Async action filter in MVC 4

Question

I have an action filter that when used in certain specific conditions has to perform a web service call to ensure that the current state is valid. This initially seemed like an ideal candidate for async/await, but I have encountered a snag:

Assume a request to: /Test/FilteredAction

• MyCustomActionFilter begins executing
  • The first "await" statement is reached
• TestController.FilteredAction starts executing
• MyCustomActionFilter resumes executing

Traditionally I would expect the action filter to resume executing and then complete before the controller action starts executing, but this does not happen.

Now I assume this is because I am using:

public class MyCustomActionFilter : ActionFilterAttribute 
{
    public override **async** void OnActionExecuting(FilterContext context) 
    {
        var foo = await WebServiceCall();
    }
}

So I think my question is: Is there an async-aware action filter class built into MVC 4, or should I just block on the calls in here?

Answer 1

MVC does not have an async-compatible action filter (but WebAPI does have one).

For now, I recommend you use blocking calls in OnActionExecuting. Hopefully MVC will have a better story in the future.

Update: You can vote here for the MVC team to add async filters.