MqttConnectingFailedException: Error while authenticating. Received packet 'PubAck: [PacketIdentifier=21584] [ReasonCode=Success]' at an unexpected time.

[Huntk23]

Describe the bug

I am trying to setup a broker/server instance in a .NET 6 minimal Web API project and then connect to it using a BackgroundService for testing. When trying to use mqttClient.ConnectAsync I receive an error while authenticating message when I did not setup any kind of authentication.

I've spent hours going through documentation and countless examples. I know 4.0 is new with a lot of changes.. Am I somehow missing something?

Which component is your bug related to?

• MqttClient

To Reproduce

Steps to reproduce the behavior:

1. Using this version of MQTTnet 4.0.0-preview5
2. Run the code below in a new Program.cs .NET 6.0 minimal Web API project.

Expected behavior

I expected the client to connect.

Screenshots

N/A

Additional context / logging

MQTTnet.Adapter.MqttConnectingFailedException: Error while authenticating. Received packet 'PubAck: [PacketIdentifier=21584] [ReasonCode=Success]' at an unexpected time.
 ---> MQTTnet.Exceptions.MqttProtocolViolationException: Received packet 'PubAck: [PacketIdentifier=21584] [ReasonCode=Success]' at an unexpected time.
   at MQTTnet.Client.MqttClient.TryProcessReceivedPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
   at MQTTnet.PacketDispatcher.MqttPacketAwaitable`1.WaitOneAsync(TimeSpan timeout)
   at MQTTnet.Client.MqttClient.SendAndReceiveAsync[TResponsePacket](MqttBasePacket requestPacket, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.AuthenticateAsync(MqttClientOptions options, CancellationToken cancellationToken)
   --- End of inner exception stack trace ---
   at MQTTnet.Client.MqttClient.AuthenticateAsync(MqttClientOptions options, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.ConnectAsync(MqttClientOptions options, CancellationToken cancellationToken)
   at MQTTnet.Client.MqttClient.ConnectAsync(MqttClientOptions options, CancellationToken cancellationToken)
   at Premier.MQTT.Broker.Worker.ExecuteAsync(CancellationToken stoppingToken) in C:\Development\Premier-MQTT\src\Premier.MQTT.Broker\Worker.cs:line 18
   at Microsoft.Extensions.Hosting.Internal.Host.TryExecuteBackgroundServiceAsync(BackgroundService backgroundService)

Code example

.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="MQTTnet" Version="4.0.0-preview5" />
    <PackageReference Include="MQTTnet.AspNetCore" Version="4.0.0-preview5" />
  </ItemGroup>

</Project>

Program.cs

using MQTTnet;
using MQTTnet.AspNetCore;
using MQTTnet.Client;
using MQTTnet.Server;

var builder = WebApplication.CreateBuilder(args);

builder.WebHost.UseKestrel(options => options.ListenAnyIP(1883));

// Add services to the container.
builder.Services.AddMqttServer();
builder.Services.AddConnections();

builder.Services.AddHostedService<Worker>();

var app = builder.Build();

// Configure the HTTP request pipeline.
app.UseRouting();

app.UseEndpoints(routeBuilder => { routeBuilder.MapMqtt("/mqtt"); });

app.UseMqttServer(server =>
{
    server.StartedAsync += args =>
    {
        _ = Task.Run(async () =>
        {
            var mqttApplicationMessage = new MqttApplicationMessageBuilder()
                .WithPayload("Test application message from MQTTnet server.")
                .WithTopic("message")
                .Build();

            while (true)
            {
                try
                {
                    await server.InjectApplicationMessage(new MqttInjectedApplicationMessage(mqttApplicationMessage)
                    {
                        SenderClientId = "server"
                    });
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                }
                finally
                {
                    await Task.Delay(TimeSpan.FromSeconds(5));
                }
            }
        });

        return Task.CompletedTask;
    };
});

app.Run();

public class Worker : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var options = new MqttClientOptionsBuilder()
            .WithClientId("TestClient")
            .WithTcpServer("127.0.0.1")
            .Build();

        var factory = new MqttFactory();
        var mqttClient = factory.CreateMqttClient();

        await mqttClient.ConnectAsync(options, CancellationToken.None);

        while (!stoppingToken.IsCancellationRequested)
        {
            await Task.Delay(5000);
        }
    }
}

[Huntk23]

Well! After going home and eating dinner and starring at the code a little longer. I realized I missed something:

builder.WebHost.UseKestrel(options => options.ListenAnyIP(1883));

Should be:

builder.WebHost.UseKestrel(options => options.ListenAnyIP(1883, listenOptions => listenOptions.UseMqtt()));

The error message threw me bad. I now have a very simple .NET 6 minimal Web API project hosting MQTTnet successfully. Thanks!

[SuperCatss]

Well! After going home and eating dinner and starring at the code a little longer. I realized I missed something:

builder.WebHost.UseKestrel(options => options.ListenAnyIP(1883));

Should be:

builder.WebHost.UseKestrel(options => options.ListenAnyIP(1883, listenOptions => listenOptions.UseMqtt()));

The error message threw me bad. I now have a very simple .NET 6 minimal Web API project hosting MQTTnet successfully. Thanks!

Hi Huntk, I would like to ask, will it work for WebSocket?

[Huntk23]

I don't use it but may attempt to turn it on at some point. I'm sure it works.

[SuperCatss]

I don't use it but may attempt to turn it on at some point. I'm sure it works.

It doesn't look like my code is much different from yours, but mine doesn't work for my websockets.
https://github.com/dotnet/MQTTnet/issues/1484

[Huntk23]

I just added

o.ListenAnyIP(5000);

and

app.UseEndpoints(
    endpoints =>
    {
        endpoints.MapConnectionHandler<MqttConnectionHandler>(
            "/mqtt",
            httpConnectionDispatcherOptions => httpConnectionDispatcherOptions.WebSockets.SubProtocolSelector =
                protocolList => protocolList.FirstOrDefault() ?? string.Empty);
    });

Seems I am able to connect to /mqtt over port 5000 now.