UDP打洞原理及代码

来源：http://www.fenbi360.net/Content.aspx?id=1021&t=jc

UDP"打洞"原理

1.       NAT分类

根据Stun协议(RFC3489),NAT大致分为下面四类

1)      Full Cone

这种NAT内部的机器A连接过外网机器C后,NAT会打开一个端口.然后外网的任何发到这个打开的端口的UDP数据报都可以到达A.不管是不是C发过来的.

例如 A:192.168.8.100 NAT:202.100.100.100 C:292.88.88.88
A(192.168.8.100:5000) -> NAT(202.100.100.100 : 8000) -> C(292.88.88.88:2000)
任何发送到 NAT(202.100.100.100:8000)的数据都可以到达A(192.168.8.100:5000)

2)      Restricted Cone

这种NAT内部的机器A连接过外网的机器C后,NAT打开一个端口.然后C可以用任何端口和A通信.其他的外网机器不行.

例如 A:192.168.8.100 NAT:202.100.100.100 C:292.88.88.88
A(192.168.8.100:5000) -> NAT(202.100.100.100 : 8000) -> C(292.88.88.88:2000)
任何从C发送到 NAT(202.100.100.100:8000)的数据都可以到达A(192.168.8.100:5000)

3)      Port Restricted Cone

这种NAT内部的机器A连接过外网的机器C后,NAT打开一个端口.然后C可以用原来的端口和A通信.其他的外网机器不行.

例如 A:192.168.8.100 NAT:202.100.100.100 C:292.88.88.88
A(192.168.8.100:5000) -> NAT(202.100.100.100 : 8000) -> C(292.88.88.88:2000)
C(202.88.88.88:2000)发送到 NAT(202.100.100.100:8000)的数据都可以到达A(192.168.8.100:5000)

以上三种NAT通称Cone NAT.我们只能用这种NAT进行UDP打洞.

4)      Symmetic

对于这种NAT.连接不同的外部目标.原来NAT打开的端口会变化.而Cone NAT不会.虽然可以用端口猜测.但是成功的概率很小.因此放弃这种NAT的UDP打洞.

2.       UDP hole punching

对于Cone NAT.要采用UDP打洞.需要一个公网机器C来充当”介绍人”.内网的A,B先分别和C通信.打开各自的NAT端口.C这个时候知道A,B的公网IP: Port. 现在A和B想直接连接.比如A给B发.除非B是Full Cone.否则不能通信.反之亦然.但是我们可以这样.

A要连接B.A给B发一个UDP包.同时.A让那个介绍人给B发一个命令,让B同时给A发一个UDP包.这样双方的NAT都会记录对方的IP,然后就会允许互相通信.

3.       同一个NAT后面的情况

如果A,B在同一个NAT后面.如果用上面的技术来进行互连.那么如果NAT支持loopback(就是本地到本地的转换),A,B可以连接,但是比较浪费带宽和NAT.有一种办法是,A,B和介绍人通信的时候,同时把自己的local IP也告诉服务器.A,B通信的时候,同时发local ip和公网IP.谁先到就用哪个IP.但是local ip就有可能不知道发到什么地方去了.比如A,B在不同的NAT后面但是他们各自的local ip段一样.A给B的local IP发的UDP就可能发给自己内部网里面的某某某了.

还有一个办法是服务器来判断A,B是否在一个NAT后面.(网络拓朴不同会不会有问题?)

WellKnown.cs

//WellKnown公用库
using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using System.Net;
using System.Net.Sockets;
using System.Collections;

namespace P2PWellKnown
{
    /// <summary>
    /// UDP用户登录事件委托
    /// </summary>
    /// <param name="sender">事件源对象</param>
    /// <param name="e">事件实体</param>
    public delegate void UdpUserLogInDelegate(object sender, UDPSockEventArgs e);

    /// <summary>
    /// 一般UDP消息事件委托
    /// </summary>
    /// <param name="sender">事件源对象</param>
    /// <param name="e">事件实体</param>
    public delegate void UdpMessageDelegate(object sender, UDPSockEventArgs e);

    /// <summary>
    /// 初始化一个新连接的事件委托
    /// </summary>
    /// <param name="sender">事件源对象</param>
    /// <param name="e">事件实体</param>
    public delegate void UdpNewConnectDelegate(object sender, UDPSockEventArgs e);

