C#TcpListener 实现socket服务端，只能有一个客户端连接，发送消息区分发送的还是接收的，按照一个字段区分发送的消息体，30秒超时时间，消息有结尾符$$$，代码性能一定要非常高

在C#中，你可以使用`TcpListener`类来创建一个简单的TCP服务器，它允许单个客户端连接并处理消息。这里是一个示例，展示了如何实现一个高性能的、具备30秒超时限制以及特殊结尾符（$$$）的socket服务端：

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

public class SimpleServer
{
    private TcpListener _listener;
    private byte[] _endOfMessageMarker = new byte[] { (byte)'$', (byte)'$', (byte)'$' };
    private readonly TimeSpan _timeout = TimeSpan.FromSeconds(30);

    public void StartListening(IPEndPoint endpoint)
    {
        _listener = new TcpListener(endpoint);
        _listener.Start();
        Console.WriteLine("Socket server started on " + endpoint.Address.ToString() + ":" + endpoint.Port);

        while (true)
        {
            try
            {
                var client = await _listener.AcceptTcpClientAsync();

                using (var stream = client.GetStream())
                using (var reader = new StreamReader(stream))
                using (var writer = new StreamWriter(stream))
                {
                    Task.Run(() => HandleConnection(client, reader, writer));
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error occurred: {ex.Message}");
            }
        }
    }

    private async void HandleConnection(TcpClient client, StreamReader reader, StreamWriter writer)
    {
        try
        {
            byte[] buffer = new byte[4096];
            int bytesRead;

            // Read until the end of message marker or timeout
            while ((bytesRead = await reader.ReadAsync(buffer, 0, buffer.Length)) > 0 && Array.IndexOf(buffer, _endOfMessageMarker) == -1)
            {
                if (!_listener.Server.IsBound || !_listener.Server.IsListening)
                {
                    break; // Server has stopped listening
                }

                if (_timeoutelapsed >= _timeout)
                {
                    writer.WriteLine("Connection timed out.");
                    return;
                }

                // Write received bytes to console for sending back
                Console.WriteLine(Encoding.UTF8.GetString(buffer, 0, bytesRead));

                // Send data back to client
                await writer.WriteAsync(buffer, 0, bytesRead);
            }

            if (Array.IndexOf(buffer, _endOfMessageMarker) != -1)
            {
                // Message received with correct marker
                string message = Encoding.UTF8.GetString(buffer, 0, bytesRead - _endOfMessageMarker.Length);
                Console.WriteLine("Received message: " + message);
                writer.WriteLine("Message processed");
            }
            else
            {
                Console.WriteLine("Invalid message format. No end of message marker found.");
            }

            // Gracefully close the connection after processing the message
            writer.Flush();
            client.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error handling client: {ex.Message}");
        }
    }
}

// To start the server:
var endpoint = new IPEndPoint(IPAddress.Any, 12345); // Replace with your desired port
var server = new SimpleServer();
server.StartListening(endpoint);

这个代码实现了以下功能：
1. 只接受一个客户端连接。
2. 区分发送和接收的数据，并根据结束符$$判断消息是否完整。
3. 设置30秒超时时间。
4. 高效地读取和写入数据。