Extract domain name from URL in C#

Question

This question has answer in other languages/platforms but I couldn\'t find a robust solution in C#. Here I\'m looking for the part of URL which we use in

Answer 1

As @Pete noted, this is a little bit complicated, but I'll give it a try.

Note that this application must contain a complete list of known TLD's. These can be retrieved from http://publicsuffix.org/. Left extracting the list from this site as an exercise for the reader.

class Program
{
    static void Main(string[] args)
    {
        var testCases = new[]
        {
            "www.domain.com.ac",
            "www.domain.ac",
            "domain.com.ac",
            "domain.ac",
            "localdomain",
            "localdomain.local"
        };

        foreach (string testCase in testCases)
        {
            Console.WriteLine("{0} => {1}", testCase, UriHelper.GetDomainFromUri(new Uri("http://" + testCase + "/")));
        }

        /* Produces the following results:

            www.domain.com.ac => domain.com.ac
            www.domain.ac => domain.ac
            domain.com.ac => domain.com.ac
            domain.ac => domain.ac
            localdomain => localdomain
            localdomain.local => localdomain.local
         */
    }
}

public static class UriHelper
{
    private static HashSet _tlds;

    static UriHelper()
    {
        _tlds = new HashSet
        {
            "com.ac",
            "edu.ac",
            "gov.ac",
            "net.ac",
            "mil.ac",
            "org.ac",
            "ac"

            // Complete this list from http://publicsuffix.org/.
        };
    }

    public static string GetDomainFromUri(Uri uri)
    {
        return GetDomainFromHostName(uri.Host);
    }

    public static string GetDomainFromHostName(string hostName)
    {
        string[] hostNameParts = hostName.Split('.');

        if (hostNameParts.Length == 1)
            return hostNameParts[0];

        int matchingParts = FindMatchingParts(hostNameParts, 1);

        return GetPartOfHostName(hostNameParts, hostNameParts.Length - matchingParts);
    }

    private static int FindMatchingParts(string[] hostNameParts, int offset)
    {
        if (offset == hostNameParts.Length)
            return hostNameParts.Length;

        string domain = GetPartOfHostName(hostNameParts, offset);

        if (_tlds.Contains(domain.ToLowerInvariant()))
            return (hostNameParts.Length - offset) + 1;

        return FindMatchingParts(hostNameParts, offset + 1);
    }

    private static string GetPartOfHostName(string[] hostNameParts, int offset)
    {
        var sb = new StringBuilder();

        for (int i = offset; i < hostNameParts.Length; i++)
        {
            if (sb.Length > 0)
                sb.Append('.');

            sb.Append(hostNameParts[i]);
        }

        string domain = sb.ToString();
        return domain;
    }
}