我有一个函数，可以<a href>在链接之前和</a>之后添加标签。但是，某些网页会中断。您将如何改善此功能？谢谢！

function processString($s) 
{
    // check if there is a link

    if(preg_match("/http:\/\//",$s))
    {
        print preg_match("/http:\/\//",$s);


        $startUrl =  stripos($s,"http://");

        // if the link is in between text
        if(stripos($s," ",$startUrl)){
            $endUrl = stripos($s," ",$startUrl);
        }
        // if link is at the end of string
        else {$endUrl = strlen($s);}

        $beforeUrl = substr($s,0,$startUrl);
        $url = substr($s,$startUrl,$endUrl-$startUrl);
        $afterUrl = substr($s,$endUrl);

        $newString = $beforeUrl."<a href=\"$url\">".$url."</a>".$afterUrl;

        return $newString;
    }

    return $s;
}