IP & Domain to gethostbyname to preg_match - php

Question

I would like to have an input box where someone can input a domain and it will validate the domain then convert it to an IP, then validate the IP. If the IP doesn't validate it will echo none.
So, I'm wondering if this is the best way to do this, or is there a better way to do this?
$input = 'somedoaminhere.com';
$ValidIp = "/^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$/";
$parse = parse_url($input);
$ip = gethostbyname($parse['host']);
if (preg_match("$ValidIp", "$ip")) {
echo "$ip";
} else {
echo "none";
}

Answer 1

"then validate the IP" What is the point of validating the the IP if it is returned by gethostbyname it should be a valid IP.
However, I would do it like this.
$ip = "127.0.0.300";
$octals = explode(".",$ip);
$isValid=true;
foreach($octals as $oct)
{
if($oct<0 || $oct>255)
{$isValid=false;}
}
if($isValid)
{echo "Is Valid";}
else
{echo "Is no Valid";}
You can of course clean up the code. I kept it step by step so that reasons/steps were obvious.

Answer 2

PHP has a powerful set of functions built-in for validating & sanitising input: Filter
If you're just validating an IP address then use this:
$ip = '1.2.3.4';
$f = filter_var($ip, FILTER_VALIDATE_IP); // $f == '1.2.3.4'
$ip = '1.2.3.300';
$f = filter_var($ip, FILTER_VALIDATE_IP); // $f == false
You can do more with the filter function if you use the flags. For example, validate IPV4 address and exclude private ranges:
$f = filter_var($ip, FILTER_VALIDATE_IP, array('flags'=>FILTER_FLAG_IPV4 | FILTER_FLAG_NO_PRIV_RANGE));
There's little point in doing this if you're getting your IP address from gethostbyname() since that should return a valid address.
You can do a lot more with the filter_*() functions, including, for example, validating and sanitising all your user data in $_GET or $_POST in a single function call. Check the PHP Reference