ASP.NET MVC Custom Error Handling Application_Error Global.asax?

Question

I have some basic code to determine errors in my MVC application. Currently in my project I have a controller called Error with action methods HTTPError404(), HTTPError500(), and General(). They all accept a string parameter error. Using or modifying the code below. What is the best/proper way to pass the data to the Error controller for processing? I would like to have a solution as robust as possible.

protected void Application_Error(object sender, EventArgs e)
{
    Exception exception = Server.GetLastError();
    Response.Clear();

    HttpException httpException = exception as HttpException;
    if (httpException != null)
    {
        RouteData routeData = new RouteData();
        routeData.Values.Add("controller", "Error");
        switch (httpException.GetHttpCode())
        {
            case 404:
                // page not found
                routeData.Values.Add("action", "HttpError404");
                break;
            case 500:
                // server error
                routeData.Values.Add("action", "HttpError500");
                break;
            default:
                routeData.Values.Add("action", "General");
                break;
        }
        routeData.Values.Add("error", exception);
        // clear error on server
        Server.ClearError();

        // at this point how to properly pass route data to error controller?
    }
}

Retroact

Answer 1

Instead of creating a new route for that, you could just redirect to your controller/action and pass the information via querystring. For instance:

protected void Application_Error(object sender, EventArgs e) {
  Exception exception = Server.GetLastError();
  Response.Clear();

  HttpException httpException = exception as HttpException;

  if (httpException != null) {
    string action;

    switch (httpException.GetHttpCode()) {
      case 404:
        // page not found
        action = "HttpError404";
        break;
      case 500:
        // server error
        action = "HttpError500";
        break;
      default:
        action = "General";
        break;
      }

      // clear error on server
      Server.ClearError();

      Response.Redirect(String.Format("~/Error/{0}/?message={1}", action, exception.Message));
    }

Then your controller will receive whatever you want:

// GET: /Error/HttpError404
public ActionResult HttpError404(string message) {
   return View("SomeView", message);
}

There are some tradeoffs with your approach. Be very very careful with looping in this kind of error handling. Other thing is that since you are going through the asp.net pipeline to handle a 404, you will create a session object for all those hits. This can be an issue (performance) for heavily used systems.

Epicalyx

When you say "be careful of looping" what exactly do you mean? Is there a better way to handle this type of error redirect (assuming it WAS a heavily used system) ? – Retroact

By looping I mean when you have an error in your error page, then you would be redirected to your error page again and again... (for instance, you want to log your error in a database and it is down). – Epicalyx

Redirecting on errors goes against the architecture of the web. The URI should remain the same when the server responds the correct HTTP status code so the client knows the exact context of the failure. Implementing HandleErrorAttribute.OnException or Controller.OnException is a better solution. And if those fail, do a Server.Transfer("~/Error") in Global.asax. – Spoke

@asbjornu - If an entity is not found, it may be perfectly acceptable to redirect rather than return a 404 error, as long as you set the HTTP response code correclty, e.g. to 301 (permanent redirect) using Response.RedirectPermanent(...) – Messeigneurs

@Chris, It's acceptable, but not best practice. Especially since it's often redirected to a resource file that is served with an HTTP 200 status code, which leaves the client to believe that everything went okay. – Spoke

@asbjornu - That's not correct :( In fact, when you use Response.RedirectPermanent(...) the server will return an HTTP 301 ("moved permanently") redirect response containing the URL, which asks the client to request the new URL. It's this second call which (correctly) returns an HTTP 200 status code for the page that is then served up. If you use Response.Redirect(...) the same occurs, but with an HTTP 302 ("moved temporarily") response code. (If using Google Chrome Dev Tools, switch 'Preserve Log upon Navigation' in the Network tab footer to see this in action). – Messeigneurs

@Chris, I am fully aware of the existence of RedirectPermanent(), which HTTP status code it emits and so forth. What I point out is that redirecting is moving the focus away from the original resource that emits a 500 status code to another resource that might or might not emit a 500 status code. More often than not, what you're redirecting to emits a "200 OK", which is not OK. Doing a 302 to a 500 is fine, but that just doesn't happen, at least not on Microsoft's stack. – Spoke

I had to add <httpErrors errorMode="Detailed" /> to the web.config to make this work on the server. – Stidham

Working Fine. Thanks :) – Latoshalatouche

Answer 2

To answer the initial question "how to properly pass routedata to error controller?":

IController errorController = new ErrorController();
errorController.Execute(new RequestContext(new HttpContextWrapper(Context), routeData));

Then in your ErrorController class, implement a function like this:

[AcceptVerbs(HttpVerbs.Get)]
public ViewResult Error(Exception exception)
{
    return View("Error", exception);
}

This pushes the exception into the View. The view page should be declared as follows:

<%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage<System.Exception>" %>

And the code to display the error:

<% if(Model != null) { %>  <p><b>Detailed error:</b><br />  <span class="error"><%= Helpers.General.GetErrorMessage((Exception)Model, false) %></span></p> <% } %>

Here is the function that gathers the all exception messages from the exception tree:

    public static string GetErrorMessage(Exception ex, bool includeStackTrace)
    {
        StringBuilder msg = new StringBuilder();
        BuildErrorMessage(ex, ref msg);
        if (includeStackTrace)
        {
            msg.Append("\n");
            msg.Append(ex.StackTrace);
        }
        return msg.ToString();
    }

    private static void BuildErrorMessage(Exception ex, ref StringBuilder msg)
    {
        if (ex != null)
        {
            msg.Append(ex.Message);
            msg.Append("\n");
            if (ex.InnerException != null)
            {
                BuildErrorMessage(ex.InnerException, ref msg);
            }
        }
    }

Select

Answer 3

I found a solution for ajax issue noted by Lion_cl.

global.asax:

protected void Application_Error()
    {           
        if (HttpContext.Current.Request.IsAjaxRequest())
        {
            HttpContext ctx = HttpContext.Current;
            ctx.Response.Clear();
            RequestContext rc = ((MvcHandler)ctx.CurrentHandler).RequestContext;
            rc.RouteData.Values["action"] = "AjaxGlobalError";

            // TODO: distinguish between 404 and other errors if needed
            rc.RouteData.Values["newActionName"] = "WrongRequest";

            rc.RouteData.Values["controller"] = "ErrorPages";
            IControllerFactory factory = ControllerBuilder.Current.GetControllerFactory();
            IController controller = factory.CreateController(rc, "ErrorPages");
            controller.Execute(rc);
            ctx.Server.ClearError();
        }
    }

ErrorPagesController

public ActionResult AjaxGlobalError(string newActionName)
    {
        return new AjaxRedirectResult(Url.Action(newActionName), this.ControllerContext);
    }

AjaxRedirectResult

public class AjaxRedirectResult : RedirectResult
{
    public AjaxRedirectResult(string url, ControllerContext controllerContext)
        : base(url)
    {
        ExecuteResult(controllerContext);
    }

    public override void ExecuteResult(ControllerContext context)
    {
        if (context.RequestContext.HttpContext.Request.IsAjaxRequest())
        {
            JavaScriptResult result = new JavaScriptResult()
            {
                Script = "try{history.pushState(null,null,window.location.href);}catch(err){}window.location.replace('" + UrlHelper.GenerateContentUrl(this.Url, context.HttpContext) + "');"
            };

            result.ExecuteResult(context);
        }
        else
        {
            base.ExecuteResult(context);
        }
    }
}

AjaxRequestExtension

public static class AjaxRequestExtension
{
    public static bool IsAjaxRequest(this HttpRequest request)
    {
        return (request.Headers["X-Requested-With"] != null && request.Headers["X-Requested-With"] == "XMLHttpRequest");
    }
}

Toothache

While implementing this I got the following error: 'System.Web.HttpRequest' does not contain a definition for 'IsAjaxRequest'. This article has a solution: #14629804 – Plattdeutsch

Answer 4

I struggled with the idea of centralizing a global error handling routine in an MVC app before. I have a post on the ASP.NET forums.

It basically handles all your application errors in the global.asax without the need for an error controller, decorating with the [HandlerError] attribute, or fiddling with the customErrors node in the web.config.

Linis

Answer 5

This may not be the best way for MVC ( https://mcmap.net/q/183610/-asp-net-mvc-global-error-handling )

Below is how you render a view in Application_Error and write it to http response. You do not need to use redirect. This will prevent a second request to server, so the link in browser's address bar will stay same. This may be good or bad, it depends on what you want.

Global.asax.cs

protected void Application_Error()
{
    var exception = Server.GetLastError();
    // TODO do whatever you want with exception, such as logging, set errorMessage, etc.
    var errorMessage = "SOME FRIENDLY MESSAGE";

    // TODO: UPDATE BELOW FOUR PARAMETERS ACCORDING TO YOUR ERROR HANDLING ACTION
    var errorArea = "AREA";
    var errorController = "CONTROLLER";
    var errorAction = "ACTION";
    var pathToViewFile = $"~/Areas/{errorArea}/Views/{errorController}/{errorAction}.cshtml"; // THIS SHOULD BE THE PATH IN FILESYSTEM RELATIVE TO WHERE YOUR CSPROJ FILE IS!

