Global Exception Handling using Middleware in .NET Core

Exception handling for some of us is all about using try and catch blocks and throw statements in the application. Most of the time proper analysis or design approach never gets identified for the exception handling. Today we will see how to enable Global Exception Handling using Middleware in .NET Core-based applications like API or MVC apps.

Today in this article, we will cover below aspects,

In our previous article, we already talked about the below aspects in detail which are important while considering proper design around exception handling,

• Business exception Vs Technical Exception
• Exception handling
  • Using Global Exception-handler in .NET Core
  • Using Exception Filters in .NET Core
  • Using simple Try -Catch-Throw best practices

In this article, we will see another preferred approach of using a global middleware component for handling exceptions in the ASP.NET Core application.

Let’s first understand the middleware’s role in the API pipeline. As shown in the below figure each middleware component in the request pipeline is responsible for invoking the next middleware component in the pipeline.

Now let’s use this concept and if we add first middleware as our own exception middleware component shouldn’t it suffice as our global exception handler? The answer is Yes. This component will handle all exceptions happening across API or Business or any other component including other middleware which are part of the application.

Getting started

Create an ASP.NET Core API

Please choose either .NET Core 3.1 or .NET 5 project template.

Overall creating a middleware component is just a 2-3 steps process.

Adding Middleware component

• The first step is to add a public class as ExceptionMiddleware.

public class ExceptionMiddleware
    {
        private readonly RequestDelegate _next;

        public ExceptionMiddleware(RequestDelegate next)
        {
            _next = next;
        }

        public async Task InvokeAsync(HttpContext httpContext)
        {
            try
            {
                await _next(httpContext);
            }
            catch (Exception ex)
            {
                await HandleGlobalExceptionAsync(httpContext, ex);
            }
        }

        private static Task HandleGlobalExceptionAsync(HttpContext context, Exception exception)
        {
            context.Response.ContentType = "application/json";
            context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
            return context.Response.WriteAsync(new GlobalErrorDetails()
            {
                StatusCode = context.Response.StatusCode,
                Message = "Something went wrong !Internal Server Error"
            }.ToString());
        }
    }

• The next step is to create a public static class GlobalExceptionMiddleware

public static class GlobalExceptionMiddleware
    {
        public static void UseGlobalExceptionMiddleware(this IApplicationBuilder app)
        {
            app.UseMiddleware<ExceptionMiddleware>();
        }
    }

• The last step is to enable this middleware in Startup.cs as shown below.

Generic Exception Code and Message

Now let’s test controller logic with some exceptions. Error response for most exceptions will be generic as below,

Tips:

As a good practice, the above-mentioned logic can be centralized in the form of a library/Nuget package. This library can be shared across any project so that there is uniformity across error handling.

• It’s very crucial to understand how to try -catch-throws work. Follow best practices on throw Vs throw-ex statements here Understanding throw vs throw-ex with examples.

• Also, try to throw an exception from other layers of your application like the BAL/Domain layer and make only the highest layer of your application swallow it. A throw will keep your stack trace details intact allowing you to log exception details.

Other references :

Using Global Exception Handler for ASP.NET Core exception handler

• Global Exception-Handler in .NET Core for Exception Handling

Logging exceptions in the Global Middleware component

• Logging exceptions in the Global Middleware component

Summary

Today we learned about global exception handling using the middleware approach in .NET Core. Centralize exception handling using the middleware approach brings uniformity across, how exceptions are handled in the applications. Proper exception handling /error handling helps in resolving the business/technical issues and is very critical for business success.

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