parse string for subdomain in php

Question

How can i find if a string has subdomain existing if there is no scheme / host present.

eg: $url="sub.main.com/images/sample.jpg";

I am trying to parse the url for images, and I am using parse_url for most cases.

But given the url strings can some in different flavors, eg:

/images/sample.jpg
//main.com/images/sample.jpg
images/sample.jpg

etc, I am trying to address the different cases one by one. Right now, I am finding it hard to detect if a string has subdomain present or not.

so for a string such as $url="sub.main.com/images/sample.jpg";` i would like to extract the subdomain, and for a string such as images/sample.jpg, i would like to find out that there is no subdomain

Answer 1

Interesting problem. I've fiddled around with this for a while; this method inevitably isn't perfect, but it may start you down the right path.

My solution begins with the two source files in this repository: https://github.com/usrflo/registered-domain-libs/tree/master/PHP

First, you may need to modify regDomain.inc.php to change an instance of $signingDomainParts = split('\.', $signingDomain); to $signingDomainParts = preg_split('/\./', $signingDomain); if split is deprecated in your php version.

Once you've got those saved, try this testing code, I put all of the URLs mentioned in the thread here as test cases:

<?php
require_once("effectiveTLDs.inc.php");
require_once("regDomain.inc.php");
$tests = Array("/images/sample.jpg","//main.com/images/sample.jpg","images/sample.jpg", "sub.main.com/images/sample.jpg", "http://www.example.com/www.google.com/sample.jpg", "amazon.co.uk/images/sample.jpg", "amazon.com/images/sample.jpg", "http://sub2.sub.main.co.uk/images/sample.jpg", "sub2.sub.main.co.uk/images/sample.jpg");
foreach($tests as $test)
{
    echo "Attempting $test.<BR/>";
    $one = parse_url($test);
    if(!array_key_exists("host", $one))
    {
        echo "Converting to: http://$test";
        echo "<BR/>";
        $one = parse_url("http://$test");
    }
    if(!$one){echo "<BR/>";continue;}
    echo "parse_url parts: ";
    print_r($one);
    echo "<BR/>";
    if($one && array_key_exists("host", $one))
    {
        $domain = getRegisteredDomain($one["host"], $tldTree);
        if(sizeof($domain))
        {
            $two = explode(".", $domain);
            echo "domain parts: ";
            print_r($two);
            echo "<BR/>";
            if(sizeof($two))
            {
                $three = array_diff(explode(".", $one["host"]), $two);
                if(sizeof($three))
                {
                    echo "Hark! A subdomain!: ";
                    print_r($three);
                    echo "<BR/>";
                }
            }
        }
    }
    echo "<BR/>";

}

?>

This code identifies the following of the test-cases as having subdomains:

Attempting sub.main.com/images/sample.jpg.
Hark! A subdomain!: Array ( [0] => sub ) 

Attempting http://www.example.com/www.google.com/sample.jpg.
Hark! A subdomain!: Array ( [0] => www ) 

Attempting http://sub2.sub.main.co.uk/images/sample.jpg.
Hark! A subdomain!: Array ( [0] => sub2 [1] => sub ) 

Attempting sub2.sub.main.co.uk/images/sample.jpg.
Hark! A subdomain!: Array ( [0] => sub2 [1] => sub )