crash during discovery

[ispysoftware]

Hey @vmartos thanks for your library! I'm getting an exception on using Discover

try
            {
                var onvifDiscovery = new OnvifDiscovery.Discovery();
                var devices = (await onvifDiscovery.Discover(5)).ToList();
                lock (_lock)
                {
                    _discoveredDevices = devices;
                }
            }
            catch(Exception ex)
            {
                Logger.LogException(ex, "ONVIF Discovery");
            }           

• it's always throwing an exception after the timeout finishes with "An existing connection was forcibly closed by the remote host".

_discoveredDevices is never populated. This is a net standard 2.0 project.

Stack trace:

" at System.Net.Sockets.Socket.DoBeginReceiveFrom(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, EndPoint endPointSnapshot, SocketAddress socketAddress, OverlappedAsyncResult asyncResult)
at System.Net.Sockets.Socket.BeginReceiveFrom(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags, EndPoint& remoteEP, AsyncCallback callback, Object state)
at System.Net.Sockets.UdpClient.BeginReceive(AsyncCallback requestCallback, Object state)
at System.Threading.Tasks.TaskFactory1.FromAsyncImpl(Func3 beginMethod, Func2 endFunction, Action1 endAction, Object state, TaskCreationOptions creationOptions)
at System.Net.Sockets.UdpClient.ReceiveAsync()
at OnvifDiscovery.Client.OnvifUdpClient.d__3.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at OnvifDiscovery.Common.ExtensionMethods.d__01.MoveNext() at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at OnvifDiscovery.Common.ExtensionMethods.<WithCancellation>d__01.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at OnvifDiscovery.Discovery.d__4.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at OnvifDiscovery.Discovery.d__3.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at CoreLogic.Onvif.Discovery.d__6.MoveNext() in D:\Projects\agent-service\CoreLogic2\Onvif\Discovery.cs:line 51"

[ispysoftware]

... needed to add

catch(Exception ex) {
// Other exception
}

to line 91 of Discovery.cs

[vicmaeg]

Hello @ispysoftware, Thanks for reporting the issue. Can I know in which OS and target runtime is running the .netstandard library? I could not reproduce it. Did you reproduce it constantly? or some of the times? just to know if some sort of a race condition between the udpClient.Close() and udpClient.ReceiveAsync(). Also I need the Exception Type is it a ObjectDisposedException or SocketException

You need to add the following to make it working?

} finally {
  try {
    client.Close ();
  } catch {
    // socket close failed
  }
}

or the following?

} catch (OperationCanceledException) {
// Either the user canceled the action or the timeout has fired
} catch (Exception) {
// ReceiveAsync failed
} finally {
  client.Close ();
}

But yeah this can happen because UdpClient.ReceiveAsync does not have a CancellationToken, so what I do is the following:

                /// <summary>
		/// Used to provide cancellation possibility to any Async Methods returning a Task
		/// </summary>
		internal static async Task<T> WithCancellation<T> (this Task<T> task, CancellationToken cancellationToken)
		{
			var tcs = new TaskCompletionSource<bool> ();
			using (cancellationToken.Register (s => ((TaskCompletionSource<bool>)s).TrySetResult (true), tcs)) {
				if (task != await Task.WhenAny (task, tcs.Task)) {
					throw new OperationCanceledException (cancellationToken);
				}
			}
			return await task;
		}

This just returns when the initial task (ReceiveAsync) finishes or the cancellationToken is cancelled, but in fact the ReceiveAsync is still executing...

I will investigate if there is a better solution to manage the cancellation of the opened Udp socket.

[ispysoftware]

it was working for ages but then one of my cameras started malfunctioning and closing the request which triggered the exception in the library so reproducing it is hard unless you build a virtual client that just closes the response. Until I rebooted the camera it was happening on every run of the discovery code.

Running on Windows 10, .Net Framework 4.7

adding the catch-all case after OperationCanceledException "fixed" it.