Working on the cluster i/o

+package org.onlab.onos.store.cluster.impl;
+
+import org.onlab.nio.AcceptorLoop;
+import org.onlab.packet.IpPrefix;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.nio.channels.ServerSocketChannel;
+import java.nio.channels.SocketChannel;
+
+import static java.net.InetAddress.getByAddress;
+
+/**
+ * Listens to inbound connection requests and accepts them.
+ */
+public class ClusterConnectionListener extends AcceptorLoop {
+
+    private static final long SELECT_TIMEOUT = 50;
+    private static final int COMM_BUFFER_SIZE = 32 * 1024;
+
+    private static final boolean SO_NO_DELAY = false;
+    private static final int SO_SEND_BUFFER_SIZE = COMM_BUFFER_SIZE;
+    private static final int SO_RCV_BUFFER_SIZE = COMM_BUFFER_SIZE;
+
+    private final WorkerFinder workerFinder;
+
+    ClusterConnectionListener(IpPrefix ip, int tcpPort,
+                              WorkerFinder workerFinder) throws IOException {
+        super(SELECT_TIMEOUT, new InetSocketAddress(getByAddress(ip.toOctets()), tcpPort));
+        this.workerFinder = workerFinder;
+    }
+
+    @Override
+    protected void acceptConnection(ServerSocketChannel channel) throws IOException {
+        SocketChannel sc = channel.accept();
+        sc.configureBlocking(false);
+
+        Socket so = sc.socket();
+        so.setTcpNoDelay(SO_NO_DELAY);
+        so.setReceiveBufferSize(SO_RCV_BUFFER_SIZE);
+        so.setSendBufferSize(SO_SEND_BUFFER_SIZE);
+
+        workerFinder.findWorker().acceptStream(sc);
+    }
+
+}

+package org.onlab.onos.store.cluster.impl;
+
+import org.onlab.nio.IOLoop;
+import org.onlab.nio.MessageStream;
+import org.onlab.onos.cluster.DefaultControllerNode;
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+import org.onlab.onos.store.cluster.messaging.ClusterMessageStream;
+import org.onlab.onos.store.cluster.messaging.SerializationService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.channels.ByteChannel;
+import java.nio.channels.SelectionKey;
+import java.nio.channels.SocketChannel;
+import java.util.List;
+import java.util.Objects;
+
+import static org.onlab.packet.IpPrefix.valueOf;
+
+/**
+ * Performs the IO operations related to a cluster-wide communications.
+ */
+public class ClusterIOWorker extends
+        IOLoop<ClusterMessage, ClusterMessageStream> {
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    private static final long SELECT_TIMEOUT = 50;
+
+    private final ConnectionManager connectionManager;
+    private final CommunicationsDelegate commsDelegate;
+    private final SerializationService serializationService;
+    private final ClusterMessage helloMessage;
+
+    /**
+     * Creates a new cluster IO worker.
+     *
+     * @param connectionManager    parent connection manager
+     * @param commsDelegate        communications delegate for dispatching
+     * @param serializationService serialization service for encode/decode
+     * @param helloMessage         hello message for greeting peers
+     * @throws IOException if errors occur during IO loop ignition
+     */
+    ClusterIOWorker(ConnectionManager connectionManager,
+                    CommunicationsDelegate commsDelegate,
+                    SerializationService serializationService,
+                    ClusterMessage helloMessage) throws IOException {
+        super(SELECT_TIMEOUT);
+        this.connectionManager = connectionManager;
+        this.commsDelegate = commsDelegate;
+        this.serializationService = serializationService;
+        this.helloMessage = helloMessage;
+    }
+
+    @Override
+    protected ClusterMessageStream createStream(ByteChannel byteChannel) {
+        return new ClusterMessageStream(serializationService, this, byteChannel);
+    }
+
+    @Override
+    protected void processMessages(List<ClusterMessage> messages, MessageStream<ClusterMessage> stream) {
+        for (ClusterMessage message : messages) {
+            commsDelegate.dispatch(message);
+        }
+    }
+
+    @Override
+    public ClusterMessageStream acceptStream(SocketChannel channel) {
+        ClusterMessageStream stream = super.acceptStream(channel);
+        try {
+            InetSocketAddress sa = (InetSocketAddress) channel.getRemoteAddress();
+            log.info("Accepted connection from node {}", valueOf(sa.getAddress().getAddress()));
+            stream.write(helloMessage);
+
+        } catch (IOException e) {
+            log.warn("Unable to accept connection from an unknown end-point", e);
+        }
+        return stream;
+    }
+
+    @Override
+    protected void connect(SelectionKey key) throws IOException {
+        try {
+            super.connect(key);
+            ClusterMessageStream stream = (ClusterMessageStream) key.attachment();
+            stream.write(helloMessage);
+
+        } catch (IOException e) {
+            if (!Objects.equals(e.getMessage(), "Connection refused")) {
+                throw e;
+            }
+        }
+    }
+
+    @Override
+    protected void removeStream(MessageStream<ClusterMessage> stream) {
+        DefaultControllerNode node = ((ClusterMessageStream) stream).node();
+        if (node != null) {
+            log.info("Closed connection to node {}", node.id());
+            connectionManager.removeNodeStream(node);
+        }
+        super.removeStream(stream);
+    }
+
+}

