apm (asynchronous programming model)

APM/Client/Client.cs

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+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+
+namespace Client;
+
+internal class Client
+{
+	static void Main(string[] args)
+	{
+		Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+		IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 20000);
+
+		socket.BeginConnect(endPoint, ConnectCompleted, socket);
+
+		while (true)
+		{
+			string str = Console.ReadLine() ??	string.Empty;
+			socket.Send(Encoding.UTF8.GetBytes(str));
+		}
+	}
+
+	private static void ConnectCompleted(IAsyncResult ar)
+	{
+		if (ar.AsyncState == null)
+			return;
+
+		Socket socket = (Socket)ar.AsyncState;
+		socket.EndConnect(ar);
+
+		string str = Console.ReadLine() ?? string.Empty;
+		byte[] buffer = Encoding.UTF8.GetBytes(str);
+
+		socket.BeginSend(buffer, 0, buffer.Length, SocketFlags.None, SendCompleted, socket);
+	}
+
+	private static void SendCompleted(IAsyncResult ar)
+	{
+		if (ar.AsyncState == null)
+			return;
+
+		Socket socket = (Socket)ar.AsyncState;
+		socket.EndSend(ar);
+
+		string str = Console.ReadLine() ?? string.Empty;
+		byte[] buffer = Encoding.UTF8.GetBytes(str);
+
+		socket.BeginSend(buffer, 0, buffer.Length, SocketFlags.None, SendCompleted, socket);
+	}
+}

APM/Client/Client.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>