Question

I’m building a RESTful API and I would like to control all possible output to my consumers. I’m implementing an ExceptionFilterAttribute to filter all exceptions raised in my controllers. This, however, doesn’t give me control over errors that might happen in my application prior reaching controller code – such as routing errors. Default behaviour sends back a standard serialized HttpError giving away too much internal information to my taste, such as controller classnames etc. I would like to avoid that. What is the best way of changing this behaviour?

Answer 1

You can add a MessageHandler to do this.
MessageHandlers run first and last in the pipeline, allowing you to process raw incoming request and raw outgoing response.

For example:

public class ErrorHandler : DelegatingHandler
{
    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var response = await base.SendAsync(request, cancellationToken);

        if (!response.IsSuccessStatusCode)
        {
                Debug.WriteLine("something happened! - " + response.ReasonPhrase);
        }

        return response;
    }
}

And then register in your GlobalConfiguration

config.MessageHandlers.Add(new ErrorHandler());

This basically inspects the outgoing response and checks if the status code is 2xx. If not you can do something with it – log, or perhaps reset the content of the response to hide whatever you wanna hide.