Understanding Middleware in ASP.NET Core

A Complete Guide to Building a Robust Request Pipeline

Introduction

Middleware plays a crucial role in ASP.NET Core applications, forming the backbone of the request and response pipeline. By understanding middleware, you can efficiently control how HTTP requests are processed, authenticated, and routed within your application. In this blog, we’ll cover everything you need to know about middleware in ASP.NET Core, from its basics to creating custom middleware components for real-world scenarios.

What is Middleware?

Middleware in ASP.NET Core is a component that handles requests and responses in the application pipeline. Middleware components are executed in a sequence, forming a pipeline where each component can process the incoming request, modify it, and pass it to the next component.

For example, middleware can handle tasks like logging, authentication, authorization, exception handling, and response caching.

Understanding the Middleware Pipeline

The middleware pipeline in ASP.NET Core is configured in the Program.cs or Startup.cs file. The order in which middleware components are added to the pipeline determines their execution order.

Here’s a visual representation of a middleware pipeline:

• Request starts
• Authentication Middleware
• Authorization Middleware
• Custom Middleware (e.g., logging)
• Routing Middleware
• Endpoint Middleware
• Response ends

Example

app.Use(async (context, next) =>
{
    // Before the next middleware
    await context.Response.WriteAsync("Request handled by Middleware 1\n");
    await next.Invoke();
    // After the next middleware
    await context.Response.WriteAsync("Response processed by Middleware 1\n");
});

app.Run(async (context) =>
{
    await context.Response.WriteAsync("Request reached the final Middleware\n");
});

Built-in Middleware in ASP.NET Core

ASP.NET Core comes with several built-in middleware components to handle common tasks. Here are some key middleware components:

• Static Files Middleware: Serves static files like HTML, CSS, and JavaScript.
• Routing Middleware: Matches HTTP requests to endpoints.
• Authentication Middleware: Validates user credentials.
• Authorization Middleware: Ensures users have the necessary permissions.
• Exception Handling Middleware: Handles application-level exceptions.
• CORS Middleware: Configures cross-origin requests.

Example: Adding Static File Middleware

app.UseStaticFiles();

Creating Custom Middleware in ASP.NET Core

Sometimes, built-in middleware may not meet your specific requirements. In such cases, you can create custom middleware. Custom middleware can be created using a simple class and added to the pipeline.

Steps to Create Custom Middleware

1. Create a new class for your middleware.
2. Implement the middleware logic in the Invoke or InvokeAsync method.
3. Register the middleware in the pipeline using UseMiddleware<T>().

Example

public class LoggingMiddleware
{
    private readonly RequestDelegate _next;

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

    public async Task InvokeAsync(HttpContext context)
    {
        Console.WriteLine($"Request: {context.Request.Path}");
        await _next(context);
        Console.WriteLine($"Response: {context.Response.StatusCode}");
    }
}

Register the middleware in Program.cs:

app.UseMiddleware<LoggingMiddleware>();

Best Practices for Middleware

Follow these best practices when working with middleware in ASP.NET Core:

• Order your middleware correctly in the pipeline to avoid unexpected behaviors.
• Keep middleware logic simple and focused on a single responsibility.
• Use built-in middleware whenever possible to save time and reduce complexity.
• Avoid blocking or long-running tasks in middleware.
• Test your custom middleware thoroughly to ensure it works in all scenarios.

Conclusion

Middleware is an essential concept in ASP.NET Core that allows you to control the flow of requests and responses in your application. By understanding how middleware works, using built-in middleware effectively, and creating custom middleware as needed, you can build robust and maintainable web applications. Start experimenting with middleware today to unlock its full potential!

© 2025 Sandeep Mhaske. All rights reserved.

Follow me on LinkedIn | GitHub