Introduce
上篇博文中，介绍了WebSocket的基本原理，以及一个简单的Demo用来对其有一个大致的认识。这篇博文讲的是我们平常在网站上可能会经常遇到的——实时聊天，本文就是来讲在.NET-Core使用WebSocket来实现一个“乞丐版”的在线实时聊天Demo。
关键词：Middleware,Real-Time,WebSocket
Before You Read.
这个和我们上一篇博文中Demo 有何不同的呢？有何共同之处呢？
相同的点是，都是网页作为客户端，使用JavaScript来发送和接收请求，.NET-Core 服务端接收到请求，发送该请求给客户端。
不同的地方呢，就像我下面这张图这样：
一次同时有多个客户端在，所以应该很清楚，我们只要在上面例子的基础上，对当前的已存在的Socket进行轮询，发送回应即可达到我们想要的效果。
Create WebSocket Middleware
在上个Demo的例子中，我们直接在Startup 的Configure 中直接写接受WebSocket请求。这次我们换成Middleware形式来处理。在写Middleware之前，在之前的介绍中，我们知道，需要有多个WebSocket，那么肯定需要一些对WebSocket 的Get/Set 处理。我简单的写了一个下面WebScoket Manger Class
//WebSocketManager.cs
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace WebSocketManage
{
public class WSConnectionManager
{
private static ConcurrentDictionary<string, WebSocket> _socketConcurrentDictionary = new ConcurrentDictionary<string, WebSocket>();
public void AddSocket(WebSocket socket)
{
_socketConcurrentDictionary.TryAdd(CreateGuid(), socket);
}
public async Task RemoveSocket(WebSocket socket)
{
_socketConcurrentDictionary.TryRemove(GetSocketId(socket), out WebSocket aSocket);
await aSocket.CloseAsync(
closeStatus: WebSocketCloseStatus.NormalClosure,
statusDescription: "Close by User",
cancellationToken: CancellationToken.None).ConfigureAwait(false);
}
public string GetSocketId(WebSocket socket)
{
return _socketConcurrentDictionary.FirstOrDefault(k => k.Value == socket).Key;
}
public ConcurrentDictionary<string, WebSocket> GetAll()
{
return _socketConcurrentDictionary;
}
public string CreateGuid()
{
return Guid.NewGuid().ToString();
}
}
}
上面主要是对WebSocket 进行了简单的存取操作进行了封装。下面也把WebSocket 的Send 和Recieve 操作进行了封装。
using System;
using System.Collections.Generic;
using System.IO;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace WebSocketManage
{
public class WSHandler
{
protected WSConnectionManager _wsConnectionManager;
public WSHandler(WSConnectionManager wSConnectionManager)
{
_wsConnectionManager = wSConnectionManager;
}
public async Task SendMessageAsync(
WebSocket socket,
string message,
CancellationToken cancellationToken = default(CancellationToken))
{
var buffer = Encoding.UTF8.GetBytes(message);
var segment = new ArraySegment<byte>(buffer);
await socket.SendAsync(segment, WebSocketMessageType.Text, true, cancellationToken);
}
public async Task<string> RecieveAsync(WebSocket webSocket, CancellationToken cancellationToken)
{
var buffer = new ArraySegment<byte>(new byte[1024 * 8]);
using (var ms = new MemoryStream())
{
WebSocketReceiveResult result;
do
{
cancellationToken.ThrowIfCancellationRequested();
result = await webSocket.ReceiveAsync(buffer, cancellationToken);
ms.Write(buffer.Array, buffer.Offset, result.Count);
}
while (!result.EndOfMessage);
ms.Seek(0, SeekOrigin.Begin);
if (result.MessageType != WebSocketMessageType.Text)
{
return null;
}
using (var reader = new StreamReader(ms, Encoding.UTF8))
{
return await reader.ReadToEndAsync();
}
}
}
}
}
有了上面两个辅助类之后，接下来就可以写我们自己的RealTimeWebSocketMiddlerware 了，
using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using WebSocketManage;
namespace Robert.Middleware.WebSockets
{
public class RealTimeWSMiddleware
{
private readonly RequestDelegate _next;
