Middlewares in C#

What is Middleware in ASP.NET Core?

Middleware is a piece of code that processes HTTP requests and responses in a pipeline.
Each middleware can:

• Do something before and/or after the next middleware runs.

• Either pass the request along or stop it.

In short: Middleware = A request handler that sits in the HTTP pipeline.

Steps to Create and Add Custom Middleware

1. Create a Custom Middleware Class

using Microsoft.AspNetCore.Http;
using System.Threading.Tasks;

public class MyCustomMiddleware
{
    private readonly RequestDelegate _next;

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

    public async Task InvokeAsync(HttpContext context)
    {
        // Code before next middleware
        Console.WriteLine(" Request incoming: " + context.Request.Path);

        // Call the next middleware in the pipeline
        await _next(context);

        // Code after next middleware
        Console.WriteLine(" Response outgoing: " + context.Response.StatusCode);
    }
}

2. Create an Extension Method (optional but recommended)

using Microsoft.AspNetCore.Builder;

public static class MyCustomMiddlewareExtensions
{
    public static IApplicationBuilder UseMyCustomMiddleware(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware();
    }
}

3. Register Middleware in Program.cs or Startup.cs

For .NET 6 / .NET 7 / .NET 8

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.UseMyCustomMiddleware();  // Custom middleware added here

app.MapControllers();
app.Run();

For older versions (Startup.cs)

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseMyCustomMiddleware();
    app.UseMvc();
}

4. Run the Application

When you send a request (e.g., to an API endpoint), you’ll see logs like:

 Request incoming: /api/values
 Response outgoing: 200

Why Use Custom Middleware?

Logging or request tracking, Authentication / Authorization , Exception handling , Request/Response modification ,Performance monitoring

Summary

In Short : Custom Middleware = Your own code logic that runs in the ASP.NET Core request pipeline before or after the main app logic.