基本的.NET Core应用程序混合了多个请求

Question

I'm working with .NET 5/Core and created the most basic ASP.NET Core web application to understand .NET Core basics (my code below), but my private class field/property is behaving like a static field and preserving its value between HTTP requests. I would like to understand why, how to solve this in a simplest way, and if there are multiple solutions/approaches.

I am declaring 'Output' string as private non-static field and I'm assuming it should be reset with each new HTTP request, but instead it behaves like a static field/property and each new page refresh results in a longer and longer output, preserving previous value and adding a new one. For example the web page first shows output / , but after refreshing the page couple more times I see the following 5 outputs merged

/
/favicon.ico
/
/favicon.ico
/

favicon.ico is not a problem and I understand that my web browser is requesting it. The output above shows after first 3 page refreshes, while each additional page refresh outputs two more of these lines since the web browser submits 2 HTTP requests. I probably could come up with a solution using services.AddScoped or services.AddTransient , but not sure why services would be needed in this case since each HTTP request seems to be handled separately and should re-initialize my RequestHandler class. Am I missing something simple and is there a way to handle this at the simplicity level of my sample code?

My whole app consists of the Startup.cs below:

using System.Threading.Tasks;
using Microsoft.AspNet.Builder;
using Microsoft.AspNet.Http;

namespace BasicApp
{
    public class Startup
    {
        public static void Main()
        {
        }

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

    public class RequestHandler
    {
        RequestDelegate _next;
        private string Output = "";

        public RequestHandler(RequestDelegate next)
        {
            _next = next;
        }

        public async Task Invoke(HttpContext context)
        {
            Output += context.Request.Path + "\n";
            await context.Response.WriteAsync(Output);
        }
    }
}

Answer 1

Middleware classes are only instantiated once through IApplicationBuilder.UseMiddleware{T} , and put into the request pipeline. The ASP.NET documentation on this does a pretty good job of explaining the process.

You could achieve a simple response through the IApplicationBuilder.Run method:

public void Configure(IApplicationBuilder app)
{
    app.Run(async context =>
    {
        await context.Response.WriteAsync(context.Request.Path);
    });
}

Another way to think of it would be that a middleware class instantiates your RequestHandler with each request:

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
    }

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

    public static void Main(string[] args) => WebApplication.Run<Startup>(args);
}

public class RequestHandlerMiddleware
{
    RequestDelegate _next;

    public RequestHandlerMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        var handler = new RequestHandler();
        await handler.HandleRequestAsync(context);
        await _next.Invoke(context); // invoke the next delegate in the pipeline
    }
}

public class RequestHandler
{
    private string Output = "";

    public async Task HandleRequestAsync(HttpContext context)
    {
        Output += context.Request.Path + "\n";
        await context.Response.WriteAsync(Output);
    }
}