UdpSocket. Java SE 7+/Android 4+ UDP client and server, MIT (c) 2025-2026 miktim@mail.ru
  
Extends the Java MulticastSocket class  
  
  
Advantage of MulticastSocket class:  
  - this class is supported by old and current versions of Java and Android.  
  
Disadvantage:  
  - does not support source-specific multicast (see Java MulticastChannel class).  
  
Notes:  
  - the UDP protocol does not guarantee datagram delivery, ordering,
    or duplicate protection;  
  - the maximum safe UDP payload size is ~508 bytes;  
  - don't forget to open the required UDP port in your firewall.  
  
The jar ./dist/udpsocket-... file was generated with debugging info using JDK1.8 for target JRE1.7  
  
    package org.miktim.udpsocket  
  
    Class UdpSocket extends MulticastSocket implements Closeable, AutoCloseable  
  
      Constants:  
        String VERSION = "4.2.1"  
  
      Constructors:  
        Constructors create unbounded sockets with reuse enabled,
        broadcast on, loopback disabled and TTL=1.
        Sets the network interface (may be null) for the remote
        multicast address and joins the multicast group.

        UdpSocket(InetSocketAddress remoteSoc, NetworkInterface netIf) throws IOException; 
        UdpSocket(InetAddress remoteAddr, int remotePort, String netIfName) throws IOException;
  
      Methods:  
        static void isAvailable(int port);  
          - checks whether the port is available. Not very reliable.

        boolean isMulticast();
          - returns true if the remote address is a multicast address
        InetSocketAddress getRemote();
          - returns remote socket address
        InetSocketAddress getLocal() throws IOException;
          - returns socket address based on remote port, interface
            and remote address type (IPv4/IPv6)
            See also: java.net.MulticastSocket.getInterface()
        UdpSocket bind() throws IOException;
          - binds unbound socket to the remote port
            
        UdpSocket setPayloadSize(int size);
          - sets the size of the DatagramPacket's buffer for received datagrams
        int getPayloadSize();
          - default: 1500 bytes

        Receiving methods bind an unbound socket to the remote port.  
        Sending methods set the unassigned address/port of the datagram
        to the address/port of the remote socket.  
  
        void send(DatagramPacket dp) throws IOException;
          - send datagram
        void send(byte[] buf) throws IOException;
          - send bytes
        void send(byte[] buf, int off, int len) throws IOException;
          - send bytes
        DatagramPacket receive() throws IOException;
          - wait datagram;
        void receive(DatagramPacket dp) throws IOException;
          - wait datagram
            See also: java.net.DatagramSocket.setSoTimeout(int timeout)

        void receive(UdpSocket.Handler handler);
          - calls handler onStart method and starts receiving datagrams
        boolean isReceiving();
          - returns receiving state
  
        void close();
          - [stops receiving,] [leaves initial multicast group,]
            [calls the handler's onClose method,] closes socket
  
      interface UdpSocket.Handler {
        void onStart(UdpSocket us);
        void onError(UdpSocket us, Exception e);
          - the socket will be closed after the method exits
        void onPacket(UdpSocket us, DatagramPacket dp);
        void onClose(UdpSocket us);
          - called before closing datagram socket
      }
    
      String toString();  
        - returns socket info  
  
  See also inherited DatagramSocket and MulticastSocket methods:  
      https://docs.oracle.com/javase/7/docs/api/java/net/DatagramSocket.html  
      https://docs.oracle.com/javase/7/docs/api/java/net/MulticastSocket.html  
      https://docs.oracle.com/javase/7/docs/api/java/net/DatagramPacket.html  
  
  Android Multicast Troubleshooting:  
      https://stackoverflow.com/questions/13221736/android-device-not-receiving-multicast-package  
      https://stackoverflow.com/questions/27917605/android-multicastsocket-joingroup-doesnt-trigger-sending-igmp-message