Exception Middleware

This project is a small extension for ASP.NET Core Applications, which provides the functionality to throw exceptions that are caught by a filter and translated to an error response. Additionally it is possible to add the ErrorResponse model and the additional

Getting started

After adding the package to an ASP.NET Core project

dotnet add package Aspnetcore.ExceptionMiddleware

the application can be configured to to use the exception middleware by adding the following code to method ConfigureServices, usually located in the Startup.cs file:

services.AddControllers().AddExceptions();

It is also possible to add Controllers with exceptions as one call, by replacing:

services.AddControllers();

with

services.AddControllersWithExceptions();

Please note that this automatically replaces the errors sent on validation error with an ErrorResponse containing the appropriate content

When using Swashbuckle.AspNetCore for swagger generation, the schema for ErrorResponse and the ErrorCodes can be added to the generated OpenAPI specification of the api by changing the configuration of the swagger generation:

services.AddSwaggerGen(c =>
{
  // other configurations

  c.AddExceptions();
});

In order to enable the application to automatically respond with an ErrorResponse if an error is encountered during parameter validation add the following line to the Startup.cs or application configuration:

services.AddValidationSupport();

Note

In order for the ErrorResponse to be shown in the OpenAPI specification as the error response an endpoint, one should annotate the Controller with the ProducesErrorResponseType attribute. While it is possible to use the ProducesResponseType or ProducesResponseType<T> attribute on a per method level, the margin of error is smaller when defining the error response type on a controller level.

Adding additional exceptions

Even though the package already provides some exceptions that are commonly used when developing a Web-API, it is also possible to add additional exceptions for special use. The only issue is, that in C# it is not possible to extend an enum. This means that if you want to add the new error codes to the OpenAPI specification, they have to be added manually as seen in ExceptionDocumentFilter.cs.

The newly added Exception has to be derived from the class AppException<T>, provided by this package. The class AppException<T> is abstract but does not contain any abstract member. This is used to prevent users from throwing a raw AppException<T> by accident.

The generic type of AppException<T> has a type-constraint, so that the given type has to be derived from ObjectResult. The given generic type is used for the error response and thus has impact, for example, on the status code.

Additional features

In addition to the previously mentioned features, the package also contains multiple type definitions for types derived from ObjectResult:

• ForbiddenObjectResult
• InternalServerErrorObjectResult
• InternalServerErrorResult
• NotImplementedObjectResult