用c#和websocket做服务器端主动发消息给web客户端？

在C#中使用WebSocket实现服务器端向Web客户端主动发送消息，需要遵循以下步骤：

1. 创建WebSocket服务器

首先，你需要创建一个WebSocket服务器来接收客户端连接并处理消息。

csharp
复制代码
using System;
using System.Net;
using System.Net.WebSockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

public class WebSocketServer
{
    private HttpListener listener;

    public WebSocketServer(string[] prefixes)
    {
        listener = new HttpListener();
        foreach (string prefix in prefixes)
        {
            listener.Prefixes.Add(prefix);
        }
    }

    public async Task Start()
    {
        listener.Start();
        Console.WriteLine("Listening for connections...");

        while (true)
        {
            HttpListenerContext context = await listener.GetContextAsync();
            if (context.Request.IsWebSocketRequest)
            {
                ProcessWebSocketRequest(context);
            }
            else
            {
                context.Response.StatusCode = 400;
                context.Response.Close();
            }
        }
    }

    private async void ProcessWebSocketRequest(HttpListenerContext context)
    {
        WebSocketContext webSocketContext = null;
        try
        {
            webSocketContext = await context.AcceptWebSocketAsync(null);
            Console.WriteLine("WebSocket connection established.");

            await HandleWebSocket(webSocketContext.WebSocket);
        }
        catch (Exception ex)
        {
            context.Response.StatusCode = 500;
            context.Response.Close();
            Console.WriteLine($"WebSocket error: {ex.Message}");
        }
    }

    private async Task HandleWebSocket(WebSocket webSocket)
    {
        try
        {
            byte[] buffer = new byte[1024];
            while (webSocket.State == WebSocketState.Open)
            {
                WebSocketReceiveResult result = await webSocket.ReceiveAsync(new ArraySegment<byte>(buffer), CancellationToken.None);
                if (result.MessageType == WebSocketMessageType.Text)
                {
                    string clientMessage = Encoding.UTF8.GetString(buffer, 0, result.Count);
                    Console.WriteLine($"Received from client: {clientMessage}");

                    // Echo back to client (for demonstration purposes)
                    byte[] responseBuffer = Encoding.UTF8.GetBytes($"Server received: {clientMessage}");
                    await webSocket.SendAsync(new ArraySegment<byte>(responseBuffer, 0, responseBuffer.Length), WebSocketMessageType.Text, true, CancellationToken.None);
                }
                else if (result.MessageType == WebSocketMessageType.Close)
                {
                    await webSocket.CloseAsync(WebSocketCloseStatus.NormalClosure, string.Empty, CancellationToken.None);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"WebSocket error: {ex.Message}");
        }
        finally
        {
            if (webSocket != null)
            {
                webSocket.Dispose();
            }
        }
    }

    public async Task Stop()
    {
        listener.Stop();
        listener.Close();
        await Task.CompletedTask;
    }
}

2. 启动WebSocket服务器

csharp
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class Program
{
    static async Task Main(string[] args)
    {
        string[] prefixes = { "http://localhost:8080/" }; // Replace with your desired URL
        WebSocketServer server = new WebSocketServer(prefixes);
        await server.Start();

        Console.WriteLine("Press any key to stop the server...");
        Console.ReadKey();

        await server.Stop();
    }
}

3. Web客户端连接和消息处理

在Web客户端，你可以使用JavaScript来连接WebSocket并处理来自服务器的消息。

javascript
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const socket = new WebSocket('ws://localhost:8080/');

socket.onopen = function(event) {
    console.log('WebSocket connected.');
};

socket.onmessage = function(event) {
    console.log('Message from server:', event.data);
};

socket.onclose = function(event) {
    console.log('WebSocket disconnected.');
};

// Example: Send message to server
function sendMessage(message) {
    socket.send(message);
}

4. 服务器端主动发送消息给客户端

在C#中，可以在WebSocket处理程序中使用SendAsync方法来主动向客户端发送消息。

csharp
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// Inside HandleWebSocket method
string messageToSend = "Hello from server!";
byte[] buffer = Encoding.UTF8.GetBytes(messageToSend);
await webSocket.SendAsync(new ArraySegment<byte>(buffer), WebSocketMessageType.Text, true, CancellationToken.None);

这样，服务器端就能够主动向连接的Web客户端发送消息了。记得处理WebSocket的连接状态和异常，以保证稳定的通信。