How to validate a domain?

[Red Squirrel]

What is the best way to programaticly validate a domain name?

At first I was thinking, easy, just need to make sure it's in format "word.ext"

Then I just make sure that word and ext don't use any special characters.

If it's www.word.ext then it is invalid because there's 3 sections, I only want 2. (don't care about subdomains in this particular case)

But here's my delima. There are domain TLDs like co.uk.

So how would I handle that? Do I need to tell my program what every single domain extension is? How do programs like cpanel do it?

 

[Markbnj]

Here's a list of TLDs. You could probably write a script to pull the values into an xml file or some other persistent structure.

https://wiki.mozilla.org/TLD_List

Or you could just do a name lookup on it and see if you get a valid record back.

 

[Red Squirrel]

Hmm given that's from iana that's quite official right? Think I might go ahead and make my program use that. It will have it's own list but have an option to update with that list.

 

[Red Squirrel]

Ran into an issue. That list only has the main TLDs but not the "Sub" TLDs like co.uk and stuff. So I don't know how to make my program know the difference between:

subdomain.domain.com

and

domain.co.uk

The 2nd one should either be rejected or truncated as I only want domain.com while the 2nd is valid because co.uk is actually a tld and not a domain.

This is a program where users will enter data, so I have to make it fool proof or it could render the entire hosting environment screwed up, like if someone decides to add co.uk as a domain then nobody will be able to add something.co.uk as the other person will own that domain. Or do I just let them put whatever they want and solve these issues as they come?

This is for a control panel, so it's equivalent to "addon domains" in cpanel. Anyone know how cpanel handles this? I don't have a cpanel server to test with.