+package org.onlab.onos.store.cluster.impl;
+
+import org.onlab.onos.cluster.DefaultControllerNode;
+
+/**
+ * Simple back interface through which connection manager can interact with
+ * the cluster store.
+ */
+public interface ClusterNodesDelegate {
+
+    /**
+     * Notifies about a new cluster node being detected.
+     *
+     * @param node newly detected cluster node
+     */
+    void nodeDetected(DefaultControllerNode node);
+
+    /**
+     * Notifies about cluster node going offline.
+     *
+     * @param node cluster node that vanished
+     */
+    void nodeVanished(DefaultControllerNode node);
+
+}

+package org.onlab.onos.store.cluster.impl;
+
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+
+/**
+ * Simple back interface for interacting with the communications service.
+ */
+public interface CommunicationsDelegate {
+
+    /**
+     * Dispatches the specified message to all registered subscribers.
+     *
+     * @param message message to be dispatched
+     */
+    void dispatch(ClusterMessage message);
+
+    /**
+     * Sets the sender.
+     *
+     * @param messageSender message sender
+     */
+    void setSender(MessageSender messageSender);
+
+}

+package org.onlab.onos.store.cluster.impl;
+
+import org.onlab.onos.cluster.DefaultControllerNode;
+import org.onlab.onos.cluster.NodeId;
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+import org.onlab.onos.store.cluster.messaging.ClusterMessageStream;
+import org.onlab.onos.store.cluster.messaging.HelloMessage;
+import org.onlab.onos.store.cluster.messaging.SerializationService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.SocketAddress;
+import java.nio.channels.SocketChannel;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.Timer;
+import java.util.TimerTask;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import static java.net.InetAddress.getByAddress;
+import static org.onlab.util.Tools.namedThreads;
+
+/**
+ * Manages connections to other controller cluster nodes.
+ */
+public class ConnectionManager implements MessageSender {
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    private static final long CONNECTION_CUSTODIAN_DELAY = 1000L;
+    private static final long CONNECTION_CUSTODIAN_FREQUENCY = 5000;
+
+    private static final long START_TIMEOUT = 1000;
+    private static final int WORKERS = 3;
+
+    private ClusterConnectionListener connectionListener;
+    private List<ClusterIOWorker> workers = new ArrayList<>(WORKERS);
+
+    private final DefaultControllerNode localNode;
+    private final ClusterNodesDelegate nodesDelegate;
+    private final CommunicationsDelegate commsDelegate;
+    private final SerializationService serializationService;
+
+    // Nodes to be monitored to make sure they have a connection.
+    private final Set<DefaultControllerNode> nodes = new HashSet<>();
+
+    // Means to track message streams to other nodes.
+    private final Map<NodeId, ClusterMessageStream> streams = new ConcurrentHashMap<>();
+
+    // Executor pools for listening and managing connections to other nodes.
+    private final ExecutorService listenExecutor =
+            Executors.newSingleThreadExecutor(namedThreads("onos-comm-listen"));
+    private final ExecutorService commExecutors =
+            Executors.newFixedThreadPool(WORKERS, namedThreads("onos-comm-cluster"));
+    private final ExecutorService heartbeatExecutor =
+            Executors.newSingleThreadExecutor(namedThreads("onos-comm-heartbeat"));
+
+    private final Timer timer = new Timer("onos-comm-initiator");
+    private final TimerTask connectionCustodian = new ConnectionCustodian();
+
+    private final WorkerFinder workerFinder = new LeastUtilitiedWorkerFinder();
+
+
+    /**
+     * Creates a new connection manager.
+     */
+    ConnectionManager(DefaultControllerNode localNode,
+                      ClusterNodesDelegate nodesDelegate,
+                      CommunicationsDelegate commsDelegate,
+                      SerializationService serializationService) {
+        this.localNode = localNode;
+        this.nodesDelegate = nodesDelegate;
+        this.commsDelegate = commsDelegate;
+        this.serializationService = serializationService;
+
+        commsDelegate.setSender(this);
+        startCommunications();
+        startListening();
+        startInitiating();
+        log.info("Started");
+    }
+
+    /**
+     * Shuts down the connection manager.
+     */
+    void shutdown() {
+        connectionListener.shutdown();
+        for (ClusterIOWorker worker : workers) {
+            worker.shutdown();
+        }
+        log.info("Stopped");
+    }
+
+    /**
+     * Adds the node to the list of monitored nodes.
+     *
+     * @param node node to be added
+     */
+    void addNode(DefaultControllerNode node) {
+        nodes.add(node);
+    }
+
+    /**
+     * Removes the node from the list of monitored nodes.
+     *
+     * @param node node to be removed
+     */
