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javasocketsudpp2p

Java peer to peer udp chatting room

I'm new to Java socket programming and I'm currently developing a small peer to peer UDP chatting room application which allow multiple clients to chat with each other.

My question is how do I make a client discover all other connected clients once he hit the connect button providing only one of the connected clients ip and port? The program only runs on local network.

Solution

  • You can use a unique feature of UDP which is broadcasting

    On IPv4 (which you are probably using) the address for broadcasting is 255.255.255.255. Any datagram sent to that address will be sent to all UDP clients on the network for that port.

    What you can do for your chat application is to have each client send a packet to the UDP broadcast identifying itself, such as maybe the nickname of the user. All the other clients will see that packet, and you will be able to parse the packet and display a list of all the chat clients on the network.

    Here is an example of sending a Datagram to broadcast:

        DatagramSocket s = new DatagramSocket();
    s.setBroadcast(true);
    DatagramPacket dp = new DatagramPacket("insert data here".getBytes(), "insert data here".length(), new InetSocketAddress("255.255.255.255", 5000));
    s.send(dp);

    Another client can receive it like this:

    DatagramSocket s = new DatagramSocket();
s.setBroadcast(true);
DatagramPacket dp = new DatagramPacket(new byte[1024], 1024);
s.receive(dp);

    The received DatagramPacket will contain the IP and port of the client who had broadcasted it.