c# - React with .NET can't access localhost

Question

I'm trying to access my application through localhost, but I get exceptions which I dont understand. I'm not even proxying my front end to my backend, so I don't understand what the problem is. When I run dotnet run, there is no problem but when I try to access localhost:5001 I get this error message

IOException: The response ended prematurely.
System.Net.Http.HttpConnection.FillAsync(bool async)

HttpRequestException: An error occurred while sending the request.
System.Net.Http.HttpConnection.SendAsyncCore(HttpRequestMessage request, bool async, CancellationToken cancellationToken)

HttpRequestException: Failed to proxy the request to http://localhost:61509/, because the request to the proxy target failed. Check that the proxy target server is running and accepting requests to http://localhost:61509/.

The underlying exception message was 'An error occurred while sending the request.'.Check the InnerException for more details.
Microsoft.AspNetCore.SpaServices.Extensions.Proxy.SpaProxy.PerformProxyRequest(HttpContext context, HttpClient httpClient, Task<Uri> baseUriTask, CancellationToken applicationStoppingToken, bool proxy404s)


at Microsoft.AspNetCore.Builder.SpaProxyingExtensions.<>c__DisplayClass2_0.<<UseProxyToSpaDevelopmentServer>b__0>d.MoveNext()
--- End of stack trace from previous location ---
 
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();

            services.AddSpaStaticFiles(configuration =>
                configuration.RootPath = "./client/build"
            );
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
           if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            // Docker container 
            // app.UseHttpsRedirection();
            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseSpaStaticFiles();
 
            app.UseRouting();
 
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller}/{action=Index}/{id?}");
            });
 
            app.UseSpa(spa =>
            {
                spa.Options.SourcePath = "client";
 
                if (env.IsDevelopment())
                {
                    spa.UseReactDevelopmentServer(npmScript: "start");
                }
            });
        }

Answer 1

等待大神答复