src/main/java/com/google/code/gossip/manager/PassiveGossipThread.java

package com.google.code.gossip.manager;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.net.SocketException;
import java.util.ArrayList;
import java.util.concurrent.atomic.AtomicBoolean;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import com.google.code.gossip.GossipMember;
import com.google.code.gossip.GossipService;
import com.google.code.gossip.RemoteGossipMember;

/**
 * [The passive thread: reply to incoming gossip request.]
 * This class handles the passive cycle, where this client
 * has received an incoming message.  For now, this message
 * is always the membership list, but if you choose to gossip
 * additional information, you will need some logic to determine
 * the incoming message.
 */
abstract public class PassiveGossipThread implements Runnable {
	
	/** The socket used for the passive thread of the gossip service. */
	private DatagramSocket _server;
	
	private GossipManager _gossipManager;

	private AtomicBoolean _keepRunning;

	public PassiveGossipThread(GossipManager gossipManager) {
		_gossipManager = gossipManager;
		try {
		  SocketAddress socketAddress = new InetSocketAddress(_gossipManager.getMyself().getHost(), _gossipManager.getMyself().getPort());
		  _server = new DatagramSocket(socketAddress);
		  GossipService.LOGGER.info("Gossip service successfully initialized on port " + _gossipManager.getMyself().getPort());
		  GossipService.LOGGER.debug("I am " + _gossipManager.getMyself());
		} catch (SocketException ex) {
		  GossipService.LOGGER.error(ex);
			_server = null;
			throw new RuntimeException(ex);
		}
		_keepRunning = new AtomicBoolean(true);
	}

  @Override
  public void run() {
    while (_keepRunning.get()) {
      try {
        byte[] buf = new byte[_server.getReceiveBufferSize()];
        DatagramPacket p = new DatagramPacket(buf, buf.length);
        _server.receive(p);
        GossipService.LOGGER.debug("A message has been received from " + p.getAddress() + ":"
                + p.getPort() + ".");

        int packet_length = 0;
        for (int i = 0; i < 4; i++) {
          int shift = (4 - 1 - i) * 8;
          packet_length += (buf[i] & 0x000000FF) << shift;
        }

        // Check whether the package is smaller than the maximal packet length.
        // A package larger than this would not be possible to be send from a GossipService,
        // since this is check before sending the message.
        // This could normally only occur when the list of members is very big,
        // or when the packet is misformed, and the first 4 bytes is not the right in anymore.
        // For this reason we regards the message.
        if (packet_length <= GossipManager.MAX_PACKET_SIZE) {
          byte[] json_bytes = new byte[packet_length];
          for (int i = 0; i < packet_length; i++) {
            json_bytes[i] = buf[i + 4];
          }
          String receivedMessage = new String(json_bytes);
          GossipService.LOGGER.debug("Received message (" + packet_length + " bytes): "
                  + receivedMessage);
          try {
            ArrayList<GossipMember> remoteGossipMembers = new ArrayList<GossipMember>();
            RemoteGossipMember senderMember = null;
            GossipService.LOGGER.debug("Received member list:");
            JSONArray jsonArray = new JSONArray(receivedMessage);
            for (int i = 0; i < jsonArray.length(); i++) {
              JSONObject memberJSONObject = jsonArray.getJSONObject(i);
              if (memberJSONObject.length() == 4) {
                RemoteGossipMember member = new RemoteGossipMember(
                        memberJSONObject.getString(GossipMember.JSON_HOST),
                        memberJSONObject.getInt(GossipMember.JSON_PORT),
                        memberJSONObject.getString(GossipMember.JSON_PORT),
                        memberJSONObject.getInt(GossipMember.JSON_HEARTBEAT));
                GossipService.LOGGER.debug(member.toString());
                // This is the first member found, so this should be the member who is communicating
                // with me.
                if (i == 0) {
                  senderMember = member;
                }
                remoteGossipMembers.add(member);
              } else {
                GossipService.LOGGER
                        .error("The received member object does not contain 4 objects:\n"
                                + memberJSONObject.toString());
              }

            }

            // Merge our list with the one we just received
            mergeLists(_gossipManager, senderMember, remoteGossipMembers);
          } catch (JSONException e) {
            GossipService.LOGGER
                    .error("The received message is not well-formed JSON. The following message has been dropped:\n"
                            + receivedMessage);
          }

        } else {
          GossipService.LOGGER
                  .error("The received message is not of the expected size, it has been dropped.");
        }

      } catch (IOException e) {
        e.printStackTrace();
        _keepRunning.set(false);
      }
    }
  }
	
	/**
	 * Abstract method for merging the local and remote list.
	 * @param gossipManager The GossipManager for retrieving the local members and dead members list.
	 * @param senderMember The member who is sending this list, this could be used to send a response if the remote list contains out-dated information.
	 * @param remoteList The list of members known at the remote side.
	 */
	abstract protected void mergeLists(GossipManager gossipManager, RemoteGossipMember senderMember, ArrayList<GossipMember> remoteList);
}