ASP.NET Core Configurations – Program Startup Middleware AppSettings

The ASP.NET Core Configurations settings are configured on 3 files:

1. The Project File also known as “.csproj” file.
2. The Startup class.
3. appsettings.json file

These configuration settings tell the ASP.NET Core app – how it should behave. In this tutorial we will look into the various ASP.NET Core Configurations which will provide you with a solid foundation for understanding the coming topics. I will start by creating a new project using empty template.

Create Project using Empty Template

When you create a project using Empty Template you have to do the ASP.NET Core Configurations by yourself. This is a great way to understand the things correctly. This includes:

• Adding Folders for Controllers, Views & Models.
• Adding files like appsettings.json.
• Adding the layout View.

Start with opening your Visual Studio and then select Create a new project from the file menu. You will see the option – ASP.NET Core Web Application, so select it.

Specify the location on your drive where you want the application to be created. Give the name of your application as Configuation.

Then click the ‘Create’ Button.

Now you will get another dialog box. Here you select Empty template, and also select the Framework, Version, Template and Authentication.

Make the follow settings (as shown by the below image):

• .NET Core
• ASP.NET Core 5.0
• Empty (for template)
• No Authentication

This will create your ASP.NET Core MVC with Empty Template.

What is .csproj Project File

The “.csproj” is the Project file of an ASP.NET Core project. It contains name of the SDK, ASP.NET Core Version, references to Packages which the project is using, and many such things. The Project .csproj file is named as NameofProject.csproj. In this application the .csproj file is named as Configuration.csproj as we named the project “Configuration” during the time of creation. This file is hidden by Visual Studio and can be accessed by right clicking the project on Solution Explorer and selecting Edit Configuration.csproj.

The initial context of the “Configuration.csproj” file is shown below:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>

</Project>

The csproj can be used to install a NuGet Package to your ASP.NET Core project. You simply have to reference the package to the csproj file and Visual Studio will downloads that package for you. Similarly when you remove any package refrence from the csproj file then Visual Studio removes that package from your application.

Json.NET – Newtonsoft is a popular high-performance JSON package for .NET. It is used to serialize and deserialize JSON. To install this package I reference it on the .csproj file by adding ItemGroup and PackageReference as shown below.

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
  </ItemGroup>
	
</Project>

As soon as you save the csproj file, VS will download this package from NuGet and install it to your project.

Intall Package from NuGet Package Manager

NuGet Package Manager is a tool in Visual Studio for doing the management of NuGet packages through an easy-to-use interface. Select Tools ➤ NuGet Package Manager ➤ Manage NuGet Packages for Solution to open it. Click the “Browse tab” and enter the name of package in the text box. When you see you searched package on the list, select it and then click the ‘Install’ button.

In the below image I have searched for Json.NET, and then selecting and installing it.

There is also another way to insall the package and this is through Package Manger Console. To open it follow the below procedure:

Select Tools ➤ NuGet Package Manager ➤ Packages Manager Console in your Visual Studio then enter the below given line (and press enter key) to install the Json.NET package.

PM> Install-Package Newtonsoft.Json

This command is given on Nuget for every package. Check this link to find the command for Json.NET package.

ASP.NET Core Program Class

The Program Class is the entry point of an ASP.NET Core app. It has a method called Main() which is called when the app starts. The Main method creates a host for the web application. On the root folder of your application you will find the Program.cs for the application.

The default code of the Program Class is shown below:

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Configuation
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

The Main method in the Program class calls a CreateHostBuilder function which configures the ASP.NET Core like setting up the hosting environment.

Inside the CreateHostBuilder function, you will find it calling the CreateDefaultBuilder() function which configures the application with the Most Suitable Settings. By Most Suitable Settings I mean the settings which are suitable for most of the ASP.NET Core applications.

Although Program class has very little use and mostly you won’t need to even touch it. Only in some advanced projects you will need to configure it, for example, in Certificate Authentication I configured Kestrel settings on the Program.cs class so that the application always require child certificates. You can see how I did it at Configure Kestrel to require certificates.

The webBuilder.UseStartup<Startup> function calls the Startup.cs class which is also kept on the application root folder. The Startup.cs class provides application specific configuration. In the next section you will learn more about Startup Class.

The Build() function builds the application and if no errors are found then will run your application on the browser.

Inside the CreateHostBuilder() function you can provide individual configuration settings. In the below code I have provided 2 individual settings – UseContentRoot & UseIISIntegration.

public static IHostBuilder CreateHostBuilder(string[] args) =>
  Host.CreateDefaultBuilder(args)
      .ConfigureWebHostDefaults(webBuilder =>
      {
          webBuilder.UseContentRoot(Directory.GetCurrentDirectory())
          .UseIISIntegration()
          .UseStartup<Startup>();
      });

Some important settings are:

Kestrel is an open-source, cross-platform web server for hosting ASP.NET applications on any platform (Windows, Linux, macOS). It is used automatically when running ASP.NET Core application with IIS. You can use Kestrel by itself or with a reverse proxy server, such as “IIS, Nginx, or Apache”. A reverse proxy server receives HTTP requests from the Internet and forwards them to Kestrel after some preliminary handling.

In order to use Kestrel by itself for running ASP.NET Core application, you click the arrow on the right of IIS Express button in Visual Studio then select the “name of your application”. In this application it will be Configuration.

Once selected the name of your application you have to run your application (shortcut F5 key). Now your application will now run on Kestrel only.

