Two-way Server and Client sockets using C#

Server socket is implemented as a Console Application. It uses a dictionary object to store conversion rates to simplify the process. The client is a windows application that creates a client socket, which connects to server.

The focus of this example is to show how two-way communication between client and server sockets takes place.

Creating Server Socket - CurrencyServer

1. Create a new project using File->New Project.
2. Select Visual C# as the language and select Console Application as the project type. Enter CurrencyServer as the name of the project.
3. Enter the following code in Program.cs.

   using System;
   using System.Collections.Generic;
   using System.Text;
   using System.Net.Sockets;
   
   namespace CurrencyServer
   {
       class Program
       {
           public static void Main()
           {
               Dictionary rates = new Dictionary(); 
               // put some sample data into dictionary object. Values are not accurate and important
               rates.Add("usd", 47.5); 
               rates.Add("eur", 60.4);
               rates.Add("ukp", 78.8);
   
               // create a server socket with port number 2000
               TcpListener l = new TcpListener(2000);
               l.Start();  // start listening for client requests
               Console.WriteLine("Server has started.Waiting for clients...");
               while (true)
               {
                   TcpClient c = l.AcceptTcpClient();  // wait and accept client request
                   Console.WriteLine("Opened connection with client..");
                   NetworkStream ns = c.GetStream(); // get stream to send and receive data
                   byte[] buf;
                   while (true)
                   {
                       buf = new byte[10];
                       ns.Read(buf, 0, 10); // read symbol from client
                       // convert bytes to string
                       string symbol = System.Text.Encoding.ASCII.GetString(buf);
                       symbol = symbol.Substring(0, 3); // take only first 3 characters
                       
                       if (symbol == "end") break;  // stop if symbol is "end"
                       
                       // find out the corresponding rate
                       byte[] result;
                       try
                       {
                           double value = rates[symbol];
                           result = System.Text.Encoding.ASCII.GetBytes(value.ToString());
                       }
                       catch (Exception ex)
                       {
                           result = System.Text.Encoding.ASCII.GetBytes("Invalid");
                           Console.WriteLine(ex);
                       }
                       ns.Write(result, 0, result.Length); // write rate or error message to client
                   }
                   // close connection
                   ns.Close();  
                   c.Close();
                   Console.WriteLine("Closed connection with client..");
               }
           }
       }
   }
   
   

Run Server Socket

1. Build the project using Build->Build Solution.
2. Go to Command line.
3. Go to project folder for CurrencyServer project.
4. Run CurrencyServer.exe, which is in bin\debug folder inside the project folder.

Creating Client Socket - CurrencyClient

1. Create a new project using File->New Project.
2. Select Visual C# and Windows Forms Application.
3. Enter application name as CurrencyClient.
4. Place the controls (as shown in the form below) on the form and change the required properties. For Combobox use Items property to enter currency symbols that we used in CurrencyServer.

   

   Write the following code to connect to server in the constructor and code for click events of buttons.

   using System;
   using System.Collections.Generic;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Text;
   using System.Windows.Forms;
   using System.Net.Sockets;
   
   namespace CurrencyClient
   {
       public partial class Form1 : Form
       {
           TcpClient c = null;
           NetworkStream ns;
   
           public CurrencyClient()
           {
               InitializeComponent();
               
               // get connection to server
               c = new TcpClient("localhost", 2000);
               ns = c.GetStream();
           }
   
           private void button1_Click(object sender, EventArgs e)
           {
               string symbol = ddlSymbols.SelectedItem.ToString();  // get selected symbol from combo box
               byte[] buf = System.Text.Encoding.ASCII.GetBytes(symbol);
               ns.Write(buf, 0, symbol.Length); // send symbol to server
               
               byte[] rate = new byte[100];
               ns.Read(rate, 0, 100);  // read data from server 
               
               lblRate.Text =  System.Text.Encoding.ASCII.GetString(rate);  // place rate or error message into Label
           }
   
           private void button2_Click(object sender, EventArgs e)
           {
               // send "end" to server so that connection to client is closed
               byte[] buf = System.Text.Encoding.ASCII.GetBytes("end"); 
               ns.Write(buf, 0, 3);
               this.Dispose(); // close form and application
           }
       }
   }
   
   

   Run the client application using F5 from Visual Studio. Select a symbol from drop down list and click on Get Rate button. Once done, click on Exit button to close client and connect to server.