Socket connection error

[1246]

Hello.
I'm having an error in a server-client application I made using arrays. I don't exactly know what the problem is, but it's something like the second socket and higher don't connect to the listener. (?)

Here is my server code:

Public Class Form1



    Dim max_players As Integer = 0
    Dim tcp_listener() As System.Net.Sockets.TcpListener
    Dim socket() As System.Net.Sockets.Socket
    Dim network_stream As System.Net.Sockets.NetworkStream
    Dim streamreader As System.IO.StreamReader
    Dim serving As Boolean = False
    Dim player_connected() As Boolean
 
   
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        CheckForIllegalCrossThreadCalls = False

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        If serving = False Then
            Dim slots As Integer = Replace(TextBox1.Text, " ", Nothing)
            If IsNumeric(slots) Then
                If slots > 0 And slots < 11 Then
                    serving = True
                    Button1.Text = "Serving..."
                    Dim start_port As Integer = 21760
                    max_players = slots
                    ReDim socket(max_players)
                    ReDim tcp_listener(max_players)
                    ReDim player_connected(max_players)
                    For a As Integer = 0 To max_players - 1
                        player_connected(a) = False
                        tcp_listener(a) = New System.Net.Sockets.TcpListener(start_port)
                        tcp_listener(a).Start()
                        start_port = start_port + 1
                        Timer1.Start()
                        Timer5.Start()
                    Next
                    Dim thread As New System.Threading.Thread(AddressOf Listen)
                    thread.Start()
                End If
            End If
        End If

    End Sub


' I added these test_connected booleans, these msgboxes and changed some things so I could trap the error as I was trying to chat with a friend of mine (two connections). Didn't work as well :(
  
    Dim test1_connected As Boolean = False
    Dim test2_connected As Boolean = False

    Private Sub Listen()

        Do While serving = True
            For a As Integer = 0 To max_players - 1
                If test1_connected = True And test2_connected = True Then
                    MsgBox("0")
                    'Exit Sub
                Else
                    If test1_connected = False Then
                        MsgBox("1")
                        socket(0) = tcp_listener(0).AcceptSocket()
                        test1_connected = True
                        network_stream = New System.Net.Sockets.NetworkStream(socket(0))
                        Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes("connection1|")
                        network_stream.Write(data, 0, data.Length)
                    Else
                        MsgBox("2")
                        socket(1) = tcp_listener(1).AcceptSocket()
                        MsgBox("yes123")
                        test2_connected = True
                        network_stream = New System.Net.Sockets.NetworkStream(socket(1))
                        Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes("connection1|")
                        network_stream.Write(data, 0, data.Length)
                        'Exit For
                    End If
                End If
                'network_stream = New System.Net.Sockets.NetworkStream(socket(a))
                'Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes("connection1|")
                'network_stream.Write(data, 0, data.Length)
            Next
        Loop

    End Sub

    
End Class

Client code:

Dim connecting As Boolean = False
    Dim tcp_client As System.Net.Sockets.TcpClient
    Dim current_port As Integer = "21760"
    Dim network_stream As System.Net.Sockets.NetworkStream


    Private Sub Connect(ByVal port As Integer)

        Try
            current_port = port
            tcp_client = New System.Net.Sockets.TcpClient
            tcp_client.Connect("ip.ip.ip.ip", port)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        If connecting = False Then
            connecting = True
            Button1.Text = "Connecting..."
            TextBox1.ReadOnly = True
            username = TextBox1.Text
            tcp_client = New System.Net.Sockets.TcpClient
            Dim thread As New System.Threading.Thread(AddressOf Connect)
            thread.Start(current_port)
            Timer4.Start()
        Else
            MsgBox("Connection failed.", MsgBoxStyle.Critical, "Error")
        End If

    End Sub

    Private Sub Timer4_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer4.Tick

        If tcp_client.Connected = True Then
            Timer4.Stop()
        Else
            If connecting = True Then
                Me.Text = Me.Text & "123"
                If current_port = "21760" Then ' max port number
                    connecting = False
                End If
                Dim thread As New System.Threading.Thread(AddressOf Connect)
                thread.Start(current_port + 1)
                Timer4.Stop()
                Timer4.Start()
            Else
                Button1.Text = "Connect"
                TextBox1.ReadOnly = False
                Timer4.Stop()
                MsgBox("Connection timeout.", MsgBoxStyle.Critical, "Error")
            End If
        End If

    End Sub



End Class

Thanks.

