I am wondering what the best way to obtain the current domain is in ASP.NET?
http://www.domainname.com/subdir/ should yield http://www.domainname.com
http://www.sub.domainname.com/subdir/ should yield http://sub.domainname.com
As a guide, I should be able to add a url like "/Folder/Content/filename.html" (say as generated by Url.RouteUrl() in ASP.NET MVC) straight onto the URL and it should work.
Same answer as MattMitchell's but with some modification. This checks for the default port instead.