ASP.NET Core Startup Class

Every ASP.NET Core app contains a Startup class called Startup.cs which is called when the application starts. Actually the Program.cs calls the Startup Class using webBuilder.UseStartup<Startup> method. You will find the Startup.cs on your application’s root folder. In the file you can provide a lot of application specific configuration which you will see in the coming sections.

The Startup class can have any name. For example – you can create a class called Batman.cs and call it from Program class as webBuilder.UseStartup<Batman>. Now the Batman class becomes the Startup class for your application.

Startup class has 2 main methods which are responsible for doing a number of things like registering services, routing, authentication, authorization and many more tasks. These methods are:

1. ConfigureServices
2. Configure

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapGet("/", async context =>
            {
                await context.Response.WriteAsync("Hello World!");
            });
        });
    }
}

If you open the Startup class you will see it like shown below:

Let us understand these 2 methods of the startup class.

What ConfigureServices method does in Startup class

The ConfigureServices method is used to register the services so that they can be used throughout the application. Some of the commonly used services which we register in this method are:

• services.AddControllersWithViews – which adds services for controllers, API-related features, and views in the application.
• services.AddRazorPages – which adds services for Razor Pages.
• services.AddDbContext – registers a context which is commonly Entity Framework Core services.
• services.AddDefaultIdentity – registers Identity services to the application.

See below code of ConfigureServices method where I am registering some of these services.

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<AppDbContext>(options =>
        options.UseSqlServer(
            Configuration.GetConnectionString("MyConnection")));
    services.AddDefaultIdentity<IdentityUser>(
        options => options.SignIn.RequireConfirmedAccount = true)
        .AddEntityFrameworkStores<ApplicationDbContext>();

    services.AddRazorPages();

    services.AddControllersWithViews();
} 

Note that the ConfigureServices method is called before the Configure method.

What Configure method does in Startup class

In the Configure method we configure HTTP Request pipeline for the ASP.NET Core app. The request pipeline is configured by adding middleware components to an “IApplicationBuilder” instance. The most common methods we add in the configure method are:

• app.UseDeveloperExceptionPage – adds the “ExceptionHandler” middleware that will show developer exception page with detailed information whenever unhandled request exceptions arises in the app. It should be used only when the app is running in the Development environment.
• app.UseExceptionHandler – adds “ExceptionHandler” middleware to catch exceptions and logs them. It should be used in Production environment i.e. when the app is running in Production.
• app.UseHsts – adds HSTS Middleware which enables HSTS header. HSTS full form is (HTTP Strict Transport Security).
• app.UseHttpsRedirection – adds HTTPS Redirection Middleware to enforce HTTPS by redirecting all HTTP requests to HTTPS.
• app.UseStaticFiles – adds Static File Middleware which enables static files to be served.
• app.UseRouting – adds Routing middleware which matches request to an endpoint.
• app.UseAuthorization – adds Authorization middleware.
• app.UseAuthentication – adds Authentication middeware.
• add.UseEndpoints – adds Endpoint Routing Middleware to execute the matched endpoint.

I have shown these settings in the below code.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        app.UseHsts();
    }
    app.UseHttpsRedirection();
    app.UseStaticFiles();

    app.UseRouting();

    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllerRoute(
            name: "default",
            pattern: "{controller=Home}/{action=Index}/{id?}");
    });
}

What are ASP.NET Core Services

An ASP.NET Core Service can be anything in which does a particular task and is available all through the application. Examples can be:

1. Service for sending a text verification code to user’s email address.
2. Service for validating mobile number through OTP.
3. Service that helps in recovering the user’s account password when lost.
4. Entity Framework Core service.
5. Identity Service.

I will create a small ASP.NET Core Service that provides the application with the total number of registered users.

Start by creating a folder in your application’s root folder and name it Services or anything you like. Inside this Services folder create a class and name it TotalUsers.cs and add the following code to it:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
 
namespace Configuation.Services
{
    public class TotalUsers
    {
        public long TUsers()
        {
            Random rnd = new Random();
            return rnd.Next(100, int.MaxValue);
        }
    }
}

This method Tusers() returns the total number of users registered in the application which is just a random number between 100 and max value of Int.

The next step involves registering this class in the Startup class so that ASP.NET Core can make this service available throughout the application.

So go the Startup.cs class and import the namespace – using Configuation.Services.

Next add the following codes inside the ConfigureServices() method:

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<TotalUsers>();
}

The services.AddSingleton() will add the service which can now be shared all thought the application.

Next, inside the Configure() method you will find app.UseEndpoints() method (shown below).

app.UseEndpoints(endpoints =>
{
    endpoints.MapGet("/", async context =>
    {
        await context.Response.WriteAsync("Hello World!");
    });
});

Replace it to:

app.UseEndpoints(endpoints =>
{
    endpoints.MapDefaultControllerRoute();
});

So the Startup class will now look like:

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<TotalUsers>();
        services.AddControllersWithViews();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapDefaultControllerRoute();
        });
    }
}

The service is now created and available through in the application.

Inject ASP.NET Core Service to Controller from Dependency Injection

We can make a service available to a Controller from Dependency Injection feature. We injects the object of the service class through the constructor of the controller. In the below shown code I have created a constructor for the HomeController and added to it a parameter of “TotalUsers” class.

