Need help in "Socket Programming" using Visual C# (Dot Net Framework 4.0)?

Question

Recently, I was given an assignment...

"To develop a Windows Forms application which can be installed on various windows machines at an office or enterprise. There would be a database in just one machine(ALPHA machine).. This database would be used by applications on other Beta machines to access data. The application would itself manage to check if it is an Alpha or a Beta (Has Database file with it?) and hence has to act as a server or a client."

I can do everything except the Network and Inter-Application Communication requirements. So, I started to learn Socket Programming over the Internet and I have gone through this link...

The idea I am working on is...

1. To have the client send the message to server.
2. To have the server accept this message and put this message in queue.
3. Read the message to get Client's IP Address and the its Request for Data.
4. Apply this request on database and get the result.
5. Convert the result in string.
6. Send it to the requesting client.

I can manage to perform steps 3,4 & 5. I am stuck on 1, 2 & 6.

Towards this...

I have created a function for Server as well as for client who return the Sockets when called. I create a separate function as I like my code to be clean, tidy and understandable after years.

Check my code below...

For Server...

 private Socket GetServerReady()
    {
           IPEndPoint RemoteEP = new IPEndPoint(IPAddress.Any, 8000);
            Socket newSock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            newSock.Connect(RemoteEP);
            newSock.Listen(10);
            return (newSock);
    }

You will notice there is no Accept() method anywhere, This is because I wish to call it like below for further use...

Socket CltSock = GetServerReady().Accept();

The Code for Client is...

private Socket GetClientReady()
    {
        IPEndPoint RemoteEP = new IPEndPoint(IPAddress.Parse(txtBxHost2.Text.Trim()), 8000);
        Socket ServerSock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        ServerSock.Connect(RemoteEP);
        return (ServerSock);
    }

Finally, The questions are....

• "Where is the appropriate place to call the functions I wrote above?"

• "Should I call the Server and Client Function in Form_Load() Event?"

• "What must be the next step towards my main intention which is point 1,2 & 6 mentioned above?"

I don't expect the full code that I can just copy as it is. Just the correct procedure and a little detail over the concept would do.

I would be using just a single PC for testing purpose. Also, another limitation is, It would all be coded in a single application. I don't want to write two separate applications for client & server.

I hope I made it all clear for you to understand.

Thanks a Lot.

Awaiting the response.

Answer 1

I was struggling to get things done and somehow managed to get the solution.

Below is my solution:

Server Side code: (I put this code in a function which loops back the execution if any exception is caught)

private void Looper()
    {
        int i = 0;
        int AttemptCount = 1;
        while (i == 0)
        {
            try
            {
                TcpListener tL = new TcpListener(Network.GetLocalIPAddress(), 56009);
                tL.Start(10);
                Socket tS = tL.AcceptSocket();

                if (tS.Connected)
                {
                    NetworkStream nS = new NetworkStream(tS);
                    StreamReader Reader = new StreamReader(nS);

                    Output = Reader.ReadToEnd().Trim();

                    Reader.Close();
                    nS.Close();
                    tS.Close();
                    tL.Stop();

                    //If Done, End Execution
                    i = 1;
                }
                else
                {
                    MessageBox.Show("The connection to the client is broken or failed..!!\n\nPlease check connection and try again.","Error",MessageBoxButtons.OK,MessageBoxIcon.Error);
                }
            }
            catch (SystemException ex)
            {
                //If Not, Loop Execution Again
                if (MessageBox.Show("Exception: " + ex.Message + "\n\nAttempt Count: " + AttemptCount + "\n\nDo you want to terminate the transmission?", "Error", MessageBoxButtons.YesNo, MessageBoxIcon.Error) == DialogResult.Yes)
                {
                    i = 1;
                    ResetTimer.Stop();
                }
                else
                {
                    i = 0;
                    AttemptCount++;
                }
            }
        }
    }

When above function is called, The server waits to accept any incoming socket. If there is any error somewhere due to port re-usage or anything, It loops back itself and resets the server. (So, we don't have to manually call the server function again & again.)

Once the server accepts any incoming socket, the execution ends up successfully. Lot's of time we don't want to keep invoking server even after a successful reception. So, I, instead of calling this function in a button "click_event", I called it in a timer Tick_Event. So, the human need is eliminated at server side.

This leads to a problem. Once the server starts waiting to accept, It is in blocking mode. It hangs all the processes and controls in same thread. So, I moved the call to above function to BackgroundWorker's "Do_Work" Event.

Check below Code:

private void GetServerReady()
    {
        if (!bW.IsBusy)
        {
            bW.RunWorkerAsync();
            txtBxHistory.Text += "\r\n" + Output;
        }
    }

    private void bW_DoWork(object sender, DoWorkEventArgs e)
    {
        Looper();
    }

    private void ResetTimer_Tick(object sender, EventArgs e)
    {
        GetServerReady();
    }

1. "bW" is "BackgroundWorker".
2. "Output" is a variable I defined globally.

The reason we need a variable is that,

BackgroundWorker has its own thread to execute the code placed in its "Do_Work" Event. So, a TextBox from our application's thread can't be used by BackgroundWorker to store the received output. Doing this to a variable and then setting TextBox's Text property to this variable does the trick.

Client Side code:

private void btnSend_Click(object sender, EventArgs e)
    {
        TcpClient socketForServer;
            try
            {
                socketForServer = new TcpClient(txtBxDestIP.Text.Trim(), 56009);
            }
            catch
            {
                MessageBox.Show("Failed to connect to server at " + txtBxDestIP.Text.Trim() + ":999", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                return;
            }
            NetworkStream networkStream = socketForServer.GetStream();
            StreamWriter streamWriter = new System.IO.StreamWriter(networkStream);
            try
            {
                string InputString;
                InputString = Network.GetLocalIPAddress() + ": " + txtBxData.Text;
                streamWriter.Write(InputString);
                streamWriter.Flush();
                socketForServer.Close();
                txtBxHistory.Text += "\r\nMe: " + txtBxData.Text.Trim();
                txtBxData.Clear();
            }
            catch
            {
                MessageBox.Show("Exception reading from Server.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            streamWriter.Close();
            networkStream.Close();
            socketForServer.Close();
    }

1. "txtBxDestIP" is a TextBox having the Destination IP address as Text.
2. "txtBxData" is a TextBox having the text to be sent.

This code works flawless for me. With above solution I can achieve all my motives from step 1 to 6 (Mentioned in the question above.)

I hope it helps others too. Please suggest if there is a better and efficient way to perform this.

Thanks. Regards.