相对路径转化成绝对路径

提取 Gregarius中的一个函数。可以把网页中的相对路径自动转化成绝对路径。
<?
function relative_to_absolute($content, $feed_url) {
preg_match('/(http|https|ftp):\/\//', $feed_url, $protocol);
$server_url = preg_replace("/(http|https|ftp|news):\/\//", "", $feed_url);
$server_url = preg_replace("/\/.*/", "", $server_url);

if ($server_url == '') {    
    return $content;    
}    

if (isset($protocol[0])) {    
    $new_content = preg_replace('/href="\//', 'href="'.$protocol[0].$server_url.'/', $content);    
    $new_content = preg_replace('/src="\//', 'src="'.$protocol[0].$server_url.'/', $new_content);    
} else {    
    $new_content = $content;    
}    
return $new_content;    

}
?>