I’ve managed to write a csharp websocket server and clients can connect, however the clients send a ping message but the server doesnt respond with a pong so the client drops the connection.

On further investigation, it turns out I need to have a ReadAsync running to capture the ping message, but then it’s in an await state so blocks everything!

I would love to get to the underlying socket so I could do a socket.available to check for read data but thats not possible.

So how are you supposed to write a websocket server in c# (and dont say SignalR!) that responds to a ping and can determine if the client has dropped!

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

class Program
{
    static async Task ClientHandler(HttpContext context)
    {
        using WebSocket socket = await context.WebSockets.AcceptWebSocketAsync();
        Console.WriteLine("Websocket client connected from {0}", socket.SubProtocol);

        var buffer = new byte[1024 * 4];
        WebSocketReceiveResult payload = await socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);

        string? message = Encoding.UTF8.GetString(buffer);
        Console.WriteLine("Received {0}", message);

        // workaround for replying to ping from client which requires ReceiveAsync to be active
        // Task.Run(async () =>
        // {
        //     await socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
        // });

        while (socket.State == WebSocketState.Open)
        {
            Console.WriteLine("Sending message...");
            byte[] msg = System.Text.Encoding.Default.GetBytes("Hello, World!");
            await socket.SendAsync(new ArraySegment<byte>(msg, 0, msg.Length), payload.MessageType, true, CancellationToken.None);

            Thread.Sleep(200);
        }

        await socket.CloseAsync(WebSocketCloseStatus.NormalClosure, "No more messages", CancellationToken.None);
        Console.WriteLine("Connection closed");
    }

    static void Main()
    {
        var app = WebApplication.CreateBuilder().Build();

        app.UseWebSockets();

        app.Use(async (context, next) =>
        {
            if (context.Request.Path == "/")
                if (context.WebSockets.IsWebSocketRequest)
                    await ClientHandler(context);
                else
                    context.Response.StatusCode = StatusCodes.Status400BadRequest;
            else
                await next(context);
        });

        app.Run("http://127.0.0.1:8001");
    }
}