在C#中實現WebSocket接口后端的話，可以使用ASP.NET Core中的WebSocket類庫來實現。以下是一個簡單的示例代碼：

using System;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;

public class WebSocketHandler
{
    private readonly WebSocket _socket;

    public WebSocketHandler(WebSocket socket)
    {
        _socket = socket;
    }

    public async Task HandleWebSocketRequest(HttpContext context)
    {
        var buffer = new byte[1024];
        WebSocketReceiveResult result = await _socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);

        while (!result.CloseStatus.HasValue)
        {
            // 處理接收到的數據
            string message = System.Text.Encoding.UTF8.GetString(buffer);
            Console.WriteLine($"Received message: {message}");

            // 發送響應數據
            string responseMessage = "Hello from server!";
            byte[] responseBuffer = System.Text.Encoding.UTF8.GetBytes(responseMessage);
            await _socket.SendAsync(new ArraySegment<byte>(responseBuffer), WebSocketMessageType.Text, true, CancellationToken.None);

            result = await _socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
        }

        await _socket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
    }
}

在你的ASP.NET Core應用程序中，可以通過一個中間件來處理WebSocket請求：

app.UseWebSockets();
app.Use(async (context, next) =>
{
    if (context.WebSockets.IsWebSocketRequest)
    {
        WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();
        var handler = new WebSocketHandler(webSocket);
        await handler.HandleWebSocketRequest(context);
    }
    else
    {
        await next();
    }
});

在這個示例中，我們創建了一個WebSocketHandler類來處理WebSocket連接，并在中間件中進行處理。當接收到WebSocket請求時，會創建一個新的WebSocketHandler實例，并調用HandleWebSocketRequest方法來處理WebSocket消息。

希望這個簡單示例可以幫助你在C#中實現WebSocket接口后端。