Performs broadcast and multicast peer detection.
//package com.ryanm.util.net;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.util.ArrayList;
import java.util.List;
/**
* Performs broadcast and multicast peer detection. How well this
* works depends on your network configuration
*
* @author ryanm
*/
public class PeerDiscovery
{
private static final byte QUERY_PACKET = 80;
private static final byte RESPONSE_PACKET = 81;
/**
* The group identifier. Determines the set of peers that are able
* to discover each other
*/
public final int group;
/**
* The port number that we operate on
*/
public final int port;
/**
* Data returned with discovery
*/
public int peerData;
private final DatagramSocket bcastSocket;
private final InetSocketAddress broadcastAddress;
private boolean shouldStop = false;
private List<Peer> responseList = null;
/**
* Used to detect and ignore this peers response to it's own query.
* When we send a response packet, we set this to the destination.
* When we receive a response, if this matches the source, we know
* that we're talking to ourselves and we can ignore the response.
*/
private InetAddress lastResponseDestination = null;
/**
* Redefine this to be notified of exceptions on the listen thread.
* Default behaviour is to print to stdout. Can be left as null for
* no-op
*/
public ExceptionHandler rxExceptionHandler = new ExceptionHandler();
private Thread bcastListen = new Thread( PeerDiscovery.class.getSimpleName()
+ " broadcast listen thread" ) {
@Override
public void run()
{
try
{
byte[] buffy = new byte[ 5 ];
DatagramPacket rx = new DatagramPacket( buffy, buffy.length );
while( !shouldStop )
{
try
{
buffy[ 0 ] = 0;
bcastSocket.receive( rx );
int recData = decode( buffy, 1 );
if( buffy[ 0 ] == QUERY_PACKET && recData == group )
{
byte[] data = new byte[ 5 ];
data[ 0 ] = RESPONSE_PACKET;
encode( peerData, data, 1 );
DatagramPacket tx =
new DatagramPacket( data, data.length, rx.getAddress(), port );
lastResponseDestination = rx.getAddress();
bcastSocket.send( tx );
}
else if( buffy[ 0 ] == RESPONSE_PACKET )
{
if( responseList != null && !rx.getAddress().equals( lastResponseDestination ) )
{
synchronized( responseList )
{
responseList.add( new Peer( rx.getAddress(), recData ) );
}
}
}
}
catch( SocketException se )
{
// someone may have called disconnect()
}
}
bcastSocket.disconnect();
bcastSocket.close();
}
catch( Exception e )
{
if( rxExceptionHandler != null )
{
rxExceptionHandler.handle( e );
}
}
};
};
/**
* Constructs a UDP broadcast-based peer
*
* @param group
* The identifier shared by the peers that will be
* discovered.
* @param port
* a valid port, i.e.: in the range 1025 to 65535
* inclusive
* @throws IOException
*/
public PeerDiscovery( int group, int port ) throws IOException
{
this.group = group;
this.port = port;
bcastSocket = new DatagramSocket( port );
broadcastAddress = new InetSocketAddress( "255.255.255.255", port );
bcastListen.setDaemon( true );
bcastListen.start();
}
/**
* Signals this {@link PeerDiscovery} to shut down. This call will
* block until everything's timed out and closed etc.
*/
public void disconnect()
{
shouldStop = true;
bcastSocket.close();
bcastSocket.disconnect();
try
{
bcastListen.join();
}
catch( InterruptedException e )
{
e.printStackTrace();
}
}
/**
* Queries the network and finds the addresses of other peers in
* the same group
*
* @param timeout
* How long to wait for responses, in milliseconds. Call
* will block for this long, although you can
* {@link Thread#interrupt()} to cut the wait short
* @param peerType
* The type flag of the peers to look for
* @return The addresses of other peers in the group
* @throws IOException
* If something goes wrong when sending the query packet
*/
public Peer[] getPeers( int timeout, byte peerType ) throws IOException
{
responseList = new ArrayList<Peer>();
// send query byte, appended with the group id
byte[] data = new byte[ 5 ];
data[ 0 ] = QUERY_PACKET;
encode( group, data, 1 );
DatagramPacket tx = new DatagramPacket( data, data.length, broadcastAddress );
bcastSocket.send( tx );
// wait for the listen thread to do its thing
try
{
Thread.sleep( timeout );
}
catch( InterruptedException e )
{
}
Peer[] peers;
synchronized( responseList )
{
peers = responseList.toArray( new Peer[ responseList.size() ] );
}
responseList = null;
return peers;
}
/**
* Record of a peer
*
* @author ryanm
*/
public class Peer
{
/**
* The ip of the peer
*/
public final InetAddress ip;
/**
* The data of the peer
*/
public final int data;
private Peer( InetAddress ip, int data )
{
this.ip = ip;
this.data = data;
}
@Override
public String toString()
{
return ip.getHostAddress() + " " + data;
}
}
/**
* Handles an exception.
*
* @author ryanm
*/
public class ExceptionHandler
{
/**
* Called whenever an exception is thrown from the listen
* thread. The listen thread should now be dead
*
* @param e
*/
public void handle( Exception e )
{
e.printStackTrace();
}
}
/**
* @param args
*/
public static void main( String[] args )
{
try
{
int group = 6969;
PeerDiscovery mp = new PeerDiscovery( group, 6969 );
boolean stop = false;
BufferedReader br = new BufferedReader( new InputStreamReader( System.in ) );
while( !stop )
{
System.out.println( "enter \"q\" to quit, or anything else to query peers" );
String s = br.readLine();
if( s.equals( "q" ) )
{
System.out.print( "Closing down..." );
mp.disconnect();
System.out.println( " done" );
stop = true;
}
else
{
System.out.println( "Querying" );
Peer[] peers = mp.getPeers( 100, ( byte ) 0 );
System.out.println( peers.length + " peers found" );
for( Peer p : peers )
{
System.out.println( "\t" + p );
}
}
}
}
catch( Exception e )
{
e.printStackTrace();
}
}
private static int decode( byte[] b, int index )
{
int i = 0;
i |= b[ index ] << 24;
i |= b[ index + 1 ] << 16;
i |= b[ index + 2 ] << 8;
i |= b[ index + 3 ];
return i;
}
private static void encode( int i, byte[] b, int index )
{
b[ index ] = ( byte ) ( i >> 24 & 0xff );
b[ index + 1 ] = ( byte ) ( i >> 16 & 0xff );
b[ index + 2 ] = ( byte ) ( i >> 8 & 0xff );
b[ index + 3 ] = ( byte ) ( i & 0xff );
}
}
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