How to Use ASP.NET Core Middleware in Your Web Applications

ASP.NET Core is a modern web framework that offers a lot of flexibility and power for building web applications. One of the key features of ASP.NET Core is the concept of middleware, which are components that can handle requests and responses in the HTTP pipeline. Middleware can perform various tasks, such as authentication, logging, error handling, caching, routing, and more. In this article, we will learn what middleware is, how to use it, and how to create custom middleware in ASP.NET Core.

What is ASP.NET Core Middleware?

Middleware is a term that describes software components that are assembled into an application pipeline to handle requests and responses. Each component chooses whether to pass the request on to the next component in the pipeline, and can perform certain actions before or after the next component is invoked. Middleware components are registered in the Startup class of the ASP.NET Core application, using the Use, Run, or Map extension methods on the IApplicationBuilder interface. The order of registration determines the order of execution of the middleware components.

How to Use ASP.NET Core Middleware?

ASP.NET Core provides several built-in middleware components that can be used to perform common tasks, such as:

• UseStaticFiles – Serves static files, such as images, CSS, and JavaScript, from the web root folder (wwwroot by default).
• UseRouting – Enables routing, which maps requests to endpoints based on patterns and constraints.
• UseAuthentication – Enables authentication, which identifies the user making the request.
• UseAuthorization – Enables authorization, which determines whether the user is allowed to access the requested resource.
• UseEndpoints – Executes the endpoint that was selected by routing, which can be a controller action, a Razor page, a SignalR hub, or a custom delegate.

To use these middleware components, you need to add them to the Configure method of the Startup class, in the order that you want them to run. For example, the following code shows a typical configuration of middleware components for an ASP.NET Core web application:

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

    app.UseStaticFiles();

    app.UseRouting();

    app.UseAuthentication();

    app.UseAuthorization();

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

How to Create Custom ASP.NET Core Middleware?

Sometimes, you may need to create your own middleware components to perform custom logic or functionality that is not provided by the built-in middleware components. To create a custom middleware component, you need to follow these steps:

1. Create a class that has a constructor that accepts a RequestDelegate parameter, which represents the next middleware component in the pipeline.
2. Create a public method named Invoke or InvokeAsync that accepts a HttpContext parameter, which represents the current HTTP context, and optionally other parameters that are injected by dependency injection.
3. Write the logic for your middleware component inside the Invoke or InvokeAsync method, using the HttpContext parameter to access or modify the request or response. You can also call the next middleware component in the pipeline by invoking the RequestDelegate parameter, and optionally await its completion.
4. Register your custom middleware component in the Startup class, using the UseMiddleware extension method on the IApplicationBuilder interface, and specify the type of your middleware class as a generic argument.

For example, the following code shows a custom middleware component that logs the request path and query string to the console:

public class RequestLoggingMiddleware
{
    private readonly RequestDelegate _next;

    public RequestLoggingMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        Console.WriteLine($"Request: {context.Request.Path}{context.Request.QueryString}");

        await _next(context);
    }
}

To use this middleware component, you need to add it to the Configure method of the Startup class, before or after the other middleware components, depending on when you want it to run. For example, the following code shows how to register the custom middleware component at the beginning of the pipeline:

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

    // Other middleware components
}

Conclusion

ASP.NET Core middleware is a powerful and flexible way to handle requests and responses in the HTTP pipeline. You can use the built-in middleware components to perform common tasks, such as serving static files, enabling routing, authentication, and authorization, and executing endpoints. You can also create your own custom middleware components to perform custom logic or functionality that is not provided by the built-in middleware components. By using middleware, you can modularize your web application and make it easier to maintain and extend.