tcpipSocket/APM/Server/Server.cs

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

namespace Server;

internal class Server
{
	private static readonly int BUFFER_SIZE = 256;

	static void Main(string[] args)
	{
		Socket serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
		IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 20000);
		serverSocket.Bind(endPoint);
		serverSocket.Listen(1000);

		serverSocket.BeginAccept(AcceptCompleted, serverSocket);

		while (true)
		{
			Thread.Sleep(1000);
		}
	}

	private static void AcceptCompleted(IAsyncResult ar)
	{
		if (ar.AsyncState == null)
			return;

		Socket serverSocket = (Socket)ar.AsyncState;
		Socket clientSocket = serverSocket.EndAccept(ar);

		Console.WriteLine(clientSocket.RemoteEndPoint);

		serverSocket.BeginAccept(AcceptCompleted, serverSocket);

		byte[] buffer = new byte[BUFFER_SIZE];
		clientSocket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, ReceiveCompleted, (clientSocket, buffer)); // state: tuple
	}

	private static void ReceiveCompleted(IAsyncResult ar)
	{
		if (ar.AsyncState == null)
			return;

		(Socket clientSocket, byte[] buffer) = ((Socket, byte[]))ar.AsyncState;
		int n1 = clientSocket.EndReceive(ar);
		if (n1 < 1)
		{
			Console.WriteLine("Client is disconnected");
			clientSocket.Dispose();
			return;
		}

		Console.WriteLine(Encoding.UTF8.GetString(buffer));

		byte[] newBuffer = new byte[BUFFER_SIZE];
		clientSocket.BeginReceive(newBuffer, 0, newBuffer.Length, SocketFlags.None, ReceiveCompleted, (clientSocket, newBuffer)); // state: tuple
	}
}