private WSConnectionManager _wSConnectionManager { get; set; }
private WSHandler _wsHanlder { get; set; }
public RealTimeWSMiddleware(
RequestDelegate next,
WSConnectionManager wSConnectionManager,
WSHandler wsHandler)
{
_next = next;
_wSConnectionManager = wSConnectionManager;
_wsHanlder = wsHandler;
}
public async Task Invoke(HttpContext httpContext)
{
if (httpContext.WebSockets.IsWebSocketRequest)
{
var cancellationToken = httpContext.RequestAborted;
var currentWebSocket = await httpContext.WebSockets.AcceptWebSocketAsync();
_wSConnectionManager.AddSocket(currentWebSocket);
while (true)
{
if (cancellationToken.IsCancellationRequested) break;
var response = await _wsHanlder.ReceiveAsync(currentWebSocket, cancellationToken);
if (string.IsNullOrEmpty(response) && currentWebSocket.State != WebSocketState.Open) break;
foreach (var item in _wSConnectionManager.GetAll())
{
if (item.Value.State == WebSocketState.Open)
{
await _wsHanlder.SendMessageAsync(item.Value, response, cancellationToken);
}
continue;
}
}
await _wSConnectionManager.RemoveSocket(currentWebSocket);
}
else
{
await _next(httpContext);
}
}
}
}
有了上面两个辅助类之后，接下来就可以写我们自己的RealTimeWebSocketMiddlerware 了，
using Microsoft.AspNetCore.Http;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using WebSocketManage;
namespace Robert.Middleware.WebSockets
{
public class RealTimeWSMiddleware
{
private readonly RequestDelegate _next;
private WSConnectionManager _wSConnectionManager { get; set; }
private WSHandler _wsHanlder { get; set; }
public RealTimeWSMiddleware(
RequestDelegate next,
WSConnectionManager wSConnectionManager,
WSHandler wsHandler)
{
_next = next;
_wSConnectionManager = wSConnectionManager;
_wsHanlder = wsHandler;
}
public async Task Invoke(HttpContext httpContext)
{
if (httpContext.WebSockets.IsWebSocketRequest)
{
var cancellationToken = httpContext.RequestAborted;
var currentWebSocket = await httpContext.WebSockets.AcceptWebSocketAsync();
_wSConnectionManager.AddSocket(currentWebSocket);
while (true)
{
if (cancellationToken.IsCancellationRequested) break;
var response = await _wsHanlder.ReceiveAsync(currentWebSocket, cancellationToken);
if (string.IsNullOrEmpty(response) && currentWebSocket.State != WebSocketState.Open) break;
foreach (var item in _wSConnectionManager.GetAll())
{
if (item.Value.State == WebSocketState.Open)
{
await _wsHanlder.SendMessageAsync(item.Value, response, cancellationToken);
}
continue;
}
}
await _wSConnectionManager.RemoveSocket(currentWebSocket);
}
else
{
await _next(httpContext);
}
}
}
}
其实到这里，核心部分已经讲完了，接下来就是页面显示，发现信息，交互的问题了。在客户端还是像上篇文章中的一样，直接使用 JavaScript发送WebScoket请求。
下面主要演示一下效果，在上篇博文的基础上，加上了用户名。
<script>$(function () {var protocol = location.protocol === "https:" ? "wss:" : "ws:";var Uri = protocol + "//" + window.location.host + "/ws";var socket = new WebSocket(Uri);socket.onopen = e => {console.log("socket opened", e);};socket.onclose = function (e) {console.log("socket closed", e);};//function to receive from server.socket.onmessage = function (e) {console.log("Message:" + e.data);$('#msgs').append(e.data + '<br />');};socket.onerror = function (e) {console.error(e.data);};});</script>当写好了页面文件后，运行站点。最终运行的效果图，界面以实用为主，不求美观。
