Java实现UDP穿透NAT试验

早就听说用UDP穿透NAT可以解决P2P软件中的两个通过NAT上网的客户端直接通信的问题。当然，需要一个中介来帮助找到对方。终于用Java做了这个试验。

代码贴出来吧。

UDPAgent.java:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.util.regex.Pattern;

/**
*
* @author Leo Luo
*
*/
public class UDPAgent implements Runnable {

public static void main(String[] args) throws Exception {
   new UDPAgent(-1).start();
}

DatagramSocket ds;

byte[] recbuf = new byte[1024];

DatagramPacket rec = new DatagramPacket(recbuf, recbuf.length);

static String ipPattern = "([0-9]{1,3}.){3}[0-9]{1,3}";

static String portPattern = "[0-9]{1,5}";

static Pattern sendPattern = Pattern.compile("send " + ipPattern + " "
    + portPattern + " .*");

int port;

public UDPAgent(int port) {
   this.port = port;

}

public void init() throws Exception {
   if (port < 1024 || port > 655535) {
    ds = new DatagramSocket();
   } else {
    ds = new DatagramSocket(port);
   }
}

public void start() throws Exception {
   println("start");
   println("LocalPort:" + port);
   init();
   new Thread(this).start();// recive thread
   receive();
}

public void receive() {
   for (;;) {
    try {
     ds.receive(rec);
     String msg = new String(rec.getData(), rec.getOffset(), rec
       .getLength());
     String line = rec.getSocketAddress() + ":" + msg;
     println(line);
     onReceive(rec);
    } catch (Exception e) {
     e.printStackTrace();
    }
   }
}

public void onReceive(DatagramPacket rec) {

}

public void doCommand(String cmd) throws Exception {
   // command:
   // 1. send xxx.xxx.xxx.xxx xxx *******************
   if (sendPattern.matcher(cmd).matches()) {
    doSend(cmd);
   }
}

public void doSend(String cmd) throws Exception {
   println("CMD: " + cmd);
   String[] s = cmd.split(" ", 4);
   int port = Integer.parseInt(s[2]);
   InetSocketAddress target = new InetSocketAddress(s[1], port);
   byte[] bs = s[3].getBytes();
   doSend(target, bs);
}

public void doSend(SocketAddress addr, byte[] data) throws Exception {
   DatagramPacket pack = new DatagramPacket(data, data.length, addr);
   ds.send(pack);
}

public void run() {
   BufferedReader reader = new BufferedReader(new InputStreamReader(
     System.in));
   try {
    String line = reader.readLine();
    while (!"exit".equals(line)) {
     doCommand(line);
     line = reader.readLine();
    }
    System.exit(0);
   } catch (Exception e) {
    e.printStackTrace();
   }
}

public void println(String s) {
   System.out.println(System.currentTimeMillis() + ":" + s);
}
}

UDPClient.java

____________________________________________________

import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketAddress;

public class UDPClient extends UDPAgent {

/**
* @param args
*/
public static void main(String[] args) throws Exception {
   new UDPClient("www.javadoc.cn", 2008, -1).start();
}

String serverName;

int serverPort;

SocketAddress server;

public UDPClient(String host, int port, int localPort) {
   super(localPort);
   this.server = new InetSocketAddress(host, port);

}

public void start() throws Exception {
   println("start");
   init();
   register();
   new Thread(this).start();// recive thread
   receive();
}

public void onReceive(DatagramPacket rec) {
   try {
    report(rec);
    if (rec.getSocketAddress().equals(server)) {
     doCommand(new String(rec.getData(), rec.getOffset(), rec
       .getLength()));
    }
   } catch (Exception e) {
    e.printStackTrace();
   }

}

public void report(DatagramPacket rec) throws Exception {
   String s = rec.getSocketAddress()
     + new String(rec.getData(), rec.getOffset(), rec.getLength());
   byte[] buf = s.getBytes();
   ds.send(new DatagramPacket(buf, buf.length, server));
}

public void register() throws Exception {
   String msg = "register " + getLocalAddress() + " " + ds.getLocalPort();
   doSend(server, msg.getBytes());
}

public String getLocalAddress() throws Exception {
   InetAddress addr = InetAddress.getLocalHost();
   return addr.getHostAddress();
}
}

UDPServer.java

_______________________________________________________________

public class UDPServer extends UDPAgent {

public static void main(String[] args) throws Exception {
   new UDPServer(2008).start();
}

public UDPServer(int port) {
   super(port);
}
}

1。启动一个Server.

2。启动两个Client.

然后从Server端的Console里边可以看到两个Client的NAT后的地址和端口。

在Server段输入命令 send a.a.a.a A send b.b.b.b B hello

a.a.a.a是第一个Client的NAT后的ip,A端口号。

b是第二个。。。

输入这个命令后，A就会直接发给B一个 hello。 发送成功。 如果是同一个NAT后边，可能要让A发送到B的内网地址才能成功。