一、WebSocket編程概念

1.1 什么是WebSocket

WebSocket 是一種全雙工通信協議，允許在客戶端（通常是瀏覽器）和服務器之間建立持久連接，以實現實時的雙向通信。它是 HTML5 標準的一部分，相比傳統的 HTTP 請求，WebSocket 提供了更低的延遲和更高的性能，特別適合于需要實時更新數據的應用程序，如在線聊天、實時監控、游戲等

1.2 WebSocket的基本使用步驟

1.2.1 ）服務器端

1.2.1.1）使用System.Net.WebSocket命名空間

using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;
using System.Text;

1.2.1.2） 創建WebSocket服務器端點

public async Task HandleWebSocketConnection(HttpContext context)
{if (context.WebSockets.IsWebSocketRequest){WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();await EchoWebSocket(webSocket);}else{context.Response.StatusCode = 400;}
}

1.2.1.3）處理WebSocket消息

private async Task EchoWebSocket(WebSocket webSocket)
{var buffer = new byte[1024 * 4];WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);while (!result.CloseStatus.HasValue){// 發送接收到的消息回客戶端await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), result.MessageType, result.EndOfMessage, CancellationToken.None);// 繼續接收下一條消息result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);}// 關閉 WebSocket 連接await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);
}

1.2.1.4）啟動服務器

public static async Task Main(string[] args)
{var webSocketServer = new WebSocketServer();await webSocketServer.Start();
}

1.2.2 ）客戶端

1.2.2.1）使用System.Net.WebSocket.ClientWebSocket 命名空間

using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;
using System.Text;

1.2.2.2）創建WebSocket客戶端并連接到服務器

public async Task ConnectToWebSocketServer()
{using (var clientWebSocket = new ClientWebSocket()){Uri serverUri = new Uri("ws://localhost:8080/ws");await clientWebSocket.ConnectAsync(serverUri, CancellationToken.None);await SendAndReceiveData(clientWebSocket);}
}

1.2.2.3）發送和接收數據

private async Task SendAndReceiveData(ClientWebSocket clientWebSocket)
{var buffer = new byte[1024 * 4];string message = "Hello, WebSocket Server!";var sendBuffer = new ArraySegment<byte>(Encoding.UTF8.GetBytes(message));await clientWebSocket.SendAsync(sendBuffer, WebSocketMessageType.Text, true, CancellationToken.None);WebSocketReceiveResult result = await clientWebSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);string receivedMessage = Encoding.UTF8.GetString(buffer, 0, result.Count);Console.WriteLine($"Received: {receivedMessage}");
}

1.2.2.4）啟動客戶端

public static async Task Main(string[] args)
{var webSocketClient = new WebSocketClient();await webSocketClient.ConnectToWebSocketServer();
}

1.2.3) 運行步驟

1.2.3.1）先啟動服務器程序，服務器將開始監聽請求。
1.2.3.2）再啟動客戶端程序，客戶端會連接到服務器并發送一條消息。
1.2.3.3）服務器接收到消息后，打印消息并回復。
1.2.3.4）客戶端接收到服務器的回復并打印。

1.3 完整代碼示例

1.3.1）服務器端

using System;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;
using System.Text;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;namespace WebSocketServerExample
{public class WebSocketServer{private readonly IWebHost _webHost;public WebSocketServer(){_webHost = new WebHostBuilder().UseKestrel().ConfigureServices(services => services.AddRouting()).Configure(app =>{app.UseWebSockets();app.Use(async (context, next) =>{if (context.WebSockets.IsWebSocketRequest){WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync();await EchoWebSocket(webSocket);}else{context.Response.StatusCode = 400;}});}).Build();}public async Task Start(){await _webHost.StartAsync();}private async Task EchoWebSocket(WebSocket webSocket){var buffer = new byte[1024 * 4];WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);while (!result.CloseStatus.HasValue){// 發送接收到的消息回客戶端await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), result.MessageType, result.EndOfMessage, CancellationToken.None);// 繼續接收下一條消息result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);}// 關閉 WebSocket 連接await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);}}class Program{static async Task Main(string[] args){var webSocketServer = new WebSocketServer();await webSocketServer.Start();}}
}// 代碼解釋
// 創建 WebSocket 服務器端點：
// app.UseWebSockets();：啟用 WebSocket 中間件。
// context.WebSockets.IsWebSocketRequest：檢查請求是否為 WebSocket 請求。
// context.WebSockets.AcceptWebSocketAsync()：接受 WebSocket 請求并創建 WebSocket 對象。// 處理 WebSocket 消息：
// await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);：接收客戶端發送的消息。
// await webSocket.SendAsync(new ArraySegment<byte>(buffer, 0, result.Count), result.MessageType, result.EndOfMessage, CancellationToken.None);：將接收到的消息發送回客戶端。
// await webSocket.CloseAsync(result.CloseStatus.Value, result.CloseStatusDescription, CancellationToken.None);：當收到關閉請求時，關閉連接。

?

1.3.2）客戶端

using System;
using System.Net.WebSockets;
using System.Threading;
using System.Threading.Tasks;
using System.Text;namespace WebSocketClientExample
{public class WebSocketClient{public async Task ConnectToWebSocketServer(){using (var clientWebSocket = new ClientWebSocket()){Uri serverUri = new Uri("ws://localhost:8080/ws");await clientWebSocket.ConnectAsync(serverUri, CancellationToken.None);await SendAndReceiveData(clientWebSocket);}}private async Task SendAndReceiveData(ClientWebSocket clientWebSocket){var buffer = new byte[1024 * 4];string message = "Hello, WebSocket Server!";var sendBuffer = new ArraySegment<byte>(Encoding.UTF8.GetBytes(message));await clientWebSocket.SendAsync(sendBuffer, WebSocketMessageType.Text, true, CancellationToken.None);WebSocketReceiveResult result = await clientWebSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);string receivedMessage = Encoding.UTF8.GetString(buffer, 0, result.Count);Console.WriteLine($"Received: {receivedMessage}");}}class Program{static async Task Main(string[] args){var webSocketClient = new WebSocketClient();await webSocketClient.ConnectToWebSocketServer();}}
}// 代碼解釋
// 創建 WebSocket 客戶端并連接到服務器：
// new ClientWebSocket()：創建 WebSocket 客戶端對象。
// clientWebSocket.ConnectAsync(serverUri, CancellationToken.None);：連接到服務器。發送和接收數據：
// await clientWebSocket.SendAsync(sendBuffer, WebSocketMessageType.Text, true, CancellationToken.None);：向服務器發送消息。
// await clientWebSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);：接收服務器的消息。

1.4 注意事項

1.4.1）端口號和URI : 確保服務器和客戶端使用相同的端口號和URI路徑

1.4.2）異常處理 ：在實際應用中，需要添加適當的異常處理代碼，例如處理連接失敗、接收或發送消息時的異常等

1.4.3）多客戶端處理 ：上述服務器端代碼僅處理一個客戶端，對于多客戶端場景，需要使用更復雜的邏輯，例如使用? ConcurrentDictionary? 來管理多個客戶端連接