+    void removeNode(DefaultControllerNode node) {
+        nodes.remove(node);
+        ClusterMessageStream stream = streams.remove(node.id());
+        if (stream != null) {
+            stream.close();
+        }
+    }
+
+    /**
+     * Removes the stream associated with the specified node.
+     *
+     * @param node node whose stream to remove
+     */
+    void removeNodeStream(DefaultControllerNode node) {
+        nodesDelegate.nodeVanished(node);
+        streams.remove(node.id());
+    }
+
+    @Override
+    public boolean send(NodeId nodeId, ClusterMessage message) {
+        ClusterMessageStream stream = streams.get(nodeId);
+        if (stream != null) {
+            try {
+                stream.write(message);
+                return true;
+            } catch (IOException e) {
+                log.warn("Unable to send a message about {} to node {}",
+                         message.subject(), nodeId);
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Kicks off the IO loops and waits for them to startup.
+     */
+    private void startCommunications() {
+        HelloMessage hello = new HelloMessage(localNode.id(), localNode.ip(),
+                                              localNode.tcpPort());
+        for (int i = 0; i < WORKERS; i++) {
+            try {
+                ClusterIOWorker worker =
+                        new ClusterIOWorker(this, commsDelegate,
+                                            serializationService, hello);
+                workers.add(worker);
+                commExecutors.execute(worker);
+            } catch (IOException e) {
+                log.warn("Unable to start communication worker", e);
+            }
+        }
+
+        // Wait for the IO loops to start
+        for (ClusterIOWorker loop : workers) {
+            if (!loop.awaitStart(START_TIMEOUT)) {
+                log.warn("Comm loop did not start on-time; moving on...");
+            }
+        }
+    }
+
+    /**
+     * Starts listening for connections from peer cluster members.
+     */
+    private void startListening() {
+        try {
+            connectionListener =
+                    new ClusterConnectionListener(localNode.ip(), localNode.tcpPort(),
+                                                  workerFinder);
+            listenExecutor.execute(connectionListener);
+            if (!connectionListener.awaitStart(START_TIMEOUT)) {
+                log.warn("Listener did not start on-time; moving on...");
+            }
+        } catch (IOException e) {
+            log.error("Unable to listen for cluster connections", e);
+        }
+    }
+
+    /**
+     * Initiates open connection request and registers the pending socket
+     * channel with the given IO loop.
+     *
+     * @param loop loop with which the channel should be registered
+     * @throws java.io.IOException if the socket could not be open or connected
+     */
+    private void initiateConnection(DefaultControllerNode node,
+                                    ClusterIOWorker loop) throws IOException {
+        SocketAddress sa = new InetSocketAddress(getByAddress(node.ip().toOctets()), node.tcpPort());
+        SocketChannel ch = SocketChannel.open();
+        ch.configureBlocking(false);
+        ch.connect(sa);
+        loop.connectStream(ch);
+    }
+
+
+    /**
+     * Attempts to connect to any nodes that do not have an associated connection.
+     */
+    private void startInitiating() {
+        timer.schedule(connectionCustodian, CONNECTION_CUSTODIAN_DELAY,
+                       CONNECTION_CUSTODIAN_FREQUENCY);
+    }
+
+    // Sweeps through all controller nodes and attempts to open connection to
+    // those that presently do not have one.
+    private class ConnectionCustodian extends TimerTask {
+        @Override
+        public void run() {
+            for (DefaultControllerNode node : nodes) {
+                if (node != localNode && !streams.containsKey(node.id())) {
+                    try {
+                        initiateConnection(node, workerFinder.findWorker());
+                    } catch (IOException e) {
+                        log.debug("Unable to connect", e);
+                    }
+                }
+            }
+        }
+    }
+
+    // Finds the least utilitied IO loop.
+    private class LeastUtilitiedWorkerFinder implements WorkerFinder {
+
+        @Override
+        public ClusterIOWorker findWorker() {
+            ClusterIOWorker leastUtilized = null;
+            int minCount = Integer.MAX_VALUE;
+            for (ClusterIOWorker worker : workers) {
+                int count = worker.streamCount();
+                if (count == 0) {
+                    return worker;
+                }
+
+                if (count < minCount) {
+                    leastUtilized = worker;
+                    minCount = count;
+                }
+            }
+            return leastUtilized;
+        }
+    }
+
+}

