Diagnostics Exception Handler override

[MoeHamdan]

Hello

I want to override ExceptionHandlerMiddleware and DeveloperExceptionPageMiddleware to enable them to support "application/json" content type, so they could return proper json error when the content is json. However your invoke method is not marked as virtual, may you mark it as virtual so we could extend this?

[Tratcher]

The Invoke method is the bulk of the middleware, you'd be better off writing a new middleware.

[MoeHamdan]

Hello @Tratcher

If write a new middleware I will lose all the functionality implemented by these middleware, I will need to re implement all functionalities, it does not make sense to do so.

[Tratcher]

If you override Invoke you'll need to re-implement most of it anyways. What do you gain?

Maybe you could give an example of what you had in mind?

[MoeHamdan]

Well all I want is to check if the content type is JSON then return JSON error instead of HTML, which is a couple of simple lines, I wonder why this is not there, it used to be part of .NET.

[Tratcher]

I don't see how this applies to the ExceptionHandlerMiddleware, it doesn't generate any HTML, it forwards the request to a component that can such as an MVC controller. You can already enhance that component to serve HTML or JSON.

The DeveloperExceptionPage is only for use in a development environment so the format of the error should be less relevant, it's not intended for programmatic processing. As for changing that to JSON, the only code you would still want is inside the Invoke method (https://github.com/aspnet/Diagnostics/blob/8dce01f654962580e22e7c96ad4f313574407a40/src/Microsoft.AspNetCore.Diagnostics/DeveloperExceptionPage/DeveloperExceptionPageMiddleware.cs#L70-L107) so overriding it doesn't help you.

[MoeHamdan]

Hello @Tratcher

Thank you very much for your help. I know that DeveloperExceptionPage is for development, it is very important to us as you know most of the time you are in development mode, so the thing is I would like to keep the current behavior of the HTML part and introduce the JSON behavior as well when the content type is "application/json". If you see that inheriting the middleware is not the best practice, is it possible that you enhance these middleware to server JSON?

Thanks,

[Tratcher]

Adding JSON support directly is a different matter. That's tracked over at #2573.