OortComet.java

/*
 * Copyright (c) 2008-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.cometd.oort;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ScheduledExecutorService;

import org.cometd.bayeux.Channel;
import org.cometd.bayeux.Message;
import org.cometd.bayeux.client.ClientSessionChannel;
import org.cometd.client.BayeuxClient;
import org.cometd.client.transport.ClientTransport;

/**
 * <p>The Oort comet client connects a local Oort comet server to a remote Oort comet server.</p>
 */
public class OortComet extends BayeuxClient {
    private final ConcurrentMap<String, ClientSessionChannel.MessageListener> _subscriptions = new ConcurrentHashMap<>();
    private final Oort _oort;
    private final String _cometURL;
    private volatile boolean _subscriptionsAllowed;

    public OortComet(Oort oort, String cometURL, ScheduledExecutorService scheduler, ClientTransport transport, ClientTransport... transports) {
        super(cometURL, scheduler, transport, transports);
        _oort = oort;
        _cometURL = cometURL;
        // Add listener for handshake response
        getChannel(Channel.META_HANDSHAKE).addListener(new HandshakeListener());
    }

    protected void subscribe(Set<String> observedChannels) {
        // Guard against concurrent subscription clearing from the handshake callback
        if (!_subscriptionsAllowed) {
            return;
        }

        for (String channel : observedChannels) {
            if (_subscriptions.containsKey(channel)) {
                continue;
            }

            ClientSessionChannel.MessageListener listener = new ClientSessionChannel.MessageListener() {
                @Override
                public void onMessage(ClientSessionChannel channel, Message message) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Republishing message {} from {}", message, _cometURL);
                    }
                    // BayeuxServer may sweep channels, so calling bayeux.getChannel(...)
                    // may return null, and therefore we use the client to send the message.
                    _oort.getOortSession().getChannel(message.getChannel()).publish(message);
                }
            };

            ClientSessionChannel.MessageListener existing = _subscriptions.putIfAbsent(channel, listener);
            if (existing == null) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Subscribing to messages on {} from {}", channel, _cometURL);
                }
                getChannel(channel).subscribe(listener);
            }
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Subscriptions to messages on {} from {}", _subscriptions, _cometURL);
        }
    }

    protected void unsubscribe(String channel) {
        ClientSessionChannel.MessageListener listener = _subscriptions.remove(channel);
        if (listener != null) {
            if (logger.isDebugEnabled()) {
                logger.debug("Unsubscribing to messages on {} from {}", channel, _cometURL);
            }
            getChannel(channel).unsubscribe(listener);
        }
    }

    protected void clearSubscriptions() {
        for (String channel : _oort.getObservedChannels()) {
            unsubscribe(channel);
        }
    }

    @Override
    public String toString() {
        return String.format("%s@%x[%s@%s]",
                getClass().getSimpleName(),
                System.identityHashCode(this),
                _cometURL,
                getId());
    }

    private class HandshakeListener implements ClientSessionChannel.MessageListener {
        @Override
        public void onMessage(ClientSessionChannel channel, Message message) {
            if (!message.isSuccessful()) {
                return;
            }

            Map<String, Object> ext = message.getExt();
            if (ext == null) {
                return;
            }

            Object oortExtObject = ext.get(Oort.EXT_OORT_FIELD);
            if (!(oortExtObject instanceof Map)) {
                return;
            }

            batch(new Runnable() {
                @Override
                public void run() {
                    // Subscribe to cloud notifications
                    getChannel(Oort.OORT_CLOUD_CHANNEL).subscribe(new ClientSessionChannel.MessageListener() {
                        @Override
                        public void onMessage(ClientSessionChannel channel, Message message) {
                            if (message.isSuccessful()) {
                                _oort.joinComets(message);
                            }
                        }
                    });

                    // It is possible that a call to Oort.observeChannel() (which triggers
                    // the call to subscribe()) is performed concurrently with the handshake
                    // of this OortComet with a remote comet.
                    // For example, Seti calls Oort.observeChannel() on startup and this may
                    // be called while the Oort cloud is connecting all the comets together.
                    // In this case, below we will clear existing subscriptions, but we will
                    // subscribe them again just afterwards, ensuring only one subscriber
                    // (and not multiple ones) is subscribed.
                    clearSubscriptions();
                    _subscriptionsAllowed = true;

                    Set<String> channels = _oort.getObservedChannels();
                    if (logger.isDebugEnabled()) {
                        logger.debug("Handshake completed, observing channels {}", channels);
                    }
                    subscribe(channels);

                    // Advertise the remote node that we have joined
                    Map<String, Object> data = new HashMap<>(2);
                    data.put(Oort.EXT_OORT_ID_FIELD, _oort.getId());
                    data.put(Oort.EXT_OORT_URL_FIELD, _oort.getURL());
                    getChannel(Oort.OORT_SERVICE_CHANNEL).publish(data);

                    // Advertise our own network
                    getChannel(Oort.OORT_CLOUD_CHANNEL).publish(new ArrayList<>(_oort.getKnownComets()));
                }
            });
        }
    }
}