+package org.onlab.onos.store.cluster.impl;
+
+import org.onlab.onos.cluster.NodeId;
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+
+/**
+ * Created by tom on 9/29/14.
+ */
+public interface MessageSender {
+
+    /**
+     * Sends the specified message to the given cluster node.
+     *
+     * @param nodeId  node identifier
+     * @param message mesage to send
+     * @return true if the message was sent sucessfully; false if there is
+     * no stream or if there was an error
+     */
+    boolean send(NodeId nodeId, ClusterMessage message);
+
+}

-package org.onlab.onos.store.cluster.impl;
-
-import org.onlab.nio.AbstractMessage;
-
-import java.util.Objects;
-
-import static com.google.common.base.MoreObjects.toStringHelper;
-
-/**
- * Base message for cluster-wide communications using TLVs.
- */
-public class TLVMessage extends AbstractMessage {
-
-    private final int type;
-    private final byte[] data;
-
-    /**
-     * Creates an immutable TLV message.
-     *
-     * @param type   message type
-     * @param data   message data bytes
-     */
-    public TLVMessage(int type, byte[] data) {
-        this.length = data.length + TLVMessageStream.METADATA_LENGTH;
-        this.type = type;
-        this.data = data;
-    }
-
-    /**
-     * Returns the message type indicator.
-     *
-     * @return message type
-     */
-    public int type() {
-        return type;
-    }
-
-    /**
-     * Returns the data bytes.
-     *
-     * @return message data
-     */
-    public byte[] data() {
-        return data;
-    }
-
-    @Override
-    public int hashCode() {
-        return Objects.hash(type, data);
-    }
-
-    @Override
-    public boolean equals(Object obj) {
-        if (this == obj) {
-            return true;
-        }
-        if (obj == null || getClass() != obj.getClass()) {
-            return false;
-        }
-        final TLVMessage other = (TLVMessage) obj;
-        return Objects.equals(this.type, other.type) &&
-                Objects.equals(this.data, other.data);
-    }
-
-    @Override
-    public String toString() {
-        return toStringHelper(this).add("type", type).add("length", length).toString();
-    }
-
-}

