Middleware

Context: Middleware components are assembled into a pipeline to handle requests and responses. Common in ASP.NET Core.

public delegate Task RequestDelegate(HttpContext context);

public class MiddlewarePipeline
{
    private readonly List<Func<RequestDelegate, RequestDelegate>> _components = new();

    public void Use(Func<RequestDelegate, RequestDelegate> middleware)
    {
        _components.Add(middleware);
    }

    public RequestDelegate Build()
    {
        RequestDelegate app = context => Task.CompletedTask;
        for (int i = _components.Count - 1; i >= 0; i--)
            app = _components[i](app);
        return app;
    }
}

// Example middleware
app.Use(async (context, next) =>
{
    Console.WriteLine("Before");
    await next();
    Console.WriteLine("After");
});

Real-world usage example

HTTP request pipeline: ASP.NET Core uses middleware for authentication, logging, static files, CORS, exception handling, and MVC. Each middleware can short‑circuit the pipeline or pass to the next.

Example: ASP.NET Core middleware documentation shows built‑in middleware like UseAuthentication, UseAuthorization, UseStaticFiles. Custom middleware for request logging, API rate limiting, or adding correlation IDs.

Middleware

Real-world usage example

Related sections