Q: How can I get the root domain URI in ASP.NET? Let's say I'm hosting a website at http://www.foobar.com. 
Is there a way I can programmatically ascertain "http://www.foobar.com/" in my code behind (i.e. without having to hardcode it in my web config)?

A: HttpContext.Current.Request.Url can get you all the info on the URL. And can break down the url into its fragments.

A: Match match = Regex.Match(host, "([^.]+\\.[^.]{1,3}(\\.[^.]{1,3})?)$");
string domain = match.Groups[1].Success ? match.Groups[1].Value : null;

host.com => return host.com
s.host.com => return host.com
host.co.uk => return host.co.uk
www.host.co.uk => return host.co.uk
s1.www.host.co.uk => return host.co.uk

A: If example Url is http://www.foobar.com/Page1
HttpContext.Current.Request.Url; //returns "http://www.foobar.com/Page1"


HttpContext.Current.Request.Url.Host; //returns "www.foobar.com"


HttpContext.Current.Request.Url.Scheme; //returns "http/https"


HttpContext.Current.Request.Url.GetLeftPart(UriPartial.Authority); //returns "http://www.foobar.com"


A: --Adding the port can help when running IIS Express
Request.Url.Scheme + "://" + Request.Url.Host + ":" + Request.Url.Port


A: string domainName = Request.Url.Host


A: I know this is older but the correct way to do this now is 
string Domain = HttpContext.Current.Request.Url.Authority

That will get the DNS or ip address with port for a server.

A: This works also:

string url = HttpContext.Request.Url.Authority;


A: string hostUrl = Request.Url.Scheme + "://" + Request.Url.Host; //should be "http://hostnamehere.com"


A: string baseUrl = Request.Url.GetLeftPart(UriPartial.Authority);

Uri::GetLeftPart Method: 

The GetLeftPart method returns a string containing the leftmost portion of the URI string, ending with the portion specified by part. 

UriPartial Enumeration: 

The scheme and authority segments of the URI.


A: To get the entire request URL string:
HttpContext.Current.Request.Url

To get the www.foo.com portion of the request:
HttpContext.Current.Request.Url.Host

Note that you are, to some degree, at the mercy of factors outside your ASP.NET application. If IIS is configured to accept multiple or any host header for your application, then any of those domains which resolved to your application via DNS may show up as the Request Url, depending on which one the user entered.

A: For anyone still wondering, a more complete answer is available at http://devio.wordpress.com/2009/10/19/get-absolut-url-of-asp-net-application/.
public string FullyQualifiedApplicationPath
{
    get
    {
        //Return variable declaration
        var appPath = string.Empty;

        //Getting the current context of HTTP request
        var context = HttpContext.Current;

        //Checking the current context content
        if (context != null)
        {
            //Formatting the fully qualified website url/name
            appPath = string.Format("{0}://{1}{2}{3}",
                                    context.Request.Url.Scheme,
                                    context.Request.Url.Host,
                                    context.Request.Url.Port == 80
                                        ? string.Empty
                                        : ":" + context.Request.Url.Port,
                                    context.Request.ApplicationPath);
        }

        if (!appPath.EndsWith("/"))
            appPath += "/";

        return appPath;
    }
}


A: C# Example Below:
string scheme = "http://";
string rootUrl = default(string);
if (Request.ServerVariables["HTTPS"].ToString().ToLower() == "on")
{
  scheme = "https://";
}
rootUrl = scheme + Request.ServerVariables["SERVER_NAME"].ToString();


A: string host = Request.Url.Host;
Regex domainReg = new Regex("([^.]+\\.[^.]+)$");
HttpCookie cookie = new HttpCookie(cookieName, "true");
if (domainReg.IsMatch(host))
{
  cookieDomain = domainReg.Match(host).Groups[1].Value;                                
}


A: This will return specifically what you are asking.
Dim mySiteUrl = Request.Url.Host.ToString()

I know this is an older question.  But I needed the same simple answer and this returns exactly what is asked (without the http://).
