ASP.NET Middleware Order Pitfalls That Break APIs
In ASP.NET Core, middleware components are the building blocks of your application’s request pipeline. Think of them as a series of checkpoints on an assembly line. Each request passes through these checkpoints in a specific order, and each one has a chance to inspect, modify, or even short-circuit the request.
While this architecture is incredibly powerful, it has a critical dependency: order matters. A lot. Arranging your middleware in the wrong sequence can lead to security vulnerabilities, broken functionality, and hours of frustrating debugging. Let’s dive into the most common ordering pitfalls that can silently break your APIs and how to fix them.
The Request Pipeline: A Two-Way Street
Before we get to the pitfalls, it’s essential to understand how the pipeline works. When an HTTP request arrives, it travels “down” the pipeline, passing through each middleware component in the order they were registered in Program.cs.
Once the request hits the end (usually your API endpoint), the response is generated and travels back “up” the pipeline in the reverse order. This two-way flow is why some middleware can act on both the incoming request and the outgoing response.
The golden rule is simple: Middleware registered earlier runs earlier on the request and later on the response.
Common Middleware Ordering Pitfalls
Let’s look at some classic mistakes. We’ll use the modern minimal API style with top-level statements for our …
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