    /// <summary>
    /// P2P共享数据类
    /// </summary>
    public class P2PConsts
    {
        /// <summary>
        /// UDP服务器监听端口
        /// </summary>
        public const int UDP_SRV_PORT = ;

        /// <summary>
        ///TCP服务器监听端口
        /// </summary>
        public const int TCP_SRV_PORT = ;
    }

    /// <summary>
    /// FormatterHelper 序列化，反序列化消息的帮助类
    /// </summary>
    public class FormatterHelper
    {

        public static byte[] Serialize(object obj)
        {
            BinaryFormatter binaryF = new BinaryFormatter();
            MemoryStream ms = new MemoryStream( * );
            binaryF.Serialize(ms, obj);
            ms.Seek(, SeekOrigin.Begin);
            byte[] buffer = new byte[(int)ms.Length];
            ms.Read(buffer, , buffer.Length);
            ms.Close();
            return buffer;
        }

        public static object Deserialize(byte[] buffer)
        {
            BinaryFormatter binaryF = new BinaryFormatter();
            MemoryStream ms = new MemoryStream(buffer, , buffer.Length, false);
            object obj = binaryF.Deserialize(ms);
            ms.Close();
            return obj;
        }

    }

    /// <summary>
    /// 用于承载UDPSock信息的事件类
    /// </summary>
    public class UDPSockEventArgs : EventArgs
    {
        /// <summary>
        /// 要承载的消息
        /// </summary>
        private string m_strMsg;

        /// <summary>
        /// 用户信息
        /// </summary>
        private string m_strUserName;

        /// <summary>
        /// 触发该事件的公共终端
        /// </summary>
        private IPEndPoint m_EndPoint;

        /// <summary>
        /// 初始化UDPSock事件
        /// </summary>
        /// <param name="sMsg">用户发送的信息</param>
        public UDPSockEventArgs(string sMsg)
            : base()
        {
            this.m_strMsg = sMsg;
        }

        /// <summary>
        /// 远端用户名
        /// </summary>
        public string RemoteUserName
        {
            get
            {
                return m_strUserName;
            }
            set
            {
                m_strUserName = value;
            }
        }

        /// <summary>
        /// 一般套接字消息
        /// </summary>
        public string SockMessage
        {
            get
            {
                return m_strMsg;
            }
            set
            {
                m_strMsg = value;
            }
        }

        /// <summary>
        /// 公共远端节点
        /// </summary>
        public IPEndPoint RemoteEndPoint
        {
            get
            {
                return m_EndPoint;
            }
            set
            {
                m_EndPoint = value;
            }
        }
    }
}

UDPP2PSock.cs

//UDPP2PSock.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Threading;

using P2PWellKnown;

namespace UDPP
{
    /// <summary>
    /// UDPP2P套接字管理类
    /// </summary>
    public class UDPP2PSock
    {
        /// <summary>
        /// 用户登录事件
        /// </summary>
        public event UdpUserLogInDelegate OnUserLogInU;

        /// <summary>
        /// 一般UDP消息事件
        /// </summary>
        public event UdpMessageDelegate OnSockMessageU;

        /// <summary>
        /// 初始化一个新连接事件
        /// </summary>
        public event UdpNewConnectDelegate OnNewConnectU;

        /// <summary>
        /// UDP服务器
        /// </summary>
        private UdpClient m_udpServer;

        /// <summary>
        /// UDP客户端
        /// </summary>
        private UdpClient m_udpClient;

        /// <summary>
        /// 服务器实际上在本地机器上监听的
        /// 端口，用于当一台计算机上同时启
        /// 动两个可两以上服务器进程时，标
        /// 识不同的服务器进程
        /// </summary>
        private int m_iMyServerPort;

        /// <summary>
        /// 客户端在本地机器上实际使用的端口，
        /// 用于当一台计算机上同时有两个或两
        /// 个以上客户端进程在运行时，标识不
        /// 同的客户端进程
        /// </summary>
        private int m_iMyClientPort;

        /// <summary>
        /// 标识是否已成功创服务器
        /// </summary>
        private bool m_bServerCreated;

