Can I get an Action's return type from an Acti

Question

I have an ASP.NET MVC 2 application in which I am creating a custom action filter. This filter sits on the controllers in the application and verifies from the database whether that function is currently available.

Public Overrides Sub OnActionExecuting(ByVal filterContext As System.Web.Mvc.ActionExecutingContext)
  Try
    ' Check controller name against database.
    Dim controllerName = filterContext.Controller.GetType().Name
    controllerName = controllerName.Remove(controllerName.Length - 10)
    ' Look up availability.
    Dim available As Boolean = _coreService.GetControllerAvailability(controllerName)
    If Not available Then
      ' Redirect to unavailable notice.
      filterContext.Result = New RedirectResult("/Home/Unavailable/")
    End If
  Catch ex As Exception
    _eventLogger.LogWarning(ex, EventLogEntryType.Error)
    Throw
  End Try
End Sub

My problem is that depending on the action that has been requested I need to redirect the user to an action that returns either a view, partial views or JSON.

Given the ActionExecutingContext can I find out what the return type of the originally requested action is?

EDIT:

Ok, I'm getting closer but have another problem.

Public Overrides Sub OnActionExecuting(ByVal filterContext As System.Web.Mvc.ActionExecutingContext)
  Try
    ' Check controller name against database.
    Dim controllerName = filterContext.Controller.GetType().Name
    Dim shortName = controllerName.Remove(controllerName.Length - 10)
    ' Look up availability.
    Dim available As Boolean = _coreService.GetControllerAvailability(shortName)
    If Not available Then
      ' find out what type is expected to be returned
      Dim actionName As String = filterContext.ActionDescriptor.ActionName
      Dim controllerType = Type.GetType("Attenda.Stargate.Web." & controllerName)
      Dim actionMethodInfo = controllerType.GetMethod(actionName)
      Dim actionReturnType = actionMethodInfo.ReturnType.Name

      Select Case actionReturnType
        Case "PartialViewResult"
          filterContext.Result = New RedirectResult("/Home/UnavailablePartial/")
        Case "JsonResult"
          filterContext.Result = New RedirectResult("/Home/UnavailableJson/")
        Case Else
          filterContext.Result = New RedirectResult("/Home/Unavailable/")
      End Select

    End If
  Catch ex As Exception
    _eventLogger.LogWarning(ex, EventLogEntryType.Error)
    Throw
  End Try
End Sub

I can use reflection to find the return type of the action method. My problem is if I have the following methods on a controller:

Public Function Create() As ViewResult
  Return View()
End Function

<AcceptVerbs(HttpVerbs.Post)>
Public Function Create(values as FormCollection) As ViewResult
  ' Do stuff here
End Function

I get an AmbiguousMatchException thrown.

With the information I have in the OnActionExecuting method, is there anyway of being more precise with determining the overload that is being called?

Answer 1

I created an AuthenticationFilterAttribute based on this which returns different results based on type:

    /// <summary>
    /// Access to the action will be blocked if the user is not logged in. 
    ///  Apply this to the controller level or individual actions as an attribute.
    /// </summary>
    public class AuthenticationFilterAttribute : ActionFilterAttribute
    {
        protected const string InvalidAccess = "Invalid access";

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            // Find out if the user is logged in: 
            Controller controller = (Controller)filterContext.Controller;
            if (!controller.User.Identity.IsAuthenticated)
            {
                switch (GetExpectedReturnType(filterContext).Name)
                {
                    case "JsonResult":
                        var jsonResult = new JsonResult();
                        jsonResult.Data = new { Error = true, ErrorMessage = InvalidAccess };
                        jsonResult.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
                        filterContext.Result = jsonResult;
                        break;

                    // Assume same behaviour as ActionResult
                    default: 
                        var actionResult = new ContentResult();
                        actionResult.Content = InvalidAccess;
                        filterContext.Result = actionResult;
                        break;
                }
            }
        }

        private Type GetExpectedReturnType(ActionExecutingContext filterContext)
        {
            // Find out what type is expected to be returned
            string actionName = filterContext.ActionDescriptor.ActionName;
            Type controllerType = filterContext.Controller.GetType();
            MethodInfo actionMethodInfo = default(MethodInfo);
            try
            {
                actionMethodInfo = controllerType.GetMethod(actionName);
            }
            catch (AmbiguousMatchException ex)
            {
                // Try to find a match using the parameters passed through
                var actionParams = filterContext.ActionParameters;
                List<Type> paramTypes = new List<Type>();
                foreach (var p in actionParams)
                {
                    paramTypes.Add(p.Value.GetType());
                }

                actionMethodInfo = controllerType.GetMethod(actionName, paramTypes.ToArray());
            }

            return actionMethodInfo.ReturnType;
        }
    }

Answer 2

By the time OnActionExecuting is invoked, the action method has not been executed yet, so there's no way you know whether that action method is going to return which subclass of ActionResult. So, unless you can go with CIL analysis implementation (which I think can get ugly very quickly), I don't think what you want to do is possible.

That said, isn't the fact that you redirect users to a view when the controller isn't available enough? I mean, I don't understand why you want to redirect users to a JSON result or a partial view.

Answer 3

Ok, this is the solution I have come up with.

Public Overrides Sub OnActionExecuting(ByVal filterContext As System.Web.Mvc.ActionExecutingContext)
  Try
    ' Check controller name against database.
    Dim controllerName = filterContext.Controller.GetType().Name
    Dim shortName = controllerName.Remove(controllerName.Length - 10)
    ' Look up availability.
    Dim available As Boolean = _coreService.GetControllerAvailability(shortName)
    If Not available Then
      ' find out what type is expected to be returned
      Dim actionName As String = filterContext.ActionDescriptor.ActionName
      Dim controllerType = Type.GetType("Attenda.Stargate.Web." & controllerName)
      Dim actionMethodInfo As MethodInfo
      Try
        actionMethodInfo = controllerType.GetMethod(actionName)
      Catch ex As AmbiguousMatchException
        ' Try to find a match using the parameters passed through
        Dim actionParams = filterContext.ActionParameters
        Dim paramTypes As New List(Of Type)
        For Each p In actionParams
          paramTypes.Add(p.Value.GetType())
        Next
        actionMethodInfo = controllerType.GetMethod(actionName, paramTypes.ToArray)
      End Try
      Dim actionReturnType = actionMethodInfo.ReturnType.Name

      Select Case actionReturnType
        Case "PartialViewResult"
          filterContext.Result = New RedirectResult("/Home/UnavailablePartial/")
        Case "JsonResult"
          filterContext.Result = New RedirectResult("/Home/UnavailableJson/")
        Case Else
          filterContext.Result = New RedirectResult("/Home/Unavailable/")
      End Select

    End If
  Catch ex As Exception
    _eventLogger.LogWarning(ex, EventLogEntryType.Error)
    Throw
  End Try
End Sub

If the Type.GetMethod(string) call fails to identify the method requested, I fetch the parameters collection from the ActionExecutingContext.ActionParameters collection and build an array of the types of the parameters passed in the request. I can then use the Type.GetMethod(string,type()) overload to be more specific about my request.