1 Introduction

In this series we are going to be looking at TCP IP, Client / Servers and what a massive world of opportunities this knowledge opens up to us, from Chat and Video Conferencing, to Invisible process communication, and even Service Management. But today let’s get the framework done.

2 Building the Sample

The sample is built in Visual Studio 2012 Ultimate as an x86 targeted application using .Net Framework 4. We will be using NuGet packages, a number of 3rd party libraries. All of which will be fully explained to you ensuring that the final compilation of your App will be hassle free. Oh! And the sample code is verbosely commented so you should have no problem in working out what the code does.

3 Description

Communication is fundamental to us all. But it is also fundamental to many programs. When your application connects with a database it has to communicate, when your browser connects to a website, it communicates and the vast majority of the communication that occurs on the internet is does through TCP communication. In this first example we will write a client and an “echo server” which simply replies with the message you sent – pretty much like the ping command. It doesn’t sound like much but it is the basis that we will start from.

4 Creating our Application

Open Visual Studio 2012 and Create a New Project. Call the Project ClientApp. Now Click on the ClientApp Project in Solution Explorer and Add a New Project Called ServerApp. This makes it nice a simple for us to separate the Client and Server logic and code.

1. Change the form Text to Server and Client accordingly.

2. The Server is a little more complicated than the Client so we will design that first

4.1 The Server

· Add a StatusStrip to the Server Form

o Add two Labels to the StatusStrip and Set their Text Properties to

§ Number of Connections

§ 0

o Change the Second Labels Name to lblNumberOfConnections

· Add a RichTextBox to the Form and Set it’s Docking property to Fill

· Name The RichTextBox rtbServer

4.2 The Client

· Add a RichTextBox to the Form and Set it’s Docking property to Fill

· Name The RichTextBox rtbClient

4.3 Now to the Code

Ok now we have created our front ends, you can format the RichTextBoxes any way you like. We need to start our coding. Again we will start with the Server.

4.4 Server Code

Our server does three things

· It waits until a client connects

Edit|Remove

 this.tcpListener = new TcpListener(IPAddress.Loopback, 3000); // Change to IPAddress.Any for internet wide Communication
            this.listenThread = new Thread(new ThreadStart(ListenForClients));
            this.listenThread.Start();

 this.tcpListener = new TcpListener(IPAddress.Loopback, 3000); // Change to IPAddress.Any for internet wide Communication 
            this.listenThread = new Thread(new ThreadStart(ListenForClients)); 
            this.listenThread.Start();

· It Handles the client’s connection and communication

Edit|Remove

 private void ListenForClients()
        {
            this.tcpListener.Start();

            while (true) // Never ends until the Server is closed.
            {
                //blocks until a client has connected to the server
                TcpClient client = this.tcpListener.AcceptTcpClient();

                //create a thread to handle communication 
                //with connected client
                connectedClients++; // Increment the number of clients that have communicated with us.
                lblNumberOfConnections.Text = connectedClients.ToString();

                Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm));
                clientThread.Start(client);
            }
        }

 private void ListenForClients() 
        { 
            this.tcpListener.Start(); 
 
            while (true) // Never ends until the Server is closed. 
            { 
                //blocks until a client has connected to the server 
                TcpClient client = this.tcpListener.AcceptTcpClient(); 
 
                //create a thread to handle communication  
                //with connected client 
                connectedClients++; // Increment the number of clients that have communicated with us. 
                lblNumberOfConnections.Text = connectedClients.ToString(); 
 
                Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm)); 
                clientThread.Start(client); 
            } 
        }

· It replies with the same message that it received (Echoes)

Edit|Remove

 private void HandleClientComm(object client)
        {
            TcpClient tcpClient = (TcpClient)client;
            NetworkStream clientStream = tcpClient.GetStream();

            byte[] message = new byte[4096];
            int bytesRead;

            while (true)
            {
                bytesRead = 0;

                try
                {
                    //blocks until a client sends a message
                    bytesRead = clientStream.Read(message, 0, 4096);
                }
                catch
                {
                    //a socket error has occured
                    break;
                }

                if (bytesRead == 0)
                {
                    //the client has disconnected from the server
                    connectedClients--;
                    lblNumberOfConnections.Text = connectedClients.ToString();
                    break;
                }

