[Bug Report] selecting MQTT as DeviceClient transport type causes WPF app to hangs on close?

[ZmorzynskiK]

Context

• OS, version, SKU and CPU architecture used: Windows 10 Desktop x64
• Application's .NET Target Framework : net5 + WPF
• Device: Laptop
• SDK version used: 1.38.0

Description of the issue

I've stumbled upon a strange issue when creating and using DeviceClient.Create in WPF app with Transport.Mqtt.
I'm sending a message to IoT Hub and when closing the main window, the application just hangs and never terminates.
When I select TransportType.Amqp this hang does not occur and the application terminates correctly.

Code sample exhibiting the issue

Create a simple WPF application, add two buttons in XAML:

<Window x:Class="AzIoTDev.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:AzIoTDev"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <StackPanel Orientation="Horizontal" VerticalAlignment="Top">
        <Button Content="Send data MQTT" Click="Button_Click"/>
        <Button Content="Send data AMQP" Click="Button_Click_1" />
    </StackPanel>
</Window>

then in codebehind set this code (set your own credentials for device):

public partial class MainWindow : Window
	{
		public MainWindow()
		{
			InitializeComponent();
		}

		private const string DeviceId = "IoT hub device ID";
		private const string AuthKey = "IoT hub auth key for device";
		private const string ServerUrl = "IoT hub URL";
		private const int OperationTimeoutMs = 1000;

		private DeviceClient _azureClient;

		private async Task sendHello(TransportType tt)
		{
			var auth = new DeviceAuthenticationWithRegistrySymmetricKey(DeviceId, AuthKey);
			_azureClient = DeviceClient.Create(ServerUrl, auth, tt);
			_azureClient.OperationTimeoutInMilliseconds = OperationTimeoutMs;
			
			byte[] bytes = Encoding.UTF8.GetBytes("HelloPayload");
			Message eventMessage = new Message(bytes);
			eventMessage.Properties.Add("MessageType", "Hello");
			await _azureClient.SendEventAsync(eventMessage).ConfigureAwait(false);

			await _azureClient.CloseAsync().ConfigureAwait(false);
			_azureClient.Dispose();
		}

		private async void Button_Click(object sender, RoutedEventArgs e)
		{
			await sendHello(TransportType.Mqtt);
		}

		private async void Button_Click_1(object sender, RoutedEventArgs e)
		{
			await sendHello(TransportType.Amqp);
		}
	}

You will see that clicking "Send with MQTT" will hang the app when closing and "Send with AQMP" will not hang when closing.
Is there an issue or am I doing something wrong?

all the best
Krzysztof

[jamdavi]

Thanks for the repro code I will take a look.

[jamdavi]

@ZmorzynskiK Just wanted to keep an update here. The PR above does fix the issue, I just need to make sure that this implementation passes all our our tests which have had some issues the past few weeks. Once all is passing I'll update the thread.

[ZmorzynskiK]

@jamdavi great, thanks for the update.

[BillArmstrong]

@jamdavi I see that the PR is still being worked on. The original bug report indicates that the issue occurs in a WPF app. We're experiencing the same hanging issue with a simple Console application that just opens a connection and closes it again. It would be great if this could be resolved soon.

[jamdavi]

Just an update for all who might be looking at this. We tracked the issue down to a change with DotNetty. The following PR has been merged and we will take a new version of DotNetty to fix.

Azure/DotNetty#570

[jamdavi]

We had been waiting on a release from the Netty team and discussed internally the best way to handle the update. The Netty team created a new version of the Common library and we are now taking a dependency on this new version of the library.

This is not required once we release the new SDK but if you want to test this out you can also take a dependency on the latest version of DotNetty.Common and it should replace the assembly at build time.

Note, if you're targeting .NET Full framework such as net472 you'll have to use a binding redirect in your app.config. Visual Studio has an option to generate one automatically.

[jamdavi]

This is now fixed with version 1.40.0 [https://github.com/Azure/azure-iot-sdk-csharp/releases/tag/2022_01_26].