SignalR 无法启动连接

Question

I have an angular application along with an ASP.NET Core 2.2 backend that uses SignalR. When starting the connection, I receive the errors:

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

Response Headers when hitting localhost: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() is hooked to a button in HTML. But I can never get to that part! OnInit() keeps failing and the application cannot start even when the response returned from the API is 204. Response-

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

I've tried setting the same version of SignalR on both ends but it doesn't work. Is it an issue of .NET Core itself? I've also tried using Kestrel and IIS Express but to no avail. Please help me on this one.

Answer 1

I was able to solve the issue by looking at this issue here-

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

I moved the AllowAllPolicy to the configure method-

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