Recall that we have the “TotalUsers” class registered as a service on the startup class so the Dependency Injection feature will automatically provide this parameter of the constructor (TotalUsers tu) with the assigned value. The assigned value will be the random value from 100 to max value of int.

private TotalUsers totalUsers;
public HomeController(TotalUsers tu)
{
    totalUsers = tu;
}

Start by creating “Controllers” folder on the root of your application by right clicking the name of the application on the Solution Explorer and selecting Add ➤ New Folder, and then rename it to “Controllers”. Now right click on this newly created “Conrollers” folder and select Add ➤ New Item. On the items window which opens, select MVC Controller – Empty and name this controller as HomeController

Next, import the below given namespace on this controller.

using Configuation.Services;

Add the following code to the controller:

public class HomeController : Controller
{
    private TotalUsers totalUsers;
    public HomeController(TotalUsers tu)
    {
        totalUsers = tu;
    }
 
    public string Index()
    {
        return "Total Users are: " + totalUsers.TUsers();
    }
}

The controller has a constructor which has our service class called TotalUsers in it’s parameter. When ASP.NET calls this controller it sees the constructor requires an object i.e. has a dependency for the service class called TotalUsers.

MVC then goes to the Startup class and finds the TotalUsers class been configured as a service. So it will now create an instance of the TotalUsers class (by its own) and pass it to the construction of the Home Controller.

The Index action method calls the TUsers() method to get the total number of registered users. It finally returns them as string to the View.

Next, create a new folder called Views on the root of the application. Inside this folder create another folder and name it Home.

Now create a new Razor View – Empty file inside the Views ➤ Home folder and name it “Index.cshtml”. Add the following code to it.

@model string
@Model

To test the service run your application and you will see the total number of users displayed on the browser.

ASP.NET Core Middleware

An ASP.NET Core Middleware is a component that sits on the HTTP Request Pipeline and handles requests and responses. There can be one or more Middlewares sitting on the HTTP pipeline in a line. When a new HTTP request arrives, it is send to the first middleware which inspects it. This Middleware will peform one of the two things:

1. Generates a response and send it back to the client (request initiator).
2. Pass the HTTP Request to the next Middleware in the pipeline.

Note that the Middeware are processed on the same order in which they are applied for a request. The response is returned to the client in the “opposite” order in which the middleware are processed. Suppose we have 4 middeware – M1, M2, M3 and M4. They are applied in the order M1 > M2 > M3 > M4. So we can say, for a http request –

• The Middeware are processed in the Order M1 > M2 > M3 > M4.
• The Middeware response are returned to the client in the order M4 > M3 > M2 > M1. That is in last come first server order.

Why Middleware is used in ASP.NET Core? Middleware respond to http requests made to the application. This can be inhanced to build high class features like authentication, authorization, logging and so on. There are large number of Built-in Middleware in ASP.NET Core, we can use only the ones which we need in our app and remove others which we don’t need. Thus optimizing the speed of our app.

ASP.NET Core Custom Middleware

We can also build our own Custom Middleware in ASP.NET Core. The custom middleware can be any from the 4 types, these are:

1. Content-Generating Middleware.
2. Short-Circuiting Middleware.
3. Request-Editing Middleware.
4. Response-Editing Middleware.

Each Middleware must have 2 things:

1. A RequestDelegate object of Microsoft.AspNetCore.Http namespace. This object is used to process the http requests. The RequestDelegate represents the next middleware component in the http pipeline and is injected to the controller of Middleware with Dependency Injection.

2. An Invoke method which is called whenver the Middleware is called. In the Invoke method we write our custom codes.

I will now build one example each for these 4 types of Custom Middleware.

Content-Generating Middleware

The Content-Generating Middleware generates some content or Response. We create this ASP.NET Core Middeware to return Response to the client. Let us create a small exmaple of this Middleware to understand how it works.

Create a new folder on the root folder and name it Middlewares (you can name this folder anything). Next, add a class to this new folder and call it ContentMiddleware.cs. To this class add the following codes:

using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
 
namespace Configuation.Middlewares
{
    public class ContentMiddleware
    {
        private RequestDelegate nextDelegate;
        public ContentMiddleware(RequestDelegate next) => nextDelegate = next;
 
        public async Task Invoke(HttpContext httpContext)
        {
            if (httpContext.Request.Path.ToString() == "/middleware")
            {
                await httpContext.Response.WriteAsync("This is from the content middleware");
            }
            else
            {
                await nextDelegate.Invoke(httpContext);
            }
        }
    }
}

Please note that the Middleware class doesn’t implement an interface or derive from a common base class. They have a constructor that takes a parameter of type RequestDelegate which is provided to it automatically by MVC. The RequestDelegate object represents the next middleware component in the line.

The Middleware also define an Invoke method. This method is called when .NET receives an HTTP request. The Invoke method has a parameter of type HttpContext which contains Information about the HTTP request and the response that will be returned to the client.

In my ContentMiddleware.cs class the Invoke method inspects the HTTP request and checks to see whether the request has been sent to the url /middleware. If it has, then it sends a simple text response – This is from the content middleware. If a different URL has been initiated, then the request is forwarded to the next Middleware in the line.

Now register the Middleware inside the Configure method of the Startup class using the UseMiddleware() method like shown below:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {
    app.UseMiddleware<ContentMiddleware>();
}

Run the application and then go to the URL – https://localhost:44343/middleware. You will see the response from the Middleware as shown by the image below:

If the URL is not – https://localhost:44343/middleware then the Content Middleware will pass the request to the next Middleware. Note that here there is no Middleware left therefore the request is returned back.

