Exception Handling in ASP.NET Core Web API

Question:

I started using ASP.NET Core for my new REST API project after using regular ASP.NET Web API for many years. I don't see a good way to handle exceptions in ASP.NET Core Web API. I tried to implement exception handling filter/attribute:

public class ErrorHandlingFilter : ExceptionFilterAttribute
{
 public override void OnException(ExceptionContext context)
 {
 HandleExceptionAsync(context);
 context.ExceptionHandled = true;
 }

 private static void HandleExceptionAsync(ExceptionContext context)
 {
 var exception = context.Exception;

 if (exception is MyNotFoundException)
 SetExceptionResult(context, exception, HttpStatusCode.NotFound);
 else if (exception is MyUnauthorizedException)
 SetExceptionResult(context, exception, HttpStatusCode.Unauthorized);
 else if (exception is MyException)
 SetExceptionResult(context, exception, HttpStatusCode.BadRequest);
 else
 SetExceptionResult(context, exception, HttpStatusCode.InternalServerError);
 }

 private static void SetExceptionResult(
 ExceptionContext context, 
 Exception exception, 
 HttpStatusCode code)
 {
 context.Result = new JsonResult(new ApiResponse(exception))
 {
 StatusCode = (int)code
 };
 }
}

And here is my Startup filter registration:

services.AddMvc(options =>
{
 options.Filters.Add(new AuthorizationFilter());
 options.Filters.Add(new ErrorHandlingFilter());
});

The issue I was having is that when exception occurred in my AuthorizationFilter it's not being handled by ErrorHandlingFilter. I was expecting it to be caught there just like it worked with old ASP.NET Web API.

So how can I catch all application exceptions as well as any exceptions from Action Filters?

Solution:

Exception Handling Middleware

After many experiments with different exception handling approaches I ended up using middleware. It worked the best for my ASP.NET Core Web API application. It handles application exceptions as well as exceptions from filters and I have full control over exception handling and creating a response json. Here is my exception handling middleware:

public class ErrorHandlingMiddleware
{
 private readonly RequestDelegate next;

 public ErrorHandlingMiddleware(RequestDelegate next)
 {
 this.next = next;
 }

 public async Task Invoke(HttpContext context /* other dependencies */)
 {
 try
 {
 await next(context);
 }
 catch (Exception ex)
 {
 await HandleExceptionAsync(context, ex);
 }
 }

 private static Task HandleExceptionAsync(HttpContext context, Exception exception)
 {
 var code = HttpStatusCode.InternalServerError; // 500 if unexpected

 if (exception is MyNotFoundException) code = HttpStatusCode.NotFound;
 else if (exception is MyUnauthorizedException) code = HttpStatusCode.Unauthorized;
 else if (exception is MyException) code = HttpStatusCode.BadRequest;

 var result = JsonConvert.SerializeObject(new { error = exception.Message });
 context.Response.ContentType = "application/json";
 context.Response.StatusCode = (int)code;
 return context.Response.WriteAsync(result);
 }
}

Register it before MVC in Startup class:

app.UseMiddleware(typeof(ErrorHandlingMiddleware));

app.UseMvc();

Here is an example of exception response:

{ "error": "Authentication token is not valid." }

You can add stack trace, exception type name, error codes or anything you want to it. Very flexible.