Quite often you want to know who owns a given
domain. To obtain the registry information, you go to the respective registry
and start a so-called WHOIS query (lookup). The trick is that you have to know
which registry is responsible for which TLD (Top Level Domain).
The database is the so-called WHOIS database and it has one distinct property:
it provides us with a query interface via TCP port 43! And as the .NET framework
provides us with the TCPClient class, we can use this interface to directly
obtain our data.
The following example is a minimal implementation of a WHOIS lookup (whois.aspx):
<% @Page Language="VB" %>
<% @Assembly Name="System.Net" %>
<% @Import Namespace="System.Net.Sockets" %>
<% @Import Namespace="System.Text" %>
<% @Import Namespace="System.IO" %>
Dim tcpc As New TCPClient()
If 0 = tcpc.Connect("whois.networksolutions.com", 43) Then
Dim strDomain As [String] = "microsoft.com" + ControlChars.Cr + ControlChars.Lf
Dim arrDomain As [Byte]() = Encoding.ASCII.GetBytes(strDomain.ToCharArray())
Dim s As Stream = tcpc.GetStream()
s.Write(arrDomain, 0, strDomain.Length)
Dim sr As New StreamReader(tcpc.GetStream(), Encoding.ASCII)
While - 1 <> sr.Peek()
Response.Write((sr.ReadLine() + "<br>"))
Response.Write("Could not connect to WHOIS server!")
To be able to work with the TCPClient class, we need the System.Net.Sockets
namespace. We also need to add classes like System.Text or System.IO.
The TCPClient class is doing most of the work in this example: using it, I can
connect to a server on any port (the Connect method does that) and send data to
and fro (via Stream).
Sending the query warrants a little explanation: for sending I use the binary
stream without any wrappers. Therefore, I have to turn the query string (CR/LF
terminated) into a byte array (with ASCII encoding) and can then send the
desired number of bytes to the server.
Fetching the data happens via the StreamReader, which allows comfortable and
direct work with the character data. And to keep the example simple to the end,
the received data are immediately passed through to the client - the result can
be seen in the following screen shot.