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A TCP/IP socket server object for Visual Basic - An example server in VB

Len Holgate

An example server in VB

As a simple example we will develop an echo server that stores some per-connection state and can optionally shut down the connection in a variety of ways after echoing a certain number of data packets.

Our echo server consists of two forms. The first allows you to specify the port that the server should listen on and also set some parameters. When a server is created the second form is displayed, this contains a list control and handles the events that the server fires. After creating a server you can switch back to the first form, change the port number and create another server. All servers can operate independently.

The code behind the first form is fairly simple and mostly consists of managing the user interface elements and passing parameters to the second form. The work required to create the socket server itself is very simple.

Option Explicit

Private Sub Command1_Click()

   Dim server As JBSOCKETSERVERLib.server
   Set server = CreateSocketServer(CLng(Text1.Text))
   
   Dim frm As Form2
   Set frm = New Form2
   
   frm.SetServer server
   frm.ShowDataPackets.Value = ShowDataPackets.Value
   frm.DataIsBytes.Value = DataIsBytes.Value
   frm.DataIsString.Value = DataIsString.Value
   frm.SignOnAsUnicode.Value = SignOnAsUnicode.Value
   
   If ShutdownEnabled.Value Then
   
       If ShutdownSocket.Value Then
           frm.ShutdownAfter = CLng(ShutdownAfter.Text)
       ElseIf CloseSocket.Value Then
           frm.CloseAfter = CLng(ShutdownAfter.Text)
       End If
   
   End If
   
   server.StartListening
   
   frm.Show , Me

End Sub

Private Sub ShowDataPackets_Click()

   DataIsFrame.Enabled = ShowDataPackets.Value
   DataIsBytes.Enabled = ShowDataPackets.Value
   DataIsString.Enabled = ShowDataPackets.Value

End Sub

Private Sub ShutdownEnabled_Click()

   ShutdownSocket.Enabled = ShutdownEnabled.Value
   CloseSocket.Enabled = ShutdownEnabled.Value
   ShutdownAfter.Enabled = ShutdownEnabled.Value
   
End Sub

The second form is slightly more complex. The code that handles the socket server is as follows:

Option Explicit

Dim WithEvents m_server As JBSOCKETSERVERLib.server
Public ShutdownAfter As Integer
Public CloseAfter As Integer

Private ListWidth As Integer
Private ListHeight As Integer

Public Sub SetServer(server As JBSOCKETSERVERLib.server)

   Set m_server = server
   
   Caption = "Socket server listening on: " & server.LocalAddress.Port
   
End Sub

Private Sub m_server_OnConnectionClosed(ByVal Socket As JBSOCKETSERVERLib.ISocket)

   If ShowDataPackets.Value Then
       AddToList "OnConnectionClosed : " & GetAddressAsString(Socket)
   End If
   
   Dim counter As Class1
   Set counter = Socket.UserData

   If ShowDataPackets.Value Then
       AddToList "User data = " & counter.GetCount()
   End If
   
   Socket.UserData = 0

End Sub

Private Sub m_server_OnConnectionEstablished(ByVal Socket As JBSOCKETSERVERLib.ISocket)

   If ShowDataPackets.Value Then
       AddToList "OnConnectionEstablished : " & GetAddressAsString(Socket)
   End If
   
   Dim counter As Class1
   Set counter = New Class1
   
   Socket.UserData = counter
   
   Socket.WriteString "Welcome to VB echo server" & vbCrLf, SignOnAsUnicode.Value

   Socket.RequestRead

End Sub

Private Sub m_server_OnDataReceived( _
   ByVal Socket As JBSOCKETSERVERLib.ISocket, _
   ByVal Data As JBSOCKETSERVERLib.IData)

   Dim counter As Class1
   Set counter = Socket.UserData
   
   counter.IncrementCount

   If DataIsBytes.Value Then
   
       OnReceivedBytes Socket, Data, counter.GetCount
   
   ElseIf DataIsString.Value Then
   
       OnReceivedString Socket, Data, counter.GetCount

   End If

   Socket.RequestRead

   If ShutdownAfter <> 0 And ShutdownAfter = counter.GetCount Then
       Socket.Shutdown ShutdownBoth
   End If
   
   If CloseAfter <> 0 And CloseAfter = counter.GetCount Then
       Socket.Close
   End If

End Sub

Private Sub OnReceivedBytes( _
   ByVal Socket As JBSOCKETSERVERLib.ISocket, _
   ByVal Data As JBSOCKETSERVERLib.IData, _
   counter As Integer)

   Dim Bytes() As Byte
   Bytes = Data.Read()

   If ShowDataPackets.Value Then
   
       Dim stringRep As String
       
       Dim i As Integer

       For i = LBound(Bytes) To UBound(Bytes)

           stringRep = stringRep & CLng(Bytes(i)) & " "

       Next i
   
       AddToList "OnDataReceived : " & GetAddressAsString(Socket) & " - " & stringRep
   
   End If
       
   Socket.Write Bytes

End Sub

Private Sub OnReceivedString( _
   ByVal Socket As JBSOCKETSERVERLib.ISocket, _
   ByVal Data As JBSOCKETSERVERLib.IData, _
   counter As Integer)

   Dim theData As String
   theData = Data.ReadString
   
   If ShowDataPackets.Value Then
       AddToList "OnDataReceived : " & GetAddressAsString(Socket) & " - " & theData
   End If
         
   Socket.WriteString theData, False
   
End Sub

Private Function GetAddressAsString(Socket As JBSOCKETSERVERLib.ISocket) As String

   GetAddressAsString = Socket.RemoteAddress.Address & " : " & Socket.RemoteAddress.Port

End Function

The code is made more complex by the fact that we can display and echo the data and shut down the connection in all of the possible ways. Notice how we initialise our user data in the m_server_OnConnectionEstablished event and store it in the Socket. We then retrieve and use it in the m_server_OnDataReceived and m_server_OnConnectionClosed events.

Len has been programming for over 20 years, having first started with a Sinclair ZX-80. Now he runs his own consulting company, JetByte Limited. JetByte provides contract programming and consultancy services. We can provide experience in COM, Corba, C++, Windows NT and UNIX. Our speciality is the design and implementation of systems but we are happy to work with you throughout the entire project life-cycle. We are happy to quote for fixed price work, or, if required, can work for an hourly rate. We are based in London, England, but, thanks to the Internet, we can work 'virtually' anywhere...

Comments

Read Comments | Post Comment

  • Re: [2659] A TCP/IP socket server object for Visual Basic

    Posted by rossduncan on 11 May 2006

    I ran the server on one machine and the client on another and managed to get a connection and send some data. However after sending a few test messages "1234567890" I try and receive as string at the ...

  • Posted by Len Holgate on 18 Sep 2005

    There was a stupid precedence error in the original code, this may be related to it?

    LPOLESTR pOle = ((_lpa = (char*)m_pData) == NULL) ? NULL : ATLA2WHELPER((LPWSTR) alloca(m_length + 1*2), _lpa, m...

  • Posted by Len Holgate on 18 Sep 2005

    I'm afraid I don't have a free version of this code that includes client support.

  • Posted by Len Holgate on 18 Sep 2005

    Yes.

  • use as a client

    Posted by oromano on 19 May 2004

    may I use this library for a client application? do you have another dll to do this (with vb6)? great job