what is the role of the IMiddlewarFactory in asp.net core ?

The IMiddlewareFactory in ASP.NET Core is responsible for creating middleware instances for each incoming request and making sure any dependencies (like services registered in the DI container) are properly injected.

For scoped services (services that should be unique to each request), the factory ensures they’re created fresh for each request. This way, each request gets its own set of scoped services, keeping everything isolated and not shared across requests.

You don’t need to manually register middleware as scoped. The factory handles all of that -creating the middleware and injecting the correct services with the right lifetimes. Each request automatically gets its own instance of everything it needs.

Here’s an example to illustrate:

public class MyCustomMiddleware : IMiddleware
{
    private readonly IMyScopedService _myScopedService;

    public MyCustomMiddleware(IMyScopedService myScopedService)
    {
        _myScopedService = myScopedService;
    }

    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        _myScopedService.DoSomething();  // Use the scoped service
        await next(context);
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped();
    services.AddScoped();
}

public void Configure(IApplicationBuilder app)
{
    app.UseMiddleware();
}

In this example, the middleware (MyCustomMiddleware) uses a scoped service (IMyScopedService).  You don’t need to do anything extra to manage lifetimes- the factory does it for you.

Hope it helps!