gossip-revisited/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.List;
import java.util.concurrent.atomic.AtomicBoolean;

import org.apache.log4j.Logger;
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 {
  
  public static final Logger LOGGER = Logger.getLogger(PassiveGossipThread.class);

  /** 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_ID),
                        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());
              }

            }
            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) {
        GossipService.LOGGER.error(e);
        _keepRunning.set(false);
      }
    }
    shutdown();
  }

  public void shutdown() {
    _server.close();
  }

  /**
   * 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,
          List<GossipMember> remoteList);
}