Question

I think regular expressions might be able to accomplish this, if not then string manipulation is also a viable solution.

I need to turn the following inputs:

1. "http://open.thumbshots.org/image.pxf?url=www.party.com"
2. "http://www.xclicks.net/sc/ct.php?s=9971&l=http%3A//www.google.com/imgres%3F"
3. "http://whos.amung.us/pingjs/?k=yvybju40twbs&t=Mudswimmer%3A%20Spam%20%26%20Crap%3A%20Http%3AUniversity.com%3A%20No%20Animals%20Allowed..&c=c&y=htt"

into the following outputs:

1. "party.com"
2. "google.com"
3. "University.com"

I am not trying to get the host name of the URL, I want the the second domain, the one in the query string.

Answer 1

With everything that involves regular expressions there is a degree of uncertainty, for me at least, but giving your three inputs the following code works:

string[] urls = new string[] 
{ 
    "http://open.thumbshots.org/image.pxf?url=www.party.com",
    "http://www.xclicks.net/sc/ct.php?s=9971&l=http%3A//www.google.com/imgres%3F",
    "http://whos.amung.us/pingjs/?k=yvybju40twbs&t=Mudswimmer%3A%20Spam%20%26%20Crap%3A%20Http%3AUniversity.com%3A%20No%20Animals%20Allowed..&c=c&y=htt"
};

foreach (var url in urls)
{
    var result = HttpUtility.ParseQueryString(new Uri(url, UriKind.Absolute).Query);

    foreach (string item in result)
    {
        string value = result.GetValues(item).Single();

        const string DomainNamePattern = "(?:www\\.|\\b)(?<domain>([a-z0-9]([-a-z0-9]*[a-z0-9])?\\.)+((a[cdefgilmnoqrstuwxz]|aero|arpa)|(b[abdefghijmnorstvwyz]|biz)|(cat|com|coop|c[acdfghiklmnorsuvxyz])|d[ejkmoz]|(e[ceghrstu]|edu)|f[ijkmor]|(g[abdefghilmnpqrstuwy]|gov)|h[kmnrtu]|(i[delmnoqrst]|info|int)|(j[emop]|jobs)|k[eghimnprwyz]|l[abcikrstuvy]|(m[acdghklmnopqrstuvwxyz]|mil|mobi|museum)|(n[acefgilopruz]|name|net)|(om|org)|(p[aefghklmnrstwy]|pro)|qa|r[eouw]|s[abcdeghijklmnortvyz]|(t[cdfghjklmnoprtvwz]|travel)|u[agkmsyz]|v[aceginu]|w[fs]|y[etu]|z[amw]))";

        var match = Regex.Match(
            value,
            DomainNamePattern,
            RegexOptions.IgnoreCase);

        if (match.Success)
        {
            string domain = match.Groups["domain"].Value;

            Console.WriteLine(domain);
        }
    }
}

The regular expression used was adapted from here.

If you run this you get the following output:

// party.com
// google.com
// University.com