Simple middleware to test performance of the ASP .NET Core web application

Startup.cs

public class Startup
{
    // This method gets called by the runtime. Use this method to add services to the container.
    // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
    public void ConfigureServices(IServiceCollection services)
    {
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.Use(async (context, next) =>
        {
            // Do work that doesn't write to the Response.
            // e.g. change something in context 
            // or log something to database
            using StreamWriter sw = File.AppendText("some-log-file.txt");
            Stopwatch timer = new Stopwatch();

            var startTime = DateTime.Now;
            var requestId = Guid.NewGuid();
            sw.WriteLine("{0}: Request processing started at: {1}", requestId, startTime.ToString("MMM/dd/yyyy hh:mm:ss.ffffff tt"));
            timer.Start();

            // Invoke next middleware
            await next.Invoke();

            // Do logging or other work that doesn't write to the Response.
            timer.Stop();
            var endTime = DateTime.Now;
            sw.WriteLine("{0}: Request processing ended at: {1}", requestId, endTime.ToString("MMM/dd/yyyy hh:mm:ss.ffffff tt"));
            sw.WriteLine("{0}: Ticks taken by request processing ended at: {1}", requestId, timer.Elapsed.Ticks);
        });

        app.Run(async context =>
        {
            await context.Response.WriteAsync("My First .NET 5 Web App");
        });
    }
}