如何修复 C# MVC 应用程序中的“连接被拒绝”错误？

Question

我正在尝试构建一个 MVC 网站，当我尝试运行该应用程序时，我在终端中收到此响应：

fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
  An unhandled exception has occurred while executing the request.
System.Net.Http.HttpRequestException: Connection refused
---> System.Net.Sockets.SocketException (61): Connection refused
at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken 
cancellationToken)
--- End of inner exception stack trace ---
at System.Net.Http.ConnectHelper.ConnectAsync(String host, Int32 port, CancellationToken cancellationToken)
at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean allowHttp2, CancellationToken cancellationToken)
 at System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpConnectionPool.GetHttpConnectionAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request, Boolean doRequestAuth, CancellationToken cancellationToken)
at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.DiagnosticsHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at Microsoft.Extensions.Http.Logging.LoggingHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at Microsoft.Extensions.Http.Logging.LoggingScopeHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task`1 sendTask, HttpRequestMessage request, CancellationTokenSource cts, Boolean disposeCts)
at NorthwindMvc.Controllers.HomeController.Customers(String country) in /Users/steelwind/HardWay/c#and.NET/PracticalApps/NorthwindMvc/Controllers/HomeController.cs:line 139
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.MigrationsEndPointMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.Invoke(HttpContext httpContext)
at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.Invoke(HttpContext httpContext)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
info: Microsoft.AspNetCore.Hosting.Diagnostics[2]
  Request finished in 744.0667000000001ms 500 text/html; charset=utf-8

Program.cs 看起来像这样：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace NorthwindService
{
public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
                webBuilder.UseUrls("https://localhost.5001");
            });
   }
}

Startup.cs 看起来像这样：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.IO;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Formatters;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.EntityFrameworkCore;
using Microsoft.OpenApi.Models;
using Packt.Shared;
using NorthwindService.Repositories;
using Swashbuckle.AspNetCore.Swagger;
using Swashbuckle.AspNetCore.SwaggerUI;
using static System.Console;

 namespace NorthwindService
 {
  public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddCors();

        string databasePath = Path.Combine("..", "Northwind.db");

        services.AddDbContext<Northwind>(options => options.UseSqlite($"Data Source={databasePath}"));

        services.AddControllers(options =>
        {
            WriteLine("Default output formatters:");
            foreach(IOutputFormatter formatter in options.OutputFormatters)
            {
                var mediaFormatter = formatter as OutputFormatter;

                if (mediaFormatter == null)
                {
                    WriteLine($"  {formatter.GetType().Name}");
                }
                else // OutputFormatter class has SupportedMediaType
                {
                    WriteLine("  {0}, Media types: {1}",
                        arg0: mediaFormatter.GetType().Name,
                        arg1: string.Join(", ", mediaFormatter.SupportedMediaTypes));
                }
            }
        })
        .AddXmlDataContractSerializerFormatters()
        .AddXmlSerializerFormatters()
        .SetCompatibilityVersion(CompatibilityVersion.Version_3_0);

        services.AddScoped<ICustomerRepository, CustomerRepository>();

        // Register the Swagger generator and define a Swagger document
        // for Northwind services
        services.AddSwaggerGen(options => 
        {
            options.SwaggerDoc(name: "v1", info: new OpenApiInfo
                { Title = "Northwind Service API", Version = "v1"});
        });

        services.AddMvcCore();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseHttpsRedirection();

        app.UseRouting();

        app.UseAuthorization();

        // after UseRouting and before UseEndPoints
        app.UseCors(configurePolicy: options =>
        {
            options.WithMethods("GET", "POST", "PUT", "DELETE");

            options.WithOrigins("https://localhost:5002" // for MVC client
            );
        });

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });

        app.UseSwagger();

        app.UseSwaggerUI(options => 
        {
            options.SwaggerEndpoint("/swagger/v1/swagger.json", "Northwind Service API Version 1");

            options.SupportedSubmitMethods(new[] {
                SubmitMethod.Get, SubmitMethod.Post,
                SubmitMethod.Put, SubmitMethod.Delete});
        });
    }
  }
}

