How to use websockets in C# without libraries

Oct 2023
2 min

Let’s see how to use WebSockets in C# without using libraries, only with the standard code and functionalities available in .NET.

WebSockets are a technology that enables real-time bidirectional communication between a server and a client over a single TCP/IP channel.

Unlike HTTP requests, WebSockets maintain a persistent connection between the client and the server. This allows for faster and bidirectional communication.

C# provides native support for WebSockets through the System.Net.WebSockets namespace. Although it’s possible to use C#‘s native WebSockets, using them “raw” is a real pain.

But, in case someone needs it, here’s a code example. As an exercise to explain the operation, it’s not bad. If only to later appreciate the libraries we’ll see in upcoming posts (you have the links below).

Examples of Native WebSockets in .NET

Let’s see the necessary code to create a WebSocket communication in C# between a server and a client.

Server Example

This would be the server code.

using System.Net.WebSockets;
using System.Net;
using System.Text;

var httpListener = new HttpListener();
httpListener.Prefixes.Add("http://localhost:9006/");
httpListener.Start();

Console.WriteLine("Listening for WebSocket connections...");

while (true)
{
    var context = await httpListener.GetContextAsync();
    if (context.Request.IsWebSocketRequest)
    {
        var webSocketContext = await context.AcceptWebSocketAsync(subProtocol: null);
        var webSocket = webSocketContext.WebSocket;

        Console.WriteLine("Client connected");

        var receiveBuffer = new byte[1024];
        if (webSocket.State == WebSocketState.Open)
        {
            var receiveResult = await webSocket.ReceiveAsync(new ArraySegment<byte>(receiveBuffer), CancellationToken.None);
            if (receiveResult.MessageType == WebSocketMessageType.Text)
            {
                var receivedMessage = Encoding.UTF8.GetString(receiveBuffer, 0, receiveResult.Count);
                Console.WriteLine($"Received message: {receivedMessage}");

                var buffer = Encoding.UTF8.GetBytes($"Hello from server");
                await webSocket.SendAsync(new ArraySegment<byte>(buffer), WebSocketMessageType.Text, true, CancellationToken.None);
            }
            else if (receiveResult.MessageType == WebSocketMessageType.Close)
            {
                await webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, "", CancellationToken.None);
                Console.WriteLine("WebSocket closed.");
            }
        }
    }
    else
    {
        context.Response.StatusCode = 400;
        context.Response.Close();
    }
}

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Client Example

And this is the client code.

using System.Net.WebSockets;
using System.Text;

using var ws = new ClientWebSocket();

var uri = new Uri("ws://localhost:9006");
await ws.ConnectAsync(uri, CancellationToken.None);

Console.WriteLine("Connected");

var message = "Hello from client!";
var buffer = Encoding.UTF8.GetBytes(message);
await ws.SendAsync(new ArraySegment<byte>(buffer), WebSocketMessageType.Text, true, CancellationToken.None);

var receiveBuffer = new byte[1024];
var receiveResult = await ws.ReceiveAsync(new ArraySegment<byte>(receiveBuffer), CancellationToken.None);
var receivedMessage = Encoding.UTF8.GetString(receiveBuffer, 0, receiveResult.Count);

Console.WriteLine($"Received message: {receivedMessage}");

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As we can see, it’s a real pain to make a WebSocket by hand. Normally we would use some library. Here you have tutorials on the WebSocketSharp library and here tutorials on the WatsonWebsocket library to simplify the use of WebSockets in C#.