validate domain name in PHP

validate.php

<?
    /**
     * checks if a domain name is valid
     * @param  string $domain_name 
     * @return bool              
     */
    public static function domain_name($domain_name)
    {
        //FILTER_VALIDATE_URL checks length but..why not? so we dont move forward with more expensive operations
        $domain_len = strlen($domain_name);
        if ($domain_len < 3 OR $domain_len > 253)
            return FALSE;

        //getting rid of HTTP/S just in case was passed.
        if(stripos($domain_name, 'http://') === 0)
            $domain_name = substr($domain_name, 7); 
        elseif(stripos($domain_name, 'https://') === 0)
            $domain_name = substr($domain_name, 8);
        
        //we dont need the www either                 
        if(stripos($domain_name, 'www.') === 0)
            $domain_name = substr($domain_name, 4); 

        //Checking for a '.' at least, not in the beginning nor end, since http://.abcd. is reported valid
        if(strpos($domain_name, '.') === FALSE OR $domain_name[strlen($domain_name)-1]=='.' OR $domain_name[0]=='.')
            return FALSE;
                 
        //now we use the FILTER_VALIDATE_URL, concatenating http so we can use it, and return BOOL
        return (filter_var ('http://' . $domain_name, FILTER_VALIDATE_URL)===FALSE)? FALSE:TRUE;

    }

I came across this and copied to save a few minutes.
I added this block though
$dot_position = strpos($domain_name, '.');
$ext = substr($domain_name, ($dot_position) + 1);
if(strlen($ext) < 2) return false; // no single character tld yet known.