Top level domain from URL in C#

Question

I am using C# and ASP.NET for this.

We receive a lot of \"strange\" requests on our IIS 6.0 servers and I want to log and catalog these by domain.

Eg. we get

Answer 1

There may be some examples where this returns something other than what is desired, but country codes are the only ones that are 2 characters, and they may or may not have a short second level (2 or 3 characters) typically used. Therefore, this will give you what you want in most cases:

string GetRootDomain(string host)
{
    string[] domains = host.Split('.');

    if (domains.Length >= 3)
    {
        int c = domains.Length;
        // handle international country code TLDs 
        // www.amazon.co.uk => amazon.co.uk
        if (domains[c - 1].Length < 3 && domains[c - 2].Length <= 3)
            return string.Join(".", domains, c - 3, 3);
        else
            return string.Join(".", domains, c - 2, 2);
    }
    else
        return host;
}