+package org.onlab.onos.store.cluster.impl;
+
+/**
+ * Provides means to find a worker IO loop.
+ */
+public interface WorkerFinder {
+
+    /**
+     * Finds a suitable worker.
+     *
+     * @return available worker
+     */
+    ClusterIOWorker findWorker();
+}

+package org.onlab.onos.store.cluster.messaging;
+
+import org.onlab.onos.cluster.NodeId;
+
+import java.util.Set;
+
+/**
+ * Service for assisting communications between controller cluster nodes.
+ */
+public interface ClusterCommunicationService {
+
+    /**
+     * Sends a message to the specified controller node.
+     *
+     * @param message  message to send
+     * @param toNodeId node identifier
+     * @return true if the message was sent sucessfully; false if there is
+     * no stream or if there was an error
+     */
+    boolean send(ClusterMessage message, NodeId toNodeId);
+
+    /**
+     * Adds a new subscriber for the specified message subject.
+     *
+     * @param subject    message subject
+     * @param subscriber message subscriber
+     */
+    void addSubscriber(MessageSubject subject, MessageSubscriber subscriber);
+
+    /**
+     * Removes the specified subscriber from the given message subject.
+     *
+     * @param subject    message subject
+     * @param subscriber message subscriber
+     */
+    void removeSubscriber(MessageSubject subject, MessageSubscriber subscriber);
+
+    /**
+     * Returns the set of subscribers for the specified message subject.
+     *
+     * @param subject message subject
+     * @return set of message subscribers
+     */
+    Set<MessageSubscriber> getSubscribers(MessageSubject subject);
+
+}

+package org.onlab.onos.store.cluster.messaging;
+
+import org.onlab.nio.AbstractMessage;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
+
+/**
+ * Base message for cluster-wide communications.
+ */
+public abstract class ClusterMessage extends AbstractMessage {
+
+    private final MessageSubject subject;
+
+    /**
+     * Creates a cluster message.
+     *
+     * @param subject message subject
+     */
+    protected ClusterMessage(MessageSubject subject) {
+        this.subject = subject;
+    }
+
+    /**
+     * Returns the message subject indicator.
+     *
+     * @return message subject
+     */
+    public MessageSubject subject() {
+        return subject;
+    }
+
+    @Override
+    public String toString() {
+        return toStringHelper(this).add("subject", subject).add("length", length).toString();
+    }
+
+}

-package org.onlab.onos.store.cluster.impl;
+package org.onlab.onos.store.cluster.messaging;
 
 
 import org.onlab.nio.IOLoop;
 import org.onlab.nio.IOLoop;
 import org.onlab.nio.MessageStream;
 import org.onlab.nio.MessageStream;
@@ -10,29 +10,29 @@ import java.nio.channels.ByteChannel;
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.base.Preconditions.checkState;
 
 
 /**
 /**
- * Stream for transferring TLV messages between cluster members.
+ * Stream for transferring messages between two cluster members.
  */
  */
-public class TLVMessageStream extends MessageStream<TLVMessage> {
+public class ClusterMessageStream extends MessageStream<ClusterMessage> {
 
