Exception handling with Elmah installed in an ASP.NET MVC 4 Application

Question

I have built up a nice MVC4 application, decided to secure it and all is fine. Below is the filter I use to help prevent XSS attacks as an example.

public class IsPostedFromThisSiteAttribute : AuthorizeAttribute { public override void OnAuthorization(AuthorizationContext filterContext) { //TODO: - Possible problems in future: //1. Is there a way to handle the execptions and just display a friendly error page / message. if (filterContext.HttpContext != null) { if (filterContext.HttpContext.Request.UrlReferrer == null) throw new System.Web.HttpException("Invalid Submission"); //if (filterContext.HttpContext.Request.UrlReferrer.Host != "localhost/YeatsClinical.PatientPortal.Web") if (filterContext.HttpContext.Request.UrlReferrer.AbsolutePath != ConfigurationManager.AppSettings["SiteURL"]) throw new System.Web.HttpException("This form was not submitted from this site!"); } } }

My MVC app has Elmah installed and it works great too.

The problem is, I know about the error above and I don't want to display an exception message, or log it or anything like that (all of which I can do easily). Instead I want to handle it properly by displaying a nice little message to my user. How can I change the code above to allow this to either display a view or partial view with a nice little message or just output some text somewhere to let the user know what went wrong in a nice way that doesn't cause the application to crash, perhaps in this particular case, returning him to the correct login screen.

Darin Dimitrov · Accepted Answer · 2013-01-31 12:03:08Z

Just assign the Result property on the filterContext:

public class IsPostedFromThisSiteAttribute : AuthorizeAttribute { public override void OnAuthorization(AuthorizationContext filterContext) { //TODO: - Possible problems in future: //1. Is there a way to handle the execptions and just display a friendly error page / message. if (filterContext.HttpContext != null) { if (filterContext.HttpContext.Request.UrlReferrer == null) { var viewResult = new ViewResult { ViewName = "~/Views/Shared/Invalid.cshtml" }; filterContext.Result = viewResult; return; } if (filterContext.HttpContext.Request.UrlReferrer.AbsolutePath != ConfigurationManager.AppSettings["SiteURL"]) { var viewResult = new ViewResult { ViewName = "~/Views/Shared/InvalidSite.cshtml" }; filterContext.Result = viewResult; return; } } } }

This will prevent the controller action to be executed and will immediately execute the ActionResult you have assigned to the Result property of the filterContext. Basically you are short-circuiting the execution of the action. You could return whatever ActionResult you want: ViewResult, PartialViewResult, JsonResult, RedirectToRouteResult, ...

Thanks for your answer. I am getting an error but its not with this code, this is related to my login page and I am getting an error with that which is not part of the question. I made a sample project and used your code to verify it works and it does. So with that I will accept your answer, and thanks again for your help with this.

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