Socket Programming

[manasap]

Hi all!

I've written a server and a client application using asynchronous sockets.The client sends data packets for every 7 seconds.The server receives the packets.
This process proceeds smoothly without any errors but,sometimes I get the following error.

"An existing connection was forcibly closed by the remote host."

Why is this happening when i am not closing the client program?
Could someone guide me in this issue

I am sending the code.


SERVER

Imports System
Imports System.Math
Imports System.Text
Imports System.Threading
Imports System.Net
Imports System.Net.Sockets
 
Module Module1
 
    ' Global variables Section
 
    Dim str_Insert1, str_Insert2 As String
    Dim Sim_Veh_ID As Int64 = 0
    Dim str_select_simvehid As Int64 = 0
    Dim Str_Select_EmpID As String = ""
    Dim Str_Select_Mobile As String = ""
    Dim Dbl_Prev_Long, Dbl_Prev_Lat As Double
    Dim Dbl_Total_Dist As Double = 0
    Dim Str_Select_TripID As String
    Dim Dbl_Emp_Long, Dbl_Emp_Lat, Dbl_Emp_Dist As Double
 
    Sub Main()
        ' Try
        If Path() Then
            AsynchronousSocketListener.StartListening()
        End If
        ' Catch ex As Exception
        'Console.WriteLine(ex.Message)
        'Log("Error in Main Function " & ex.Message & Now)
        'End Try
    End Sub
 
    Public Class StateObject
        Public workSocket As Socket = Nothing
        Public Const BufferSize As Integer = 200
        Public buffer(BufferSize) As Byte
        Public sb As New StringBuilder
    End Class
 
    Public Class AsynchronousSocketListener
        Public Shared data As String = Nothing
        Public Shared allDone As New ManualResetEvent(False)
        Shared str_Error As String
 
 
        Public Shared Sub StartListening()
            ' Try
            Dim bytes() As Byte = New [Byte](1024) {}
            Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName())
            Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
            Dim localEndPoint As New IPEndPoint(ipAddress, str_Port)
            Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
            'Try
            listener.Bind(localEndPoint)
            listener.Listen(1000)
            While True
                allDone.Reset()
                Console.WriteLine("Waiting for a connection... on Port No:")
                Console.WriteLine(localEndPoint)
                listener.BeginAccept(New AsyncCallback(AddressOf AcceptCallback), listener)
                allDone.WaitOne()
            End While
            ' Catch e As Exception
            'Console.WriteLine(E.Message)
            'Log("Error in Sample Form StartListening Second try " & E.Message & Now)
            ''  End Try
            'Console.WriteLine(ControlChars.Cr + "Press ENTER to continue...")
            'Console.Read()
            '' Catch ex As Exception
            'Console.WriteLine(ex.Message)
            'Log("Error in Sample Form StartListening First Try " & ex.Message & Now)
            'End Try
        End Sub
 
        Public Shared Sub AcceptCallback(ByVal ar As IAsyncResult)
            ' Try
            allDone.Set()
            Dim listener As Socket = CType(ar.AsyncState, Socket)
            Dim handler As Socket = listener.EndAccept(ar)
            Dim state As New StateObject
            state.workSocket = handler
            Console.WriteLine("Connection Established........")
            handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, New AsyncCallback(AddressOf ReadCallback), state)
            'Catch ex As Exception
            '    Console.WriteLine(ex.Message)
            '    Log("Error in Sample Form Acceptcallback " & ex.Message & Now)
            'End Try
        End Sub
 
