parse string for subdomain in php - 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 )

Answer 2

Try this code
<?php
$url = 'sub.main.com/images/sample.jpg';
$arr = explode('/',$url);
$domain = $arr[0];
$string = $arr[1];
$arr2 = explode('.',$domain);
if(count($arr2)>2) {
$subdomain = $arr2[0];
echo $subdomain;
}
?>

Answer 3

<?php
$url = 'http://sub.main.com/images/sample.jpg';
$arr = explode('/',$url);
$pieces = parse_url($url);
$domain = isset($pieces['host']) ? $pieces['host'] : '';
if (preg_match('/(?P<domain>[a-z0-9][a-z0-9\-]{1,63}\.[a-z\.]{2,6})$/i', $domain, $regs))
{
$main_domain=$regs['domain'];
}
$host=$pieces['host'];
$path=$pieces['path'];
if($host != $main_domain)
{
$arr2 = explode('.',$host);
$subdomain = $arr2[0];
echo $subdomain;
}
$string=substr($path,1,strlen($path));
?>

Answer 4

Try the following:
<?php
$url="sub.main.com/images/sample.jpg";
preg_match('#^(?:http://)?([^.]+).?([^/]+)#i',$url, $hits);
print_r($hits);
?>
This should output something like:
Array ( [0] => sub.main.com [1] => sub [2] => main.com )