Sanitise host name into required format - php

Question

I am working on a script that calls a third party api, which needs a valid server hostname. Any of these format should be allowed, for example:
server.domain.com
server1.domain.com
something.domain.com
123456x.domain.tld
etc...
So, I have put together the following script to sanitize the server's hostname (in the event user inputs an invalid entry):
$server_hostname = 'test';
if (IsValidHostname($server_hostname))
{
switch (substr_count($server_hostname, '.'))
{
case 1:
$server_hostname = 'server.'. $server_hostname;
break;
case 0:
$server_hostname = 'server'. time() .'.default-domain.com';
break;
}
}
else
{
$server_hostname = 'server'. time() .'.default-domain.com';
}
var_dump($server_hostname);
function IsValidHostname($hostname)
{
// Src: http://stackoverflow.com/a/4694816
return (preg_match("/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i", $hostname)
&& preg_match("/^.{1,253}$/", $hostname)
&& preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*$/", $hostname)
);
}
The script appears to work. If an invalid hostname is supplied, it auto-generates a random one. Here are few test cases:
test -> server1451385708.default-domain.com
test.com -> server.test.com
123-test.com -> server.123-test.com
adam.test.com -> adam.test.com
e-v-e.test.com -> e-v-e.test.com
server12.test.co.uk -> server12.test.co.uk
However, I am not sure this is quite perfect yet. Here's a test that failed:
test.co.uk -> test.co.uk
I would prefer the outcome to be the following, when tld has 2 parts (e.g. co.uk):
test.co.uk -> server.test.co.uk
Any ideas on how I can achieve this?

Answer 1

Like this, this just covers the case that there are two ".":
if (IsValidHostname($server_hostname))
{
switch (substr_count($server_hostname, '.'))
{
case 1:
case 2:
$server_hostname = 'server.'. $server_hostname;
break;
case 0:
$server_hostname = 'server'. time() .'.default-domain.com';
break;
}
}
else
{
$server_hostname = 'server'. time() .'.default-domain.com';
}
or like this, which adds the info regardless of the number of ".":
if (IsValidHostname($server_hostname))
{
switch (substr_count($server_hostname, '.'))
{
case 0:
$server_hostname = 'server'. time() .'.default-domain.com';
break;
default:
$server_hostname = 'server.'. $server_hostname;
break;
}
}
else
{
$server_hostname = 'server'. time() .'.default-domain.com';
}

Answer 2

This is what I have settled on for now, let me know if there is a better way of doing it:
// Sanitize server's hostname
$serverHostname = strtolower(trim($server['hostname']));
if ($this->IsValidHostname($serverHostname)) {
switch (substr_count($serverHostname, '.')) {
case 1:
case 2:
if (substr($serverHostname, 0, 7) !== 'server.')
$serverHostname = uniqid() .'.'. $serverHostname;
break;
case 0:
$serverHostname = uniqid() .'.default-domain.com';
break;
}
} else {
$serverHostname = uniqid() .'.default-domain.com';
}