using System.Text;

using System.Net;

using System.Net.Sockets;

 

namespace ConsoleUdpServer

    class Program

    {

        static void Main(string[] args)

        {

            Socket socket = new Socket(AddressFamily.InterNetwork,

                SocketType.Dgram,

                ProtocolType.Udp);

            EndPoint localEP = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 8002);

            socket.Bind(localEP);

 

            //启动异步接收

            State state = new State(socket);

            socket.BeginReceiveFrom(

                state.Buffer, 0, state.Buffer.Length,

                SocketFlags.None,

                ref state.RemoteEP,

                EndReceiveFromCallback,

                state);

 

            Console.ReadLine();

            socket.Close();

        }

 

        //异步接收回调函数

        static void EndReceiveFromCallback(IAsyncResult iar)

        {

            State state = iar.AsyncState as State;

            Socket socket = state.Socket;

            try

            {

                //完成接收

                int byteRead = socket.EndReceiveFrom(iar, ref state.RemoteEP);

                //显示客户端地址和端口

                Console.WriteLine("客户端终结点：{0}", state.RemoteEP.ToString());

                //显示接收信息

                Console.WriteLine("接收数据字节数：{0}", byteRead);

                string message = Encoding.Default.GetString(state.Buffer, 0, byteRead);

                Console.WriteLine("来着客户端信息：{0}", message);

                //向客户端发送信息

                SendMeaage(socket, state.RemoteEP, "成功接收！");

            }

            catch (Exception e)

            {

                Console.WriteLine("发生异常！异常信息：");

                Console.WriteLine(e.Message);

            }

            finally

            {

                //非常重要：继续异步接收

                socket.BeginReceiveFrom(

                    state.Buffer, 0, state.Buffer.Length,

                    SocketFlags.None,

                    ref state.RemoteEP,

                    EndReceiveFromCallback,

                    state);

            }

        }

 

        /// <summary>

        /// 向客户端发送信息

        /// </summary>

        /// <param name="socket">本地Socket（服务器Socket）</param>

        /// <param name="remoteEndPoint">客户端终结点</param>

        /// <param name="Message">信息</param>

        static void SendMeaage(Socket socket, EndPoint remoteEndPoint, string Message)

        {

            byte[] bytes = Encoding.Default.GetBytes(Message);

            socket.SendTo(bytes, remoteEndPoint);

        }

    }

 

    /// <summary>

    /// 用于异步接收处理的辅助类

    /// </summary>

    class State

    {

        public State(Socket socket)

        {

            this.Buffer = new byte[1024];

            this.Socket = socket;

            this.RemoteEP = new IPEndPoint(IPAddress.Any, 0);

        }

        /// <summary>

        /// 获取本机（服务器）Socket

        /// </summary>

        public Socket Socket { get; private set; }

        /// <summary>

        /// 获取接收缓冲区

        /// </summary>

        public byte[] Buffer { get; private set; }

        /// <summary>

        /// 获取/设置客户端终结点

        /// </summary>

        public EndPoint RemoteEP;

    }

 

客户端:

using System;