Question

I’m trying con build a simple chat client/software (whole in on executable) wich start listen from the start on the port 5900 and when a client connect to that port the chat is established.

The problem is that only the client can chat to the server, the server cannot answer the client because the connection is working in one way.

The i’ve tried to connect from “server” to the client when it establishes a connection but the system crash warning me that the port is already on use.

This my code: (working in one way)

Imports System.Net.Sockets
Imports System.Text
Imports System.Reflection

Public Class frmComplete
  Dim Data As Integer
  Dim Message As String

  Private sServer As TcpListener
  Private sClient As New TcpClient

  Private cServer As TcpListener
  Private cClient As New TcpClient
  Private cNick As String

  Dim BufferSize(1024) As Byte

  Private Delegate Sub MessageDelegate(ByVal Message As String)

Private Sub frmComplete_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    srvListen(5900)
    btnSend.Enabled = False
End Sub

Private Sub OnServerConnect(ByVal AR As IAsyncResult)
    sClient = sServer.EndAcceptTcpClient(AR)

    sClient.GetStream.BeginRead(BufferSize, 0, BufferSize.Length, AddressOf OnRead, Nothing)

    My.Computer.Audio.Play(Application.StartupPath & "\Connected.wav", AudioPlayMode.Background)
End Sub

Private Sub OnRead(ByVal AR As IAsyncResult)
    Data = sClient.GetStream.EndRead(AR)
    Message = Encoding.ASCII.GetString(BufferSize, 0, Data)

    Dim Args As Object() = {Message}
    Me.Invoke(New MessageDelegate(AddressOf PrintMessage), Args)

    sClient.GetStream.BeginRead(BufferSize, 0, BufferSize.Length, AddressOf OnRead, Nothing)
End Sub

Private Sub PrintMessage(ByVal Message As String)
    Try
        txtChat.Text = txtChat.Text & Message & vbCrLf
        My.Computer.Audio.Play(Application.StartupPath & "\Message.wav", AudioPlayMode.Background)
    Catch ex As Exception
        MsgBox(ex.Message, MsgBoxStyle.Critical)
    End Try
End Sub

Private Sub srvListen(ByVal port As Integer)
    Try
        sServer = New TcpListener(System.Net.IPAddress.Any, 5900)
        sServer.Start()

        'THIS WILL RAISE THE EVENT WHEN A CLIENT IS CONNECTED
        sServer.BeginAcceptTcpClient(AddressOf OnServerConnect, Nothing)
    Catch ex As Exception
        MsgBox(ex.Message, MsgBoxStyle.Critical)
    End Try
End Sub



Private Sub txtMessage_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles txtMessage.KeyDown
    'FIXME (SOUND T_T)
    If e.KeyCode = Keys.Enter Then
        SendMessage(cNick & ":" & txtMessage.Text)
    End If
End Sub

Private Sub btnConnect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConnect.Click
    ConnectToServer(txtIP.Text)
    cNick = txtNickname.Text

    txtNickname.Enabled = False
    txtIP.Enabled = False
    btnConnect.Enabled = False
End Sub

Private Sub ConnectToServer(ByVal ipadress As String)
    Try
        cClient.BeginConnect(ipadress, 5900, AddressOf OnClientConnect, Nothing)
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

Private Sub OnClientConnect(ByVal AR As IAsyncResult)
    Try
        cClient.EndConnect(AR)
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSend.Click
    If Not String.IsNullOrEmpty(txtMessage.Text) Then

        txtChat.Text = txtChat.Text & "Me:" & txtMessage.Text & vbCrLf
        SendMessage(cNick & ":" & txtMessage.Text)

    End If
End Sub

Private Sub SendMessage(ByVal message As String)
    If cClient.Connected = True Then
        Dim Writer As New IO.StreamWriter(cClient.GetStream)
        Writer.Write(message)
        Writer.Flush()
    End If

    txtMessage.Text = ""
End Sub

Private Sub SendCommand(ByVal command As String)
    If cClient.Connected = True Then
        Dim Writer As New IO.StreamWriter(cClient.GetStream)
        Writer.Write(command)
        Writer.Flush()
    End If

    txtMessage.Text = ""
End Sub

Private Sub txtMessage_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtMessage.TextChanged
    If Not String.IsNullOrEmpty(txtMessage.Text) Then
        btnSend.Enabled = True
    Else
        btnSend.Enabled = False
    End If
End Sub
End Class

What I should do? use two ports? one for write and another to read? And if i need to conect multiple clients to one user? (remember the same exe is server/client)

Please help me =(

Answer 1

You aren’t reading any data coming back from the Server. You’ll notice in your OnServerConnect method you call the BeginRead — you will also need to do this for your client in the OnClientConnect method, or you’ll get a one way communication. Perhaps this is why you are not seeing any data coming through?

I’m guessing, when your Server sends back the data to the client, you aren’t getting a hard-error, just no data.

Just glancing over your code I noticed that you have both a TcpClient and TcpListener for your client and server. You don’t need this. Your SERVER will be the TcpListener, and your CLIENT will be the TcpClient. By asking if you should connect back on a different port from the server, you are shortchanging yourself of what the TCP connection really is. Once your TcpClient has connected to the TcpServer, your connection is established. There is no need further to attempt to connect.

You’re client code should be something similar to:

Private Sub OnClientConnect(ByVal AR As IAsyncResult) 
    Try 
        cClient.EndConnect(AR)
     sServer.GetStream.BeginRead(BufferSize, 0, BufferSize.Length, AddressOf OnClientRead, Nothing)
    Catch ex As Exception 
        MsgBox(ex.Message) 
    End Try 
End Sub 


Private Sub OnClientRead(ByVal AR As IAsyncResult) 
    Data = sServer.GetStream.EndRead(AR) 
    Message = Encoding.ASCII.GetString(BufferSize, 0, Data) 

    Dim Args As Object() = {Message} 
    Me.Invoke(New MessageDelegate(AddressOf PrintMessage), Args) 

    sServer.GetStream.BeginRead(BufferSize, 0, BufferSize.Length, AddressOf OnClientRead, Nothing) 
End Sub