Skip to main content

Gracefully notifying end user about application error in .Net and .Net Core versions

We generally do error logging for the application to know what error might have occurred in the application. Notifying the end user about the error is equally important. Also, it is always better to implement this at first place rather than doing at a later stage. I have seen many big company's websites ending with .NET yellow page of death. Now, it is really good that the default behavior is removed from .Net Core framework with some generic error message.

We would look how to implement generically and use in older frameworks and some tips on .Net Core as well.

The idea is to create MVC Controller for error and then redirect it from any locations like Filters or Global Exception handling. Also, we would briefly look into the global AJAX error handling system since heavy usage of AJAX in current development trend.

The few steps that we are going to do.
- Represent application errors with enum as system/application have different ways to deal with errors like though Exception or status code.
- Domain model to generate respective error message based on Enum.
- Global exception handling to catch the exception and redirect to MVC Action.

Error Enum

This can be extended as you required. I would be using Unknown as a default initialization but could be set as zero to get initial value.

 /// <summary>  
 /// Error codes for requests  
 /// </summary>  
 public enum ErrorCode  
 {  
   /// <summary>  
   /// The HTTP request error  
   /// </summary>  
   HttpRequestError,  
   /// <summary>  
   /// The page not found  
   /// </summary>  
   PageNotFound,  
   /// <summary>  
   /// The unknown  
   /// </summary>  
   Unknown,  
   /// <summary>  
   /// The unauthorized user  
   /// </summary>  
   UnauthorizedUser,  
   /// <summary>  
   /// The anti forgery token  
   /// </summary>  
   AntiForgeryToken  
 }

Domain model to generate message

This is pretty straight forward to initialize class based on ErrorCode enum which in turn gives us messages to display to the end users.

 /// <summary>  
 /// Error model  
 /// </summary>  
 public class ErrorModel  
 {  
   /// <summary>  
   /// Initializes a new instance of the <see cref="ErrorModel"/> class.  
   /// </summary>  
   /// <param name="errCode">The error code.</param>  
   public ErrorModel(ErrorCode errCode)  
   {  
     ErrorCode = errCode;  
     switch (errCode)  
     {  
       case ErrorCode.HttpRequestError:  
         ErrorHeader = "Invalid inputs given.";  
         ErrorMessage = "Request terminated. Invalid characters found. Please try putting correct values.";  
         break;  
       case ErrorCode.PageNotFound:  
         ErrorHeader = "Page Not Available";  
         ErrorMessage = "The requested page is either moved or invalid.";  
         break;  
       case ErrorCode.UnauthorizedUser:  
         ErrorHeader = "Unauthorized Access";  
         ErrorMessage = "You don't have permission to access this area.";  
         break;  
       case ErrorCode.AntiForgeryToken:  
         ErrorHeader = "Security Issue";  
         ErrorMessage = "Source and destination does not match each other. Please try again.";  
         break;  
       case ErrorCode.Unknown:  
       default:  
         ErrorHeader = "Unknown error";  
         ErrorMessage = "We are sorry but it appears that this page is missing or some error has occurred.";  
         break;  
     }  
   }  
   /// <summary>  
   /// Gets or sets the error code.  
   /// </summary>  
   /// <value>  
   /// The error code.  
   /// </value>  
   public ErrorCode ErrorCode { get; set; }  
   /// <summary>  
   /// Gets or sets the error header.  
   /// </summary>  
   /// <value>  
   /// The error header.  
   /// </value>  
   public string ErrorHeader { get; set; }  
   /// <summary>  
   /// Gets or sets the error message.  
   /// </summary>  
   /// <value>  
   /// The error message.  
   /// </value>  
   public string ErrorMessage { get; set; }  
 }

Error Controller along with View

This has a just few logic to check if it is AJAX call and response accordingly. Just in case of Unauthorized it redirects to login page.

