WebSocket Unidirectional Push Fails After Several Messages

[0use-TE]

Hello, I encountered an issue while using the nanoFramework WebSocket library. Every time the client sends about 5 requests, an error occurs.

Development Environment:

• Visual Studio 2022
• Windows 10 x64
• ESP32_REV3

Reproduction Steps:

Since the code is a bit long, you can check out the repository here:
[loTCar/Src/loTCar/LowerComputer at main · 0use-TE/loTCar](https://github.com/0use-TE/loTCar/tree/main/Src/loTCar/LowerComputer)

The program sets up a hosted server.
Here I registered the motor service and started a Web server, which checks prefixes and request headers to convert HTTP requests to WebSocket.

The key part below is where the exception occurs:

Next, I begin debugging.

Everything works fine at first:

Then I use Postman to send data:

    ++++ Exception System.ObjectDisposedException - 0x00000000 (9) ++++
    ++++ Message: 
    ++++ System.Net.Sockets.NetworkStream::Read [IP: 0009] ++++
    ++++ System.Net.WebSockets.WebSocketReceiver::ReadFixedSizeBuffer [IP: 0013] ++++
    ++++ System.Net.WebSockets.WebSocketReceiver::StartReceivingMessage [IP: 0007] ++++
    ++++ System.Net.WebSockets.ReceiveAndControllThread::WorkerThread [IP: 0026] ++++
Unhandled exception of type 'System.ObjectDisposedException' occurred in System.Net.dll

Stack Trace:

I've been debugging this for quite a while but still haven't found the cause.
Please help me!

[Ellerbach]

is it always failing after a specific number of calls?

If yes, most likely something that needs to be disposed and is not disposed.

[0use-TE]

Yes, about five or seven times. I think it's because of this problem, but I haven't solved it after looking for it for a long time😞

…

---Original--- From: "Laurent ***@***.***> Date: Tue, Jun 3, 2025 23:18 PM To: ***@***.***>; Cc: ***@***.******@***.***>; Subject: Re: [nanoframework/Home] WebSocket Unidirectional Push Fails AfterSeveral Messages (Discussion #1643) is it always failing after a specific number of calls? If yes, most likely something that needs to be disposed and is not disposed. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.Message ID: ***@***.***>

[RelaxSpirit]

A web socket assumes a permanent connection with a client established according to certain rules. Tell us in more detail, how do you establish a connection in postman? I strongly suspect that the connection closes very quickly from the client side or the web socket server cannot process the connection request correctly.

[0use-TE]

Thank you for your reply!

First,create a websocket request as follows.
second,input the websocket address and click the connect.
After that, it showed that the connection was successful. Then I filled in the data into Message. After that, I only clicked the Send button. Whether it was clicked slowly or quickly, this problem would occur after 5 to 7 clicks.

I'm sorry, but I'm unable to take screenshots of the response after a successful connection for the time being(The hardware is not at hand.)

[RelaxSpirit]

@0use-TE Please show the headers tab on the request submission screen.
There is also a suspicion that each postman request goes as a new connection, and the server closes the connection when the MaxClients parameter is exhausted.

• It seems that there is a small problem in the System.Net.WebSockets library in the Add method of the WebSocketClientsPool class :)

 public WebSocketClientsPool(int maxClients)
        {
            _webSocketClients = new Hashtable(maxClients);
            Max = maxClients;
        }


        public bool Add(WebSocketServerClient webSocket)
        {
            if (Count < Max) ///<------????
            {
                lock (_poolLock)
                {
                    _webSocketClients.Add(webSocket.RemoteEndPoint.ToString(), webSocket);
                }
                return true;
            }
            else
            {
                return false;
            }
        }

Try increasing the MaxClients to 3 in your code and retest.

AddWebSocketService(new WebSocketServerOptions
        {
            IsStandAlone = false,
            Port = 80,
            MaxClients = 3, //// <----!!!!!
		});

And count the number of times you will be able to send a new request. If the number increases before the error, it means that the postman creates new connections for some reason.

[0use-TE]

QQ202564-13214.mp4

Hi,Please look this vedio!

[0use-TE]

@RelaxSpirit
Hi,Do you need me to take a screenshot of this?If so,I will probably be able to provide it in about eight hours

Is there anything wrong with the source code? I can't spot the problem. Please point out where the problem lies

I don't think a new connection has been established. Every time a new connection is established, "connected" is printed here, but it doesn't print each time there is a concurrent connection. Moreover, I remember that I have tried to modify maxClients to 10, but it's still this problem.

