Intercept JsonResult and wrap it (as string)

Question

I have a action that return JsonResult.
I want to intercept the JsonResult return and wrap it with string.

Something like:

 public class JsonProxyAttribute : FilterAttribute
    {
        void OnActionExecuting(ExceptionContext filterContext)
        {
            var res = filterContext.Result as string;
            if (res != null)
            {
                filterContext.Result = "func("+filterContext.Result+")";
            }
        }
    }

So the ajax call will get this:

func({"MyContent":"content"})

instead of this:

{"MyContent":"content"}

Answer 1

What you need is to create a new ActionResult that will extend JsonResult and represent JSONP

public class JsonpResult : JsonResult
{
    public override void ExecuteResult(ControllerContext context)
    {
        HttpResponseBase response = context.HttpContext.Response;
        response.ContentType = ContentType ?? "application/x-javascript";
        response.ContentEncoding = ContentEncoding ?? System.Text.Encoding.UTF8;

        if (Data != null)
        {
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            string ser = serializer.Serialize(Data);
            response.Write("func(" + ser + ");");
        }
    }
}

Now if you want to intercept regular JSON results, your ActionFilter would look like this.

public class JsonProxyAttribute : FilterAttribute
{
    void OnActionExecuting(ExceptionContext filterContext)
    {
        var res = filterContext.Result as JsonResult;
        if (res != null)
        {
            filterContext.Result = new JsonpResult
            {
                ContentEncoding = res.ContentEncoding,
                ContentType = res.ContentType,
                Data = res.Data,
                JsonRequestBehavior = res.JsonRequestBehavior
            };
        }
    }
}

Or you can use JSONP directly in your controllers

public ActionResult Jsonp()
{
    var model = new List<string> { "one", "two" };
    return new JsonpResult
    {
        Data = model,
        JsonRequestBehavior = JsonRequestBehavior.AllowGet
    };
}