        /// <summary>
        /// 标识是否已成功创建客户端
        /// </summary>
        private bool m_bClientCreated;

        /// <summary>
        /// 服务器使用的线程
        /// </summary>
        private Thread m_serverThread;

        /// <summary>
        /// 客户端使用的线程
        /// </summary>
        private Thread m_clientThread;

        /// <summary>
        /// 打洞线程
        /// </summary>
        //private Thread m_burrowThread;

        /// <summary>
        /// 远端节点
        /// </summary>
        private IPEndPoint m_remotePoint;

        /// <summary>
        /// 当前进程作为客户端的公共终端
        /// </summary>
        private string m_strMyPublicEndPoint;

        /// <summary>
        /// 当前进程作为客户端的私有终端
        /// </summary>
        private string m_strMyPrivateEndPoint;

        /// <summary>
        /// 用于接受信息的 StringBuilder实例
        /// </summary>
        private StringBuilder m_sbResponse = new StringBuilder();

        /// <summary>
        /// P2P打洞时标识是否收到回应消息
        /// </summary>
        private bool m_bRecvAck = false;

        /// <summary>
        /// 请求向其方向打洞的私有终端
        /// </summary>
        private IPEndPoint m_requestPrivateEndPoint;

        /// <summary>
        /// 请求向其方向打洞的公共终端
        /// </summary>
        private IPEndPoint m_requestPublicEndPoint;

        /// <summary>
        /// 打洞消息要发向的节点
        /// </summary>
        private ToEndPoint m_toEndPoint;

        /// <summary>
        /// 用于标识是否已经和请求客户端建立点对连接
        /// </summary>
        //private bool m_bHasConnected=false ;

        /// <summary>
        /// 创建服务器或客户端的最大尝试
        /// 次数，为（65536-60000），防止
        /// 因不能创建而限入死循环或使用
        /// 无效端口
        /// </summary>
        private const int MAX_CREATE_TRY = ;

        /// <summary>
        /// 打洞时尝试连接的最大尝试次数
        /// </summary>
        private const int MAX_CONNECT_TRY = ;

        /// <summary>
        /// 构造函数，初始化UDPP2P实例
        /// </summary>
        public UDPP2PSock()
        {
            m_iMyServerPort = P2PConsts.UDP_SRV_PORT;
            m_iMyClientPort = ;
            m_bClientCreated = false;
            m_bServerCreated = false;
            m_toEndPoint = new ToEndPoint();
            m_serverThread = new Thread(new ThreadStart(RunUDPServer));
            m_clientThread = new Thread(new ThreadStart(RunUDPClient));
            //m_burrowThread = new Thread(new ThreadStart(BurrowProc));
        }

        /// <summary>
        /// 创建UDP 服务器
        /// </summary>
        public void CreateUDPSever()
        {
            int iTryNum = ;

            //开始尝试创建服务器
            while (!m_bServerCreated && iTryNum < MAX_CREATE_TRY)
            {
                try
                {
                    m_udpServer = new UdpClient(m_iMyServerPort);
                    m_bServerCreated = true;
                }
                catch
                {
                    m_iMyServerPort++;
                    iTryNum++;
                }
            }

            //创建失败，抛出异常
            if (!m_bServerCreated && iTryNum == MAX_CREATE_TRY)
            {
                throw new Exception("创建服务器尝试失败！");
            }
            m_serverThread.Start();

        }

        /// <summary>
        /// 创建UDP客户端
        /// </summary>
        /// <param name="strServerIP"& gt;服务器IP</param>
        /// <param name="iServerPort"& gt;服务器端口</param>
        public void CreateUDPClient(string strServerIP, int iServerPort)
        {
            int iTryNum = ;

            //开始尝试创建服务器
            while (!m_bClientCreated && iTryNum < MAX_CREATE_TRY)
            {
                try
                {
                    m_udpClient = new UdpClient(m_iMyClientPort);
                    m_bClientCreated = true;
                    string strIPAddress = (System.Net.Dns.GetHostAddresses("localhost")[]).ToString();
                    m_strMyPrivateEndPoint = strIPAddress + ":" + m_iMyClientPort.ToString();
                }
                catch
                {
                    m_iMyClientPort++;
                    iTryNum++;
                }
            }

