Custom error catching on ASP.NET Core 2.0 MVC

So I was recently working on an ASP.NET Core 2.0 MVC application and had the need to send errors that are unhandled elsewhere out to an external service (Sentry in this case). While that doesn’t seem too difficult on the surface I had to find a way to get the configuration data needed in order to send said data to the external service. Since ASP.NET Core uses dependency injection to handle config data and there is very little to no documentation yet on any of this, it turned out to be harder than I expected.

Use Case

I have forgotten all of the different avenues that I tried before finding the right one, but in the end I learned alot about the internals of ASP.NET Core MVC. The solution I found works really well for my use case, but there are other easier ways to capture errors. In my case I needed to capture all errors that may happen that are not handled by other code. So even though I have error handling code all over the place, there are always cases that I forget, or don’t even think about. I wanted to be able to capture these errors because these are the ones I did not or could not prepare for and potentially have the most negative side effects.

The Solution

I ended up creating an ExceptionFilterAttribute and registering it in the Startup.cs. Building the attribute and getting the settings from there were the hardest part. I had to make my way through the API blind until I found what I wanted. There was a lot of debugging and de-compiling to figure out what was going on. I could not find any documentation on this that described what I wanted to do so that made it all harder.

The Code

The ExceptionFilterAttribute

public class ExceptionCatcher : ExceptionFilterAttribute {
    public override void OnException(ExceptionContext context) {
        var ex = context.Exception;

        var features = context.HttpContext.Features;
        var service = features[typeof(IServiceProvidersFeature)] as RequestServicesFeature;
        var settingsManager = service?.RequestServices.GetService(typeof(IOptions<OtherSettings>));
        var settings = (settingsManager as OptionsManager<OtherSettings>)?.Value;
        if (settings != null) {
            // Now I have my settings and can send the exception to my external service.
        }

        base.OnException(context);
    }
}

In Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    ...

    services.AddScoped<ExceptionCatcher>();

    ...
}

On the controllers

[ServiceFilter(typeof(ExceptionCatcher))]
public class HomeController : Controller {
    ...
}