Question

I am attempting to create a php function which will check if the passes URL is a short URL. Something like this:

/**
 * Check if a URL is a short URL
 *
 * @param string $url
 * return bool
 */
function _is_short_url($url){
    // Code goes here
}

I know that a simpler and a sure shot way would be to check a 301 redirect, but this function aims at saving an external request just for checking. Neither should the function check against a list of URL shortners as that would be a less scale-able approach.

So are a few possible checks I was thinking:

1. Overall URL length – May be a max of 30 charecters
2. URL length after last ‘/’ – May be a max of 10 characters
3. Number of ‘/’ after protocol (http://) – Max 2
4. Max length of host

Any thoughts on a possible approach or a more exhaustive checklist for this?

EDIT: This function is just an attempt to save an external request, so its ok to return true for a non-short url (but a real short one). Post passing through this function, I would anyways expand all short URLs by checking 301 redirects. This is just to eliminate the obvious ones.

Answer 1

I would not recommend to use regex, as it will be too complex and difficult to understand. Here is a PHP code to check all your constraints:

function _is_short_url($url){
        // 1. Overall URL length - May be a max of 30 charecters
        if (strlen($url) > 30) return false;

        $parts = parse_url($url);

        // No query string & no fragment
        if ($parts["query"] || $parts["fragment"]) return false;

        $path = $parts["path"];
        $pathParts = explode("/", $path);

        // 3. Number of '/' after protocol (http://) - Max 2
        if (count($pathParts) > 2) return false;

        // 2. URL length after last '/' - May be a max of 10 characters
        $lastPath = array_pop($pathParts);
        if (strlen($lastPath) > 10) return false;

        // 4. Max length of host
        if (strlen($parts["host"]) > 10) return false;

        return true;
}