.NET 9 Middleware Pipeline: Advanced Patterns and Performance 🚀

TL;DR — The ASP.NET Core middleware pipeline is where your app does its real work, but most developers only scratch the surface. In .NET 9, you've got new tools like MapStaticAssets, better exception handling, and the same old performance patterns still apply: short-circuit early, order cheap before expensive, and never sync-over-async. Let's look at the patterns actually worth knowing. Pipeline Basics Here's the mental model that actually helps: your middleware pipeline is a series of functions. Every incoming HTTP request flows through them in order. Each one can: Do some work Decide whether to pass the request downstream Short-circuit and return immediately You wire it up with three extension methods: Use — does work, then calls next() to continue down the pipeline Map — forks the pipeline based on a URL path Run — terminal. No next(). The pipeline ends here. var builder = WebApplication.CreateBuilder(args); var app = builder.Build(); // 1. Use — passes through to next middleware ap