Discuz! 帖子外链自动添加nofollow的方法

function parseurl($url, $text, $scheme) {
        global $_G;
        if(!$url && preg_match("/((https?|ftp|gopher|news|telnet|rtsp|mms|callto|bctp|thunder|qqdl|synacast){1}:\/\/|www\.)[^\[\"']+/i", trim($text), $matches)) {
                $url = $matches[0];
                $length = 65;
                if(strlen($url) > $length) {
                        $text = substr($url, 0, intval($length * 0.5)).' ... '.substr($url, - intval($length * 0.3));
                }
        $url = nofollow($url);
                return '<a href="'.(substr(strtolower($url), 0, 4) == 'www.' ? 'http://'.$url : $url).'" target="_blank">'.$text.'</a>';
        } else {
                $url = substr($url, 1);
                if(substr(strtolower($url), 0, 4) == 'www.') {
                        $url = 'http://'.$url;
                }
                $url = !$scheme ? $_G['siteurl'].$url : $url;
                return '<a href="'.nofollow($url).'" target="_blank">'.$text.'</a>';
        }
}

function nofollow($url = '')
{
    $temp = array();

    if( ! empty($url))
    {
        $temp = parse_url($url);

        if(isset($temp['host']) && $temp['host'] != $_SERVER['HTTP_HOST'])
        {
            $url .= '" rel="nofollow"';
        }
    }

    unset($temp);
    return $url;
}