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  
       }  
     });  





Comments

Popular posts from this blog

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 be able to use global

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

Making FluentValidation compatible with Swagger including Enum or fixed List support

FluentValidation is not directly compatible with Swagger API to validate models. But they do provide an interface through which we can compose Swagger validation manually. That means we look under FluentValidation validators and compose Swagger validator properties to make it compatible. More of all mapping by reading information from FluentValidation and setting it to Swagger Model Schema. These can be done on any custom validation from FluentValidation too just that proper schema property has to be available from Swagger. Custom validation from Enum/List values on FluentValidation using FluentValidation.Validators; using System.Collections.Generic; using System.Linq; using static System.String; /// <summary> /// Validator as per list of items. /// </summary> /// <seealso cref="PropertyValidator" /> public class FixedListValidator : PropertyValidator { /// <summary> /// Gets the valid items /// <

Handling JSON DateTime format on Asp.Net Core

This is a very simple trick to handle JSON date format on AspNet Core by global settings. This can be applicable for the older version as well. In a newer version by default, .Net depends upon Newtonsoft to process any JSON data. Newtonsoft depends upon Newtonsoft.Json.Converters.IsoDateTimeConverter class for processing date which in turns adds timezone for JSON data format. There is a global setting available for same that can be adjusted according to requirement. So, for example, we want to set default formatting to US format, we just need this code. services.AddMvc() .AddJsonOptions(options => { options.SerializerSettings.DateTimeZoneHandling = "MM/dd/yyyy HH:mm:ss"; });

Kendo MVC Grid DataSourceRequest with AutoMapper

Kendo Grid does not work directly with AutoMapper but could be managed by simple trick using mapping through ToDataSourceResult. The solution works fine until different filters are applied. The problems occurs because passed filters refer to view model properties where as database model properties are required after AutoMapper is implemented. So, the plan is to intercept DataSourceRequest  and modify names based on database model. To do that we are going to create implementation of  CustomModelBinderAttribute to catch calls and have our own implementation of DataSourceRequestAttribute from Kendo MVC. I will be using same source code from Kendo but will replace column names for different criteria for sort, filters, group etc. Let's first look into how that will be implemented. public ActionResult GetRoles([MyDataSourceRequest(GridId.RolesUserGrid)] DataSourceRequest request) { if (request == null) { throw new ArgumentNullExce

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

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 query result from

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>",

Data seed for the application with EF, MongoDB or any other ORM.

Most of ORMs has moved to Code first approach where everything is derived/initialized from codes rather than DB side. In this situation, it is better to set data through codes only. We would be looking through simple technique where we would be Seeding data through Codes. I would be using UnitOfWork and Repository pattern for implementing Data Seeding technique. This can be applied to any data source MongoDB, EF, or any other ORM or DB. Things we would be doing. - Creating a base class for easy usage. - Interface for Seed function for any future enhancements. - Individual seed classes. - Configuration to call all seeds. - AspNet core configuration to Seed data through Seed configuration. Creating a base class for easy usage public abstract class BaseSeed<TModel> where TModel : class { protected readonly IMyProjectUnitOfWork MyProjectUnitOfWork; public BaseSeed(IMyProjectUnitOfWork MyProjectUnitOfWork) { MyProject

MongoDB navigation property or making it behave as ORM in .Net

This is an implementation to make models to have  navigation properties work like ORM does for us. What actually happens in ORM to make navigation properties work? Entity Framework has proxy classes implementation to allow lazy loading and eager loading implementation. While creating proxy classes it also changes definitions for actual classes to make navigation properties work to get values based on Model's for navigation properties. Most of ORMs work in same fashion like Telerik DataAccess has enhancer tool which changes class definition at compile time to enable navigation properties. In this implementation, we would retain the original class but we would have extension methods to allow initializing properties to have navigation proprieties work. Let's first create desire model on which we need to implement. I am picking up simple one-to-many relationship example from Person to Address. public class Person { public int PersonId { get; set; }