 public class ErrorController  
   : Controller  
 {  
   /// <summary>  
   /// Indexes the specified error code.  
   /// </summary>  
   /// <param name="id">The error code.</param>  
   /// <returns></returns>  
   [AllowAnonymous]  
   public ActionResult Index(ErrorCode id)  
   {  
     var error = new ErrorModel(id);  
     if (Request.IsAjaxRequest())  
     {  
       return Content($"{error.ErrorHeader} - {error.ErrorMessage}");  
     }  
     else if (id == ErrorCode.UnauthorizedUser)  
     {  
       return RedirectToAction("Index", "Login", new { area = "Account" });  
     }  
     return View(error);  
   }  
   /// <summary>  
   /// Error view based on Context Error code.  
   /// </summary>  
   /// <param name="statusCode">The status code.</param>  
   /// <returns>Redirects to Index</returns>  
   [AllowAnonymous]  
   [Route("Error/Code/{statusCode}")]  
   public ActionResult Code(int statusCode)  
   {  
     var errCode = ErrorCode.Unknown;  
     switch (statusCode)  
     {  
       case 404:  
         errCode = ErrorCode.PageNotFound;  
         break;  
       case 401:  
         errCode = ErrorCode.UnauthorizedUser;  
         break;  
     }  
     return RedirectToAction(nameof(Index), new { id = errCode });  
   }  
 }

In the case of  .NET Core, IsAjaxRequest won't be available. So, you can use this extension method.

 public static bool IsAjaxRequest(this HttpRequest request)  
 {  
   if (request == null)  
   {  
     throw new ArgumentNullException(nameof(request));  
   }  
   if (request.Headers != null)  
   {  
     return request.Headers["X-Requested-With"] == "XMLHttpRequest";  
   }  
   return false;  
 }

View for Action: Index.cshtml

 @model ErrorModel  
 @{  
   ViewBag.Title = "Error";  
   //Layout = "~/Views/Shared/_Layout.cshtml";  
 }  
 <h2 class="text-danger">@Model.ErrorHeader</h2>  
 <div class="text-info">  
   @Model.ErrorMessage  
 </div>

Global exception handling and redirection: Global.asax.cs

This is not applicable in .Net Core we would have another section for same.
Based on certain condition it is composing correct ErrorCode enum and redirecting to ErrorController.

 protected void Application_Error(object sender, EventArgs e)  
 {  
   // Skip error logging and page redirect if application is running on local machine  
   if (Request.IsLocal)  
   {  
     return;  
   }  
   // Get exception  
   var ex = Server.GetLastError();  
   if (ex == null)  
   {  
     return;  
   }  
   Server.ClearError();  
   ErrorCode errCode = ErrorCode.Unknown;  
   // Form error code.  
   if (ex is HttpRequestValidationException)  
   {  
     errCode = ErrorCode.HttpRequestError;  
   }  
   else if ((ex as HttpException) != null &&  
         (ex as HttpException).GetHttpCode() == 404)  
   {  
     errCode = ErrorCode.PageNotFound;  
   }  
   else if (ex as System.Web.Mvc.HttpAntiForgeryException != null)  
   {  
     errCode = ErrorCode.AntiForgeryToken;  
   }
   Log.Error(String.Format("{0} error:", errCode.ToString()), ex);  
   Response.Redirect("/error?id=" + errCode);  
 }

Since it won't work in .Net Core there have to be few extra things required.

.Net Core exception handling

A while back I had written an article Global exception handling and custom logging in AspNet Core with MongoDB. Under GlobalExceptionFilter we can hook this up and the same thing is done as well in that article.

The 401 or some others does not get properly redirected through Global exception filter in .Net Core. Maybe due to Pipeline of filters is directly associated with MVC. We can overcome by using this under Startup.cs along with GlobalExceptionFilter.

 app.UseStatusCodePagesWithReExecute("/error/code/{0}");

Client side notification

This actually depends on the approach that you might have taken for clients side scripting. If there is common functions for get, post, AJAX requests then you could hook up there. In Angular these can be hooked on observable.

