How do I set up a C# websocket server?

2 years ago
Olivia Parker
2 minutes

The method of building a WebSocket server in C# is achieved by using the WebSocket class and related namespaces.

Here is a simple example:

  1. Firstly, make sure your project references the System.Net.WebSockets namespace.
  2. Create a class for a WebSocket server and initialize a WebSocket object within it. For example:
using System;
using System.Net;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;

public class MyWebSocketServer
{
    private HttpListener _httpListener;
    private CancellationTokenSource _cts;

    public MyWebSocketServer(string url)
    {
        _httpListener = new HttpListener();
        _httpListener.Prefixes.Add(url);
        _cts = new CancellationTokenSource();
    }

    public async Task Start()
    {
        _httpListener.Start();
        Console.WriteLine("WebSocket server started.");

        while (!_cts.Token.IsCancellationRequested)
        {
            HttpListenerContext context = await _httpListener.GetContextAsync();
            if (context.Request.IsWebSocketRequest)
            {
                ProcessWebSocketRequest(context);
            }
            else
            {
                // Handle non-WebSocket request
                context.Response.StatusCode = 400;
                context.Response.Close();
            }
        }
    }

    private async void ProcessWebSocketRequest(HttpListenerContext context)
    {
        HttpListenerWebSocketContext webSocketContext = null;

        try
        {
            webSocketContext = await context.AcceptWebSocketAsync(subProtocol: null);
            Console.WriteLine("WebSocket connection established.");

            await HandleWebSocketConnection(webSocketContext.WebSocket);
        }
        catch (Exception ex)
        {
            Console.WriteLine("WebSocket connection failed: " + ex.Message);
            if (webSocketContext != null)
            {
                webSocketContext.WebSocket.CloseAsync(WebSocketCloseStatus.InternalServerError, "Internal Server Error", CancellationToken.None);
            }
        }
    }

    private async Task HandleWebSocketConnection(WebSocket webSocket)
    {
        byte[] buffer = new byte[1024];
        WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);

        while (!result.CloseStatus.HasValue)
        {
            // Handle received data
            string receivedMessage = System.Text.Encoding.UTF8.GetString(buffer, 0, result.Count);
            Console.WriteLine("Received: " + receivedMessage);

            // Echo the received message back to the client
            await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), WebSocketMessageType.Text, true, CancellationToken.None);

            // Get next message
            result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
        }

        await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
        Console.WriteLine("WebSocket connection closed.");
    }

    public void Stop()
    {
        _cts.Cancel();
        _httpListener.Stop();
        _httpListener.Close();
    }
}
  1. Create an instance of MyWebSocketServer at the entry point of the program and start the server. For example:
class Program
{
    static async Task Main(string[] args)
    {
        string url = "http://localhost:8080/";
        MyWebSocketServer server = new MyWebSocketServer(url);
        await server.Start();

        Console.WriteLine("Press any key to stop the server.");
        Console.ReadKey();

        server.Stop();
    }
}

The code above sets up a basic WebSocket server, which listens on a specified URL, and handles incoming WebSocket connections and messages. Feel free to customize and expand it according to your needs.

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