To prevent it from being my operational problem, I will record the entire process later

[RelaxSpirit]

@0use-TE
You have started two listeners on port 80.

AddWebServerService(80, HttpProtocol.Http)
......
 AddWebSocketService(new WebSocketServerOptions
        {
            IsStandAlone = false,
            Port = 80,
            MaxClients = 2,
		});
.................

 _webSocketService.Start();
_webServerDIService.Start();
.................

And accordingly, web socket clients are added from different streams twice. From your code

Debug.WriteLine("connected");
var _wsServer = (WebSocketService)_serviceProvider.GetService(typeof(WebSocketService));
//Upgrade to a websocket
_wsServer.AddWebSocket(e.Context);

And directly from the code of the library itself:

private void ListenIncommingSocketRequest() 
        { 
            _httpListener.Start();

            while (Started)
            {
                HttpListenerContext context = _httpListener.GetContext();
                if (context == null) return;

                new Thread(() =>
                {
                    try
                    {
                        if (context.Request.RawUrl == Prefix)
                        {
                            if (!AddWebSocket(context)) 
                            {

                            }
                        }
.......................................
                    }
                }).Start();
            }
        }

And from different threads.
Try changing one port from 80 to another and retest it.

*Although I missed that you have IsStandAlone = false, which means that the second listener should not be started.

Or maybe it's just that Postman doesn't respond to pings? Therefore, the connection via KeepAliveInterval is closed by the server.

*And please excuse me if I can't express myself very clearly, English is not my native language and I know it very poorly :)

[0use-TE]

Yes, the second listener should not have been activated.
I'm having a class. After class, I'll try the following
Replace the WebSocket client
2. Change the port
3. Use independent mode
4. A minimum test to rule out other causes

Haha, it's okay. I can understand the English you speak (to be precise, the translator). My English is also very poor. I usually use the translator

[0use-TE]

I tried using the independent mode and changing the port, but the problem still occurred. It seems that it's not the problem of this part

[0use-TE]

I have tried several WebSocket clients on the web side, but it seems that this is not the problem

[0use-TE]

`using nanoFramework.Networking;
using System;
using System.Diagnostics;
using System.Net;
using System.Net.WebSockets.Server;
using System.Text;
using System.Threading;

namespace MiniWebSocketServer
{
public class Program
{
public static void Main()
{
var result= WifiNetworkHelper.ConnectDhcp("ouse","80231314w",requiresDateTime:true);
if(result)
{
Console.WriteLine("Connect to wifi");
var ip= IPAddress.GetDefaultLocalAddress();
Console.WriteLine(ip.ToString());
WebSocketServer webSocketServer = new WebSocketServer(new WebSocketServerOptions
{
IsStandAlone = true,
Port=80,
MaxClients=10
});
webSocketServer.MessageReceived += WebSocketServer_MessageReceived;
webSocketServer.Start();
Thread.Sleep(Timeout.InfiniteTimeSpan);
}
else
{
Console.WriteLine("Connect failed");
}

    }

	private static void WebSocketServer_MessageReceived(object sender, System.Net.WebSockets.MessageReceivedEventArgs e)
	{
        var buffer = e.Frame.Buffer;
		Console.WriteLine($"recive {Encoding.UTF8.GetString(buffer,0,buffer.Length)}");
	}
}

}
`
The minimum version works properly. It seems to be a problem with the code. I'll look for it

[RelaxSpirit]

For good measure, in the code of the WebSocketClientsPool class need another check.

Something like that:

public int Count 
{ 
    get 
    {
         lock(lock (_poolLock)
         {
             return _webSocketClients.Count; 
         }
     }
}
....................................
public bool Add(WebSocketServerClient webSocket)
        {
            if (_webSocketClients.Count < Max)
            {
                lock (_poolLock)
                {
                     if(_webSocketClients.Count < Max)
                     {
                         _webSocketClients.Add(webSocket.RemoteEndPoint.ToString(), webSocket);
                    }
                    else
                    {
                          return false;
                    }
                }
                return true;
            }
            else
            {
                return false;
            }
        }
.........................................

In this case, customers exceeding the limit should receive an error.

[0use-TE]

this is right！

but now,But at present, it should not cause this current error.