NullReferenceException experienced with Owin on Startup .Net Core 2.0 - Settings?

Question

I'm trying to start up a WebApp to use with NancyFx in a .NET Core 2.0 project.

The package i've added to the solution to do this is

Microsoft.AspNet.WebApi.OwinSelfHost

which installs it's dependencies:

Microsoft.AspNet.WebApi.Client

Microsoft.AspNet.WebApi.Core

Microsoft.AspNet.WebApi.Owin

Microsoft.Owin

Microsoft.Owin.Host.HttpListener

Microsoft.Owin.Hosting

Newtonsoft.Json

Owin

I've also added:

Nancy

Nancy.Owin

My project is of type "xUnit Test Project (.NET Core)".

Starting with my test class, we have:

public class MyIntegrationTests : IDisposable
{
    private readonly IDisposable _webApp;
    private const string Url = "http://localhost:1234";

    public MyIntegrationTests()
    {
        _webApp = WebApp.Start<Startup>(url: Url);
    }

My startup class looks like:

public class Startup
{
    public void Configuration(IAppBuilder appBuilder)
    {
        appBuilder.UseNancy();
    }
}

I also have a NancyModule with a test route:

public class TestModule : NancyModule
{
    public TestModule()
    {

        Get("/test", args => "test");
    }
}

However, when starting my Integration Tests module (by trying to run any test within it), i am met with a Null Reference Exception. This is the stack trace:

System.NullReferenceException : Object reference not set to an instance of an object.

at Microsoft.Owin.Hosting.Utilities.SettingsLoader.FromConfigImplementation..ctor()

at Microsoft.Owin.Hosting.Utilities.SettingsLoader.b__0() at System.Threading.LazyInitializer.EnsureInitializedCore[T](T& target, Func`1 valueFactory)

at Microsoft.Owin.Hosting.Utilities.SettingsLoader.LoadFromConfig(IDictionary`2 settings)

at Microsoft.Owin.Hosting.Engine.StartContext..ctor(StartOptions options)

at Microsoft.Owin.Hosting.Starter.DirectHostingStarter.Start(StartOptions options)

at Microsoft.Owin.Hosting.Starter.HostingStarter.Start(StartOptions options)

at [redacted].IntegrationTests.MyIntegrationTests..ctor() in C:\Users[redacted]\source\repos[redacted].IntegrationTests\MyIntegrationTests.cs:line 21

What i've tried:

Adding packages one by one, with varying versions.
Changing my Startup Class to add a HttpConfiguration
Clearing localhost cookies (was suggested in other topics here)
Using this guide: https://github.com/NancyFx/Nancy/wiki/Hosting-nancy-with-owin#katana---httplistener-selfhost i receive the exact same error as previously.

To me, it looks like there is a configuration missing - or not being found. However, everything i refer to exists. Any ideas? (Worth mentioning - this test project has no appsettings.json, web.config, etc)

EDIT: Test project available here: https://www.dropbox.com/s/v1bw5pu9t0e9fwt/NancyOwinTest.zip?dl=0 Making the test project, i realise it's restoring packages at the .NET 4.6.1 level, rather than .NET Core. I may well be making a stupid mistake, but which one, i haven't figured out yet.

did you follow the steps for Katana - HttpListener (SelfHost)? github.com/NancyFx/Nancy/wiki/Hosting-nancy-with-owin check <appSettings> <add key="owin:appStartup" .... — Mate

user3012708 user3012708 · Accepted Answer · 2019-03-04T20:08:48

So, it seems the way i was doing this was not possible, due to compatibility issues. However, i stumbled upon a way to configure the csproj file directly to reference the correct packages, here: https://github.com/NancyFx/Nancy/issues/2863#issuecomment-365107613

Copying config here incase that goes down:

<Project Sdk="Microsoft.NET.Sdk.Web" ToolsVersion="15.0">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <DebugType>portable</DebugType>
    <AssemblyName>nancydemo</AssemblyName>
    <OutputType>Exe</OutputType>
    <PackageId>nancydemo</PackageId>
    <RuntimeFrameworkVersion>2.0.5</RuntimeFrameworkVersion>
    <StartupObject>NancyApplication.Program</StartupObject>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Server.Kestrel" Version="2.0.1" />
    <PackageReference Include="Microsoft.AspNetCore.Owin" Version="2.0.1" />
    <PackageReference Include="Nancy" Version="2.0.0-barneyrubble" />
  </ItemGroup>
</Project>

In combination with the startup class:

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        app.UseOwin(x => x.UseNancy());
    }
}

and the main test run snippet above replaced with:

public class MyIntegrationTests : IDisposable
    {
        private readonly IWebHost _webApp;
        private const string Url = "http://localhost:1234";

        public MyIntegrationTests ()
        {
            _webApp = new WebHostBuilder()
                .UseKestrel()
                .UseStartup<Startup>()
                .UseUrls(Url)
                .Build();

            _webApp.Start();
        }

The NancyModule stayed the same:

public class TestModule : NancyModule
{
    public TestModule()
    {

        Get("/test", args => "test");
    }
}

This now works for my needs! (A basic 'server' responding to requests for test purposes)

NullReferenceException experienced with Owin on Startup .Net Core 2.0 - Settings?

1 Answers