ASP.NET Core Middleware with Dependency Injection

We can inject services to Middleware with dependency injection. In the previous section I created a service called TotalUsers, now I will use this service in Middleware by injecting it in the constructor of the middleware. So, update the code for the “ContentMiddleware.cs” by adding constructor which recieves the object of “TotalUsers.cs” in it’s parameter. See highlighted code below:

using System.Threading.Tasks;
using Configuation.Services;
using Microsoft.AspNetCore.Http;
 
namespace Configuation.Middlewares
{
    public class ContentMiddleware
    {
        private RequestDelegate nextDelegate;
        private TotalUsers totalUsers;
 
        public ContentMiddleware(RequestDelegate next, TotalUsers tu)
        {
            nextDelegate = next;
            totalUsers = tu;
        }
 
        public async Task Invoke(HttpContext httpContext)
        {
            if (httpContext.Request.Path.ToString() == "/middleware")
            {
                await httpContext.Response.WriteAsync("This is from the content middleware, Total Users: " + totalUsers.TUsers());
            }
            else
            {
                await nextDelegate.Invoke(httpContext);
            }
        }
    }
}

Note that on line 22 I am adding the total users to the response message as totalUsers.TUsers(). Run you application and go to the URL – https://localhost:44343/middleware. Now you will also see total number of users (check the below image).

Short-Circuiting Middleware

Short-Circuiting Middleware prevents further middleware from processing the request because it short-circuits the pipeline. Let us create a Custom Short-Circuit Middleware.

Inside the Middlewares folder create a new class and name it ShortCircuitMiddleware.cs. To this class add the below code:

using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
 
namespace Configuation.Middlewares
{
    public class ShortCircuitMiddleware
    {
        private RequestDelegate nextDelegate;
        public ShortCircuitMiddleware(RequestDelegate next) => nextDelegate = next;
 
        public async Task Invoke(HttpContext httpContext)
        {
            if (httpContext.Request.Headers["User-Agent"].Any(v => v.Contains("Firefox")))
            {
                httpContext.Response.StatusCode = StatusCodes.Status401Unauthorized;
            }
            else
            {
                await nextDelegate.Invoke(httpContext);
            }
        }
    }
}

This ASP.NET Core Middleware Returns 401 Unauthorized Status Code if the client’s browser is firefox. This is done by this code line:

httpContext.Response.StatusCode = StatusCodes.Status401Unauthorized;

Now go to the Configure method of the Startup class and register this short-circuit middleware. Make sure the registration is done before the previous ‘ContentMiddleware.cs’ Middleware as shown below:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseMiddleware<ShortCircuitMiddleware>();
    app.UseMiddleware<ContentMiddleware>(); 
}

Always remember that the Middlewares execute in the order they are registered in the Configure method. I want ShortCircuitMiddleware to execute before ContentMiddleware so I have placed it at first.

The Short-Circuit Middleware checks the User-Agent in the header to find out if the browser is firefox. In that case it does not forward the request and returns unauthorized status. For other browsers it forwards the request to the ContentMiddleware.cs.

If you now run your application and open the URL – https://localhost:44343/middleware in Firefox browser. You will receive a blank page. For other browsers you will get the same response which you get previously.

The Firefox screenshot is shown below:

Request-Editing Middleware

Request-Editing Middleware does not generate response instead edits http requests. Create a class inside the Middlewares folder and name it RequestEditingMiddleware.cs. Add the given code to it:

using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
 
namespace Configuation.Middlewares
{
    public class RequestEditingMiddleware
    {
        private RequestDelegate nextDelegate;
        public RequestEditingMiddleware(RequestDelegate next) => nextDelegate = next;
 
        public async Task Invoke(HttpContext httpContext)
        {
            httpContext.Items["Firefox"] = httpContext.Request.Headers["User-Agent"].Any(v => v.Contains("Firefox"));
            await nextDelegate.Invoke(httpContext);
        }
    }
}

In the above code see that only the HTTP Request is edited and it does not sends any response. First the check is made to find out if the request is coming from firefox browser, in that case a key called Firefox is added with Boolean value ‘true’ to the HttpContext dictionary. The below given code does this work:

httpContext.Items["Firefox"] = httpContext.Request.Headers["User-Agent"].Any(v => v.Contains("Firefox"));

Now open the ShortCircuitMiddleware.cs which you made earlier. Here Delete or comment out the line which checks the User-Agent.

//if (httpContext.Request.Headers["User-Agent"].Any(v => v.Contains("Firefox")))

In place of it check the item named ‘Firefox’ in the HttpContext. See the below code:

if (httpContext.Items["Firefox"] as bool? == true)

So the updated code of ShortCircuitMiddleware.cs Class is given below:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;

namespace Configuration.Middlewares
{
    public class ShortCircuitMiddleware
    {
        private RequestDelegate nextDelegate;
        public ShortCircuitMiddleware(RequestDelegate next) => nextDelegate = next;

        public async Task Invoke(HttpContext httpContext)
        {
            //if (httpContext.Request.Headers["User-Agent"].Any(v => v.Contains("Firefox")))
            if (httpContext.Items["Firefox"] as bool? == true)
            {
                httpContext.Response.StatusCode = StatusCodes.Status401Unauthorized;
            }
            else
            {
                await nextDelegate.Invoke(httpContext);
            }
        }
    }
}

Because of this change the “Short-Circuiting Middleware” will now check for the item called “Firefox” in HttpContext. Obviously we need to register the RequestEditingMiddleware.cs before short-circuit middleware for this to work.