    var requestControllerName = Convert.ToString(HttpContext.Current.Request.RequestContext?.RouteData?.Values["controller"]);
    var requestActionName = Convert.ToString(HttpContext.Current.Request.RequestContext?.RouteData?.Values["action"]);

    var controller = new BaseController(); // REPLACE THIS WITH YOUR BASE CONTROLLER CLASS
    var routeData = new RouteData { DataTokens = { { "area", errorArea } }, Values = { { "controller", errorController }, {"action", errorAction} } };
    var controllerContext = new ControllerContext(new HttpContextWrapper(HttpContext.Current), routeData, controller);
    controller.ControllerContext = controllerContext;

    var sw = new StringWriter();
    var razorView = new RazorView(controller.ControllerContext, pathToViewFile, "", false, null);
    var model = new ViewDataDictionary(new HandleErrorInfo(exception, requestControllerName, requestActionName));
    var viewContext = new ViewContext(controller.ControllerContext, razorView, model, new TempDataDictionary(), sw);
    viewContext.ViewBag.ErrorMessage = errorMessage;
    //TODO: add to ViewBag what you need
    razorView.Render(viewContext, sw);
    HttpContext.Current.Response.Write(sw);
    Server.ClearError();
    HttpContext.Current.Response.End(); // No more processing needed (ex: by default controller/action routing), flush the response out and raise EndRequest event.
}

View

@model HandleErrorInfo
@{
    ViewBag.Title = "Error";
    // TODO: SET YOUR LAYOUT
}
<div class="">
    ViewBag.ErrorMessage
</div>
@if(Model != null && HttpContext.Current.IsDebuggingEnabled)
{
    <div class="" style="background:khaki">
        <p>
            <b>Exception:</b> @Model.Exception.Message <br/>
            <b>Controller:</b> @Model.ControllerName <br/>
            <b>Action:</b> @Model.ActionName <br/>
        </p>
        <div>
            <pre>
                @Model.Exception.StackTrace
            </pre>
        </div>
    </div>
}

Difference

This is the best way IMO. Exactly what I was looking for. – Kenyettakenyon

@SteveHarris glad it helped! :) – Difference

I'm using this approach but some error not display in error page iny idea about it but it goes to error page also. – Spelling

I would put breakpoints to the beginning of Application_Error method and to the line starting with "@if(" in the view code and then inspect if (i) execution really hits the Application_Error method, (ii) Model in view code is not null and contains an exception object and (iii) debugging is enabled. Btw, as far as I remember, breakpoints on views only work if view code is not changed since last compilation. – Difference

Answer 6

Perhaps a better way of handling errors in MVC is to apply the HandleError attribute to your controller or action and update the Shared/Error.aspx file to do what you want. The Model object on that page includes an Exception property as well as ControllerName and ActionName.

Surrebutter

How will you handle a 404 error then? since there is no controller/action designated for that? – Leeuwarden

The accepted answer includes 404s. This approach is only useful for 500 errors. – Surrebutter

Maybe you should edit that into your answer. Perhaps a better way of handling errors sounds pretty much like All Errors and not 500 only. – Leeuwarden

Answer 7

Application_Error having issue with Ajax requests. If error handled in Action which called by Ajax - it will display your Error View inside the resulting container.

Expound

Answer 8

Brian, This approach works great for non-Ajax requests, but as Lion_cl stated, if you have an error during an Ajax call, your Share/Error.aspx view (or your custom error page view) will be returned to the Ajax caller--the user will NOT be redirected to the error page.

Forgat

Answer 9

Use Following code for redirecting on route page. Use exception.Message instide of exception. Coz exception query string gives error if it extends the querystring length.

routeData.Values.Add("error", exception.Message);
// clear error on server
Server.ClearError();
Response.RedirectToRoute(routeData.Values);

Fibroma

Answer 10

I have problem with this error handling approach: In case of web.config:

<customErrors mode="On"/>

The error handler is searching view Error.shtml and the control flow step in to Application_Error global.asax only after exception

System.InvalidOperationException: The view 'Error' or its master was not found or no view engine supports the searched locations. The following locations were searched: ~/Views/home/Error.aspx ~/Views/home/Error.ascx ~/Views/Shared/Error.aspx ~/Views/Shared/Error.ascx ~/Views/home/Error.cshtml ~/Views/home/Error.vbhtml ~/Views/Shared/Error.cshtml ~/Views/Shared/Error.vbhtml at System.Web.Mvc.ViewResult.FindView(ControllerContext context) ....................

So

 Exception exception = Server.GetLastError();
  Response.Clear();
  HttpException httpException = exception as HttpException;

httpException is always null then customErrors mode="On" :( It is misleading Then <customErrors mode="Off"/> or <customErrors mode="RemoteOnly"/> the users see customErrors html, Then customErrors mode="On" this code is wrong too

---

Another problem of this code that

Response.Redirect(String.Format("~/Error/{0}/?message={1}", action, exception.Message));

Return page with code 302 instead real error code(402,403 etc)

Schematize