SignalR入坑笔记

什么是SignalR

ASP.NET Core SignalR 是一个开源库，它简化了向应用程序添加实时 web 功能的功能。实时 Web 功能使服务器端代码能够即时将内容推送到客户端。

ASP.NET Core SignalR 的一些功能:

自动管理连接
同时向所有连接的客户端发送消息。例如，聊天室
向特定客户端或客户端组发送消息
可缩放以处理不断增加的流量

SignalR 支持以下用于处理实时通信的技术:

WebSockets
服务器发送的事件
长轮询

其中Web Socket仅支持比较现代的浏览器, Web服务器也不能太老.

而 Server Sent Events 情况可能好一点, 但是也存在同样的问题.

所以SignalR采用了回落机制, SignalR有能力去协商支持的传输类型.

Web Socket是最好的最有效的传输方式, 如果浏览器或Web服务器不支持它的话, 就会降级使用SSE, 实在不行就用Long Polling.

一旦建立连接, SignalR就会开始发送keep alive消息, 来检查连接是否还正常. 如果有问题, 就会抛出异常.

因为SignalR是抽象于三种传输方式的上层, 所以无论底层采用的哪种方式, SignalR的用法都是一样的.

SignalR - 集线器(Hub)

SignalR中, 我们主要需要做的事情就是继承Hub类, 来和客户端互相发送消息; 可以察觉出, SignalR服务器是一个消息中心, 客户端将消息发送给SignalR服务器, 然后有我们来处理这些消息, 可以将这些消息广播出去, 也可以将某个客户端发过来的消息转发给另一个客户端, 实现两个客户端之间的通信;

开始使用SignalR - CountHub

这里将完成一个简单的使用SignalR服务端和客户端实时通信的例子:

客户端发起连接请求
服务器端接受请求, 并向该客户端发出计数, 从0到10
当计数到10, 服务端调用客户端Finished方法, 客户端Finished关闭连接

服务端:

建立asp.net core项目, 选择空模板

新建 CountService 类和 CountHub 类

public class CountService
{
    private int _count;

    public int GetLastestCount() => _count++;
}

public class CountHub : Hub
{
    private readonly CountService _countService;

    public CountHub(CountService countService, 
        ILoggerFactory loggerFactory)
    {
        _countService=countService;
    }

    public async Task GetLastestCount()
    {
        IClientProxy client = Clients.Caller;
        int count;
        do
        {
            count = _countService.GetLastestCount();

            await Task.Delay(1000);
            
            await client.SendAsync("ReceiveUpdate", $"ConnectionId: {Context.ConnectionId}, count: {count}");
        } while (count < 10);

        await client.SendAsync("Finished");
    }
}

在Startup类中注册Service和配置Hub路由
services.AddScoped<CountService>();
services.AddSignalR();
endpoints.MapHub<CountHub>("/countHub");

Startup

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using SingleRStudy.Hubs;
using SingleRStudy.Services;

namespace SingleR
{
    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)
        {
            services.AddScoped<CountService>();

            services.AddSignalR();

            services.AddCors(options =>
            {
                options.AddPolicy("NgClientPolicy", p =>
                {
                    p.WithOrigins("http://localhost:4200")
                    .AllowAnyHeader()
                    .AllowAnyMethod()
                    .AllowCredentials();
                });
            });
        }

        // 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.UseCors("NgClientPolicy");

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapHub<CountHub>("/countHub");
            });
        }
    }
}

由于我这边使用了Angular来作为客户端, 所以在Startup中同时配置了跨域.

客户端(Angular)

通过npm引入signalr: npm i @microsoft/signalr @types/node

导入signalr: import * as signalR from '@microsoft/signalr/'

完整的如下:

ChatComponent

import { Component, OnInit } from '@angular/core';
import * as signalR from '@microsoft/signalr/'

/**
 * 创建连接
 */
const connection = new signalR.HubConnectionBuilder()
  .withUrl('//localhost:5000/countHub')
  .build();

@Component({
  selector: 'app-chat',
  templateUrl: './chat.component.html',
  styleUrls: ['./chat.component.css']
})
export class ChatComponent implements OnInit {

  constructor() { }

  async ngOnInit() {
    connection.on('ReceiveUpdate', (message: string) => {
      console.log(message);
    });

    connection.on('Finished', () => {
      console.log('count finished');
      connection.stop();
    });

    connection.onclose(error => {
      console.error('signalR connection closed. error: ', error);
    });

    // 开始通信
    await connection.start().catch(error => {
      console.error(error);
    });
    if(connection.state === signalR.HubConnectionState.Connected)
      await connection.send('GetLastestCount', 'aaa');
  }

}

客户端定义了ReceiveUpdate 和 Finished可以让服务端调用的方法.

ReceiveUpdate方法, 将方法参数在控制台打印出来;

Finished方法则用来关闭连接.

