If I create a controller that has a method ActionResult UploadFile(HttpPostedFileBase file)  Where is the best place to add the code that will verify that this is a good and useable file?  The reason I ask, is I will have to do more checking than just the file extension.  For instance; check number of columns in spread sheet, check column names, etc..
Does a method to check the file type being uploaded belong in the controller?
asp.net mvc