简单的UDP穿透示例
实验环境，台式机win7+用VirtualBox搭建的两个虚拟机Linux环境，两个虚拟机的网络连接方式都选择为网络地址转换（NAT）。很明显两个虚拟操作系统之间不能直接通信，需要在主机win7上搭建服务器以帮助两个虚拟机互相穿透通讯。下面是实验的全部代码。
A 首先是服务器端代码，出于简洁的考虑，用C#语言实现个UDPServer
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Threading;
namespace TestServer
{
class Program
{
//服务器监听端口
public static int port = 1987;
//服务器套接口
private static Socket s;
//存储客户端IP以及端口信息
private static List<string> clientList;
//返回客户端可用的其他客户端外网端口信息
private static void RetInfo(object sock) {
EndPoint remote = (EndPoint)sock;
Console.WriteLine("新客户端接入 "+remote.ToString());
int i;
while(true)
{
bool other = false;
for (i = 0; i < clientList.Count; i++) {
//找一个不同于当前remote客户端的客户端IP和端口返回给remote
if (clientList[i] != remote.ToString())
{
string str = clientList[i];
byte[] data = new byte[1024];
data = Encoding.ASCII.GetBytes(str);
s.SendTo(data, remote);
other = true;
break;
}
}
//找到，结束当前客户端连接
if (other == true) {
break;
}
}
}
static void Main(string[] args)
{
try
{
//绑定本地UDP端口
IPEndPoint ipe = new IPEndPoint(IPAddress.Any, port);
s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
s.Bind(ipe);
clientList = new List<string>();
clientList.Clear();
Console.WriteLine("start server");
while (true)
{
IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
EndPoint remote = (EndPoint)sender;
byte[] data = new byte[1024];
int len = s.ReceiveFrom(data, ref remote);
//出于测试考虑，只限于两个客户端穿透
if (clientList.Count == 2) {
clientList.Clear();
Console.WriteLine("服务器重置");
}
clientList.Add(remote.ToString());
//创建一个线程向客户端返回其他客户端的信息，如果没有则直到新客户端加入
Thread newThread = new Thread(new ParameterizedThreadStart(RetInfo));
newThread.Start(remote);
}
//这两行代码不会运行到
s.Close();
Console.WriteLine("stop server");
}
catch (Exception err)
{
Console.WriteLine(err.ToString());
}
}
}
}服务器端主要的逻辑是接受两个客户端a，b的连接，然后分别将a和b的NAT转换后的IP以及端口信息告诉客户端b，a。这样就完成了服务器的工作了。
B 然后客户端代码如下，两个客户端代码基本一致，只是为了区分，两者发送的消息和打印的内容稍有区别，客户端用php代码模拟。首先和服务器连接，获取到别的客户端NAT转换地址后直接向别的客户端通信。
<?php
$server_ip = "192.168.197.118";
$server_port = 1987;
//连接win7服务器端
$sock = socket_create(AF_INET,SOCK_DGRAM,0);
if(!$sock){
exit(-1);
}
//向UDPServer服务器发送消息（内容随便）
$buf = "login in to server";
if(!socket_sendto($sock,$buf,strlen($buf),0,$server_ip,$server_port))
{
socket_close($sock);
exit(-1);
}
while(true){
//阻塞等待服务器响应消息
$msg = "";
if(!socket_recvfrom($sock,$msg,256,0,$server_ip,$server_port))
{
socket_close($sock);
exit(-1);
}
//如果从服务器获取到客户端B或A的IP以及端口，则跳出循环去发送消息
if(($isip = strpos($msg,":"))==true)
{
$otherinfo = split(":",$msg);
$server_ip = $otherinfo[0];
$server_port = $otherinfo[1];
//$buf = "nice to meet you A"; // 客户端B代码
$buf = "nice to meet you B"; // 客户端A代码
//用于穿透的包，其他客户端不会收到
if(!socket_sendto($sock,$buf,strlen($buf),0,"$server_ip",$server_port))
{
socket_close($sock);
exit(-1);
}
}
else
{
//循环向客户端B或A发送消息
while(true){
//$buf = "hello client A"; // 客户端B代码
$buf = "hello client B"; // 客户端A代码
if(!socket_sendto($sock,$buf,strlen($buf),0,$server_ip,$server_port))
{
socket_close($sock);
exit(-1);
}
$msg = "";
if(!socket_recvfrom($sock,$msg,256,0,$server_ip,$server_port))
{
socket_close($sock);
exit(-1);
}
//echo "Recv $msg from Client A at ".time(0)."\n"; //客户端B代码
echo "Recv $msg from Client B at ".time(0)."\n"; //客户端A代码
sleep(1);
}
}
}
?>
C 实验效果
首先运行服务器端，然后分别运行两个虚拟机中的代码 php clientA.php 以及 php clientB.php，可以看到互相之间已经能通过UDP协议发送报文了。
服务器端内容
start server 新客户端接入 192.168.197.118:54170 新客户端接入 192.168.197.118:54171客户端A的内容
ciaos@ciaos-VirtualBox:~/Public$ php clientA.php Recv hello client A from Client B at 1344308281 Recv hello client A from Client B at 1344308282 Recv hello client A from Client B at 1344308283 Recv hello client A from Client B at 1344308284 Recv hello client A from Client B at 1344308285 Recv hello client A from Client B at 1344308286 Recv hello client A from Client B at 1344308287
客户端B的内容
ciaos@ciaos-VirtualBox:~/Public$ php clientB.php Recv hello client B from Client A at 1344308281 Recv hello client B from Client A at 1344308282 Recv hello client B from Client A at 1344308283 Recv hello client B from Client A at 1344308284 Recv hello client B from Client A at 1344308285 Recv hello client B from Client A at 1344308286 Recv hello client B from Client A at 1344308287