 
-    public static final int METADATA_LENGTH = 16; // 8 + 4 + 4
-
-    private static final int LENGTH_OFFSET = 12;
-    private static final long MARKER = 0xfeedcafecafefeedL;
+    private static final int COMM_BUFFER_SIZE = 32 * 1024;
+    private static final int COMM_IDLE_TIME = 500;
 
 
     private DefaultControllerNode node;
     private DefaultControllerNode node;
+    private SerializationService serializationService;
 
 
     /**
     /**
      * Creates a message stream associated with the specified IO loop and
      * Creates a message stream associated with the specified IO loop and
      * backed by the given byte channel.
      * backed by the given byte channel.
      *
      *
-     * @param loop          IO loop
-     * @param byteChannel   backing byte channel
-     * @param bufferSize    size of the backing byte buffers
-     * @param maxIdleMillis maximum number of millis the stream can be idle
+     * @param serializationService service for encoding/decoding messages
+     * @param loop                 IO loop
+     * @param byteChannel          backing byte channel
      */
      */
-    protected TLVMessageStream(IOLoop<TLVMessage, ?> loop, ByteChannel byteChannel,
-                               int bufferSize, int maxIdleMillis) {
-        super(loop, byteChannel, bufferSize, maxIdleMillis);
+    public ClusterMessageStream(SerializationService serializationService,
+                                IOLoop<ClusterMessage, ?> loop,
+                                ByteChannel byteChannel) {
+        super(loop, byteChannel, COMM_BUFFER_SIZE, COMM_IDLE_TIME);
+        this.serializationService = serializationService;
     }
     }
 
 
     /**
     /**
@@ -40,7 +40,7 @@ public class TLVMessageStream extends MessageStream<TLVMessage> {
      *
      *
      * @return controller node
      * @return controller node
      */
      */
-    DefaultControllerNode node() {
+    public DefaultControllerNode node() {
         return node;
         return node;
     }
     }
 
 
@@ -49,47 +49,19 @@ public class TLVMessageStream extends MessageStream<TLVMessage> {
      *
      *
      * @param node controller node
      * @param node controller node
      */
      */
-    void setNode(DefaultControllerNode node) {
+    public void setNode(DefaultControllerNode node) {
         checkState(this.node == null, "Stream is already bound to a node");
         checkState(this.node == null, "Stream is already bound to a node");
         this.node = node;
         this.node = node;
     }
     }
 
 
     @Override
     @Override
-    protected TLVMessage read(ByteBuffer buffer) {
-        // Do we have enough bytes to read the header? If not, bail.
-        if (buffer.remaining() < METADATA_LENGTH) {
-            return null;
-        }
-
-        // Peek at the length and if we have enough to read the entire message
-        // go ahead, otherwise bail.
-        int length = buffer.getInt(buffer.position() + LENGTH_OFFSET);
-        if (buffer.remaining() < length) {
-            return null;
-        }
-
-        // At this point, we have enough data to read a complete message.
-        long marker = buffer.getLong();
-        checkState(marker == MARKER, "Incorrect message marker");
-
-        int type = buffer.getInt();
-        length = buffer.getInt();
-
-        // TODO: add deserialization hook here
-        byte[] data = new byte[length - METADATA_LENGTH];
-        buffer.get(data);
-
-        return new TLVMessage(type, data);
+    protected ClusterMessage read(ByteBuffer buffer) {
+        return serializationService.decode(buffer);
     }
     }
 
 
     @Override
     @Override
-    protected void write(TLVMessage message, ByteBuffer buffer) {
-        buffer.putLong(MARKER);
-        buffer.putInt(message.type());
-        buffer.putInt(message.length());
-
-        // TODO: add serialization hook here
-        buffer.put(message.data());
+    protected void write(ClusterMessage message, ByteBuffer buffer) {
+        serializationService.encode(message, buffer);
     }
     }
 
