How to detect if user input is a domain? - php

Question

I am writing some code for my website and I need to find out a way to detect a user's input and determine whether or not it is a domain or an IP. If it is a domain it will then parse the domain from e.g. http://www.google.com to google.com, then resolve it and echo it back into the user input field. If it is a IP then it will skip all of these steps and remain in the IP user input field.
This is what I have so far:
<?php
if( $_POST['submit'] )
{
$ip_address=$_POST["host"];
if (ctype_alpha($ip_address))
{
// get host name from URL
preg_match('#^(?:http://)?([^/]+)#i', $ip_address, $matches);
$host = $matches[1];
// get last two segments of host name
preg_match('/[^.]+\.[^.]+$/', $host, $matches);
$new_ip_address = $matches;
//resolve parsed ip
$presolved = gethostbyname($new_ip_address);
}
else
{
echo "Do stuff.\n";
}
}
?>

Answer 1

Have you considered looking at it from the other direction? Detecting an IP address literal is much easier than parsing and validating a DNS name.
Parse the URL with parse_url
Split $url['host'] by '.'. If the result is an array of four integer elements, then it is probably an IP address.
Bonus points for checking that each integer is in the appropriate range (e.g, 1-255 for the first octet and 0-255 for the remaining octets).
In any case, use parse_url instead of trying to crack this with the regex hammer.

Answer 2

Try using http://php.net/filter_var
var_dump(filter_var('http://example.com', FILTER_VALIDATE_URL, FILTER_FLAG_PATH_REQUIRED));

Answer 3

To check if the input was an ip, you can use php's ip2long (http://php.net/manual/en/function.ip2long.php)
See the example below, which will return an IP or false.
<?php
function checkOrMakeIp($address) {
$long = ip2long($address);
if ($long != -1 || $long !== FALSE) {
// It is a IP, just return the address
return $address;
} elseif($ip = gethostbynamel($address)) {
// It is a hostname, but now we have the ip, return it
return $ip[0];
}
return false;
}
?>
Notice the gethostbynamel, it will return FALSE if the hostname could not be resolved; otherwise an array. (http://www.php.net/manual/en/function.gethostbynamel.php)