How to specify response type in ASP.NET Core middleware

Question

My controllers return unified RequestResult:

public Task<RequestResult> SomeAction()
{
  ...
  return new RequestResult(RequestResultType.NotFound);
}

public class RequestResult
{
  public RequestResultType Type { get;set; }
  ... //actual data
}

public enum RequestResultType
{
   Success = 1,
   NotFound = 2
}

So basically RequestResult combines actual Action data and error type (if it happened). Now I need to specify Response Type at some point in case if Action returned Error. My best guess here is to use Middleware:

public class ResponseTypeMiddleware
{
  private readonly RequestDelegate next;

  public ResponseTypeMiddleware(RequestDelegate next)
  {
    this.next = next;
  }

  public async Task Invoke(HttpContext context)
  {
    await next(context);

    var response = context.Response.Body; //how to access object?
  }
}

but I can't figure out what to do with it. What I'd perfectly like to do is to check if response is of type RequestResult, then specify ResponseType equal BadRequest. But I don't see how I can do it here as what I have is just a stream. May be I can hijack into pipeline earlier, before result was serialized (Controller?).

P. S. The reason why I don't use Controller.BadRequest directly in Action is that my Action's logic is implemented via CQRS command/query handlers, so I don't have direct access to Controller.

Show more of your stack. Your Controller and its ActionResult are going to be more appropriate places to do this than middleware. How does your action communicate with your command handler? — ssmith
– ssmith, Commented Mar 31, 2017 at 0:17

Set · Accepted Answer · 2017-03-31 06:03:41Z

1

As you are going to process controller's action result (MVC), the best way is to use ActionFilter or ResultFilter here, instead of Middleware. Filters in ASP.NET Core are a part of MVC and so know about controllers, actions and so on. Middleware is a more common conception - it is an additional chain in application request-response pipeline.

public class SampleActionFilter : IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        // do something before the action executes
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        // do something after the action executes

        // get or set controller action result here
        var result = context.Result as RequestResult;
    }
}

answered Mar 31, 2017 at 6:03

Set

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