控制器文件（称为 HomeController.cs）如下所示：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using System.Net.Http; 
using Newtonsoft.Json;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using Microsoft.EntityFrameworkCore;
using NorthwindMvc.Models;
using Packt.Shared;

namespace NorthwindMvc.Controllers
{
 public class HomeController : Controller
 {
    private readonly ILogger<HomeController> _logger;

    private Northwind db;

    private readonly IHttpClientFactory clientFactory;

    public HomeController(
        ILogger<HomeController> logger,
        Northwind injectedContext,
        IHttpClientFactory httpClientFactory)
    {
        _logger = logger;
        db = injectedContext;
        clientFactory = httpClientFactory;
    }

    public async Task<IActionResult> Index()
    {
        var model = new HomeIndexViewModel
        {
            VisitorCount = (new Random()).Next(1, 1001),
            Categories = await db.Categories.ToListAsync(),
            Products = await db.Products.ToListAsync()
        };

        return View(model); // pass model to view
    }

    public IActionResult Privacy()
    {
        return View();
    }

    [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
    public IActionResult Error()
    {
        return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
    }

    public async Task<IActionResult> ProductDetail(int? id)
    {
        if (!id.HasValue)
        {
            return NotFound("You must pass a product ID in the route, for example, /Home/ProductDetail/21");
        }

        var model = await db.Products.SingleOrDefaultAsync(p => p.ProductID == id);

        if (model == null)
        {
            return NotFound($"Product with ID of {id} not found.");
        }

        return View(model); // pass model to view and then return result
    }

    public IActionResult ModelBinding()
    {
        return View(); // the page with a form to submit
    }

    [HttpPost]
    public IActionResult ModelBinding(Thing thing)
    {
        //return View(thing); // show the model bound thing

        var model = new HomeModelBindingViewModel
        {
            Thing = thing,
            HasErrors = !ModelState.IsValid,
            ValidationErrors = ModelState.Values
                .SelectMany(state => state.Errors)
                .Select(error => error.ErrorMessage)
        };

        return View(model);
    }

    public IActionResult ProductsThatCostMoreThan(decimal? price)
    {
        if (!price.HasValue)
        {
            return NotFound("You must pass a product price in the query string, for example, /Home/ProductsThatCostMoreThan?price=50");
        }

        IEnumerable<Product> model = db.Products
            .Include(p => p.Category)
            .Include(p => p.Supplier)
            .AsEnumerable() // switch to client-side
            .Where(p => p.UnitPrice > price);

        if (model.Count() == 0)
        {
            return NotFound($"No products cost more than {price:C}.");
        }
        ViewData["MaxPrice"] = price.Value.ToString("C");

        return View(model); // pass model to view
    }

    public async Task<IActionResult> Customers(string country)
    {
        string uri;

        if (string.IsNullOrEmpty(country))
        {
            ViewData["Title"] = "All Customers Worldwide";
            uri = "api/customers/";
        }
        else 
        {
            ViewData["Title"] = $"Customers in {country}";
            uri = $"api/customers/?country={country}";
        }

        var client = clientFactory.CreateClient(
            name: "NorthwindService");

        var request = new HttpRequestMessage(
            method: HttpMethod.Get, requestUri: uri);

        HttpResponseMessage response = await client.SendAsync(request);

        string jsonString = await response.Content.ReadAsStringAsync();

        IEnumerable<Customer> model = JsonConvert
            .DeserializeObject<IEnumerable<Customer>>(jsonString);

        return View(model);
    }
  }
}

我曾尝试查找解决方案，但尚未找到任何可行的解决方案。

Answer 1

在 Program.cs 这一行中：

webBuilder.UseUrls("https://localhost.5001");

必须是

webBuilder.UseUrls("https://localhost:5001");