apm (asynchronous programming model)

APM/Server/Server.cs

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+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
+	}
+}

APM/Server/Server.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>