在服务器开始监听之前打开“System.Net.WebSockets”连接

要在服务器开始监听之前打开"System.Net.WebSockets"连接，你可以使用以下代码示例：

using System;
using System.Net;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;

public static class WebSocketServer
{
    private static HttpListener _listener;

    public static async Task StartListening(string url)
    {
        _listener = new HttpListener();
        _listener.Prefixes.Add(url);
        _listener.Start();

        while (true)
        {
            var context = await _listener.GetContextAsync();
            if (context.Request.IsWebSocketRequest)
            {
                HandleWebSocketRequest(context);
            }
            else
            {
                context.Response.StatusCode = 400;
                context.Response.Close();
            }
        }
    }

    private static async void HandleWebSocketRequest(HttpListenerContext context)
    {
        var wsContext = await context.AcceptWebSocketAsync(null);
        var socket = wsContext.WebSocket;

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

        while (!result.CloseStatus.HasValue)
        {
            var message = $"{DateTime.Now}: {System.Text.Encoding.UTF8.GetString(buffer)}";
            buffer = new byte[1024];
            result = await socket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
        }

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

    public static async Task StopListening()
    {
        if (_listener != null && _listener.IsListening)
        {
            _listener.Stop();
            _listener.Close();
        }
    }
}

public static class Program
{
    public static async Task Main(string[] args)
    {
        string url = "http://localhost:8080/";

        try
        {
            await WebSocketServer.StartListening(url);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex.Message}");
        }
        finally
        {
            await WebSocketServer.StopListening();
        }
    }
}

上述代码实现了一个简单的WebSocket服务器，它监听指定的URL（例如http://localhost:8080/），并在接收到WebSocket请求时处理连接。你可以根据自己的需求进行修改和扩展。