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TCP Server

4 min read

Step-by-Step Guide: Creating a TCP Server in C#

This guide will walk you through creating a basic TCP server in C#. I’ll explain each step clearly for someone with some programming knowledge.

What is a TCP Server?

A TCP server is a program that listens for incoming connections from clients and can exchange data with them over a network using the TCP protocol (reliable, ordered communication).

Step 1: Set Up Your Project

  1. Open Visual Studio (or your preferred C# IDE)

  2. Create a new Console Application project

  3. Name it “TCPServer” or something similar

Step 2: Add Required Namespace

At the top of your Program.cs file, add:

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using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

These give us access to networking functionality.

Step 3: Create the TCP Listener

In your Main method, add this code:

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// Define the port you want to use
int port = 8080;
 
// Create a TcpListener that will listen on any IP address
TcpListener server = new TcpListener(IPAddress.Any, port);

  • **port**: Choose a port number (1024-49151 are good for custom apps)

  • **IPAddress.Any**: Means the server will listen on all network interfaces

Step 4: Start the Server

Add these lines to start listening:

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// Start the server
server.Start();
Console.WriteLine("Server started on port " + port);
Console.WriteLine("Waiting for connections...");

Step 5: Accept Client Connections

Now we’ll wait for a client to connect:

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// Accept a client connection (this blocks until a client connects)
TcpClient client = server.AcceptTcpClient();
Console.WriteLine("Client connected!");

Step 6: Set Up Streams for Communication

We’ll use NetworkStream to send/receive data:

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// Get a stream object for reading and writing
NetworkStream stream = client.GetStream();

Step 7: Communicate with the Client

Let’s add simple send/receive logic:

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// Buffer for reading data
byte[] buffer = new byte[1024];
int bytesRead;
 
// Loop to receive all the data sent by the client
while ((bytesRead = stream.Read(buffer, 0, buffer.Length)) != 0)
{
    // Convert the data to a string and display it
    string data = Encoding.ASCII.GetString(buffer, 0, bytesRead);
    Console.WriteLine("Received: " + data);
 
    // Send back a response
    string response = "Server received: " + data;
    byte[] msg = Encoding.ASCII.GetBytes(response);
    stream.Write(msg, 0, msg.Length);
    Console.WriteLine("Sent: " + response);
}

Step 8: Clean Up

After communication is done:

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// Shutdown and close connection
client.Close();
Console.WriteLine("Client disconnected.");

Step 9: Complete Example

Here’s the complete code:

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using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
 
class Program
{
    static void Main(string[] args)
    {
        int port = 8080;
 
        // Create TCP listener
        TcpListener server = new TcpListener(IPAddress.Any, port);
 
        try
        {
            // Start the server
            server.Start();
            Console.WriteLine("Server started on port " + port);
            Console.WriteLine("Waiting for connections...");
 
            // Enter the listening loop
            while (true)
            {
                // Accept a client connection
                TcpClient client = server.AcceptTcpClient();
                Console.WriteLine("Client connected!");
 
                // Get a stream object for reading and writing
                NetworkStream stream = client.GetStream();
 
                // Buffer for reading data
                byte[] buffer = new byte[1024];
                int bytesRead;
 
                // Loop to receive all the data sent by the client
                while ((bytesRead = stream.Read(buffer, 0, buffer.Length)) != 0)
                {
                    // Convert the data to a string and display it
                    string data = Encoding.ASCII.GetString(buffer, 0, bytesRead);
                    Console.WriteLine("Received: " + data);
 
                    // Send back a response
                    string response = "Server received: " + data;
                    byte[] msg = Encoding.ASCII.GetBytes(response);
                    stream.Write(msg, 0, msg.Length);
                    Console.WriteLine("Sent: " + response);
                }
 
                // Shutdown and close connection
                client.Close();
                Console.WriteLine("Client disconnected.");
            }
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception: " + e.Message);
        }
        finally
        {
            // Stop listening for new clients
            server.Stop();
        }
    }
}

How to Test Your Server

  1. Run this program in Visual Studio

  2. Open a command prompt and use telnet to connect:CopyDownload

    telnet localhost 8080

    (If telnet isn’t installed, you can enable it in Windows Features)

  3. Type messages in the telnet window - they should appear in your server console

  4. The server will echo back each message with “Server received: ” prefix

Important Notes

  1. This is a basic single-client server. For multiple clients, you’d need to use threads or async methods.

  2. The server will keep running until you stop it (Ctrl+C in console)

  3. In a real application, you’d want better error handling and logging

Would you like me to explain any part in more detail or show you how to extend this basic example?

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