In the case of jQuery, AJAX calls can be globally registered.
Sample:

   $(document).ajaxError(  
     function (e, xhr, settings) {  
       if (xhr.status == 401) {  
         // Notify user for redirection and redirect  
       }  
     });





Labels:

Comments

Post a Comment

Popular posts from this blog

Getting started with Raspberry Pi

Raspberry Pi is a small, low powered motherboard contains 512 RAM, combined CPU and GPU. It has LAN, 2 USB, HDMI input, Audio Out, SD Card reader and S-Video connectors. We can have many Linux distribution OS on it. To configure, we just need to attach SD Card to it. SD Card could range from class 4 to class 10. In some cases Raspberry Pi could support less then class 4 cards too. It could be powered through mini USB mobile charger. Let's get started with installing OS on SD Card. There are various ways to install OS. Like we can download OSes through  http://www.raspberrypi.org/downloads  and follow the instructions given on it. There is something BerryBoot multi-boot loader through which we can have more then one OS on Raspberry Pi and boot OS according to our need.  http://www.berryterminal.com/doku.php/berryboot  instructions could be followed to install OS with very simple steps. You need to have internet connection on Raspberry Pi to install OS. It coul...
Post a Comment
Read more

Trim text in MVC Core through Model Binder

Trimming text can be done on client side codes, but I believe it is most suitable on MVC Model Binder since it would be at one place on infrastructure level which would be free from any manual intervention of developer. This would allow every post request to be processed and converted to a trimmed string. Let us start by creating Model binder using Microsoft.AspNetCore.Mvc.ModelBinding; using System; using System.Threading.Tasks; public class TrimmingModelBinder : IModelBinder { private readonly IModelBinder FallbackBinder; public TrimmingModelBinder(IModelBinder fallbackBinder) { FallbackBinder = fallbackBinder ?? throw new ArgumentNullException(nameof(fallbackBinder)); } public Task BindModelAsync(ModelBindingContext bindingContext) { if (bindingContext == null) { throw new ArgumentNullException(nameof(bindingContext)); } var valueProviderResult = bindingContext.ValueProvider.GetValue(bin...
2 comments
Read more

Kendo MVC Grid DataSourceRequest with AutoMapper - Advance

The actual process to make DataSourceRequest compatible with AutoMapper was explained in my previous post  Kendo MVC Grid DataSourceRequest with AutoMapper , where we had created custom model binder attribute and in that property names were changed as data models. In this post we will be looking into using AutoMapper's Queryable extension to retrieve the results based on selected columns. When  Mapper.Map<RoleViewModel>(data)  is called it retrieves all column values from table. The Queryable extension provides a way to retrieve only selected columns from table. In this particular case based on properties of  RoleViewModel . The previous approach that we implemented is perfect as far as this article ( 3 Tips for Using Telerik Data Access and AutoMapper ) is concern about performance where it states: While this functionality allows you avoid writing explicit projection in to your LINQ query it has the same fatal flaw as doing so - it prevents the qu...
Post a Comment
Read more

Using Redis distributed cache in dotnet core with helper extension methods

Redis cache is out process cache provider for a distributed environment. It is popular in Azure Cloud solution, but it also has a standalone application to operate upon in case of small enterprises application. How to install Redis Cache on a local machine? Redis can be used as a local cache server too on our local machines. At first install, Chocolatey https://chocolatey.org/ , to make installation of Redis easy. Also, the version under Chocolatey supports more commands and compatible with Official Cache package from Microsoft. After Chocolatey installation hit choco install redis-64 . Once the installation is done, we can start the server by running redis-server . Distributed Cache package and registration dotnet core provides IDistributedCache interface which can be overrided with our own implementation. That is one of the beauties of dotnet core, having DI implementation at heart of framework. There is already nuget package available to override IDistributedCache i...
3 comments
Read more

C# Response files

Response files are similar to batch files, having some specific instruction. On execution they perform some predefined task based on instruction. Response file contains instruction to compile programs. If we have to build complex program through command line then response files are really helpful in development process. rsp is an extension for response files. By default, csc.rsp file exists under "Framework" folder Ex: C:\Windows\Microsoft.NET\Framework\v4.0.30319. csc.rsp contains long list of system references (dlls). Some contents under csc.rsp # Reference the common Framework libraries /r:Accessibility.dll /r:Microsoft.CSharp.dll /r:System.Configuration.dll /r:System.Configuration.Install.dll /r:System.Core.dll /r:System.Data.dll /r:System.Data.DataSetExtensions.dll /r:System.Data.Linq.dll .......... In same way we can have our own response file defined which might include some third party dll. Let's see an example. Suppose we have to create an appli...
Post a Comment
Read more

