Null ref exception when using IUrlHelper in a filter

[kichalla]

I was trying to redirect to a different route in my action filter and I am using RedirectToRouteResult. This expects to supply a IUrlHelper and so I placed this to be injectable on my action filter.

I registered my filter to be a singleton and noticed following Null Ref exception...yeah, I realized that registering as singleton is incorrect here as UrlHelper is created on a per-request basis...

Can we give a more meaningful exception here?...

services.AddSingleton<FooActionFilter>();

[ServiceFilter(typeof(FooActionFilter))]
public class FooController : Controller
{
    public string Get()
    {
        return "Bar";

    }

    public string Get(int id)
    {
        return "Bar:" + id;
    }
}

public class FooActionFilter : IAsyncActionFilter
{
    private IUrlHelper urlHelper = null;
    public FooActionFilter(IUrlHelper helper)
    {
        urlHelper = helper;
    }

    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
        context.Result = new RedirectToRouteResult(urlHelper, new { controller = "Foo", id = 10 });

        await next();
    }
}

Exception:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
 at Microsoft.AspNet.Mvc.UrlHelper..ctor(IContextAccessor`1 contextAccessor, IActionSelector actionSelector)
 --- End of inner exception stack trace ---
 at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
 at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
 at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark)
 at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
 at System.Activator.CreateInstance(Type type, Object[] args)
 at Microsoft.Framework.DependencyInjection.ActivatorUtilities.<>c__DisplayClass0.<CreateFactory>b__4(IServiceProvider services)
 at Microsoft.Framework.DependencyInjection.ServiceLookup.Service.Create(ServiceProvider provider)
 at Microsoft.Framework.DependencyInjection.ServiceProvider.ResolveService(IService service)
 at Microsoft.Framework.DependencyInjection.ServiceProvider.GetService(Type serviceType)
 at Microsoft.Framework.DependencyInjection.ActivatorUtilities.<>c__DisplayClass0.<CreateFactory>b__4(IServiceProvider services)
 at Microsoft.Framework.DependencyInjection.ServiceLookup.Service.Create(ServiceProvider provider)
 at Microsoft.Framework.DependencyInjection.ServiceProvider.ResolveService(IService service)
 at Microsoft.Framework.DependencyInjection.ServiceProvider.ResolveService(IService service)
 at Microsoft.Framework.DependencyInjection.ServiceProvider.GetService(Type serviceType)
 at Microsoft.AspNet.Mvc.ServiceFilterAttribute.CreateInstance(IServiceProvider serviceProvider)
 at Microsoft.AspNet.Mvc.Filters.DefaultFilterProvider.ProvideFilter(FilterProviderContext context, FilterItem filterItem)
 at Microsoft.AspNet.Mvc.Filters.DefaultFilterProvider.Invoke(FilterProviderContext context, Action callNext)
 at Microsoft.Framework.DependencyInjection.NestedProviders.NestedProviderManager`1.CallNext.CallNextProvider()
 at Microsoft.Framework.DependencyInjection.NestedProviders.NestedProviderManager`1.Invoke(T context)
 at Microsoft.AspNet.Mvc.ReflectedActionInvoker.GetFilters()
 at Microsoft.AspNet.Mvc.ReflectedActionInvoker.<InvokeActionAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Mvc.MvcRouteHandler.<RouteAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Routing.Template.TemplateRoute.<RouteAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Routing.RouteCollection.<RouteAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Builder.RouterMiddleware.<Invoke>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Security.Infrastructure.AuthenticationMiddleware`1.<Invoke>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.RequestContainer.ContainerMiddleware.<Invoke>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.VisualStudio.Web.BrowserLink.Runtime.BrowserLinkMiddleware.<ExecuteWithFilter>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Loader.IIS.KlrHttpApplication.<ProcessRequestAsyncImpl>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at Microsoft.AspNet.Loader.IIS.HttpApplicationBase.<InvokeProcessRequestAsyncImpl>d__1.MoveNext()

[Eilon]

I think this is just an artifact of aspnet/DependencyInjection#87 not yet being fixed. Right now DI provides null services when they are not available, and that is incorrect. Once we commit the PR you will get an error from DI saying it couldn't resolve the required service for your attribute.

[rynowak]

This is also a case of trying to use a scoped service in a singleton, which we don't provide diagnostics for currently.

[Eilon]

@rynowak log a bug for that?

[rynowak]

aspnet/DependencyInjection#88