How to get current domain name in ASP.NET

Here is a screenshot of Request.RequestUri and all its properties for everyone's reference.

You can try the following code :

 Request.Url.Host +
    (Request.Url.IsDefaultPort ? "" : ":" + Request.Url.Port)

Try getting the “left part” of the url, like this:

string domainName = HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Authority);

This will give you either http://localhost:5858 or https://www.somedomainname.com whether you're on local or production. If you want to drop the www part, you should configure IIS to do so, but that's another topic.

Do note that the resulting URL will not have a trailing slash.

Using Request.Url.Host is appropriate - it's how you retrieve the value of the HTTP Host: header, which specifies which hostname (domain name) the UA (browser) wants, as the Resource-path part of the HTTP request does not include the hostname.

Note that localhost:5858 is not a domain name, it is an endpoint specifier, also known as an "authority", which includes the hostname and TCP port number. This is retrieved by accessing Request.Uri.Authority.

Furthermore, it is not valid to get somedomain.com from www.somedomain.com because a webserver could be configured to serve a different site for www.somedomain.com compared to somedomain.com, however if you are sure this is valid in your case then you'll need to manually parse the hostname, though using String.Split('.') works in a pinch.

Note that webserver (IIS) configuration is distinct from ASP.NET's configuration, and that ASP.NET is actually completely ignorant of the HTTP binding configuration of the websites and web-applications that it runs under. The fact that both IIS and ASP.NET share the same configuration files (web.config) is a red-herring.