Edit Request.Form before Binding

Question

Is there a way to edit the Request.Form before the action method binds to the parameters? I already have a reflection call to enable editing of Request.Form. I just can't find a point of extensibilty where I can alter it before binding occurs.

UPDATE: So it looks like I was editing the Request.Form and didn't realize it. I was verifying by looking at the bound parameters. That is incorrect b/c by the time you get to the ActionFilter the form values have already been copied/set to/in the ValueProvider. Which I believe is where the values are pulled for binding.

So the question becomes what is the best way to apply some filtering to the form values before they are bound. I still want the binding to occur. I just want to edit the values it uses to bind.

Answer 1

Create custom filter and override OnActionExecuting():

public class CustomActionFilterAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
    }
}

Or simply override OnActionExecuting() in your controller

UPDATED:

protected override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var actionName = filterContext.ActionDescriptor.ActionName;

    if(String.Compare(actionName, "Some", true) == 0 && Request.HttpMethod == "POST")
    {  
        var form = filterContext.ActionParameters["form"] as FormCollection;

        form.Add("New", "NewValue");
    }
}

public ActionResult SomeAction(FormCollection form)
{
    ...
}

Answer 2

I ended up extending the SetProperty method on the DefaultModelBinder to check the value before proceeding with the base behavior. If the value is a string I perform my filtering.

public class ScrubbingBinder : DefaultModelBinder
{
 protected override void SetProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor, object value)
 {
  if (value.GetType() == typeof(string))
   value = HtmlScrubber.ScrubHtml(value as string, HtmlScrubber.SimpleFormatTags);
  base.SetProperty(controllerContext, bindingContext, propertyDescriptor, value);
 }
}