SignalR无法启动连接

Question

i具有一个Angular应用程序以及使用SignalR的ASP.NET Core 2.2后端。启动连接时，我会收到错误：

Error: Failed to complete negotiation with the server: Error
Error: Failed to start the connection: Error

击打本地主机时响应标头：5000/chathub-

HTTP/1.1 204 No Content
Date: Tue, 19 Feb 2019 08:52:52 GMT
Server: Kestrel
Access-Control-Allow-Headers: x-requested-with
Access-Control-Allow-Methods: POST
Access-Control-Allow-Origin: *

startup.cs-

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using RealChat.Hubs;
namespace RealChat
{
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(o => o.AddPolicy("AllowAllPolicy", builder => {
            builder
            .AllowAnyMethod()
            .AllowAnyHeader()
            .AllowAnyOrigin();
        }));
        services.AddSignalR();
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    }
    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }
        app.UseCors("AllowAllPolicy");
        app.UseSignalR(routes =>
        {
            routes.MapHub<ChatHub>("/chatHub");
        });
        //app.UseHttpsRedirection();
        app.UseMvc();
    }
}
}

chathub.cs-

using Microsoft.AspNetCore.SignalR;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace RealChat.Hubs
{
public class ChatHub : Hub
{
    public Task Send(string data)
    {
        return Clients.All.SendAsync("Receive", "Hello!!!");
    }
}
}

app-component.cs-

import { Component, OnInit } from '@angular/core';
import { HubConnection } from '@aspnet/signalr';
import * as signalR from '@aspnet/signalr';
@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
  private _hubConnection: HubConnection;
  msgs: string;
  constructor() { }
  ngOnInit(): void {
    this._hubConnection = new signalR.HubConnectionBuilder()
        .withUrl('http://localhost:5000/chatHub')
        .configureLogging(signalR.LogLevel.Information)
        .build();
    this._hubConnection.start().catch(err => console.error("SignalR startup error"));
    this._hubConnection.on('ReceiveMessage', (data) => {
        console.log(data);
    });
  }
  sendMessage(): void {
      console.log("Sending...n");
       if (this._hubConnection)
          this._hubConnection.invoke('SendMessage', 'Test');
  }
}

sendMessage（）挂在HTML中的按钮上。但是我永远无法到达那部分！OnInit（）继续失败，即使从API返回的响应为204，应用程序也无法启动。响应 -

info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
  Request starting HTTP/1.1 OPTIONS http://localhost:5000/chatHub/negotiate
info: Microsoft.AspNetCore.Cors.Infrastructure.CorsService[4]
  CORS policy execution successful.
info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
  Request finished in 0.6942ms 204

我尝试在两端设置相同版本的SignalR，但它不起作用。是.NET核心本身的问题吗？我还尝试使用Kestrel和IIS Express，但无济于事。请帮助我。

Answer 1

我能够通过在此处查看此问题来解决问题 -

https://github.com/aspnet/signalr/issues/2095#issuecomment-383899098

我将允许的allpolicy移至配置方法 -

app.UseCors(builder =>
            {
                builder.WithOrigins("http://localhost:4200")
                .AllowAnyHeader().AllowAnyMethod().AllowCredentials();
            });