Parsing string for Domain / hostName

Question

Out customers can enter websites from domain names. They also can enter mailadresses from their contacts.

Know we need to find customers which websited whoose domain can be associated to the domains of the mailadresses.

So my idea is to extract the host from the webadress and from the url and compare them

So what's the most reliable algorithm to get the hostname from a url?

for example a host can be:

foo.com
www.foo.com
http://foo.com
https://foo.com
https://www.foo.com

The result should always be foo.com

Answer 1

Rather than relying on unreliable regex use System.Uri to do the parsing for you. Use a code like this:

string uriStr = "www.foo.com";
if (!uriStr.Contains(Uri.SchemeDelimiter)) {
    uriStr = string.Concat(Uri.UriSchemeHttp, Uri.SchemeDelimiter, uriStr);
}
Uri uri = new Uri(uriStr);
string domain = uri.Host; // will return www.foo.com

Now to get just the top-level domain you can use:

string tld = uri.GetLeftPart( UriPartial.Authority ); // will return foo.com

Answer 2

Here's a regular expression that will match the url's you have provided. Basically http and https etc are optional, as is the www Everything is then matched up to a possible path;

var expression = /(https?:\/\/)?(www\.)?([^\/]*)(\/.*)?$/;

This would mean that;

var result = 'https://www.foo.com.vu/blah'.replace(expression, '$3')

Would evaluate to

result === 'foo.com.vu'