        Public Shared Sub ReadCallback(ByVal ar As IAsyncResult)
            '  Try
            Dim state As StateObject = CType(ar.AsyncState, StateObject)
            Dim handler As Socket = state.workSocket
            Dim bytesRead As Integer
            bytesRead = state.sb.Capacity
            bytesRead = handler.EndReceive(ar)
            If bytesRead > 0 Then
                state.sb.Append(Encoding.Default.GetString(state.buffer, 0, bytesRead))
                state.sb.Replace(" ", "")
                state.sb.Replace(Chr(13), "")
                state.sb.Replace(vbCr, "")
                If InStr(state.sb.ToString, "<") > 0 And InStr(state.sb.ToString, ">") > 0 Then
                    Dim str_MSG As String
                    str_MSG = state.sb.ToString.Trim
                    Console.WriteLine(str_MSG)
                    Dim ch_tmp, TmpMsg As String
                    str_MSG = Mid(str_MSG, InStr(str_MSG, "<"), InStr(str_MSG, ">"))
                    ch_tmp = str_MSG
                    TmpMsg = ""
                    For i As Integer = 1 To Len(str_MSG)
                        ch_tmp = ""
                        ch_tmp = Mid(str_MSG, i, 1)
                        If (Asc(ch_tmp) >= 65 And Asc(ch_tmp) <= 90) Or (Asc(ch_tmp) >= 97 And Asc(ch_tmp) <= 122) Or (Asc(ch_tmp) >= 48 And Asc(ch_tmp) <= 57) Or Asc(ch_tmp) = 60 Or Asc(ch_tmp) = 62 Or Asc(ch_tmp) = 40 Or Asc(ch_tmp) = 41 Or Asc(ch_tmp) = 44 Or Asc(ch_tmp) = 32 Or Asc(ch_tmp) = 46 Or Asc(ch_tmp) = 58 Or Asc(ch_tmp) = 35 Or Asc(ch_tmp) = 42 Then
                            TmpMsg = TmpMsg & ch_tmp
                        End If
                    Next
                    str_MSG = TmpMsg.Trim
                    Dim i1, i2 As Integer
                    i1 = InStr(state.sb.ToString, "<")
                    i2 = InStr(state.sb.ToString, ">")
                    Dim str_Value As String = Process(str_MSG)
                    Console.WriteLine(str_Value)
                    If Not str_Value Is Nothing Then
                        If str_Value.Length > 1 Then
                            Send(handler, str_Value)
                        End If
                    End If
                    state.sb.Remove(0, i2 - 1)
                End If
                handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, New AsyncCallback(AddressOf ReadCallback), state)
            End If
            'Catch ex As Exception
            '    Console.WriteLine(ex.Message)
            '    Log("Error in Sample Form ReadCallBack function" & ex.Message & Now)
            'End Try
        End Sub
 
        Private Shared Sub Send(ByVal handler As Socket, ByVal data As [String])
            'Try
            Dim byteData As Byte() = Encoding.ASCII.GetBytes(data)
            handler.BeginSend(byteData, 0, byteData.Length, 0, New AsyncCallback(AddressOf SendCallback), handler)
            'Catch ex As Exception
            '    Console.WriteLine(ex.Message)
            '    Log("Error in Sample Form Send " & ex.Message & " " & Now)
            'End Try
        End Sub
 
        Private Shared Sub SendCallback(ByVal ar As IAsyncResult)
            ' Try
            Dim handler As Socket = CType(ar.AsyncState, Socket)
            Dim bytesSent As Integer = handler.EndSend(ar)
            Console.WriteLine(bytesSent.ToString)
            handler.Shutdown(SocketShutdown.Both)
            handler.Close()
            'Catch e As Exception
            '    Console.WriteLine(e.Message)
            '    Log("Error in Sample Form Sendcallback " & e.Message & " " & Now)
            'End Try
        End Sub
 

CLIENT

Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Text
 
Public Class Form1
 
    ' The port number for the remote device.
    Private Shared port As Integer = 8001
 
    ' ManualResetEvent instances signal completion.
    Private Shared connectDone As New ManualResetEvent(False)
    Private Shared sendDone As New ManualResetEvent(False)
 
    ' The response from the remote device.
    Private Shared response As [String] = [String].Empty
    Dim simid As String
    Dim msg1 As String = "<A," '"<V,1234,AO,,,,,,,,,>" '063514,220207
    Dim msg2 As String = ",1727.9723,7829.4798,0.000>"
    Dim str_date As String
 
    Dim fn_msg As String
 
 
    Public Class StateObject
        ' Client socket.
        Public workSocket As Socket = Nothing
        ' Size of receive buffer.
        Public BufferSize As Integer = 256
        ' Receive buffer.
        Public buffer(256) As Byte
        ' Received data string.
        Public sb As New StringBuilder()
    End Class 'StateObj
 
    Private Sub StartClient()
        ' Connect to a remote device.  192.168.15.8
        Try
            Dim ipAddress As IPAddress = Net.IPAddress.Parse("192.168.15.8")
            Dim remoteEP As New IPEndPoint(ipAddress, port)
 
            '  Create a TCP/IP socket.
            Dim client As New Socket(AddressFamily.InterNetwork, _
                SocketType.Stream, ProtocolType.Tcp)
 
            ' Connect to the remote endpoint.
            client.BeginConnect(remoteEP, AddressOf ConnectCallback, client)
            connectDone.WaitOne()
            ' Send test data to the remote device.
 
            Send(client, fn_msg)
            sendDone.WaitOne()
 
            ' Thread.Sleep(1000)
 
            'client.Shutdown(SocketShutdown.Both)
            ' client.Close()
 
        Catch e As Exception
            'Console.WriteLine(e.ToString())
            Log("Errot In StartClient" & e.Message)
 
        End Try
    End Sub 'StartClient
 
 
    Private Sub ConnectCallback(ByVal ar As IAsyncResult)
        Try
            ' Retrieve the socket from the state object.
            Dim client As Socket = CType(ar.AsyncState, Socket)
 
            ' Complete the connection.
            client.EndConnect(ar)
 
            ' Signal that the connection has been made.
            connectDone.Set()
        Catch e As Exception
 
            Log("Error in connect call back" & e.ToString())
        End Try
    End Sub 'ConnectCallback
 
 
    Private Sub Send(ByVal client As Socket, ByVal data As [String])
        Try
            ' Convert the string data to byte data using ASCII encoding.
 
