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.
Controllers and Razor pages work with data that comes from HTTP requests. For example, route data may provide a record key, and posted form fields may provide values for the properties of the model. Writing code to retrieve each of these values and convert them from strings to .NET types would be tedious and error-prone. Model binding automates this process. The model binding system: Retrieves data from various sources such as route data, form fields, and query strings. Provides the data to controllers and Razor pages in method parameters and public properties. Converts string data to .NET types. Updates properties of complex types.