WebSocket Libraries for C# (.NET): SignalR, Fleck, WebSocketSharp

WebSocket Libraries for C# (.NET): SignalR, Fleck, and WebSocketSharp

WebSocket is a full-duplex communication protocol over TCP, allowing the server and client to exchange data in real time without constant HTTP requests. In the C# (.NET) ecosystem, there are several libraries that simplify WebSocket integration. In this article, we will look at three of the most popular solutions: SignalR (official Microsoft library), Fleck (lightweight server), and WebSocketSharp (universal client-server).

1. SignalR — Official Tool from Microsoft

SignalR is a high-level library for ASP.NET Core that automatically selects the best transport (WebSocket, Server-Sent Events, Long Polling) depending on client capabilities. It is ideal for creating chats, dashboards, and games.

Key Features:

• Automatic transport switching.
• Groups and broadcast messaging.
• Scalability support (Redis, Azure SignalR Service).
• Integration with clients on JavaScript, .NET, Java.

Example Server Hub in C#:

using Microsoft.AspNetCore.SignalR;

public class ChatHub : Hub{    public async Task SendMessage(string user, string message)    {        // Broadcast the message to all connected clients        await Clients.All.SendAsync("ReceiveMessage", user, message);    }

    public override async Task OnConnectedAsync()    {        await Clients.Caller.SendAsync("Notify", "You have connected to the chat");        await base.OnConnectedAsync();    }}

Example Client in C# (Console):

using Microsoft.AspNetCore.SignalR.Client;

var connection = new HubConnectionBuilder()    .WithUrl("https://yourserver.com/chathub")    .Build();

connection.On<string, string>("ReceiveMessage", (user, message) =>{    Console.WriteLine($"{user}: {message}");});

await connection.StartAsync();await connection.InvokeAsync("SendMessage", "User1", "Hello!");

2. Fleck — Minimalistic WebSocket Server

Fleck is a lightweight library for creating WebSocket servers without dependencies on ASP.NET. It is ideal for simple applications where complex SignalR abstractions are not needed.

Features:

• Works on pure TCP (without HTTP).
• Supports SSL (WSS).
• No built-in scaling — only a single process.

Example Server with Fleck:

using Fleck;

var server = new WebSocketServer("ws://0.0.0.0:8181");var connections = new List<IWebSocketConnection>();

server.Start(socket =>{    socket.OnOpen = () =>    {        Console.WriteLine("Client connected");        connections.Add(socket);    };    socket.OnClose = () =>    {        Console.WriteLine("Client disconnected");        connections.Remove(socket);    };    socket.OnMessage = message =>    {        // Send message to all        foreach (var client in connections)        {            client.Send($"Echo: {message}");        }    };});

Console.WriteLine("Server started on ws://localhost:8181");Console.ReadLine();

3. WebSocketSharp — Universal Client and Server

WebSocketSharp is an open-source library that provides both client and server WebSocket functionality. It is independent of ASP.NET and works on .NET Framework and .NET Core.

Key Features:

• Support for SSL/TLS and proxies.
• Event-driven model (OnOpen, OnClose, OnMessage, OnError).
• Sending binary data (byte[]).

Example Client with WebSocketSharp:

using WebSocketSharp;

using (var ws = new WebSocket("wss://echo.websocket.org")){    ws.OnMessage += (sender, e) =>