[honeybee]

It looks like you have all the listeners listening on the same port. If the port is opened and used by one listener object, I am not sure you could use it for another listener object.

Without knowing exactly what you are trying to achieve, it's hard to tell, but I am guessing the design of your app can be improved. If you are going to use just one port, instead of maintaining an array of listeners, create a thread that listens onto the specific port and alerts the application whenever any data is received on that port.

.

[1246]

It looks like you have all the listeners listening on the same port. If the port is opened and used by one listener object, I am not sure you could use it for another listener object.

Without knowing exactly what you are trying to achieve, it's hard to tell, but I am guessing the design of your app can be improved. If you are going to use just one port, instead of maintaining an array of listeners, create a thread that listens onto the specific port and alerts the application whenever any data is received on that port.

.

If you look closely you will see that I create a variable start_port which contains the port for the first listener and then in the For Loop it keeps increasing to each listener.
I don't think anybody needs to know but I am trying to make a 2D online game.
I had all working but I wanted to make the game work without the runtime winsock files (before I was using winsock) so I moved to sockets and tcp listeners. Until here, all okay.
But then I also wanted to make it so I didn't have to copy&paste the player info for each player I wanted. So I made it using arrays. The problem is in the connection or listening part.

And I will use the same ports as the slots number, which can be 1, 2, 3...

[1246]

Bump.

+10 threads have been created since mine and all of them got answered more than once.

[Shaggy Hiker]

What do you really expect? You haven't told us what error message you are getting, or even if you are getting an error message. You only say that there is an error in your application. You even suggest that you don't know what the error is. Do you know what it is doing that it should not be doing? Do you know what it is not doing that it should be doing? Throw us a bone here. Heck, I'm impressed that HB rooted through all that code looking for nobody knows what just enough to get even that comment.

The typical way to work with TCP would be to listen on a port, then when you get a client request you would spin off a thread to handle that request, during which the listener goes back to listening. On the other hand, the last time I was working with games, they were using UDP rather than TCP, so there weren't even connections. Online may be different, though.

[1246]

I am not getting any error message.
What I wanted was that someone copied my code and pasted it in a VB application and try it out.

Also, as I told, the first socket connects perfectly, the problem is with the next.

[Shaggy Hiker]

Yes, but you haven't said what the problem is. You are leaving it up to us to test your code, guess at what the problem is, figure out the answer and reply. Oddly, somebody might actually do that, now that you have stated what it is you want.

Having had a glance at it, there are many things worth fixing. First thing to try is turning Option Strict ON, as it will cause you to fix a few bugs and will make the code faster.

I notice that you are creating an array of listeners and starting them all off. You then go into a thread that appears to run a nearly perpetual loop. This seems woefully inefficient, as it seems like it would peg one CPU core regardless of whether or not there was any traffic, but inside that loop you run another loop from 0 to max players. That doesn't surprise me, but you then only deal with listener(0) and listener(1). What happened to all the other listeners? It seems like you never deal with them again after starting them listening.

You also get a socket back. I realize that you are more familiar with sockets, but .NET deals more in TCPClient objects, so you might consider moving in that direction.

I haven't worked with TCP in a long time, but doesn't that raise an event or something when a client requests a connection, thereby removing the need for that servicing loop?

[1246]

Having had a glance at it, there are many things worth fixing. First thing to try is turning Option Strict ON, as it will cause you to fix a few bugs and will make the code faster.

That causes +10 errors in the code.

I notice that you are creating an array of listeners and starting them all off. You then go into a thread that appears to run a nearly perpetual loop. This seems woefully inefficient, as it seems like it would peg one CPU core regardless of whether or not there was any traffic, but inside that loop you run another loop from 0 to max players. That doesn't surprise me, but you then only deal with listener(0) and listener(1). What happened to all the other listeners? It seems like you never deal with them again after starting them listening.

