Get Domain Name using asp.net in Generic handler page

I want to get domain name not for remote ip. i have two domain(website). example www.a1.com and www.a2.com. in a2 domain send a request to a1 domain's page like GetRequest.ashx

the example of http request is

http://www.a1.com/GetRequest.ashx?username=bala&password=123456

in my GetRequest.ashx page example coding

<%@ WebHandler Language="VB" Class="Handler" %>

Imports System
Imports System.Web

Public Class GetRequest : Implements IHttpHandler

   Public Sub ProcessRequest(ByVal context As HttpContext) Implements     IHttpHandler.ProcessRequest

          c开发者_C百科ontext.Response.ContentType = "text/plain"
          Dim username As String = context.Request.QueryString("username")
          Dim password As String = context.Request.QueryString("password")
 **'//Here i need a coding to get requested domain name that is who send the request to my page**

   End Sub

   Public ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
       Get
         Return False
      End Get
  End Property
End Class

i already use the following coding but not solve my problem. because it return ip address. i need domain only not for ip.

context.Request.ServerVariables("REMOTE_ADDR")
context.Request.ServerVariables("REMOTE_HOST")

Dim domain As String
Dim url As Uri = HttpContext.Current.Request.Url
domain = url.AbsoluteUri.Replace(url.PathAndQuery, String.Empty)

the variable domain contain www.a1.com but i need www.a2.com

use google analytics api to solve my problem? then how to use this api can any one explain

Page.Request.Url.Host contains the host name of the url (www.a1.com in your example)

If a request on the www.a2.com site calls a page on the www.a1.com site, the hostname will always be www.a1.com since that is the host that was used to call the page. I recommend passing a query string variable if you need to know that the request originated from www.a2.com.

You can access the request object through HttpContext, like so:

EDIT: Changed to get host name of referring URL

string host = HttpContext.Current.Request.UrlReferrer.Host;

EDIT: UrlReferrer is returning null. Alternative using HTTP_REFERER:

if (!String.IsNullOrEmpty(Request.ServerVariables["HTTP_REFERER"]))
{
    Uri referringUrl = new Uri(Request.ServerVariables["HTTP_REFERER"]);
    string referringHostName = referringUrl .Host;
}

Check the Referrer:

HttpContext.Current.Request.UrlReferrer.Host

Inside your code:

   Public Sub ProcessRequest(ByVal context As HttpContext) Implements     IHttpHandler.ProcessRequest

          context.Response.ContentType = "text/plain"
          Dim username As String = context.Request.QueryString("username")
          Dim password As String = context.Request.QueryString("password")
 **'//Here i need a coding to get requested domain name that is who send the request to my page**
          Dim domain as string = context.Request.UrlReferrer.Host

   End Sub