使用WebSocketSharp获取验证码Token时遇平台不支持及对象已释放异常

我尝试从Habbo的验证码接口获取Token，用WebSocketSharp搭建本地WebSocket服务配合Tampermonkey脚本传输，但出现以下错误：

29/08/2022 22:00:05|Error|QueueUserWorkItemCallbackDefaultContext.Execute|Operation is not supported on this platform.
29/08/2022 22:00:06|Fatal|<>c__DisplayClass48_0.<ReadBytesAsync>b__0|System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'System.Net.Sockets.NetworkStream'.
at System.Net.Sockets.NetworkStream.<ThrowIfDisposed>g__ThrowObjectDisposedException|63_0()
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
at WebSocketSharp.Ext.<>c__DisplayClass48_0.<ReadBytesAsync>b__0(IAsyncResult ar)

Tampermonkey脚本代码：

// ==UserScript==
// @name         Captcha Service
// @namespace    mservice
// @version      1.0
// @description  no description
// @author       Moch
// @match        https://www.habbo.com.br/api/public/captcha*
// @grant        none
// ==/UserScript==

(function () {
    'use strict';

    var socket = new WebSocket("ws://127.0.0.1:8080");
    socket.onopen = () => {
        const urlParams = new URLSearchParams(window.location.search);
        if (urlParams.has("token") && urlParams.get("token") !== "") {
            socket.send(urlParams.get("token"));
        }
    }
})();

C#服务端代码：

using WebSocketSharp;
using WebSocketSharp.Server;
public class Laputa : WebSocketBehavior
{
    protected override void OnMessage(MessageEventArgs e)
    {
        Console.WriteLine(e.Data);
    }
}

static void Main(string[] args)
{
    var wssv = new WebSocketServer("ws://127.0.0.1:8080");

    wssv.AddWebSocketService<Laputa>("/");
    wssv.Start();
    Console.ReadKey(true);
    wssv.Stop();
}

已尝试切换至WebSocketSharp-netstandard和WebSocketSharkFork，错误依旧。

1. 平台兼容性问题 #

第一个错误Operation is not supported on this platform说明WebSocketSharp在当前运行的.NET平台上存在API兼容问题，比如旧版本对异步IO的处理和.NET Core/.NET 5+的网络栈不兼容。

解决办法：

• 改用.NET原生的System.Net.WebSockets实现，兼容性更好。示例服务端代码：

  using System;
  using System.Net;
  using System.Net.WebSockets;
  using System.Text;
  using System.Threading;
  using System.Threading.Tasks;
  
  class Program
  {
      static async Task Main(string[] args)
      {
          var listener = new HttpListener();
          listener.Prefixes.Add("http://127.0.0.1:8080/");
          listener.Start();
          Console.WriteLine("WebSocket服务已启动，等待连接...");
  
          while (true)
          {
              var context = await listener.GetContextAsync();
              if (context.Request.IsWebSocketRequest)
              {
                  var webSocketContext = await context.AcceptWebSocketAsync(null);
                  _ = HandleWebSocketConnection(webSocketContext.WebSocket);
              }
              else
              {
                  context.Response.StatusCode = 400;
                  context.Response.Close();
              }
          }
      }
  
      private static async Task HandleWebSocketConnection(WebSocket webSocket)
      {
          var buffer = new byte[1024 * 4];
          WebSocketReceiveResult result;
          try
          {
              do
              {
                  result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
                  var message = Encoding.UTF8.GetString(buffer, 0, result.Count);
                  Console.WriteLine("收到Token: " + message);
              } while (!result.CloseStatus.HasValue);
  
              await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
          }
          catch (Exception ex)
          {
              Console.WriteLine("连接异常: " + ex.Message);
              if (webSocket.State == WebSocketState.Open)
              {
                  await webSocket.CloseAsync(WebSocketCloseStatus.InternalServerError, "服务器异常", CancellationToken.None);
              }
          }
          finally
          {
              webSocket.Dispose();
          }
      }
  }
  

2. 连接过早关闭问题 #

第二个错误Cannot access a disposed object: System.Net.Sockets.NetworkStream通常是因为WebSocket连接在异步操作完成前就被释放了。原Tampermonkey脚本发送完Token后没有保持连接，浏览器可能主动关闭连接，导致服务端异步读取失败。

解决办法：

• 修改脚本，发送完Token后延迟关闭连接，或者添加错误/关闭事件处理：

  // ==UserScript==
  // @name         Captcha Service
  // @namespace    mservice
  // @version      1.0
  // @description  no description
  // @author       Moch
  // @match        https://www.habbo.com.br/api/public/captcha*
  // @grant        none
  // ==/UserScript==
  
  (function () {
      'use strict';
  
      var socket = new WebSocket("ws://127.0.0.1:8080");
      socket.onopen = () => {
          const urlParams = new URLSearchParams(window.location.search);
          if (urlParams.has("token") && urlParams.get("token") !== "") {
              socket.send(urlParams.get("token"));
              // 延迟1秒关闭，确保服务端接收完成
              setTimeout(() => socket.close(), 1000);
          }
      };
  
      socket.onerror = (error) => {
          console.error("WebSocket错误:", error);
      };
  
      socket.onclose = (event) => {
          console.log("连接关闭:", event.code, event.reason);
      };
  })();
  

3. 替代第三方库 #

如果坚持用第三方库，推荐使用Fleck，它是轻量且兼容性更好的WebSocket服务端库：

• 安装NuGet包：Install-Package Fleck
• 示例代码：

  using Fleck;
  
  class Program
  {
      static void Main(string[] args)
      {
          var server = new WebSocketServer("ws://127.0.0.1:8080");
          server.Start(socket =>
          {
              socket.OnOpen = () => Console.WriteLine("客户端已连接");
              socket.OnMessage = message => Console.WriteLine("收到Token: " + message);
              socket.OnClose = () => Console.WriteLine("客户端已断开");
              socket.OnError = error => Console.WriteLine("错误: " + error);
          });
  
          Console.ReadKey(true);
          server.Dispose();
      }
  }
  

内容的提问来源于stack exchange，提问作者PercivallAkihiko