ASP.NET Core introduced a new concept called Middleware. Middleware is software that's assembled into an app pipeline to handle requests and responses. Each component:
- Chooses whether to pass the request to the next component in the pipeline.
- Can perform work before and after the next component in the pipeline.
Request delegates are used to build the request pipeline. The request delegates handle each HTTP request. Request delegates are configured using Run, Map, and Use extension methods. An individual request delegate can be specified in-line as an anonymous method (called in-line middleware), or it can be defined in a reusable class. These reusable classes and in-line anonymous methods are middleware, also called middleware components. Each middleware component in the request pipeline is responsible for invoking the next component in the pipeline or short-circuiting the pipeline. When a middleware short-circuits, it's called a terminal middleware because it prevents further middleware from processing the request.
In the classic ASP.NET, HttpHandlers and HttpModules were part of request pipeline. Middleware is similar to HttpHandlers and HttpModules where both needs to be configured and executed in each request.
Typically, there will be multiple middleware in ASP.NET Core web application. It can be either framework provided middleware, added via NuGet or your own custom middleware. We can set the order of middleware execution in the request pipeline. Each middleware adds or modifies http request and optionally passes control to the next middleware component.
1. Use: chain multiple request delegates together. The next parameter represents the next delegate in the pipeline. You can short-circuit the pipeline by not calling the next parameter.
2. Run: delegates don't receive a next parameter. The first Run delegate is always terminal and terminates the pipeline.
3. Map: extensions are used as a convention for branching the pipeline. Map branches the request pipeline based on matches of the given request path. If the request path starts with the given path, the branch is executed.