That's because I was having the past error so I wanted to try it to only allow the first and second connections but it didn't work. It normally is to be an array to max_players. I will change that when this issue gets solved but I can't solve it by myself so I posted in here.

You also get a socket back. I realize that you are more familiar with sockets, but .NET deals more in TCPClient objects, so you might consider moving in that direction.

Then networkstream won't work as it is an array. At least I didn't manage it to as I did try with tcpclient.

I haven't worked with TCP in a long time, but doesn't that raise an event or something when a client requests a connection, thereby removing the need for that servicing loop?

I don't THINK so.

What happens when I run server and client:
The server starts serving.
First client connects - all okay, server sends check data, client receives and sends back answer.
Second client connects - nothing appears, no data is sent.

[Shaggy Hiker]

Yes, turning Option Strict ON will create MANY compilation errors until you form better habits. What leaving it off allows you to do is make implicit conversions. These can lead to very subtle bugs, but the biggest single problem is that it makes your code slower. In your case, for what you are doing, that penalty is probably not going to be acceptable in the long run. For long running code, I found about a 50% performance boost when I turned Option Strict ON and fixed all the issues it identified. That's too small to notice for most programs, but for a game server that could be HUGE.

As for the events, I think Atheist posted some example of using TCPListener for multiple clients. I thought he had put a thread in the CodeBank on the subject. You can look at his signature for a link to a thread on the subject, but that appears to have a link to this

http://www.vbforums.com/showpost.php...24&postcount=2

thread, which has a pretty good example, too. That might give you some ideas. It uses a perpetual loop, but the accept method is blocking, so the loop doesn't gobble up CPU time. It looks like you are using something similar, so you might not be using the CPU all that much either, though you also won't be able to end the thread by toggling your Boolean, since the loop will only run when a connection is requested. If there are no connections, the Boolean will never be tested.

Here's the original thread from Atheists signature. He put another client server TCP example at the end of it:

http://www.vbforums.com/showthread.php?t=502795

[1246]

Alright, so I have successfully corrected all the compile errors caused by Option Strict being on and adapted Atheist code to mine.
Now I face another problem which is that everytime I try to connect to the listener, the error "Object reference not set to an instance of an object" gets trapped into the try-catch.

Any hint?

[formlesstree4]

Post the details of the said exception. It should reveal more information on what is exactly wrong.

[moti barski]

i want to learn this subject
what is Sockets.TcpClient ?
what is System.Net.Sockets.NetworkStream ?

what do they do, how do i use them ?

[formlesstree4]

i want to learn this subject
what is Sockets.TcpClient ?
what is System.Net.Sockets.NetworkStream ?

what do they do, how do i use them ?

Don't hi-jack someone's thread. Make a new thread instead, and you'll have to elaborate on what you want to do with them.

[1246]

System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="WindowsApplication2"
StackTrace:
in WindowsApplication1.Form1.Listen(Object index) in C:\Users\username\Desktop\Visual Basic\Visual Basic 2008\Game\WindowsApplication2\Form1.vb:line 114
in System.Threading.ThreadHelper.ThreadStart_Context(Object state)
in System.Threading.ExecutionContext.runTryCode(Object userData)
in System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
in System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
in System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
in System.Threading.ThreadHelper.ThreadStart(Object obj)
InnerException:

[Shaggy Hiker]

We'd have to see the new version of the code, especially the line that throws the exception. If you don't know what line that is because it just shows up in the exception handler, you can change the exception behavior to break when the exception is raised. That can be found under Debug|Exceptions.

In general, that particular message always has the same general solution. The first step is to find the line that raises the exception, then examine every object in that line. One of the objects, which might be the return from a method, is Nothing, so when you look at each one, you will find one that is Nothing, which will greatly aid your search for the problem.

[1246]

Private Sub Listen(ByVal index As Object)

Do
            'Try
            'tcp_client(CInt(index)) = New System.Net.Sockets.TcpClient
            tcp_client(CInt(index)) = tcp_listener(CInt(index)).AcceptTcpClient 'line that throws exception
            'Catch ex As Exception
            'MsgBox(ex.Message)
            'End Try
Loop

End Sub

[1246]

Nevermind. I just had to add "ReDim tcp_client(max_players)" to my code. Now it works.

