limitedrangewalker.java

JXTA&#8482 is a set of open, generalized peer-to-peer (P2P) protocols that allow any networked devi

/*
 * Copyright (c) 2002-2007 Sun Microsystems, Inc.  All rights reserved.
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package net.jxta.impl.rendezvous.limited;

import java.io.IOException;

import java.util.logging.Level;

import net.jxta.logging.Logging;

import java.util.logging.Logger;

import net.jxta.document.MimeMediaType;
import net.jxta.document.XMLDocument;
import net.jxta.endpoint.Message;
import net.jxta.endpoint.MessageElement;
import net.jxta.endpoint.TextDocumentMessageElement;
import net.jxta.peer.PeerID;

import net.jxta.impl.protocol.LimitedRangeRdvMsg;
import net.jxta.impl.rendezvous.RdvWalker;
import net.jxta.impl.rendezvous.rpv.PeerViewElement;

/**
 * The Limited Range Walker is designed to be used by Rendezvous Peer in
 * order to propagate a message amongst them. A target destination peer
 * is used in order to send the message to a primary peer. Then, depending
 * on the TTL, the message is duplicated into two messages, each of them
 * being sent in opposite "directions" of the RPV.
 */
public class LimitedRangeWalker implements RdvWalker {

    /**
     * Logger
     */
    private final static transient Logger LOG = Logger.getLogger(LimitedRangeWalker.class.getName());

    /**
     * The walk we are associated with.
     */
    private final LimitedRangeWalk walk;

    /**
     * Constructor
     *
     * @param walk The walk we will be associated with.
     */
    public LimitedRangeWalker(LimitedRangeWalk walk) {
        this.walk = walk;
    }

    /**
     * {@inheritDoc}
     */
    public void stop() {
    }

    /**
     * {@inheritDoc}
     * <p/>
     * Sends message on :
     * <pre>
     *  "LR-Greeter"&lt;groupid>/&lt;walkSvc>&lt;walkParam>
     *  </pre>
     * <p/>
     * XXX bondolo 20060720 This method will currently fail to walk the
     * message to the DOWN peer if there is a failure sending the message to
     * the UP peer. Perhaps it would be better to ignore any errors from
     * sending to either peer?
     */
    private void walkMessage(Message msg, LimitedRangeRdvMsg rdvMsg) throws IOException {

        LimitedRangeRdvMsg.WalkDirection dir = rdvMsg.getDirection();

        if ((dir == LimitedRangeRdvMsg.WalkDirection.BOTH) || (dir == LimitedRangeRdvMsg.WalkDirection.UP)) {
            PeerViewElement upPeer = walk.getPeerView().getUpPeer();

            if ((upPeer != null) && upPeer.isAlive()) {
                Message newMsg = msg.clone();

                if (Logging.SHOW_FINE && LOG.isLoggable(Level.FINE)) {
                    LOG.fine("Walking " + newMsg + " [UP] to " + upPeer);
                }

                rdvMsg.setDirection(LimitedRangeRdvMsg.WalkDirection.UP);

                updateRdvMessage(newMsg, rdvMsg);
                upPeer.sendMessage(newMsg, walk.getWalkServiceName(), walk.getWalkServiceParam());
            }
        }

        if ((dir == LimitedRangeRdvMsg.WalkDirection.BOTH) || (dir == LimitedRangeRdvMsg.WalkDirection.DOWN)) {
            PeerViewElement downPeer = walk.getPeerView().getDownPeer();

            if ((downPeer != null) && downPeer.isAlive()) {
                Message newMsg = msg.clone();

                if (Logging.SHOW_FINE && LOG.isLoggable(Level.FINE)) {
                    LOG.fine("Walking " + newMsg + " [DOWN] to " + downPeer);
                }

                rdvMsg.setDirection(LimitedRangeRdvMsg.WalkDirection.DOWN);

                updateRdvMessage(newMsg, rdvMsg);
                downPeer.sendMessage(newMsg, walk.getWalkServiceName(), walk.getWalkServiceParam());
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    public void walkMessage(PeerID destination, Message msg, String srcSvcName, String srcSvcParam, int ttl) throws IOException {

        if (Logging.SHOW_FINE && LOG.isLoggable(Level.FINE)) {
            LOG.fine("Walking " + msg + " to " + srcSvcName + "/" + srcSvcParam);
        }

        // Check if there is already a Rdv Message
        LimitedRangeRdvMsg rdvMsg = LimitedRangeWalk.getRdvMessage(msg);

        if (rdvMsg == null) {
            if (Logging.SHOW_FINE && LOG.isLoggable(Level.FINE)) {
                LOG.fine("Creating new Walk Header for " + msg + " with TTL=" + ttl);
            }

            // Create a new one.
            rdvMsg = new LimitedRangeRdvMsg();

            rdvMsg.setTTL(Integer.MAX_VALUE); // will be reduced.
            rdvMsg.setDirection(LimitedRangeRdvMsg.WalkDirection.BOTH);
            rdvMsg.setSrcPeerID(walk.getPeerGroup().getPeerID());
            rdvMsg.setSrcSvcName(srcSvcName);
            rdvMsg.setSrcSvcParams(srcSvcParam);
        } else {
            // decrement TTL before walk.
            rdvMsg.setTTL(rdvMsg.getTTL() - 1);
        }

        int useTTL = Math.min(ttl, rdvMsg.getTTL());

        useTTL = Math.min(useTTL, walk.getPeerView().getView().size() + 1);

        rdvMsg.setTTL(useTTL);

        if (useTTL <= 0) {
            if (Logging.SHOW_FINE && LOG.isLoggable(Level.FINE)) {
                LOG.fine("LimitedRangeWalker was not able to send " + msg + " : No TTL remaining");
            }

            return;
        }

        // Forward the message according to the direction set in the Rdv Message.
        if (null != destination) {
            Message tmp = msg.clone();

            updateRdvMessage(tmp, rdvMsg);
            sendToPeer(destination, walk.getWalkServiceName(), walk.getWalkServiceParam(), tmp);
        } else {
            walkMessage(msg, rdvMsg);
        }
    }

    /**
     * Replace the old version of the rdvMsg
     *
     * @param msg    The message to be updated.
     * @param rdvMsg The LimitedRangeRdvMsg which will update the message.
     * @return the updated message
     */
    private Message updateRdvMessage(Message msg, LimitedRangeRdvMsg rdvMsg) {
        XMLDocument asDoc = (XMLDocument) rdvMsg.getDocument(MimeMediaType.XMLUTF8);
        MessageElement el = new TextDocumentMessageElement(LimitedRangeWalk.ELEMENTNAME, asDoc, null);

        msg.replaceMessageElement("jxta", el);

        return msg;
    }

    /**
     * Sends the provided message to the specified peer. The peer must be a
     * current member of the PeerView.
     *
     * @param dest     The destination peer.
     * @param svcName  The destinations service.
     * @param svcParam The destination service params.
     * @param msg      The message to send.
     * @throws IOException Thrown for problems sending the message.
     */
    private void sendToPeer(PeerID dest, String svcName, String svcParam, Message msg) throws IOException {
        PeerViewElement pve = walk.getPeerView().getPeerViewElement(dest);

        if (null == pve) {
            throw new IOException("LimitedRangeWalker was not able to send " + msg + " : no pve");
        }

        if (!pve.sendMessage(msg, svcName, svcParam)) {
            throw new IOException("LimitedRangeWalker was not able to send " + msg + " : send failed");
        }
    }
}