TCP Server Catching Unexpected Disconnecting

Hi,

I wrote a TCP Server tool which communicate with microcontroller. I use BackgroundWorker for threading. Here is my listen sub :

Code:

---

Sub listen_port2(ByVal b As BackgroundWorker)
        Dim server As TcpListener
        Dim ts As TimeSpan
        Dim ReturnValue As Integer
        server = Nothing
        Try

            Dim port As Int32 = 8081

            server = New TcpListener(IP, port)

            server.Start()

            Dim bytes(1024) As Byte
            Dim data As String = Nothing
         

            While True
                Dim client As Sockets.TcpClient = server.AcceptTcpClient()
                Dim ipend As Net.IPEndPoint = client.Client.RemoteEndPoint
                PublicIP = ""
                If Not ipend Is Nothing Then
                    PublicIP = ipend.Address.ToString
                End If
                b.ReportProgress(1)
                Dim stream As NetworkStream = client.GetStream()

                Dim i As Int32
                Dim k As Short
                For k = 0 To 1024
                    bytes(k) = 0
                Next
                i = stream.Read(bytes, 0, bytes.Length)

                While (i <> 0)

                    Debug.Print(i)
                    data = ""
                    data = System.Text.Encoding.ASCII.GetString(bytes, 0, i)
                    Send_SQL(data)
                    i = stream.Read(bytes, 0, bytes.Length)
                End While
                client.Close()
            End While
        Catch e As Exception
            Write_Error("listen_port2" & vbCrLf & e.Message) ' Write exception to a file
        Finally
            server.Stop()
        End Try
    End Sub

---

My problem is that i can't catch unexpected disconnects (when network cable is unpluged from client microcontorller or when microcontorller shut down)

I used a TCP server tools(Hercules) and they behave such : When microcontroller has gone they can't catch it but when microcontroller wants to connect again this tool shows that a disconnect message then it gives a connected message. When i try samething at my code i receive this error :

"Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host"

So what should i do for a stable TCP server? And i read sone articles about "TCP KeepAlive". Is it possible to Implement it to my code?


Your advices will be great help for me.

Regards.

Bump

The reason your not getting any answers is that you've posted your question in the codebank section which is intended for working code submissions rather than posting questions and answers. I'm moving your thread to the main forum where, hopefully, you'll get some response.

Quote:

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Originally Posted by simsekm

...
I used a TCP server tools(Hercules) and they behave such : When microcontroller has gone they can't catch it but when microcontroller wants to connect again this tool shows that a disconnect message then it gives a connected message. When i try samething at my code i receive this error :

"Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host"

So what should i do for a stable TCP server? And i read sone articles about "TCP KeepAlive". Is it possible to Implement it to my code?...

---

It sounds like when the Hercules tool gets the exeception you noted "Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host", it closes the existing port and Listens for a new connection.
You should do the same.
Wrap pretty much the code in the whole sub in a loop, so if you get an exception, rather than fall out of the sub, you loop back up (after closing/disposing the old server), and the code at the top will open a new server and way for another connection.

Thanks for this good idea. In fact that I had same idea about it but my barrier was my threads are Backgroundworker . It's not easy to restart it. I tried to client.close() method when I have got this exception but it didn't work. I think backgroundworker object is not a good choice for a TCP server. And my other idea is TCPListener class is not good choice as much as a socket class. What do you think about it?

Well, I haven't had occasion to use a Background worker, but I don't see that it should be a problem in this case.
I assume you've kicked off the background worker, and it calls this function passing a reference to itself.
If everything works well, it looks like the code should loop in this sub forever and continue to receive data.
All I'm saying is to put a loop around this loop, so you can keep from exiting the sub, so remain active either reading from a connection, or waiting for a connection.

While I haven't used a background worker for this, I do kickoff background threads to do this type of thing, and which should be for the most part, the same result.
The reason I haven't used a background worker is that I perceive the use for background workers is to do a job that will take some amount of time and when they're done, should report the job done and exit.
Since the purpose of a network connection in the cases I've dealt with is to provide a communication path between two or more programs, or machines, it needs to exist for the life of the program, so is just kicked off in a background thread to do its work until we exit.

So, what I envisioned for your existing code, without too many changes, is just add another loop around what you already have.
If you get an exception, stop the server, dispose of it, hit the bottom of the outer loop, loop back up and create a new server and listen for another connection. You could change the Write_Error to say you're restarting the connection.

Code:

---

Sub listen_port2(ByVal b As BackgroundWorker)
        Dim server As TcpListener
        Dim ts As TimeSpan
        Dim ReturnValue As Integer
    Do
        server = Nothing
        Try

            Dim port As Int32 = 8081

            server = New TcpListener(IP, port)

            server.Start()

            Dim bytes(1024) As Byte
            Dim data As String = Nothing
         

            While True
                Dim client As Sockets.TcpClient = server.AcceptTcpClient()
                Dim ipend As Net.IPEndPoint = client.Client.RemoteEndPoint
                PublicIP = ""
                If Not ipend Is Nothing Then
                    PublicIP = ipend.Address.ToString
                End If
                b.ReportProgress(1)
                Dim stream As NetworkStream = client.GetStream()

                Dim i As Int32
                Dim k As Short
                For k = 0 To 1024
                    bytes(k) = 0
                Next
                i = stream.Read(bytes, 0, bytes.Length)

                While (i <> 0)

                    Debug.Print(i)
                    data = ""
                    data = System.Text.Encoding.ASCII.GetString(bytes, 0, i)
                    Send_SQL(data)
                    i = stream.Read(bytes, 0, bytes.Length)
                End While
                client.Close()
            End While
        Catch e As Exception
            Write_Error("listen_port2" & vbCrLf & e.Message) ' Write exception to a file
        Finally
            server.Stop()
            server.Dispose()
        End Try
    Loop
End Sub

---

p.s. To be clear, I don't usually code endless loops like this in my background threads, but loop as long as a boolean flag is true (or false), e.g.

Code:

---

  Do While Running  'Loop while running is true (loop while flag is true)
  '...
  Loop

  Do Until Leaving  'Loop until Leaving is True (loop while flag is false)
  '...
  Loop

---

That way I set the flag when closing the main form to give the loop a chance to exit, and the background thread a chance to exit naturally.

p.s. Perhaps the Finally clause will need to be reworked, because I'm not sure exactly how that works since we're not actually leaving the Sub at the time of the exception. Anyway, this gives you the general idea of where I was coming from.