Error/ exception handling

 # Error Handling

1.  There are 3 middleware components that deal with status code pages in asp.net core

    UseStatusCodePages
    UseStatusCodePagesWithRedirects
    UseStatusCodePagesWithReExecute

2. UseStatusCodePages middleware
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseStatusCodePages();
    }
    app.UseStaticFiles();
    app.UseMvc(routes =>
    {
        routes.MapRoute("default", "{controller=Home}/{action=Index}/{id?}");
    });

3. UseStatusCodePagesWithRedirects Middleware
    - In a production quality application we want to intercept these non-success http status codes and return a custom error view. To achieve this, we can either use UseStatusCodePagesWithRedirects middleware or UseStatusCodePagesWithReExecute middleware.

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseStatusCodePagesWithRedirects("/Error/{0}");
        }
        app.UseStaticFiles();
        app.UseMvc(routes =>
        {
            routes.MapRoute("default", "{controller=Home}/{action=Index}/{id?}");
        });
    }
    With the following line in place, if there is a 404 error, the user is redirected to /Error/404.

4. Create custom ErrorController to handle different errors
    public class ErrorController : Controller
    {
        // If there is 404 status code, the route path will become Error/404
        [Route("Error/{statusCode}")]
        public IActionResult HttpStatusCodeHandler(int statusCode)
        {
            switch (statusCode)
            {
                case 404:
                    ViewBag.ErrorMessage = "Sorry, the resource you requested could not be found";
                    break;
            }

            return View("NotFound");
        }
    }
5.  For a non-development environment, add the Exception Handling Middleware to the request processing pipeline using UseExceptionHandler() method. We do this in the Configure() method of the Startup class.

    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Error");
        }

        // Rest of the code
    }
    - Now implement ErrorController
    
    public class ErrorController : Controller
    {
        [AllowAnonymous]
        [Route("Error")]
        public IActionResult Error()
        {
            // Retrieve the exception Details
            var exceptionHandlerPathFeature =
                    HttpContext.Features.Get<IExceptionHandlerPathFeature>();

            ViewBag.ExceptionPath = exceptionHandlerPathFeature.Path;
            ViewBag.ExceptionMessage = exceptionHandlerPathFeature.Error.Message;
            ViewBag.StackTrace = exceptionHandlerPathFeature.Error.StackTrace;

            return View("Error");
        }
    }

   
6. UseDeveloperExceptionPage Middleware must be plugged into the request processing pipeline as early as possible, so it can handle the exception and display the Developer Exception Page if the subsequent middleware components in the pipeline raises an exception.