Thanks a lot to all of you.

[formlesstree4]

Please mark your thread as Resolved in the "Thread Tools" menu at the top right hand side of the screen.

[1246]

Thanks. Forgot it.

[shekoasinger]

great job, seems like u got ur help already.. If u need something professional like this. look at this its 100% amazing: http://www.vbforums.com/showthread.p...highlight=chat

[Shaggy Hiker]

One thing I would add is that you ought to have a look at the List (of T). This was a new object added in VS2005. If you are using arrays that need to be re-sized, the List is a vast improvement over the array. You can add or insert items, remove items, and so on, and the sizing of the list is handled efficiently for you without any extra effort. In your case you would be using a List(of TCPListener). Rather than sizing the thing, you would add new ones with:

.Add(New TCPListener)

or whatever you chose. This is also strongly typed, such that if you make a List (of Integer), then it can ONLY hold integers. If you make a List(of TCPListener) then it can ONLY hold TCPListener...or anything derived from TCPListener.

Very convenient, and has largely replaced arrays except for those cases where the array is of a fixed size that, once set, doesn't change.

[1246]

Okay. First it appeared to work (I am able to connect to the sever) when I was improving my game, but when I tried to connect with another client it didn't connect.

Here's my server code:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        If Not serving Then
            Dim slots As Integer = CInt(Replace(TextBox1.Text, " ", Nothing))
            If IsNumeric(slots) Then
                If slots > 0 And slots < 11 Then
                    serving = True
                    Button1.Text = "Serving..."
                    Dim port As Integer = 21760
                    max_players = slots
                    ReDim tcp_listener(max_players)
                    ReDim tcp_client(max_players)
                    For a As Integer = 0 To max_players - 1
                        tcp_listener(a) = New System.Net.Sockets.TcpListener(System.Net.IPAddress.Any, port)
                        tcp_listener(a).Start()
                        port = port + 1
                        Timer1.Start()
                        Timer5.Start()
                    Next
                    Dim thread As New System.Threading.Thread(AddressOf Listen)
                    thread.IsBackground = True
                    thread.Start()
                Else
                    MsgBox("The slots number must be between 1 and 10.", MsgBoxStyle.Critical, "Error")
                End If
            Else
                MsgBox("The slots number must be a number.", MsgBoxStyle.Critical, "Error")
            End If
        End If

   End Sub

   Private Sub Listen(ByVal index As Object)

        Do
            Try
                tcp_client(CInt(index)) = tcp_listener(CInt(index)).AcceptTcpClient
                tcp_listener(CInt(index)).Stop()
                Dim data As String = "connection1|"
                Dim stream_writer As New System.IO.StreamWriter(tcp_client(CInt(index)).GetStream)
                stream_writer.Write(data)
                stream_writer.Flush()
                tcp_client(CInt(index)).GetStream.BeginRead(readBuffer, 0, 255, AddressOf Data_Arrival, Nothing)
                Exit Sub
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try
        Loop

    End Sub

Client code:

 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        If Not connecting Then
            connecting = True
            Button1.Text = "Connecting..."
            TextBox1.ReadOnly = True
            username = TextBox1.Text
            Dim thread As New System.Threading.Thread(AddressOf Connect)
            thread.IsBackground = True
            thread.Start(current_port)
            Timer4.Start()
        End If

    End Sub

    Private Sub Connect(ByVal port As Object)

        Try
            current_port = CInt(port)
            tcp_client = New System.Net.Sockets.TcpClient("ip.ip.ip.ip", CInt(port))
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

    End Sub

If you need any further info just ask.

[formlesstree4]

Were any errors thrown? What happened exactly? Were there any messages displayed? The only thing that I could see being wrong is somewhere in the server code.

[1246]

I get no errors. It just doesn't connect.

[1246]

Is it to ask too much asking if someone could actually try the code?

[1246]

Ok. Nevermind. I fixed it myself. See you never.