ExceptionCatcherMiddleware 1.0.3

ExceptionCatcherMiddleware

This is a small package that provides a simple way to catch exceptions in middleware and map them to the appropriate status code and DTO that will be sent to the client. It integrated with ASP.NET content negotiation, so you don't need to worry about serializing the DTO.

Instalation

ExceptionCatcherMiddleware is available on NuGet and can be installed via the below commands:

$ Install-Package ExceptionCatcherMiddleware

or via the .NET Core CLI:

$ dotnet add package ExceptionCatcherMiddleware

Getting started

To add your own mapper you need to create class that implements IExceptionMapper<T> where T represents the type of exception that the mapper will map. Example for ArgumentException:

using ExceptionCatcherMiddleware.Mappers.CreatingCustomMappers;

public class ArgumentExceptionMapper : IExceptionMapper<ArgumentException>
{
    public BadResponse Map(ArgumentException exception)
    {
        return new BadResponse()
        {
            StatusCode = 400,
            ResponseDto = new
            {
                Title = "Argument Exception occurred during execution",
                Detail = exception.Message
            }
        };
    }
}

Exception mappers should map from TException to BadResponse. BadResponse class is utilized by the middleware.

• StatusCode will be applied to response's status code.
• ResponseDto will be used as the response body. Since the package is connected to ASP.NET content negotiation, the framework will handle the serialization of the DTO.

Adding mapper to middleware

builder.Services.AddExceptionCatcherMiddlewareServices(optionsBuilder =>
{
    optionsBuilder.RegisterExceptionMapper<ArgumentException, ArgumentExceptionMapper>();
});

This method has the following signature RegisterExceptionMapper<TException, TMapper>.

• TException is a type of exception that mapper will map.
• TMapper is a type of mapper for that exception

Note: TMapper must be bound strictly to TException. For instance, if your mapper implements IExceptionMapper<ArgumentException>, you can register it only for ArgumentException and not for ArgumentOutOfRangeException

Adding Middelware to pipeline

app.UseExceptionCatcherMiddleware();

That's it! Now, any ArgumentException and its derived exceptions, such as ArgumentOutOfRangeException, ArgumentNullException, and so on, will be mapped by the registered mapper. If an exception occurs that doesn't inherit from ArgumentException, it will be mapped by the default mapper for Exception. You can override this by registering your own IExceptionMapper<Exception>.