Reconnection issue between Winsock Server(VB6) and TCP Client (VB.NET)
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From: albertleng on 4 Aug 2010 13:20 I have a program (Winsock Server) written with VB6 which is connected by a TCP Client (written in VB.NET). The developer who writes the TCP Client told me that the TCP Client can't reconnect to my Program (Winsock Server) after TCP Client crashes or restarts. It can only reconnect to my program after my program's restarted. I did the same testing with a simple Winsock Client i wrote and everything works fine. What i notice is that when TCP Client tries to reconnect, Winsock ConnectionRequest event is not being fired anymore. Having no working knowledge about VB.NET, please advise the workaround of this issue. Below is my Winsock Server code (I removed other part of the program which is unrelated to this issue). Private Sub Form_Load() On Error GoTo fixerr ' Set the LocalPort property to an integer. ' Then invoke the Listen method. tcpServer.LocalPort = 500 tcpServer.Listen Text1.Text = Text1.Text & " Listening via port " & tcpServer.LocalPort & " at " & Now & vbCr fixerr: If Err.Number <> 0 Then Text1.Text = Text1.Text & "error " & Err.Number & " " & Err.Description & vbCr End If End Sub Private Sub tcpServer_Close() On Error GoTo fixerr tcpServer.Close Text1.Text = Text1.Text & " Client Disconnected via port " & tcpServer.LocalPort & " at " & Now & vbCr tcpServer.LocalPort = 500 tcpServer.Listen Text1.Text = Text1.Text & " Listening via port " & tcpServer.LocalPort & " at " & Now & vbCr fixerr: If Err.Number <> 0 Then Text1.Text = Text1.Text & "error " & Err.Number & " " & Err.Description & vbCr End If End Sub Private Sub tcpServer_ConnectionRequest _ (ByVal requestID As Long) On Error GoTo fixerr ' Check if the control's State is closed. If not, ' close the connection before accepting the new ' connection. Text1.Text = Text1.Text & " Client attempts to connect via port " & tcpServer.LocalPort & " at " & Now & vbCr If tcpServer.State <> sckClosed Then tcpServer.Close End If ' Accept the request with the requestID ' parameter. tcpServer.Accept requestID If tcpServer.State = sckConnected Then Text1.Text = Text1.Text & " Connected by client via port " & tcpServer.LocalPort & " at " & Now & vbCr End If fixerr: If Err.Number <> 0 Then Text1.Text = Text1.Text & "error " & Err.Number & " " & Err.Description & vbCr End If End Sub Private Sub tcpServer_DataArrival _ (ByVal bytesTotal As Long) On Error GoTo fixerr ' Declare a variable for the incoming data. ' Invoke the GetData method and set the Text ' property of a TextBox named txtOutput to ' the data. Dim strData As String tcpServer.GetData strData txtOutput.Text = strData fixerr: If Err.Number <> 0 Then Text1.Text = Text1.Text & "error " & Err.Number & " " & Err.Description & vbCr End If End Sub
From: Nobody on 4 Aug 2010 14:00 "albertleng" <albertleng(a)gmail.com> wrote in message news:8a5f7303-cba8-4fda-aa82-758b89e0d318(a)g6g2000pro.googlegroups.com... >I have a program (Winsock Server) written with VB6 which is connected > by a TCP Client (written in VB.NET). > > The developer who writes the TCP Client told me that the TCP Client > can't reconnect to my Program (Winsock Server) after TCP Client > crashes or restarts. It can only reconnect to my program after my > program's restarted. > > I did the same testing with a simple Winsock Client i wrote and > everything works fine. > What i notice is that when TCP Client tries to reconnect, Winsock > ConnectionRequest event is not being fired anymore. > > Having no working knowledge about VB.NET, please advise the workaround > of this issue. > > Below is my Winsock Server code (I removed other part of the program > which is unrelated to this issue). I think that the problem with your code is that Close event is not fired when a client crashes(regardless of language). In that case, Error event fires instead with error codes 11053, or 10054. So a quick fix is to close the connection manually, then call tcpServer_Close() when you see these errors. Note that calling the Close method on the server to close a client doesn't fire Close event on the server(At fires only at the other side). However, your code doesn't support more than one client. If you want that, go to "Winsock Control" in MSDN, and click on "See Also", then "Using the Winsock Control", then scroll down to "Accepting More than One Connection Request".