OpenId Authentication with AspNet Identity Core

This is a very simple trick to make AspNet Identity work with OpenId Authentication. More of all both approach is completely separate to each other, there is no any connecting point. I am using  Microsoft.AspNetCore.Authentication.OpenIdConnect  package to configure but it should work with any other. Configuring under Startup.cs with IAppBuilder app.UseCookieAuthentication(new CookieAuthenticationOptions { AuthenticationScheme = CookieAuthenticationDefaults.AuthenticationScheme, LoginPath = new PathString("/Account/Login"), CookieName = "MyProjectName", }) .UseIdentity() .UseOpenIdConnectAuthentication(new OpenIdConnectOptions { ClientId = "<AzureAdClientId>", Authority = String.Format("https://login.microsoftonline.com/{0}", "<AzureAdTenant>"), ResponseType = OpenIdConnectResponseType.IdToken, PostLogoutRedirectUri = "<my website url>", ...
Post a Comment
Read more

Centralized model validation both for MVC/WebApi and SPA client-side validation using FluentValidation

Validation is one of the crucial parts of any application. It has to validate on both client side and server side requests. What are target features or implementation from this article? Model validation for any given model. Centralized/One code for validation on both server-side and client-side. Automatic validation of model without writing any extra codes on/under actions for validation.  NO EXTRA/ANY codes on client-side to validate any form. Compatible with SPA. Can be compatible with any client-side validation framework/library. Like Angular Reactive form validation or any jquery validation libraries. Tools used in the implementation? FluentValidation : I feel DataAnnotation validation are excellent and simple to use, but in case of complex validation or writing any custom validations are always tricker and need to write a lot of codes to achieve whereas FluentValidations are simple even in case of complex validation. Generally, we need to validate inc...
2 comments
Read more

Implementing/Automating audit logs in Telerik Data Access

Audit logs can be tedious task if done manually, also developer might miss to update audit log implementation on certain level. The codes would be repeated on all places if not centralized. There are many approach available to maintain change history of model/table. Like having single history table and manage all changes of all models in same table. We may maintain in same table with some flags and JSON data for change list. We will look for maintaining history table based on each required data models with minimum effort and performance. To reduce code, I am going to use T4 to generate history models automatically based on original model. Also we are going to take care of Artificial type values. Step 1 - Create a custom attribute to mark model that history need to be maintained. /// <summary> /// Attribute to maintain history table /// </summary> [AttributeUsage(AttributeTargets.Class)] public class ManageHistoryAttribute : Attribute ...
Post a Comment
Read more

main method return value

Mainly we used to write "static void main" for entry point in console application. Placement of void denotes return type. In main function we could have "int" too but what does it really mean. "int main" signifies return type as integer. The return type of main function tells about execution status of application. Even if we have specified void as return type then it would be marked as successful program execution. If we mark int as return type then we are able to control the execution status. Now, what is the benefit of making main function as int. Windows OS saves result in  %ERRORLEVEL% environment variable of OS. If we create batch file and execute application through it then we will able to get status and based on result we can trigger something else through batch file. Let's suppose we have created program called TEST.EXE. Batch file script: @echo off REM Execute main program REM TEST.EXE @if  "%ERRORLEVEL%" == "0...
Post a Comment
Read more

Elegantly dealing with TimeZones in MVC Core / WebApi

In any new application handling TimeZone/DateTime is mostly least priority and generally, if someone is concerned then it would be handled by using DateTime.UtcNow on codes while creating current dates and converting incoming Date to UTC to save on servers. Basically, the process is followed by saving DateTime to UTC format in a database and keep converting data to native format based on user region or single region in the application's presentation layer. The above is tedious work and have to be followed religiously. If any developer misses out the manual conversion, then that area of code/view would not work. With newer frameworks, there are flexible ways to deal/intercept incoming or outgoing calls to simplify conversion of TimeZones. These are steps/process to achieve it. 1. Central code for storing user's state about TimeZone. Also, central code for conversion logic based on TimeZones. 2. Dependency injection for the above class to ...
4 comments
Read more