Convert subdomain to domain name (sub TLD vs TLD)

Question

I have written a function that "extract" the domain from hostname. e.g.

www.domain.com -> domain.com
domain.net -> domain.net
www.domain.co.uk -> domain.co.uk
www.subdomain.domain.tx.us -> domain.tx.us

and so on.

However I was unable to find list of all subTDL's.

Function also return wrong result for domains such nominet.uk

Any suggestions where I can find all of them?

Or any other way to do same function, but with using let say DNS?

Answer 1

There is publicly available file describing all sub TLD's located at:

http://mxr.mozilla.org/mozilla-central/source/netwerk/dns/effective_tld_names.dat?raw=1

Answer 2

It's impossible to this using the DNS (or any other algorithm for that matter) as there's no formal definition of what is a "subdomain".

The only practical solution at the moment is the "public suffix" list available via http://publicsuffix.org/.

This list contains those domains known to the administrators where different subdomains are issued to different third parties.

Its primary use is to help enforce cross-domain security policies - for example a server for "foo.co.uk" mustn't be able to set a domain cookie on "co.uk" which is then served to any other subdomain.