            //创建失败，抛出异常
            if (!m_bClientCreated && iTryNum == MAX_CREATE_TRY)
            {
                throw new Exception("创建客户端尝试失败！");
            }

            IPEndPoint hostPoint = new IPEndPoint(IPAddress.Parse(strServerIP), iServerPort);
            string strLocalIP = (System.Net.Dns.GetHostAddresses("localhost"))[].ToString();
            SendLocalPoint(strLocalIP, m_iMyClientPort, hostPoint);
            m_clientThread.Start();
        }

        /// <summary>
        /// 运行UDP 服务器
        /// </summary>
        private void RunUDPServer()
        {
            while (true)
            {
                byte[] msgBuffer = m_udpServer.Receive(ref m_remotePoint);
                m_sbResponse.Append(System.Text.Encoding.Default.GetString(msgBuffer));
                CheckCommand();
                Thread.Sleep();
            }
        }

        /// <summary>
        /// 运行UDP客户端
        /// </summary>
        private void RunUDPClient()
        {
            while (true)
            {
                byte[] msgBuffer = m_udpClient.Receive(ref m_remotePoint);
                m_sbResponse.Append(System.Text.Encoding.Default.GetString(msgBuffer));
                CheckCommand();
                Thread.Sleep();
            }
        }

        /// <summary>
        /// 销毁UDP 服务器
        /// </summary>
        public void DisposeUDPServer()
        {
            m_serverThread.Abort();
            m_udpServer.Close();
        }

        /// <summary>
        /// 销毁UDP客房端
        /// </summary>
        public void DisposeUDPClient()
        {
            m_clientThread.Abort();
            m_udpClient.Close();
        }

        /// <summary>
        /// 发送消息
        /// </summary>
        /// <param name="strMsg"& gt;消息内容</param>
        /// <param name="REP"& gt;接收节点</param>
        public void SendData(string strMsg, IPEndPoint REP)
        {
            byte[] byMsg = System.Text.Encoding.Default.GetBytes(strMsg.ToCharArray());
            m_udpClient.Send(byMsg, byMsg.Length, REP);
        }

        /// <summary>
        /// 发送消息，服务器专用
        /// </summary>
        /// <param name="strMsg"& gt;消息内容</param>
        /// <param name="REP"& gt;接收节点</param>
        private void ServerSendData(string strMsg, IPEndPoint REP)
        {
            byte[] byMsg = System.Text.Encoding.Default.GetBytes(strMsg.ToCharArray());
            m_udpServer.Send(byMsg, byMsg.Length, REP);
        }

        /// <summary>
        /// 发送本地节点信息
        /// </summary>
        /// <param name="strLocalIP"& gt;本地IP</param>
        /// <param name="iLocalPort"& gt;本地端口</param>
        public void SendLocalPoint(string strLocalIP, int iLocalPort, IPEndPoint REP)
        {
            string strLocalPoint = "\x01\x02" + strLocalIP + ":" + iLocalPort.ToString() + "\x02\x01";
            SendData(strLocalPoint, REP);
        }

        /// <summary>
        /// 同时向指定的终端（包括公共终端和私有终端）打洞
        /// </summary>
        /// <param name="pubEndPoint"& gt;公共终端</param>
        /// <param name="prEndPoint"& gt;私有终端</param>
        /// <returns>打洞成功返回true,否则返回false</returns>
        public void StartBurrowTo(IPEndPoint pubEndPoint, IPEndPoint prEndPoint)
        {
            Thread burrowThread = new Thread(new ThreadStart(BurrowProc));
            m_toEndPoint.m_privateEndPoint = prEndPoint;
            m_toEndPoint.m_publicEndPoint = pubEndPoint;
            burrowThread.Start();
        }

        /// <summary>
        /// 打洞线程
        /// </summary>
        private void BurrowProc()
        {
            IPEndPoint prEndPoint = m_toEndPoint.m_privateEndPoint;
            IPEndPoint pubEndPoint = m_toEndPoint.m_publicEndPoint;
            int j = ;
            for (int i = ; i < MAX_CONNECT_TRY; i++)
            {
                SendData("\x01\x07\x07\x01", prEndPoint);
                SendData("\x01\x07\x07\x01", pubEndPoint);

