How to add Custom Middleware and Global Exception Handling to a .NET 8 API?

Code on Github

Don’t want to wait? To download the source code for this blog post, you can visit my GitHub repo:

https://github.com/fillegar/dotnet-6-crud-api-jwt-sql-server

What is ASP.NET Core Middleware?

Middleware is a piece of code in an application pipeline used to handle requests and responses.

For example, we may have a middleware component to authenticate a user, another piece of middleware to handle errors, and another middleware to serve static files such as JavaScript files, CSS files, images, etc.  Middleware can be built-in as part of the .NET Core framework, added via NuGet packages, or can be custom middleware.  For this article, we will be building a custom middleware to handle errors globally with custom middleware.  

Handling Errors Globally With the Custom Middleware

Let’s create a new folder named CustomExceptionMiddleware and a class ExceptionMiddleware.cs inside it.

We are going to modify that class:

public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILoggerManager _logger;

    public ExceptionMiddleware(RequestDelegate next, ILoggerManager logger)
    {
        _logger = logger;
        _next = next;
    }

    public async Task InvokeAsync(HttpContext httpContext)
    {
        try
        {
            await _next(httpContext);
        }
        catch (Exception ex)
        {
            _logger.LogError($"Something went wrong: {ex}");
            await HandleExceptionAsync(httpContext, ex);
        }
    }

    private async Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

        await context.Response.WriteAsync(new ErrorDetails()
        {
            StatusCode = context.Response.StatusCode,
            Message = "Internal Server Error from the custom middleware."
        }.ToString());
    }
}

Customizing Error Messages

If you want, you can always customize your error messages from the error handler. There are different ways of doing that, but we are going to show you the basic two ways.

Using the IExceptionHandler Interface from .NET 8

IExceptionHandler is an interface that we can use to handle exceptions in ASP.NET Core applications. It defines an interface that we can implement to handle exceptions globally. This allows us to write custom logic for handling individual exceptions or groups of exceptions based on their type, in turn providing tailored responses, error messages as well as logging. 

Since we already have an article on this topic, feel free to read it here. You will find all the information you need to use this interface, which will improve the handling logic as well.

Conclusion

That was awesome.

We have learned, how to handle errors in a more sophisticated way and cleaner as well. The code is much more readable and our exception handling logic is now reusable for the entire project.

Thank you for reading this article. We hope you have learned new useful things.