From: albertleng on 4 Aug 2010 21:20 based on my testing, there is no error generated when the tcp client crashes. basically, my program doesn't detect anything when tcp client crashes. this does not happen with the winsock client I wrote though. thanks On Aug 5, 2:00 am, "Nobody" <nob...(a)nobody.com> wrote: > "albertleng" <albertl...(a)gmail.com> wrote in message > > news:8a5f7303-cba8-4fda-aa82-758b89e0d318(a)g6g2000pro.googlegroups.com... > > > > > > >I have a program (Winsock Server) written with VB6 which is connected > > by a TCP Client (written in VB.NET). > > > The developer who writes the TCP Client told me that the TCP Client > > can't reconnect to my Program (Winsock Server) after TCP Client > > crashes or restarts. It can only reconnect to my program after my > > program's restarted. > > > I did the same testing with a simple Winsock Client i wrote and > > everything works fine. > > What i notice is that when TCP Client tries to reconnect, Winsock > > ConnectionRequest event is not being fired anymore. > > > Having no working knowledge about VB.NET, please advise the workaround > > of this issue. > > > Below is my Winsock Server code (I removed other part of the program > > which is unrelated to this issue). > > I think that the problem with your code is that Close event is not fired > when a client crashes(regardless of language). In that case, Error event > fires instead with error codes 11053, or 10054. So a quick fix is to close > the connection manually, then call tcpServer_Close() when you see these > errors. Note that calling the Close method on the server to close a client > doesn't fire Close event on the server(At fires only at the other side). > > However, your code doesn't support more than one client. If you want that, > go to "Winsock Control" in MSDN, and click on "See Also", then "Using the > Winsock Control", then scroll down to "Accepting More than One Connection > Request".
From: Nobody on 5 Aug 2010 10:53 There is no socket listening for incoming connections all the time in your software, so if something goes wrong with the current connection, there is nothing waiting for the client to reconnect to. You have to implement support for more than one client. At least, you have to add tcpListener control, then keep that in Listen mode all the time. Example: Private Sub Form_Load() tcpServer.LocalPort = 500 tcpListener.LocalPort = 500 tcpListener.Listen End Sub Private Sub tcpListener_ConnectionRequest(ByVal requestID As Long) If tcpServer.State <> sckClosed Then tcpServer.Close End If ' Accept the request with the requestID ' parameter. tcpServer.Accept requestID End Sub Note how I moved the code from tcpServer_ConnectionRequest() to tcpListener_ConnectionRequest(). "tcpListener" will remain in listening mode forever. There is no need to call "Listen" anywhere again, including in Close event. The code above will allow one client to connect, even after crashing, but if there is a second client trying to connect, the first client is disconnected. To really support more than one client, you have to turn tcpServer into a control array, like the MSDN article shows. The MSDN article has a little problem, it doesn't reuse existing closed sockets, so after 32767 connections, your software would show an error message and stops accepting new connections. To fix this, you need to loop through the control array, and reuse sockets. Example: Found = False For i = tcpServer.LBound To tcpServer.UBound If tcpServer(i).State = sckClosed Then ' Reuse this one Found = True Exit For End If Next If Found Then ' Accept the request with the requestID ' parameter. tcpServer(i).Accept requestID Else i = tcpServer.UBound+1 Load tcpServer(i) tcpServer(i).Accept requestID End If
From: albertleng on 6 Aug 2010 11:48
Great!!! By having a Winsock control which solely listens for connection request and pass the request to another Winsock control works! The next thing i'll try to implement is to allow multiple clients connections. Thanks a lot! :) On Aug 5, 10:53 pm, "Nobody" <nob...(a)nobody.com> wrote: > There is no socket listening for incoming connections all the time in your > software, so if something goes wrong with the current connection, there is > nothing waiting for the client to reconnect to. You have to implement > support for more than one client. At least, you have to add tcpListener > control, then keep that in Listen mode all the time. Example: > > Private Sub Form_Load() > tcpServer.LocalPort = 500 > tcpListener.LocalPort = 500 > tcpListener.Listen > End Sub > > Private Sub tcpListener_ConnectionRequest(ByVal requestID As Long) > > If tcpServer.State <> sckClosed Then > tcpServer.Close > End If > ' Accept the request with the requestID > ' parameter. > tcpServer.Accept requestID > > End Sub > > Note how I moved the code from tcpServer_ConnectionRequest() to > tcpListener_ConnectionRequest(). "tcpListener" will remain in listening mode > forever. There is no need to call "Listen" anywhere again, including in > Close event. > > The code above will allow one client to connect, even after crashing, but if > there is a second client trying to connect, the first client is > disconnected. To really support more than one client, you have to turn > tcpServer into a control array, like the MSDN article shows. The MSDN > article has a little problem, it doesn't reuse existing closed sockets, so > after 32767 connections, your software would show an error message and stops > accepting new connections. To fix this, you need to loop through the control > array, and reuse sockets. Example: > > Found = False > For i = tcpServer.LBound To tcpServer.UBound > If tcpServer(i).State = sckClosed Then > ' Reuse this one > Found = True > Exit For > End If > Next > If Found Then > ' Accept the request with the requestID > ' parameter. > tcpServer(i).Accept requestID > Else > i = tcpServer.UBound+1 > Load tcpServer(i) > tcpServer(i).Accept requestID > End If |