So Register the Request Editing Middleware on the Configure() method of Statup class:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseMiddleware<RequestEditingMiddleware>();
    app.UseMiddleware<ShortCircuitMiddleware>();
    app.UseMiddleware<ContentMiddleware>();
}

Run the application and upon the URL – https://localhost:44343/middleware in firefox. You will get a blank page due to unauthorized HTTP request condition.

Response-Editing Middleware

As the name suggest the Response-Editing Middleware edits only the response generated by other Middleware.

Right now we are getting a blank page on the Firefox browser. Blank page is no good for real applications, we should also show some proper message. The Response-Editing Middleware will come to use here, I will provide text response which users will see only on the firefox browser.

Add a new class inside the Middlewares folder and name it ResponseEditingMiddleware.cs. Add the below code to it:

using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
 
namespace Configuation.Middlewares
{
    public class ResponseEditingMiddleware
    {
        private RequestDelegate nextDelegate;
        public ResponseEditingMiddleware(RequestDelegate next)
        {
            nextDelegate = next;
        }
 
        public async Task Invoke(HttpContext httpContext)
        {
            await nextDelegate.Invoke(httpContext);
            if (httpContext.Response.StatusCode == 401)
            {
                await httpContext.Response.WriteAsync("Firefox browser not authorized");
            }
            else if (httpContext.Response.StatusCode == 404)
            {
                await httpContext.Response.WriteAsync("No Response Generated");
            }
        }
    }
}

In the above code if the HTTP status code in the response is 401 then I am adding text – Firefox browser not authorized to the response. Recall that the 401 un-authorized response is generated by Short-Circuiting Middleware.

Since the Response-Editing Middleware only edits the response of other Middleware it has to be placed before other Middleware in the HTTP pipeline. So register it below other Middleware in the Configure() method of Startup class:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseMiddleware<ResponseEditingMiddleware>();
    app.UseMiddleware<RequestEditingMiddleware>();
    app.UseMiddleware<ShortCircuitMiddleware>();
    app.UseMiddleware<ContentMiddleware>();
}

Now run your application and go to URL – https://localhost:44343/middleware in the Firefox browser. You will get the response text – Firefox browser not authorized. This is shown in the image below.

In the Response-Editing Middleware there is an else if block:

else if (httpContext.Response.StatusCode == 404)
{
    await httpContext.Response.WriteAsync("No Response Generated");
}

This will execute when status code is 404. This status code is automatically generated when there is no resource found in the application for a url.

Open any random url which is not served by the application like – https://localhost:44343/tutorials. You will see No Response Generated message on your browser.

Routing Middleware

The Startup Class Configure() method has a parameter of type IApplicationBuilder Interface. This Interface allows the Middleware pipeline to be created.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    //.....
}

An important use of IApplicationBuilder Interface is to configure the ASP.NET Core Routes.

Open Startup file of your application and check the Configure method. There you add app.UseRouting() which adds an Endpoint Routing middleware to your app.

Next use the Endpoint Routing like:

app.UseEndpoints(endpoints =>
{
    endpoints.MapDefaultControllerRoute();
});

I have shown these necessary codes in highlighted way below:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    //...

    app.UseRouting();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapDefaultControllerRoute();
    });
}

ASP.NET Core Hosting Environment

ASP.NET Core Hosting Environment determines the environment in which the application is running. Environments can be of 3 types:

1. Development
2. Staging
3. Production

ASP.NET Core Get Hosting Environment

We can get the Hosting Environment in the Startup Class Configure() method by the use of IWebHostEnvironment. The Configure method has IWebHostEnvironment type parameter which provides information about the hosting environment.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
//...
}

The IWebHostEnvironment has the following 3 methods to determine the hosting environment.

• IsDevelopment – returns true if environment is Development.
• IsStaging – returns true if environment is Staging.
• IsProduction – returns true if environment is Production.

In the below code I have shown how to use these 3 method to execute code blocks based on an envirnment.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        // do something
    }

    if (env.IsStaging())
    {
        // do something
    }

    if (env.IsProduction())
    {
        // do something
    }
}

The IWebHostEnvironment has some important properties which are listed below.

ASP.NET Core Set Hosting Environment

We can set the ASP.NET Core Hosting Environment through the “Properties” page of the application. In the Solution Explorer and right click on your application name and select Properties.

In the properties page select the Debug option. There you will see the current hosting environment is set as “Development” by a variable called ASPNETCORE_ENVIRONMENT. You can change it’s value to an of the 3:

1. Development
2. Staging
3. Production

When you are done save by pressing CTRL+S. Check the below image where I have illustrated this thing.

Once you save by pressing CTRL+S in Property page of the app. Visual Studio stores the environment in the launchSettings.json file. This file is located inside the Properties folder of the app.

Notice the line 15 and 22 which contains the ASPNETCORE_ENVIRONMENT variable value as Development. This means we have hosting envirnment set as Development for our app.