 
 }
 }

+package org.onlab.onos.store.cluster.messaging;
+
+import org.onlab.onos.cluster.NodeId;
+
+/**l
+ * Echo heart-beat message that nodes send to each other.
+ */
+public class EchoMessage extends ClusterMessage {
+
+    private NodeId nodeId;
+
+    // For serialization
+    private EchoMessage() {
+        super(MessageSubject.HELLO);
+        nodeId = null;
+    }
+
+    /**
+     * Creates a new heart-beat echo message.
+     *
+     * @param nodeId    sending node identification
+     */
+    public EchoMessage(NodeId nodeId) {
+        super(MessageSubject.HELLO);
+        nodeId = nodeId;
+    }
+
+    /**
+     * Returns the sending node identifer.
+     *
+     * @return node identifier
+     */
+    public NodeId nodeId() {
+        return nodeId;
+    }
+
+}

+package org.onlab.onos.store.cluster.messaging;
+
+import org.onlab.onos.cluster.NodeId;
+import org.onlab.packet.IpPrefix;
+
+/**
+ * Hello message that nodes use to greet each other.
+ */
+public class HelloMessage extends ClusterMessage {
+
+    private NodeId nodeId;
+    private IpPrefix ipAddress;
+    private int tcpPort;
+
+    // For serialization
+    private HelloMessage() {
+        super(MessageSubject.HELLO);
+        nodeId = null;
+        ipAddress = null;
+        tcpPort = 0;
+    }
+
+    /**
+     * Creates a new hello message for the specified end-point data.
+     *
+     * @param nodeId    sending node identification
+     * @param ipAddress sending node IP address
+     * @param tcpPort   sending node TCP port
+     */
+    public HelloMessage(NodeId nodeId, IpPrefix ipAddress, int tcpPort) {
+        super(MessageSubject.HELLO);
+        nodeId = nodeId;
+        ipAddress = ipAddress;
+        tcpPort = tcpPort;
+    }
+
+    /**
+     * Returns the sending node identifer.
+     *
+     * @return node identifier
+     */
+    public NodeId nodeId() {
+        return nodeId;
+    }
+
+    /**
+     * Returns the sending node IP address.
+     *
+     * @return node IP address
+     */
+    public IpPrefix ipAddress() {
+        return ipAddress;
+    }
+
+    /**
+     * Returns the sending node TCP listen port.
+     *
+     * @return TCP listen port
+     */
+    public int tcpPort() {
+        return tcpPort;
+    }
+}

+package org.onlab.onos.store.cluster.messaging;
+
+/**
+ * Representation of a message subject.
+ */
+public enum MessageSubject {
+
+    /** Represents a first greeting message. */
+    HELLO,
+
+    /** Signifies a heart-beat message. */
+    ECHO
+
+}

+package org.onlab.onos.store.cluster.messaging;
+
+/**
+ * Represents a message consumer.
+ */
+public interface MessageSubscriber {
+
+    /**
+     * Receives the specified cluster message.
+     *
+     * @param message message to be received
+     */
+    void receive(ClusterMessage message);
+
+}

+package org.onlab.onos.store.cluster.messaging;
+
+import java.nio.ByteBuffer;
+
+/**
+ * Service for serializing/deserializing intra-cluster messages.
+ */
+public interface SerializationService {
+
+    /**
+     * Decodes the specified byte buffer to obtain a message within.
+     *
+     * @param buffer byte buffer with message(s)
+     * @return parsed message
+     */
+    ClusterMessage decode(ByteBuffer buffer);
+
+    /**
+     * Encodes the specified message into the given byte buffer.
+     *
+     * @param message message to be encoded
+     * @param buffer byte buffer to receive the message data
+     */
+    void encode(ClusterMessage message, ByteBuffer buffer);
+
+}