                // 等待接收线程标记修改
                for (j = ; j < MAX_CONNECT_TRY; j++)
                {
                    if (m_bRecvAck)
                    {
                        m_bRecvAck = false;
                        SendData("\x01\x07\x07\x01", prEndPoint);
                        Thread.Sleep();
                        SendData("\x01\x07\x07\x01", pubEndPoint);

                        UDPSockEventArgs args = new UDPSockEventArgs("");
                        args.RemoteEndPoint = pubEndPoint;
                        if (OnNewConnectU != null)
                        {
                            OnNewConnectU(this, args);
                        }
                        //Thread .Sleep (System .Threading.Timeout .Infinite );
                        return;
                    }
                    else
                    {
                        Thread.Sleep();
                    }
                }

                //如果没有收到目标主机的回应，表明本次打
                // 洞尝试失败,等待100毫秒后尝试下一次打洞
                Thread.Sleep();
            }

            //MAX_CONNECT_TRY 尝试都失败，表明打洞失败，抛出异常
            //throw new Exception(" 打洞失败！");
            System.Windows.Forms.MessageBox.Show("打洞失败！");////////////
        }

        /// <summary>
        /// 转发打洞请求消息，在服务器端使用
        /// </summary>
        /// <param name="strSrcPrEndpoint"& gt;请求转发的源私有终端</param>
        /// <param name="strSrcPubEndPoint"& gt;请求转发的源公共终端</param>
        /// <param name="REP"& gt;转发消息到达的目的终端</param>
        public void SendBurrowRequest(string strSrcPrEndpoint, string strSrcPubEndPoint, IPEndPoint REP)
        {
            string strBurrowMsg = "\x04\x07" + strSrcPrEndpoint + " " + strSrcPubEndPoint + "\x07\x04";
            ServerSendData(strBurrowMsg, REP);
        }

        /// <summary>
        /// 检查字符串中的命令
        /// </summary>
        private void CheckCommand()
        {
            int nPos;
            string strCmd = m_sbResponse.ToString();

            //如果接收远端用户名
            if ((nPos = strCmd.IndexOf("\x01\x02")) > -)
            {
                ReceiveName(strCmd, nPos);

                // 反馈公共终给端远端主机
                string strPubEPMsg = "\x03\x07" + m_remotePoint.ToString() + "\x07\x03";
                SendData(strPubEPMsg, m_remotePoint);

                return;
            }

            //如果接收我的公共终端
            if ((nPos = strCmd.IndexOf("\x03\x07")) > -)
            {
                ReceiveMyPublicEndPoint(strCmd, nPos);
                return;
            }

            //如果是打洞请求消息
            if ((nPos = strCmd.IndexOf("\x04\x07")) > -)
            {
                ReceiveAndSendAck(strCmd, nPos);
                return;
            }

            //如果是打洞回应消息
            if ((nPos = strCmd.IndexOf("\x01\x07")) > -)
            {
                m_bRecvAck = true;
                int nPos2 = strCmd.IndexOf("\x07\x01");
                if (nPos2 > -)
                {
                    m_sbResponse.Remove(nPos, nPos2 - nPos + );
                }

                return;
            }

            //一般聊天消息
            m_sbResponse.Remove(, strCmd.Length);
            RaiseMessageEvent(strCmd);
        }

        /// <summary>
        /// 接收远端用户名
        /// </summary>
        /// <param name="strCmd"& gt;包含用户名的控制信息</param>
        /// <param name="nPos"></param>
        private void ReceiveName(string strCmd, int nPos)
        {
            int nPos2 = strCmd.IndexOf("\x02\x01");
            if (nPos2 == -)
            {
                return;
            }
            m_sbResponse.Remove(nPos, nPos2 - nPos + );

            string strUserName = strCmd.Substring(nPos + , nPos2 - nPos - );
            UDPSockEventArgs e = new UDPSockEventArgs("");
            e.RemoteUserName = strUserName;
            e.RemoteEndPoint = m_remotePoint;

            //触发用户登录事件
            if (OnUserLogInU != null)
            {
                OnUserLogInU(this, e);
            }
        }

