tcpipSocket/Echo/Server/Server.cs

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

namespace Server;

internal class Server
{
	static void Main(string[] args)
	{
		using (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(20);

			using (Socket clientSocket = serverSocket.Accept())
			{
				Console.WriteLine(clientSocket.RemoteEndPoint);

				while (true)
				{
					byte[] headerBuffer = new byte[2];
					int headerReceive = clientSocket.Receive(headerBuffer);
					if (headerReceive < 1)
					{
						Console.WriteLine("Disconnecting client...");
						return;
					}
					else if (headerReceive == 1)
					{
						clientSocket.Receive(headerBuffer, 0, 1, SocketFlags.None);
					}

					short dataSize = IPAddress.NetworkToHostOrder(BitConverter.ToInt16(headerBuffer));
					byte[] dataBuffer = new byte[dataSize];
					int dataReveiced = 0;
					while (dataReveiced < dataSize)
					{
						int n = clientSocket.Receive(dataBuffer, dataReveiced, dataSize - dataReveiced, SocketFlags.None);
						dataReveiced += n;
					}

					string str = Encoding.UTF8.GetString(dataBuffer);
					Console.WriteLine(str);

					byte[] echoBuffer = new byte[2 + dataBuffer.Length];
					Array.Copy(headerBuffer, 0, echoBuffer, 0, headerBuffer.Length);
					Array.Copy(dataBuffer, 0, echoBuffer, 2, dataBuffer.Length);
					clientSocket.Send(echoBuffer);
				}
			}
		}
	}
}