{
  "iisSettings": {
    "windowsAuthentication": false,
    "anonymousAuthentication": true,
    "iisExpress": {
      "applicationUrl": "http://localhost:57432",
      "sslPort": 44327
    }
  },
  "profiles": {
    "IIS Express": {
      "commandName": "IISExpress",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    },
    "Configuation": {
      "commandName": "Project",
      "launchBrowser": true,
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      },
      "dotnetRunMessages": "true",
      "applicationUrl": "https://localhost:5001;http://localhost:5000"
    }
  }
}

If you are comfortable in editing json files then you can change hosting environment for the ASPNETCORE_ENVIRONMENT variable here itseft without going through the “Properties” page. Suppose you want to change the environment as “Production” so you have to change line 15 and 22 of launchSettings.json file as:

"ASPNETCORE_ENVIRONMENT": "Production"

We created Middleware in the previous section. In the below code I made sure the Middleware are registered only if the environment is Production.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsProduction())
    {
        app.UseMiddleware<ResponseEditingMiddleware>();
        app.UseMiddleware<RequestEditingMiddleware>();
        app.UseMiddleware<ShortCircuitMiddleware>();
        app.UseMiddleware<ContentMiddleware>();
    }
}

In Program.cs you can get the Hosting Environment by adding “ConfigureAppConfiguration” to the “ConfigureWebHostDefaults” method and then using “HostingEnvironment” property to get the environment name. I have shown this in the below code.

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.ConfigureAppConfiguration((hostingContext, config) =>
            {
                var env = hostingContext.HostingEnvironment;
                if (env.IsDevelopment())
                {
                    // do something
                }
            }).UseStartup<Startup>();
        });

We can Get the Hosting Environment in the Controller by injecting IWebHostEnvironment into the constructor of the controller. Next we can use the env.IsDevelopment(), env.IsStaging() and env.IsProduction() methods to find out the environment.

Check the below given code to understand this.

public class SomeController : Controller
{
    private IWebHostEnvironment hostingEnvironment;
  
    public SomeController (IWebHostEnvironment environment)
    {
        hostingEnvironment = environment;
    }

    public ActionResult Index()
    {
        if (env.IsDevelopment())
        {
            // ...
        }
 
        if (env.IsStaging())
        {
            // ...
        }
 
        if (env.IsProduction())
        {
            // ...
        }
        return View();
    }   
}

The WebRootPath property of IWebHostEnvironment gives path of the application’s static content folder. This is the wwwroot folder. You can use this property inside a Controller inorder to get the absolute path of the files that lies in this folder.

At times we want to bind the src attribute of img tag with images kept inside the ‘wwwroot’ folder. To do this we need to get the WebRootPath of the ‘wwwroot’ folder of the application. So first inject the IWebHostEnvironment to the parameter of the constructor. The ASP.NET Core Dependency Injection will automatically provide the IWebHostEnvironment object value to the constructor. Now you can simply use the WebRootPath property to get the absolute path. See the below code where I have shown the same thing.

public class MediaController : Controller
{
    private IWebHostEnvironment hostingEnvironment;
 
    public MediaController(IWebHostEnvironment environment)
    {
        hostingEnvironment = environment;
    }
 
    public ActionResult Index()
    {
        string absolutePath = Path.Combine(hostingEnvironment.WebRootPath, "file1.jpg"); 
        ViewBag.ImagePath = absolutePath;
        return View();
    }   
}

We can now show the image on the img tag on the view by binding scr attribute with the ViewBag:

<img src="@ViewBag.ImagePath" alt="WebRootPath example" />

ASP.NET Core UseStaticFiles to serve Static files

In order to make the application serve images, JavaScript files, CSS stylesheets which are kept inside the wwwroot folder you have to add – app.UseStaticFiles() inside the configure method of the Startup class.

Put it just before you call app.UseRouting() method.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    //...
    app.UseStaticFiles();
    app.UseRouting();
    //...
}

ASP.NET Core Exception Handling Middleware

Since we created our application from empty template therefore we need to add the Exceptional Handling Middleware to get detailed message about error coming in the application. You can check it by running your application and then go to some non-existing URL like https://localhost:44343/Game. You will see a message on the browser saying – No Response Generated.

This is an Exception but the message does not state anything regarding it’s cause. User must see some proper messages like 404 for non-existing page, 401 for un-authorized, 403 for forbidden. To do this you have to enable Exception Handling.

We handle Exceptions in DOT NET by adding ExceptionHandler Middleware in the “Configure” method of the startup class. This is done by adding UseDeveloperExceptionPage to the IApplicationBuilder to generate HTML error responses.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseDeveloperExceptionPage();
    //...
}

You can also add app.UseStatusCodePages() to handle responses with status codes between 400 and 599 that do not have a body. Add the below given 2 code lines which are shown in highlighted color to the Configure method.

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseDeveloperExceptionPage();
    app.UseStatusCodePages();
   //...
}

Before you check how it works, make sure you comment out the line where the Response Editing Middleware is added in the startup class. This is because this Custom Middleware is providing a specific message for 404 errors.

//app.UseMiddleware<ResponseEditingMiddleware>();

Now re-run your application and re-visit the URL – https://localhost:44343/Game. You will see the full exception details:

The above Exception was caused by the non-existing action method i.e. a resource which is not found. In fact Exceptions can be cause by a number of ways, mainly due to wrong codes. I will show what happens when exception occurs inside an action method code.

Go to the Home Controller and add an action method called Exception which throws a NullReferenceException type of exception.

public IActionResult Exception()
{
    throw new System.NullReferenceException();
}

Now re-run your application and visit the URL – https://localhost:44343/Home/Exception. You will see full Exception message with Stack Trace to explore the cause of the exception.

This full Exception message with Stack Trace is very helpful to developers but it should not be shown the common users of the site.

