Java UDP穿透NAT试验

<转自http://nonconductor.bokee.com/5042360.html>

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。

 

参考文档：

 

P2P之UDP穿透NAT的原理与实现 http://www.lihuasoft.net/news/show.php?id=2478