C# 实现WebSocket服务端教程

针对“C# 实现WebSocket服务端教程”，我将提供完整的攻略。下面是详细的步骤：

步骤一：创建一个空的C#控制台应用程序

可以使用Visual Studio进行创建，也可以使用命令行创建，此处不再赘述。在创建时，需要选择.NET Core 3.x或者.NET 5+作为Target Framework。

步骤二：添加NuGet包

在控制台中输入以下命令，添加System.Net.WebSockets NuGet包：

dotnet add package System.Net.WebSockets

步骤三：实现WebSocketServer

在应用程序的根目录下，创建WebSocketServer.cs文件，实现WebSocket服务端的代码。以下是一个很简单的示例：

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

namespace WebSocketServerDemo
{
    public class WebSocketServer
    {
        private readonly HttpListener httpListener;
        private readonly CancellationTokenSource cts = new CancellationTokenSource();

        public WebSocketServer(string[] prefixes)
        {
            httpListener = new HttpListener();

            foreach (var prefix in prefixes)
            {
                httpListener.Prefixes.Add(prefix);
            }
        }

        public async Task StartAsync()
        {
            httpListener.Start();

            Console.WriteLine("WebSocket server started.");

            while (!cts.Token.IsCancellationRequested)
            {
                var listenerContext = await httpListener.GetContextAsync();

                if (listenerContext.Request.IsWebSocketRequest)
                {
                    var webSocketContext = await listenerContext.AcceptWebSocketAsync(subProtocol: null);

                    await HandleWebSocketRequestAsync(webSocketContext.WebSocket);
                }
                else
                {
                    listenerContext.Response.StatusCode = 400;
                    listenerContext.Response.Close();
                }
            }
        }

        private async Task HandleWebSocketRequestAsync(WebSocket webSocket)
        {
            var buffer = new byte[1024];
            var receiveResult = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), cts.Token);

            while (!receiveResult.CloseStatus.HasValue)
            {
                var message = Encoding.UTF8.GetString(buffer, 0, receiveResult.Count);
                Console.WriteLine($"Received message: {message}");

                var response = Encoding.UTF8.GetBytes($"[Echo] {message}");
                await webSocket.SendAsync(new ArraySegment<byte>(response, 0, response.Length), WebSocketMessageType.Text, true, CancellationToken.None);

                receiveResult = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), cts.Token);
            }

            await webSocket.CloseAsync(receiveResult.CloseStatus.Value, receiveResult.CloseStatusDescription, CancellationToken.None);
        }

        public void Stop()
        {
            cts.Cancel();
            httpListener.Stop();
        }
    }
}

步骤四：启动WebSocket服务端

在Program.cs文件中，编写启动WebSocket服务端的代码。以下是示例代码：

using System;
using System.Threading.Tasks;

namespace WebSocketServerDemo
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var server = new WebSocketServer(new[] { "http://localhost:8000/" });

            await server.StartAsync();
        }
    }
}

这将启动一个WebSocket服务端，监听在http://localhost:8000/地址。

示例一：使用JavaScript进行测试

如果WebSocket服务端启动成功，在浏览器中打开Html文件时就可以使用WebSocket发送消息，观察服务端是否正常接收。

以下是Html文件中示例的JavaScript代码：

const webSocket = new WebSocket('ws://localhost:8000/');
webSocket.onopen = function (event) {
    console.log('WebSocket is open now.');
}
webSocket.onmessage = function (event) {
    console.log(`WebSocket received message: ${event.data}`);
}
webSocket.onerror = function (event) {
    console.error('WebSocket error: ', event);
}
webSocket.onclose = function (event) {
    console.log('WebSocket close: ', event);
}

webSocket.send('Hello, WebSocket!');

当JavaScript代码过程中调用了send方法时，会向WebSocket服务端发送一条消息。

示例二：使用C# HttpClient进行测试

以下是通过C# HttpClient进行测试的代码：

using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace WebSocketServerDemo
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var server = new WebSocketServer(new[] { "http://localhost:8000/" });

            _ = server.StartAsync();

            using (var httpClient = new HttpClient())
            {
                await httpClient.GetStringAsync("http://localhost:8000/");

                using (var webSocketClient = new ClientWebSocket())
                {
                    await webSocketClient.ConnectAsync(new Uri("ws://localhost:8000/"), default);

                    var buffer = new byte[1024];
                    var message = new ArraySegment<byte>(buffer);

                    foreach (var msg in new[] { "Hello, WebSocket!", "Are you there?" })
                    {
                        Console.WriteLine($"Send message: {msg}");

                        var messageSegment = new ArraySegment<byte>(Encoding.UTF8.GetBytes(msg));
                        await webSocketClient.SendAsync(messageSegment, WebSocketMessageType.Text, endOfMessage: true, CancellationToken.None);

                        var receiveResult = await webSocketClient.ReceiveAsync(message, CancellationToken.None);
                        var response = Encoding.UTF8.GetString(buffer, 0, receiveResult.Count);

                        Console.WriteLine($"Receive message: {response}");
                    }

                    await webSocketClient.CloseAsync(WebSocketCloseStatus.NormalClosure, "Close from WebSocketClient.", default);
                }
            }

            server.Stop();
        }
    }
}

当代码过程中创建了一个ClientWebSocket时，就可以使用其发送和接收WebSocket消息。