运行结果:

开始使用SignalR - ChatRoom

服务端:

建立 ChatHub 类

ChatHub

using Microsoft.AspNetCore.SignalR;

namespace SignalRStudy.Hubs
{
    public class ChatHub : Hub
    {
        public async void SendMessage(string username, string message)
        {
           await Clients.All.SendAsync("ReceiveMessage", username, message);
        }
    }
}

Startup中要配置一下:

app.UseEndpoints(endpoints =>
{
    ...
    endpoints.MapHub<ChatHub>("/chat");
});

服务端很简单, 就是把收到的消息转发给所有连接着的客户端

客户端(Angular):

ChatService

ChatService

import { Injectable, EventEmitter } from '@angular/core';
import * as signalr from '@microsoft/signalr'
import { Observable, of, Subscribable, Subscriber } from 'rxjs';

const connection = new signalr.HubConnectionBuilder()
  .withUrl('http://localhost:5000/chat')
  .build();

@Injectable()
export class ChatService {
  receivedMessage$ = new Observable<any>(observer => {
    connection.on('ReceiveMessage', (username: string, message: string) => {
      observer.next({
        username,
        message
      });
    });
  });
  username: string = '匿名用户';

  constructor() { 
    // connection.on('ReceiveMessage', this.receiveMessage);
  }

  async startChat() {
    await connection.start();
  }

  async sendMessage(message: string) {
    // 等待连接或断开连接操作完成
    while(connection.state === signalr.HubConnectionState.Connecting 
      || connection.state === signalr.HubConnectionState.Disconnecting);
    // 如果未连接服务器, 则尝试进行连接
    if(connection.state === signalr.HubConnectionState.Disconnected) {
      await connection.start().catch(err => console.error('signalr failed to connect to server.'));
    }
    if(connection.state === signalr.HubConnectionState.Connected) {
      await connection.send('SendMessage', this.username, message);
    }
  }
}

ChatService中处理了SignalR交互的逻辑, 组件可以通过订阅ReceivedMessage$来获取最新的消息...

下面放一下相关组件的代码:

chat.component.ts

import { Component, OnInit, ViewChild, ElementRef } from '@angular/core';
import { ChatService } from '../../services/chat.service';


@Component({
  selector: 'app-chat',
  templateUrl: './chat.component.html',
  styleUrls: ['./chat.component.css']
})
export class ChatComponent implements OnInit {
  messageToSend: string = '';
  receivedMessages: any[] = [];
  @ViewChild('messageBox', { static: true }) messageBox:ElementRef;

  constructor(
    private chatServ: ChatService
  ) { 
  }

  async ngOnInit() {
    this.chatServ.username = 'laggage';
    
    await this.chatServ.startChat();
    this.chatServ.receivedMessage$.subscribe(r => {
      this.receivedMessages.push(r);
      // 滚动条滑动到最底部, 等待5ms是为了等待angular渲染完界面, 否则可能无法滚动到底部
      setTimeout(() => {
        let ele = this.messageBox.nativeElement as HTMLDivElement;
        ele.scrollTop = ele.scrollHeight;
      }, 5);
    });
  }

  get username() {
    return this.chatServ.username;
  }

  set username(value: string) {
    if(value != this.chatServ.username)
      this.chatServ.username = value;
  }

  sendMessage() {
    this.chatServ.sendMessage(this.messageToSend);
    this.messageToSend = '';
  }
}

chat.component.html

<div id="wrapper">
    <!-- chat works -->
    <div id="message-receive-area">
        <div id="message-container"
             #messageBox
             class="px-3 py-2 overflow-auto">
            <div class="message-item jumbotron p-0 px-3 py-2 mb-3"
                 *ngFor="let message of receivedMessages">
                <span> {{message.username}}说: </span>
                <span class="d-block"> {{message.message}} </span>
            </div>
        </div>
    </div>

    <div id="message-send-area"
         class="container-fluid mx-0 row">
        <div id="write-message"
             class="col col-8 pl-0">
            <textarea name="message"
                      class="h-100 w-100"
                      [(ngModel)]="messageToSend"></textarea>
        </div>
        <div class="col col-4 overflow-hidden pr-0">
            <div class="mb-3">
                <label for="">
                    用户名
                    <input type="text"
                           class="w-100"
                           name="username"
                           placeholder="用户名"
                           [(ngModel)]="username">
                </label>
            </div>
            <div class="w-100"> <button class="w-100 overflow-hidden"
                        (click)="sendMessage()">Send</button> </div>
        </div>
    </div>
</div>

chat.component.css

#message-receive-area {
    height: 60vh;
    padding: .6rem;
}

#message-container {
    border: 1px solid black;
    height: 100%;
}

#message-send-area {
    height: 40vh;
    padding: .6rem;
}

先这样...