如何在php中将部分url字符串转换为完整的url链接

I have a text as description for example "Hello, this is my website for getting access - http://www.abcxyz.com/testcontroller/testfunction"

I need to show partial text as first 70 characters of description and followed by '...'.

So result for partial text should be 'Hello, this is my website for getting access - <a href='http://www.abcxyz.com/testcontroller/testfunction'>http://www.abcxyz.com/test...</a>'. But the i need to convert the partial string to URL with full link.

I have used regular expression to convert string to url as -

function createUrlLink($text) {
        $url = '@(http)?(s)?(://)?(([a-zA-Z])([-\w]+\.)+([^\s\.]+[^\s]*)+[^,.\s])@';
        $return_text = preg_replace($url, '<a href="http$2://$4" target="_blank" title="$0">$0</a>', $text);
        return $return_text;
    }

This works fine for whole description. But i need to get this work for partial string url. Is there any solution ?