This article is first part of a two part article for people
who want to start writing socket programming with VB.
This example uses an ocx component that comes with VB. You
will need a from with a command button (command1), a socket
component (winsock1) and a listbox (list1).
We will need to do the following steps to have our hello
1- We must bind TCP/IP socket to port 1024 when form loads.
2- When we press Listen Key (command1) socket starts
listening port 1024. In this way program will be able to
accept connections. Listening socket is usually used for
just receiving TCP/IP connections. It will also queue
them until our program is free to serve them. We will
usually need another socket to service connections that
has been queued. However as we want to create a small
server we will use a single socket for both listening
and communication with client programs.
3- When a socket on a remote program opens a connection to
our program, a Connection request event is triggered and
ConnectionRequest subroutine is automatically called.
In this subroutine we can accept the connection.
4- Now that everything is prepared, whenever an accepted
socket tries to send us data another event called
DataArrival will be triggered. When we receive this event
we first read data that is sent to us and show it in a
listbox and then send a 'hello' string back to the client
program connected to us. This is why we call this server
a 'hello' server.
5- After sending data, server has no reason to keep
connection so it must close the connection.
When sending data is finished, a SendComplete event is
triggered. As we want to accept more connections we close
socket and then call listen function again to be ready
for accepting other incoming connections.
6- If any error occurs on socket an 'onerror' event is
triggered. In this case we will display an error message.
And now program source:
Private Sub Command1_Click()
Private Sub Form_Load()
Private Sub Winsock1_ConnectionRequest(ByVal requestID As Long)
If Winsock1.State <> sckClosed Then Winsock1.Close
Private Sub Winsock1_DataArrival(ByVal bytesTotal As Long)
Winsock1.GetData a$, vbString
'received data is in a$ , you can use it
List1.AddItem ("Received : " + a$)
Winsock1.SendData "hello" + vbCrLf
'The string 'hello' is sent in answer to client request
List1.AddItem ("Sent : Hello")
Private Sub Winsock1_Error(ByVal Number As Integer,
As String, ByVal Scode As Long,
As String, ByVal HelpFile As String,
HelpContext As Long,
MsgBox "Error in Socket" + Description, vbOKOnly,
Private Sub Winsock1_SendComplete()
7- Server written in this article can serve one connection
at a time. If you want you can use more connections by
loading new sockets for each incoming connection.
In next part of this article we will write a client side
program for this server.
Client program will connect server program over network and
will receive 'hello' string and then connection will be
closed by server program. You can test this program by
connecting to port 1024 using a telnet program. Whatever you
send to it, server will answer with a 'hello'.
If you need codes for this article you can visit our site
and go to ezine page. There you will find a link to zipped