        /// <summary>
        /// 接收打洞请求的消息并发送回应
        /// </summary>
        /// <param name="strCmd"></param>
        /// <param name="nPos"></param>
        private void ReceiveAndSendAck(string strCmd, int nPos)
        {
            int nPos2 = strCmd.IndexOf("\x07\x04");
            if (nPos2 == -)
            {
                return;
            }
            m_sbResponse.Remove(nPos, nPos2 - nPos + );

            string strBurrowMsg = strCmd.Substring(nPos + , nPos2 - nPos - );

            string[] strSrcPoint = strBurrowMsg.Split(' ');

            //分析控制字符串包含的节点信息
            string[] strPrEndPoint = strSrcPoint[].Split(':');
            string[] strPubEndPoint = strSrcPoint[].Split(':');
            m_requestPrivateEndPoint = new IPEndPoint(IPAddress.Parse(strPrEndPoint[]), int.Parse(strPrEndPoint[]));
            m_requestPublicEndPoint = new IPEndPoint(IPAddress.Parse(strPubEndPoint[]), int.Parse(strPubEndPoint[]));

            //向请求打洞终端的方向打洞
            StartBurrowTo(m_requestPublicEndPoint, m_requestPrivateEndPoint);
        }

        /// <summary>
        /// 接收我的公共终端
        /// </summary>
        /// <param name="strCmd"& gt;包含公共终端的控制信息</param>
        /// <param name="nPos"& gt;控制字符串的起始位置</param>
        private void ReceiveMyPublicEndPoint(string strCmd, int nPos)
        {
            int nPos2 = strCmd.IndexOf("\x07\x03");
            if (nPos2 == -)
            {
                return;
            }
            m_sbResponse.Remove(nPos, nPos2 - nPos + );

            m_strMyPublicEndPoint = strCmd.Substring(nPos + , nPos2 - nPos - );
        }

        /// <summary>
        /// 触发一般UDP消息事件
        /// </summary>
        /// <param name="strMsg"& gt;消息内容</param>
        private void RaiseMessageEvent(string strMsg)
        {
            UDPSockEventArgs args = new UDPSockEventArgs("");
            args.SockMessage = strMsg;
            args.RemoteEndPoint = m_remotePoint;
            if (OnSockMessageU != null)
            {
                OnSockMessageU(this, args);
            }
        }

        /// <summary>
        /// 获取当前进程作为客户端的公共终端
        /// </summary>
        public string MyPublicEndPoint
        {
            get
            {
                return m_strMyPublicEndPoint;
            }
        }

        /// <summary>
        /// 获取当前进程作为客户端的私有终端
        /// </summary>
        public string MyPrivateEndPoint
        {
            get
            {
                return m_strMyPrivateEndPoint;
            }
        }
    }

    /// <summary>
    /// 保存打洞消息要发向的节点信息
    /// </summary>
    class ToEndPoint
    {
        /// <summary>
        /// 私有节点
        /// </summary>
        public IPEndPoint m_privateEndPoint;

        /// <summary>
        /// 公共节点
        /// </summary>
        public IPEndPoint m_publicEndPoint;
    }
}

关于如何使用上述程序包的一些说明：
主要程序的初始化，参考代码如下：

using UDPP;
using P2PWellKnown;

//创建UDP服务器和客户端
try
{
    string strServerIP = "127.0.0.1";
    UDPP2PSock udpSock = new UDPP2PSock();
    udpSock.OnUserLogInU += new UdpUserLogInDelegate(OnUserLogInU);
    udpSock.OnNewConnectU += new UdpNewConnectDelegate(OnNewConnectU);
    udpSock.CreateUDPSever();
    udpSock.CreateUDPClient(strServerIP, P2PConsts.UDP_SRV_PORT);
}
catch (Exception ex)
{

}

经上面的初始化后，就可以使用类UDPP2PSock中的方法了。

注：

udpSock.OnUserLogInU +=new UdpUserLogInDelegate(OnUserLogInU);
udpSock.OnNewConnectU +=new UdpNewConnectDelegate(OnNewConnectU);
中的OnUserLogInU和OnNewConnectU是事件名称,如
private void test(object sender, UDPSockEventArgs e)
{
    MessageBox.Show("ok");
}

出处：http://www.cnblogs.com/hcbin/archive/2010/04/10/1709019.html