ProblemDetails middleware ignore errors from ActionFilterAttribute

[lurumad]

Hi,

I usually try to manage model validation in an ActionFilterAttribute:

public class ValidateModelStateFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        if (context.ModelState.IsValid)
        {
            return;
        }

        var validation = new ValidationProblemDetails(context.ModelState);

        context.Result = new BadRequestObjectResult(validation);
    }
}

But ProblemDetails middleware ignore errors from this ActionFilterAttribute:

I understand the first two conditionals in the method, but not the logic that decides the last:

if (context.Response.ContentLength.HasValue)
{
    return false;
}

if (string.IsNullOrEmpty(context.Response.ContentType))
{
    return true;
}

Regards!

[khellang]

Hi!

The assumption is that if Content-Length and Content-Type has been set, the response body has already been written by somone else. They're kinda redundant since we also check HasStarted, but it follows the same rules as the exception handler middleware, so I just kept it for consistency.

Someone else, in this case, is MVC's object result executor. It has already set the content type and written to the body by the time the problem details middleware is reached on the way out. This means it's too late for the middleware to write anything.

In this case it shouldn't matter whether the middleware or MVC's filter writes the response, since it's a ValidationProblemDetails instance. The JSON representation should be the same.

If you really need the MW to handle the response, you can throw a ProblemDetailsException and it should be handled automatically.

[lurumad]

Thanks @khellang

Was my fault, I've configured ApiBehaviorOptions and I don't need the ActionFilter and works together:

public static IServiceCollection AddProblemDetails(this IServiceCollection services) =>
    services.Configure<ApiBehaviorOptions>(options =>
    {
        options.InvalidModelStateResponseFactory = context =>
        {
            var problemDetails = new ValidationProblemDetails(context.ModelState)
            {
                Instance = context.HttpContext.Request.Path,
                Status = StatusCodes.Status400BadRequest,
                Type = $"https://httpstatuses.com/400",
                Detail = "Please refer to the errors property for additional details."
            };
            return new BadRequestObjectResult(problemDetails)
            {
                ContentTypes = { "application/problem+json", "application/problem+xml" }
            };
        };
    });

I have to say Hellang.Middleware.ProblemDetails is awesome, great work!!!

Regards!

[khellang]

Nice. Glad you got it working! Incidentally, I just sent a PR to MVC to copy over the result status code to the problem details object, so from 2.2, you don't have to set it explicitly; aspnet/Mvc#8118