What is a request pipeline (middleware pipeline) in ASP.NET Core?

The request pipeline (middleware pipeline) in ASP.NET Core is a sequence of components (middleware) that process HTTP requests and generate HTTP responses.

Each middleware receives a request, can perform some logic (such as authentication, logging, error handling), and then passes control to the next component in the pipeline or terminates the processing.

This allows flexible request handling configuration, adding functionality, and dividing responsibilities.

An example of a simple pipeline in the Configure method of the Startup class:

public void Configure(IApplicationBuilder app)
{
    app.Use(async (context, next) =>
    {
        // Logic before passing to the next middleware
        Console.WriteLine("Request processed by middleware 1");
        await next.Invoke();
        // Logic after processing the next middleware
    });

    app.Use(async (context, next) =>
    {
        Console.WriteLine("Request processed by middleware 2");
        await next.Invoke();
    });

    app.Run(async context =>
    {
        await context.Response.WriteAsync("Hello from final middleware!");
    });
}

Here, the request passes through middleware 1, then middleware 2, and finally a response is generated.