We can also add a common Action method which will be called everything some error occurs in our application. We also want this common action method should only be called in Production environment. Let us see how to do it.

First create an action called Error to the Home Controller.

public IActionResult Error()
{
    return View();
}

Next add a Razor View called Error inside the Views ➤ Home for the action method.

<h2>Some Problem</h2>
<p>We got some problem, please visit back after sometime.</p>

Now what we want is that:

• 1. When the application is running in production environment the users will see a simple text message telling them there is some problem which will be rectified in a moment so come back after sometime.

• 2. When the application is running in Development environment then users will see full error details.

We can now update the Configure method by adding if-else condition that will show users the proper error messages based on the environment.

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

What is UseExceptionHandler? The UseExceptionHandler adds Middleware to catch exceptions occurring in our ASP.NET Core applications. The app.UseExceptionHandler(“/Home/Error”) sets the error path which is “/Home/Error”, here custom user friendly error messages can be displayed to the user. In this case it will be the Error action of Home controller.

To test it, set the environment variable – ASPNETCORE_ENVIRONMENT to ‘Production’ since we want the else code to execute. Then run the application and visit the ‘/Home/Exception’ page. This time you will see the contents of the Error View.

ASP.NET Core appsettings.json

The appsettings.json contains keys and values for storing database connection strings, global variables and other configuration values for an ASP.NET Core application. The appsettings.json file lies on the root folder of the application. The contents of this file will look something like:

{
    "Key1": "Microsoft",
    "Key2": "Dot Net"
}

Here Key1 and Key2 are the keys and Microsoft and Dot Net are their values. You can have any names for the keys.

You can create this file by right clicking the project name in the Solution Explorer and selecting Add ➤ New Item. In the ‘Add New Item’ dialog box, search appsettings.json, and this file will show up.

The below figure shows how to select the appsettings.json from the ‘Add New Item’ dialog box.

Get Values from appsettings.json

We can get values of the keys stored in the appsettings.json file by injecting the IConfiguration interface. This interface will be resolved by dependency injection feature of ASP.NET Core. Then we can read the values of the keys by their name from IConfiguration’s object. Let us understand with an example.

In the appsettings.json file I want to store which middleware to enable in the application. So I add the following code to this file:

{
  "Middleware": {
    "EnableContentMiddleware": true,
    "EnableShortCircuitMiddleware": true,
    "EnableRequestEditingMiddleware": true,
    "EnableResponseEditingMiddleware": false
  }
}

This JSON file contains 4 keys- EnableContentMiddleware, EnableShortCircuitMiddleware, EnableRequestEditingMiddleware & EnableResponseEditingMiddleware. I have given each of them a bool value, and I will read their values in Startup class. Then based on the value I will register the Middleware i.e. if the value of the key is true only then I will register the Middleware.

You can see the EnableResponseEditingMiddleware is provided value as false and others are provided value as true. So all the Middleware except the Response Editing Middleware will be registered.

On your Startup class import the namespace – using Microsoft.Extensions.Configuration;.

Then add a property of type IConfiguration and add the constructor of the Startup class that takes the parameter of type IConfiguration. This way we will inject IConfiguration and the Dependency Injection feature will resolve it to an object which can be used to get values from appsettings.json file.

The code for the Constructor with the IConfiguration dependency is shown below:

public Startup(IConfiguration configuration)
{
    Configuration = configuration;
}
public IConfiguration Configuration { get; } 

Now we can read the values like Configuration[“Middleware:EnableResponseEditingMiddleware”]. So change the code inside the Configure method to register the 4 Middleware:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (Convert.ToBoolean(Configuration["Middleware:EnableResponseEditingMiddleware"]))
    {
        app.UseMiddleware<ResponseEditingMiddleware>();
    }
    if (Convert.ToBoolean(Configuration["Middleware:EnableRequestEditingMiddleware"]))
    {
        app.UseMiddleware<RequestEditingMiddleware>();
    }
    if (Convert.ToBoolean(Configuration["Middleware:EnableShortCircuitMiddleware"]))
    {
        app.UseMiddleware<ShortCircuitMiddleware>();
    }
    if (Convert.ToBoolean(Configuration["Middleware:EnableContentMiddleware"]))
    {
        app.UseMiddleware<ContentMiddleware>();
    }
}

In the above code I am reading the bool values of these 4 keys which are kept inside the ‘Middleware’ key. If the value is true then the corresponding Middleware is registered.

We can also read the values by using GetSection and GetValue methods as shown below:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if ((Configuration.GetSection("Middleware")?.GetValue<bool>("EnableResponseEditingMiddleware")).Value)
    {
        app.UseMiddleware<ResponseEditingMiddleware>();
    }
    if ((Configuration.GetSection("Middleware")?.GetValue<bool>("EnableRequestEditingMiddleware")).Value)
    {
        app.UseMiddleware<RequestEditingMiddleware>();
    }
    if ((Configuration.GetSection("Middleware")?.GetValue<bool>("EnableShortCircuitMiddleware")).Value)
    {
        app.UseMiddleware<ShortCircuitMiddleware>();
    }
    if ((Configuration.GetSection("Middleware")?.GetValue<bool>("EnableContentMiddleware")).Value)
    {
        app.UseMiddleware<ContentMiddleware>();
    }
}

When you run the application, all except the Response Editing Middleware will be registered.

