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.

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:

  1. 客户端发起连接请求
  2. 服务器端接受请求, 并向该客户端发出计数, 从0到10
  3. 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

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();

services.AddSignalR();

endpoints.MapHub("/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ReceiveUpdateFinished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:

SignalR入坑笔记_第1张图片

开始使用SignalR - ChatRoom

服务端:

建立 ChatHub

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">
    
    <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...

  

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