            Dim byteData As Byte() = Encoding.ASCII.GetBytes(data)
 
            ' Begin sending the data to the remote device.
            client.BeginSend(byteData, 0, byteData.Length, 0, _
                AddressOf SendCallback, client)
 
        Catch ex As Exception
            Log("Error in send " & ex.ToString())
        End Try
    End Sub 'Send
 
 
    Private Sub SendCallback(ByVal ar As IAsyncResult)
        Try
            ' Retrieve the socket from the state object.
            Dim client As Socket = CType(ar.AsyncState, Socket)
 
            ' Complete sending the data to the remote device.
            Dim bytesSent As Integer = client.EndSend(ar)
 
            ' res = "Sent " & bytesSent & " bytes to server."
 
            ' Signal that all bytes have been sent.
            sendDone.Set()
 
 
        Catch e As Exception
            'Console.WriteLine(e.ToString())
            Log("Error in send call back" & e.ToString())
        End Try
    End Sub 'SendCallback
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        simid = Trim(InputBox("Enter simid:")) & ","
        msg1 = msg1 & simid
 
        Timer1.Start()
    End Sub
 
    Private Sub Timer1_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        str_date = Format(Now().AddMinutes(-330.0), "HHmmss" & "," & "ddMMyy")
        fn_msg = msg1 + str_date + msg2
        StartClient()
        'Timer1.Stop()
    End Sub
 
    Public Sub Log(ByVal str_logerr As String)
        Dim fs As New IO.FileStream("C:\ErrorLog.txt", IO.FileMode.Append, IO.FileAccess.Write, IO.FileShare.ReadWrite)
        Dim tw As New IO.StreamWriter(fs)
        tw.WriteLine(str_logerr)
        tw.Close()
    End Sub
 
 
End Class

[setiarakesh]

[HTML]This error occurs when server recieves ZERO byte length .It means that your cleint has closed.Then this error occur

Kindly tell me what is the operatng system you are using for Server[/HTML]

[setiarakesh]

Sinec i am also working on the same problem when the rate of data transfer is very high from vclient to server . When client Socket request is pending for a long time then it happens .This is usually done by increasing the parameter value in que function.But there is limitation of this only upto 1000. and i have tested this also by setting the 100,000 in Que function and it did not work .

The only factor which i think that may work is to write the server socket in such a manner that none of the client socket had to wait for longer period to remain in que of server socket main object listening the client.Increase the number of threads accordingly to process the Data which reaches at server from client on the main socket.

I describe you what i faced in socket programme. I have requirement of large (say more than 100) clients to be connected to one server socket object that is the main socket object to listen the clients that open child sockets in asychronous manner.And the network is GPRS for Cleint(GSM Modem that open socket client and connect to server) and server in LAN is with Static IP ,port and Port opened in Firewall which routed to a PC (Where the Socket server is running ) with IP and and socket port

As i was also facing the problem of disconnecting and after this when client again tried to connect to server then server did not connect to it and there was no error in client programme.Then to sort the problem of reconnectivity i had to call the listening function of main listeting socket in socketServer again and again at regular interval of time in timer and also at the time when any client socket is disconnected. And my problem is sorted out. And the capacity of Server is raised to 70 Cleints and in each second these 70 clients are sending 5 string of 1024 byte length in 1 second( ie. one string in 20 milli seconds).
and my Server is stable and processing the strings at very faster rate.

and also i tell you when string reaches on server then it is splitted and saved into SQL Server Data Base by opening one connection object of SqlClient and using the procedure to save the data into Data base.This connection is one time declared on form load of window in C#

Now i am stucked. As i inrease the number of clients(GSM Socket) to connect to server then it stops recieving the strings from the Cleints and one by one all cleints go down and i recieve an error remote socket disconnected forcibly and cPU show 100 % usage in Task Manager as well . But when i open another port and run the another instance of same programme on the Same machine then i am able to connect more than 70 clients. CPU usage goes down and do not show 100 % usage .It means my Server is capable to listen and process only 70 Clients(GSM Modem) .

And i want to increase the number of clients on the server . so that i do not need to open more ports on the Same machine as well in Firewall.

i conclude this that if we can free the que of server socket with requests pending from client then it can happen. So try to open more threads so that strings which are recieved on server socket from Client Socket can be processed in parallel manner and CPU usage can be optimized.This was i think can be sorted out

Kindly let me know if you get success

Rakesh Setia

[ email addresses snipped; - mod ]