discuz防止跨站攻击函数dhtmlspecialchars分析

function dhtmlspecialchars($string, $flags = null) {
        if(is_array($string)) {
                foreach($string as $key => $val) {
                        $string[$key] = dhtmlspecialchars($val, $flags);
                }
        } else {
                if($flags === null) {
                        $string = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $string);
                        if(strpos($string, '&#') !== false) {
                                $string = preg_replace('/&((#(\d{3,5}|x[a-fA-F0-9]{4}));)/', '&\\1', $string);
                        }
                } else {
                        if(PHP_VERSION < '5.4.0') {
                                $string = htmlspecialchars($string, $flags);
                        } else {
                                if(strtolower(CHARSET) == 'utf-8') {
                                        $charset = 'UTF-8';
                                } else {
                                        $charset = 'ISO-8859-1';
                                }
                                $string = htmlspecialchars($string, $flags, $charset);
                        }
                }
        }
        return $string;
}