What makes something be a request feature in ASP.NET Core?

Question

There's one point in ASP.NET Core that I believe I didn't fully understand yet and that is the idea of request features. As explained in the docs:

Feature interfaces define specific HTTP features that a given request may support. Servers define collections of features, and the initial set of features supported by that server, but middleware can be used to enhance these features.

My initial understanding about this was that request features are all things a server should expose to be used on the application pipeline. That is, behaviors that a server should perform like sending a file.

On the other hand, there's, for example, the authentication request feature. Now, I'm not sure authentication falls into this category. It doesn't seem like some server behavior that the application should call, but rather, a concern of the application itself.

This makes me wonder what really makes something be a request feature. So, what makes something be a request feature in ASP.NET Core? Is my initial understanding wrong? What is behind the decision of making something a request feature?

Answer 1

My initial understanding about this was that request features are all things a server should expose to be used on the application pipeline. That is, behaviors that a server should perform like sending a file.

That's one use of http features. It's also a way to augment or light up behaviors on the HttpContext, like buffering, send file, authentication, websockets.

Middleware can also add features specific to that middleware, you can see examples of this:

• The exception handler middleware flows the exception that occurred via a request feature - https://github.com/aspnet/Diagnostics/blob/dev/src/Microsoft.AspNetCore.Diagnostics.Abstractions/IExceptionHandlerFeature.cs.
• The routing middleware adds route data to the current http context via a request feature - https://github.com/aspnet/Routing/blob/dev/src/Microsoft.AspNetCore.Routing.Abstractions/IRoutingFeature.cs

Generally it's a way to flow per request behavior and state from the server, through middleware, to the application.