How Can I Reliably Handle Exceptions from All Filters, Including Authorization Filters, in ASP.NET Core Web API?

Comprehensive Exception Handling in ASP.NET Core Web APIs

This article addresses the challenges of reliably handling exceptions originating from all filters, including authorization filters, within ASP.NET Core Web APIs. The differences between exception handling in ASP.NET Core and classic ASP.NET Web API are significant, often causing confusion for developers making the transition.

Addressing Limitations of Traditional Exception Filters

While exception filters in ASP.NET Core can handle action exceptions, they historically struggled to capture exceptions thrown within other filters, such as authorization filters. This limitation necessitates a more robust approach.

The IExceptionHandler Solution (ASP.NET Core 8 and later)

ASP.NET Core 8 and later versions introduce the IExceptionHandler interface, providing a powerful and flexible solution. IExceptionHandler allows for:

• Dependency injection (e.g., for logging).
• Customized handling based on specific exception types.
• Consistent exception handling across actions and all filter types.

Implementing IExceptionHandler:

1. Create an IExceptionHandler Implementation:

using Microsoft.AspNetCore.Diagnostics;

public class MyExceptionHandler : IExceptionHandler
{
    public async ValueTask<bool> TryHandleAsync(HttpContext context, Exception exception, CancellationToken cancellationToken)
    {
        // Implement your exception handling logic here.  This could include logging,
        // returning a custom error response, etc.
        return true; // Return true to indicate the exception was handled.
    }
}

2. Register the ExceptionHandler Middleware:

builder.Services.AddExceptionHandler<MyExceptionHandler>();
app.UseExceptionHandler(_ => { });

Key Considerations:

• Registration Order: Multiple IExceptionHandler implementations can be registered. They'll be executed sequentially in the order of registration.
• TryHandleAsync Return Value: Returning true from TryHandleAsync signals that the exception has been handled. A false return value passes the exception to subsequent handlers.

This method ensures comprehensive exception handling across your ASP.NET Core Web API, addressing the limitations of previous approaches.

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