TCP IP Server with acknowledgement and receive data again

Question

I have developed TCP/IP Server in C# listening on port and a GPS device is sending the data to server.

Initially, the device sends the IMEI number to server and server acknowledges with 01. After receiving the acknowledgement by device, a new packet of data is sent to server.

I am able to get IMEI number by TCP Server and after sending acknowledgement, i am not able to receive new packet data from client. I am including my code below also. Please let me know where i am wrong.

I have tested using hercules tcp server tool and next data packet is receiving successfully but from my application it is not working.

           try
        {
            IPAddress ipAdress = IPAddress.Parse(ConfigurationManager.AppSettings["Server"].ToString());
            // You can use local IP as far as you use the 
            //same in client

            // Initializes the Listener
            TcpListener myList = new TcpListener(ipAdress, int.Parse(ConfigurationManager.AppSettings["Port"].ToString()));

            for (; ; )
            { // Run forever, accepting and servicing connections
                //Start Listeneting at the specified port

                myList.Start();

                Console.WriteLine("Server running - Port: 8000");
                Console.WriteLine("Local end point:" + myList.LocalEndpoint);
                Console.WriteLine("Waiting for connections...");

                Socket socket = myList.AcceptSocket();
                // When accepted
                Console.WriteLine("Connection accepted from " + socket.RemoteEndPoint);

                byte[] b = new byte[1000];
                int k = socket.Receive(b);


                Console.WriteLine("echoed {0} bytes.", k);
                Console.WriteLine("Reading IMEI....");

                string hexStr = ConvertAsciiToHex(Encoding.ASCII.GetString(b, 0, b.Length));
                File.WriteAllText(@"C:\ClientFiles\testIMEI", hexStr);


                ASCIIEncoding asen = new ASCIIEncoding();
                string response = "01";
                Console.WriteLine("Ackowledgement Data - " + response);
                //
                int sentBytes = socket.Send(asen.GetBytes(response));
                Console.WriteLine("Acknowledgement data sent!\n");

                int count = 0;

                while (socket.Poll(-1, SelectMode.SelectRead))
                {
                    b = new byte[1000];
                    k = socket.Receive(b);
                    if (k > 0)
                    {
                        count++;
                        Console.WriteLine("Reading Client Data - Count - " + count.ToString() + " and lenght " + k.ToString());
                        hexStr = ConvertAsciiToHex(Encoding.ASCII.GetString(b, 0, b.Length));
                        File.WriteAllText(@"C:\ClientFiles\testData" + count.ToString(), hexStr);
                    }
                }

                socket.Shutdown(SocketShutdown.Both);
                socket.Close();
            }


            myList.Stop();
        }
        catch (Exception ex)
        {
            File.WriteAllText(@"C:\ClientFiles\Error.txt", ex.Message + "****" + ex.InnerException);
        }

Please step through with the debugger and tell us where it stucks. — Andre
Thanks Zicore for response, the next packet is empty after sending acknowledgement — hellosayeed
You're trying to receive 1000 bytes, probably it's allready in that buffer. — Andre
The 1000 bytes is a new object and I am using it for next time to receive any new packet. — hellosayeed
int k = socket.Receive(b); receices all bytes which are currently received by the socket with the defined max. of your 1000 bytes. So possibly the second packet is already in that buffer. — Andre

ja_mesa ja_mesa · Accepted Answer · 2013-06-24T10:23:42

I don't see any error in the program, except these comments:

 // Don't use the b.Length in this command:
 string hexStr = ConvertAsciiToHex(Encoding.ASCII.GetString(b, 0, b.Length));
 // use k instead, the numbers actually read, not the length of the buffer.
 string hexStr = ConvertAsciiToHex(Encoding.ASCII.GetString(b, 0, k)); 

 while (socket.Poll(-1, SelectMode.SelectRead))
 {
     // b has been allocated, don't need this
     // b = new byte[1000];
     k = socket.Receive(b);
     if (k > 0)
     {
         count++;
         Console.WriteLine("Reading Client Data - Count - " + count.ToString() + " and lenght " + k.ToString();
        // use k not Length
        hexStr = ConvertAsciiToHex(Encoding.ASCII.GetString(b, 0, k /*b.Length*/));
        File.WriteAllText(@"C:\ClientFiles\testData" + count.ToString(), hexStr);
     }
}

Do you know if the Poll command ever returns? May be it raises an error and you are missing that one. Check it out.

TCP IP Server with acknowledgement and receive data again

1 Answers