Access appsettings.json in Controller & View

We can access appsettings.json in the Controller by Injecting IConfiguration to the constructor of the Controller and they easily accessing the values of the keys as shown in the highlighted code below:

public class SomeController : Controller
{
    private IConfiguration settings;

    public ReadController(IConfiguration settings)
    {
        this.settings = settings;
    }

    public IActionResult Index()
    {
        bool contentMiddleware = Convert.ToBoolean(settings["Middleware:EnableContentMiddleware"]);
        return View();
    }
}

This is exactly the same procedure we applied in the Startup.cs class. In large applications there might be hundreds of entries in the appsettings.json so it does not make sense for the controller to get access to every key-value entries.

A good approach would be to extract the needed section (i.e. key-values) from appsettings.json, convert it to a class then use this class to access those key-value. This is the procedure we have to follow:

1. Create the class to contain the appsettings.json section values.
2. Register this class with Configure<T> on the ConfigureServices method of Startup.
3. Retrive the class on the Controller with IOptions<T>.

So, add a new section that contains API related information on the appsettings.json as shown below. Only this API section will be made available to the controller and not the full appsettings file.

{
  "Middleware": {
    "EnableContentMiddleware": true,
    "EnableShortCircuitMiddleware": true,
    "EnableRequestEditingMiddleware": true,
    "EnableResponseEditingMiddleware": false
  },
  "APIEndpoints": {
    "Name": "OpenWeatherMap",
    "Url": "http://api.openweathermap.org/",
    "IsSecured": true
  }
}

Now create a class that will contain the values of the keys given inside the APIEndpoints section. You can name this class anything but the class members must have the same name as the keys inside this section.

I named the class as MyWebApi.cs and kept it inside Models folder. Note that the class members have the same name of the keys – Name, Url and IsSecured.

public class MyWebApi
{
    public string Name { get; set; }
    public string Url { get; set; }
    public bool IsSecured { get; set; }
}

Next, go to the ConfigureServices method and Register this class with Configure<T>.

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<MyWebApi>(Configuration.GetSection("APIEndpoints"));
    //…
}

You will have to import the namespace Microsoft.Extensions.DependencyInjection for the Configure<T> method.

Now in the Controller, import the Microsoft.Extensions.Options namespace that contains “IOptions”. Then add dependency of IOptions<MyWebApi> on the constructor. The Dependency Injection will make the MyWebApi class available on the controller which you can use to read the values stored in the appsettings.json.

private IOptions<MyWebApi> settings;

public ReadController(IOptions<MyWebApi> settings)
{
    this.settings = settings;
}

public IActionResult Index()
{
    string apiName= settings.Value.Name;
    string url = settings.Value.Url;
    bool secured = settings.Value.IsSecured;
    return View();
}

You can also inject IOptions<MyWebApi> on the View. Here use the inject directive as shown by the below highlighted code:

@using Microsoft.Extensions.Options;
@using Configuation.Models;
@inject IOptions<MyWebApi> settings;

<p>@settings.Value.Name</p>
<p>@settings.Value.Url</p>
<p>@settings.Value.IsSecured</p>

Once injected the IOptions will make the MyWebAPI class available on the view. We can then access the properties as @settings.Value.PropertyName.

Multiple appsettings.json for Development and Production Connection Strings

As stated earlier the appsettings.json stores the connection string for the database. During the course of application development the programmers will want to have not 1 but 2 appsetting.json files in their application.

One that will be used during development and which will contains the connection string (or other variables) to local database.

The other one will be used during production (i.e. when you publish the website and put it on hosting server), and this one will contain the connection string to the production database i.e. the live database.

I will show you how to do this.

First add your connection string to your live database on your appsettings.json file like shown below:

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=SQL6003.site4now.net;Database=DB_A3CE39_y11;User Id=DB_PCE39_y11_admin;[email protected];"
  }
}

Now add a new appsetting.json file on your application root folder and give it the name – appsettings.development.json. Then add your local development database connection string as shown below.

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=vaio;Database=Goldentaurus;Trusted_Connection=True;"
  }
}

This newly added appsettings.development.json file will remain hidden in the solutions explorer. To view this file right click the arrow (➤) before the appsettings.json file.

The below image explains this:

Now go to the Program.cs file and change the BuildWebHost method from:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

To:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseContentRoot(Directory.GetCurrentDirectory())
            .ConfigureAppConfiguration((hostingContext, config) =>
            {
                var env = hostingContext.HostingEnvironment;
                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                      .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
            })
            .UseIISIntegration()
            .UseStartup<Startup>();
        });

Inside this method you will see a method ConfigureAppConfiguration() being called. It is used to register the appsettings.development.json file.

Now you can run your application and will find the appsettings.development.json file is used when the application runs in development (localhost), and the other appsettings.json file is used in production (live) environment.

To get the connection string, add to the ConfigureServices method of the Startup class, the following code:

services.Configure<Connections>(Configuration.GetSection("ConnectionStrings"));

Then create Connections.cs which will contain the connection string:

public class Connections
{
    public string DefaultConnection { get; set; }
}

Then on the constructor of the controller add dependency of IOptions<Connections>, and you can then get the connectionstring.

public class ReadController : Controller
{
    private IOptions<Connections> cs;

    public ReadController(IOptions<Connections> cs)
    {
        this.cs = cs;
    }

    public IActionResult Index()
    {
        string myCS = cs.Value.DefaultConnection;
        return View();
    }
}

Now the appsettings.development.json will be used when the application is running in development environment while the appsettings.json will be used when the application is running on Production.

You can download the full codes of this tutorial from the below link:

Download