                //message has successfully been received
                ASCIIEncoding encoder = new ASCIIEncoding();

                // Convert the Bytes received to a string and display it on the Server Screen
                string msg = encoder.GetString(message, 0, bytesRead);
                WriteMessage(msg);

                // Now Echo the message back

                Echo(msg, encoder, clientStream);
            }

            tcpClient.Close();
        }

 private void HandleClientComm(object client) 
        { 
            TcpClient tcpClient = (TcpClient)client; 
            NetworkStream clientStream = tcpClient.GetStream(); 
 
            byte[] message = new byte[4096]; 
            int bytesRead; 
 
            while (true) 
            { 
                bytesRead = 0; 
 
                try 
                { 
                    //blocks until a client sends a message 
                    bytesRead = clientStream.Read(message, 0, 4096); 
                } 
                catch 
                { 
                    //a socket error has occured 
                    break; 
                } 
 
                if (bytesRead == 0) 
                { 
                    //the client has disconnected from the server 
                    connectedClients--; 
                    lblNumberOfConnections.Text = connectedClients.ToString(); 
                    break; 
                } 
 
                //message has successfully been received 
                ASCIIEncoding encoder = new ASCIIEncoding(); 
 
                // Convert the Bytes received to a string and display it on the Server Screen 
                string msg = encoder.GetString(message, 0, bytesRead); 
                WriteMessage(msg); 
 
                // Now Echo the message back 
 
                Echo(msg, encoder, clientStream); 
            } 
 
            tcpClient.Close(); 
        }

4.5 Client Code

Our Client does three things

· It connects to the Server

Edit|Remove

 client.Connect(serverEndPoint);

 client.Connect(serverEndPoint);

· It sends a message

Edit|Remove

 NetworkStream clientStream = client.GetStream();

            ASCIIEncoding encoder = new ASCIIEncoding();
            byte[] buffer = encoder.GetBytes(msg);

            clientStream.Write(buffer, 0, buffer.Length);
            clientStream.Flush();

            // Receive the TcpServer.response.

            // Buffer to store the response bytes.
            Byte[]  data = new Byte[256];

 NetworkStream clientStream = client.GetStream(); 
 
            ASCIIEncoding encoder = new ASCIIEncoding(); 
            byte[] buffer = encoder.GetBytes(msg); 
 
            clientStream.Write(buffer, 0, buffer.Length); 
            clientStream.Flush(); 
 
            // Receive the TcpServer.response. 
 
            // Buffer to store the response bytes. 
            Byte[]  data = new Byte[256];

· It displays the response

Edit|Remove

 // String to store the response ASCII representation.
            String responseData = String.Empty;

            // Read the first batch of the TcpServer response bytes.
            Int32 bytes = clientStream.Read(data, 0, data.Length);
            responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes);
            
            rtbClient.AppendText(Environment.NewLine + "From Server: " + responseData);

 // String to store the response ASCII representation. 
            String responseData = String.Empty; 
 
            // Read the first batch of the TcpServer response bytes. 
            Int32 bytes = clientStream.Read(data, 0, data.Length); 
            responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes); 
             
            rtbClient.AppendText(Environment.NewLine + "From Server: " + responseData);

4.5.1 Source Code Files

· Source code ClientApp:Form1.cs – The main interface to our Client application

· Source code ServerApp:Form1.cs – The main interface to our Server application

In the next of this series we shall start making things interesting!

5 More Information

To convert the solution to a previous version of Visual Studio you can use this free application: http://vsprojectconverter.codeplex.com/ or download and use Visual Studio 2013 Express which is freely available from Microsoft from here: http://www.visualstudio.com/downloads/download-visual-studio-vs.