ResolutionFailedException Returned As Success

Question

I'm using Unity with my WebApi project, and registering types using the config file. I've been injecting dependencies into controller constructors and it has been working beautifully... until I forgot a type mapping and received the following error:

An error occurred when trying to create a controller of type 'FooController'. Make sure that the controller has a parameterless public constructor.

The problem isn't that I received the error. I can easily add the mapping to resolve it. The problem is that internals were shared with the client and the client received a HTTP Status Code of 200.

I read a similar article (Unity wraps exception to the ResolutionFailedException. How to avoid?), but those answers were not helpful; stating there is no solution or seeming off topic. It is difficult for me to accept that there is no solution, so I thought I might rephrase the question in hopes that it will receive a better answer.

How can I catch/intercept the ResolutionFailedException so that a Http Error 500 is returned instead? Is there an event I can listen for or a class I can wrap in some way? For example, can I wrap the DefaultHttpControllerActivator and use my wrapper to catch an exception and return it as a HTTP 500 error? I would expect a HTTP 500 to be filtered from the client based on the CustomErrors configuration setting. Also, I could log the error to my log file instead of returning details to the client.

Here's a example of the error as XML:

<Error>
<Message>An error has occurred.</Message>
<ExceptionMessage>
An error occurred when trying to create a controller of type 'FooController'. Make sure that the controller has a parameterless public constructor.
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace>
at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType) 
at System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage request) 
at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()
</StackTrace>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
Resolution of the dependency failed, type = "MyWebApi.API.Controllers.FooController", name = "(none)". Exception occurred while: while resolving. Exception is: InvalidOperationException - The current type, MyWebApi.DataProvider.Interfaces.IFooProvider, is an interface and cannot be constructed. Are you missing a type mapping? ----------------------------------------------- 
At the time of the exception, the container was: Resolving MyWebApi.API.Controllers.FooController,(none) Resolving parameter "FooProvider" of constructor MyWebApi.API.Controllers.FooController(MyWebApi.DataProvider.Interfaces.IFooProvider FooProvider) Resolving MyWebApi.DataProvider.Interfaces.IFooProvider,(none)
</ExceptionMessage>
<ExceptionType>
Microsoft.Practices.Unity.ResolutionFailedException
</ExceptionType>
<StackTrace>
at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides) 
at Microsoft.Practices.Unity.UnityContainer.Resolve(Type t, String name, ResolverOverride[] resolverOverrides) 
at Microsoft.Practices.Unity.UnityContainerExtensions.Resolve(IUnityContainer container, Type t, ResolverOverride[] overrides) 
at Microsoft.Practices.Unity.WebApi.UnityDependencyResolver.SharedDependencyScope.GetService(Type serviceType) 
at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator) 
at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)
</StackTrace>
<InnerException>
<Message>An error has occurred.</Message>
<ExceptionMessage>
The current type, MyWebApi.DataProvider.Interfaces.IFooProvider, is an interface and cannot be constructed. Are you missing a type mapping?
</ExceptionMessage>
<ExceptionType>System.InvalidOperationException</ExceptionType>
<StackTrace>
at Microsoft.Practices.ObjectBuilder2.DynamicMethodConstructorStrategy.ThrowForAttemptingToConstructInterface(IBuilderContext context) 
at lambda_method(Closure , IBuilderContext ) 
at Microsoft.Practices.ObjectBuilder2.DynamicBuildPlanGenerationContext.<>c__DisplayClass1.<GetBuildMethod>b__0(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.BuilderContext.NewBuildUp(NamedTypeBuildKey newBuildKey) 
at Microsoft.Practices.Unity.ObjectBuilder.NamedTypeDependencyResolverPolicy.Resolve(IBuilderContext context) 
at lambda_method(Closure , IBuilderContext ) 
at Microsoft.Practices.ObjectBuilder2.DynamicBuildPlanGenerationContext.<>c__DisplayClass1.<GetBuildMethod>b__0(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.DynamicMethodBuildPlan.BuildUp(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.BuildPlanStrategy.PreBuildUp(IBuilderContext context) 
at Microsoft.Practices.ObjectBuilder2.StrategyChain.ExecuteBuildUp(IBuilderContext context) 
at Microsoft.Practices.Unity.UnityContainer.DoBuildUp(Type t, Object existing, String name, IEnumerable`1 resolverOverrides)
</StackTrace>
</InnerException>
</InnerException>
</Error>

Answer 1

I found the answer here: catch all unhandled exceptions in ASP.NET Web Api

I learned the following things when implementing my preferred solution:

• The full error w/ stack trace is only visible because of the CustomErrors setting. I forgot that I was running everything locally and CustomErrors=RemoteOnly.
• If I only want to catch the exceptions and log them, then add an IExceptionLogger. This is the solution I implemented for my current needs.
• If I want to catch the exception and manipulate the response, then replace IExceptionHandler. This is good to know.
• Neither solution captures ALL exceptions. I'm still using Application_Error to capture exceptions that aren't caught within my ApiController methods.