+package org.onlab.onos.store.cluster.messaging.impl;
+
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Multimap;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Service;
+import org.onlab.onos.cluster.NodeId;
+import org.onlab.onos.store.cluster.impl.CommunicationsDelegate;
+import org.onlab.onos.store.cluster.impl.MessageSender;
+import org.onlab.onos.store.cluster.messaging.ClusterCommunicationService;
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+import org.onlab.onos.store.cluster.messaging.MessageSubject;
+import org.onlab.onos.store.cluster.messaging.MessageSubscriber;
+
+import java.util.Set;
+
+/**
+ * Implements the cluster communication services to use by other stores.
+ */
+@Component(immediate = true)
+@Service
+public class ClusterCommunicationManager
+        implements ClusterCommunicationService, CommunicationsDelegate {
+
+    // TODO: use something different that won't require synchronization
+    private Multimap<MessageSubject, MessageSubscriber> subscribers = HashMultimap.create();
+    private MessageSender messageSender;
+
+    @Override
+    public boolean send(ClusterMessage message, NodeId toNodeId) {
+        return messageSender.send(toNodeId, message);
+    }
+
+    @Override
+    public synchronized void addSubscriber(MessageSubject subject, MessageSubscriber subscriber) {
+        subscribers.put(subject, subscriber);
+    }
+
+    @Override
+    public synchronized void removeSubscriber(MessageSubject subject, MessageSubscriber subscriber) {
+        subscribers.remove(subject, subscriber);
+    }
+
+    @Override
+    public Set<MessageSubscriber> getSubscribers(MessageSubject subject) {
+        return ImmutableSet.copyOf(subscribers.get(subject));
+    }
+
+    @Override
+    public void dispatch(ClusterMessage message) {
+        Set<MessageSubscriber> set = getSubscribers(message.subject());
+        if (set != null) {
+            for (MessageSubscriber subscriber : set) {
+                subscriber.receive(message);
+            }
+        }
+    }
+
+    @Override
+    public void setSender(MessageSender messageSender) {
+        this.messageSender = messageSender;
+    }
+}

+package org.onlab.onos.store.cluster.messaging.impl;
+
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+import org.onlab.onos.store.cluster.messaging.MessageSubject;
+import org.onlab.onos.store.cluster.messaging.SerializationService;
+
+import java.nio.ByteBuffer;
+
+import static com.google.common.base.Preconditions.checkState;
+
+/**
+ * Factory for parsing messages sent between cluster members.
+ */
+public class MessageSerializer implements SerializationService {
+
+    private static final int METADATA_LENGTH = 16; // 8 + 4 + 4
+    private static final int LENGTH_OFFSET = 12;
+
+    private static final long MARKER = 0xfeedcafebeaddeadL;
+
+    @Override
+    public ClusterMessage decode(ByteBuffer buffer) {
+        try {
+            // Do we have enough bytes to read the header? If not, bail.
+            if (buffer.remaining() < METADATA_LENGTH) {
+                return null;
+            }
+
+            // Peek at the length and if we have enough to read the entire message
+            // go ahead, otherwise bail.
+            int length = buffer.getInt(buffer.position() + LENGTH_OFFSET);
+            if (buffer.remaining() < length) {
+                return null;
+            }
+
+            // At this point, we have enough data to read a complete message.
+            long marker = buffer.getLong();
+            checkState(marker == MARKER, "Incorrect message marker");
+
+            int subjectOrdinal = buffer.getInt();
+            MessageSubject subject = MessageSubject.values()[subjectOrdinal];
+            length = buffer.getInt();
+
+            // TODO: sanity checking for length
+            byte[] data = new byte[length - METADATA_LENGTH];
+            buffer.get(data);
+
+            // TODO: add deserialization hook here; for now this hack
+            return null; // actually deserialize
+
+        } catch (Exception e) {
+            // TODO: recover from exceptions by forwarding stream to next marker
+            e.printStackTrace();
+        }
+        return null;
+    }
+
+    @Override
+    public void encode(ClusterMessage message, ByteBuffer buffer) {
+        try {
+            int i = 0;
+            // Type based lookup for proper encoder
+        } catch (Exception e) {
+            // TODO: recover from exceptions by forwarding stream to next marker
+            e.printStackTrace();
+        }
+    }
+
+}