);<br>
$apphost = $_ENV['domain']['app'][$domain['idtype']] ? $_ENV['domain']['app'][$domain['idtype']] : $_ENV['domain']['app']['default'];<br>
$apphost = $apphost ? 'http://'.$apphost.'/' : '';<br>
switch($domain['idtype']) {<br>
case 'home':<br>
if($_G['setting']['rewritestatus'] && in_array('home_space', $_G['setting']['rewritestatus'])) {<br>
$url = rewriteoutput('home_space', 1, $apphost, $domain['id']);<br>
} else {<br>
$url = $apphost.'home.php?mod=space&uid='.$domain['id'];<br>
}<br>
break;<br>
case 'group':<br>
if($_G['setting']['rewritestatus'] && in_array('group_group', $_G['setting']['rewritestatus'])) {<br>
$url = rewriteoutput('group_group', 1, $apphost, $domain['id']);<br>
} else {<br>
$url = $apphost.'forum.php?mod=group&fid='.$domain['id'].'&page=1';<br>
}<br>
break;<br>
}<br>
}<br>
} else {<br>
$jump = true;<br>
}<br>
if(empty($url) && empty($_ENV['curapp'])) {<br>
if(!empty($_ENV['domain']['defaultindex']) && !$jump) {<br>
if($_ENV['defaultapp'][$_ENV['domain']['defaultindex']]) {<br>
$_ENV['curapp'] = $_ENV['defaultapp'][$_ENV['domain']['defaultindex']];<br>
} else {<br>
$url = $_ENV['domain']['defaultindex'];