narya/src/java/com/threerings/presents/server/PresentsClient.java

//
// $Id$
//
// Narya library - tools for developing networked games
// Copyright (C) 2002-2004 Three Rings Design, Inc., All Rights Reserved
// http://www.threerings.net/code/narya/
//
// This library is free software; you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published
// by the Free Software Foundation; either version 2.1 of the License, or
// (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

package com.threerings.presents.server;

import java.io.IOException;
import java.net.InetAddress;
import java.util.HashMap;
import java.util.Iterator;

import com.samskivert.util.HashIntMap;
import com.samskivert.util.Throttle;
import com.samskivert.util.ResultListener;
import com.threerings.util.Name;

import com.threerings.presents.Log;
import com.threerings.presents.data.ClientObject;

import com.threerings.presents.dobj.DEvent;
import com.threerings.presents.dobj.DObject;
import com.threerings.presents.dobj.ObjectAccessException;
import com.threerings.presents.dobj.ProxySubscriber;

import com.threerings.presents.net.BootstrapData;
import com.threerings.presents.net.BootstrapNotification;
import com.threerings.presents.net.Credentials;
import com.threerings.presents.net.EventNotification;
import com.threerings.presents.net.UpstreamMessage;

import com.threerings.presents.net.ForwardEventRequest;
import com.threerings.presents.net.LogoffRequest;
import com.threerings.presents.net.PingRequest;
import com.threerings.presents.net.SubscribeRequest;
import com.threerings.presents.net.UnsubscribeRequest;

import com.threerings.presents.net.DownstreamMessage;
import com.threerings.presents.net.FailureResponse;
import com.threerings.presents.net.ObjectResponse;
import com.threerings.presents.net.PongResponse;
import com.threerings.presents.net.UnsubscribeResponse;

import com.threerings.presents.server.net.Connection;
import com.threerings.presents.server.net.MessageHandler;

/**
 * A client object represents a client session in the server. It is
 * associated with a connection instance (while the client is connected)
 * and acts as the intermediary for the remote client in terms of passing
 * along events forwarded by the client, ensuring that subscriptions are
 * maintained on behalf of the client and that events are forwarded to the
 * client.
 *
 * <p><em>A note on synchronization:</em> the client object is structured
 * so that its <code>Subscriber</code> implementation (which is called
 * from the dobjmgr thread) can proceed without synchronization. This does
 * not overlap with its other client duties which are called from the
 * conmgr thread and therefore also need not be synchronized.
 */
public class PresentsClient
    implements ProxySubscriber, MessageHandler, ClientResolutionListener
{
    /** Used by {@link #setUsername} to report success or failure. */
    public static interface UserChangeListener
    {
        /** Called when the new client object has been resolved and the
         * new client object reported to the client, but the old one has
         * not yet been destroyed. Any events delivered on this callback
         * to the old client object will be delivered.
         *
         * @param rl when this method is finished with its business and
         * the old client object can be destroyed, the result listener
         * should be called.
         * */
        public void changeReported (ClientObject newObji, ResultListener rl);

        /** Called when the user change is completed, the old client
         * object is destroyed and all updates are committed. */
        public void changeCompleted (ClientObject newObj);

        /** Called if some failure occurs during the user change
         * process. */
        public void changeFailed (Exception cause);
    }

    /**
     * Returns the credentials used to authenticate this client.
     */
    public Credentials getCredentials ()
    {
        return _creds;
    }

    /**
     * Returns true if this client has been disconnected for sufficiently
     * long that its session should be forcibly ended.
     */
    public boolean checkExpired (long now)
    {
        return (getConnection() == null && (now - _networkStamp > FLUSH_TIME));
    }

    /**
     * Returns the time at which this client started their network
     * session.
     */
    public long getSessionStamp ()
    {
        return _sessionStamp;
    }

    /**
     * Returns the time at which this client most recently connected or
     * disconnected.
     */
    public long getNetworkStamp ()
    {
        return _networkStamp;
    }

    /**
     * Returns the username with which this client instance is associated.
     */
    public Name getUsername ()
    {
        return _username;
    }

    /**
     * Returns the address of the connected client or null if this client
     * is not connected.
     */
    public InetAddress getInetAddress ()
    {
        Connection conn = getConnection();
        return (conn == null) ? null : conn.getInetAddress();
    }

    /**
     * Configures this client with a custom class loader that will be used
     * when unserializing classes from the network.
     */
    public void setClassLoader (ClassLoader loader)
    {
        _loader = loader;
        Connection conn = getConnection();
        if (conn != null) {
            conn.setClassLoader(loader);
        }
    }

    /**
     * <em>Danger:</em> this method is not for general consumption. This
     * changes the username of the client, but should only be done very
     * early in a user's session, when you know that no one has mapped the
     * user based on their username or has in any other way made use of
     * their username in a way that will break. However, it should not be
     * done <em>too</em> early in the session. The client must be fully
     * resolved.
     *
     * <p> It exists to support systems wherein a user logs in with an
     * account username and then chooses a "screen name" by which they
     * will play (often from a small set of available "characters"
     * available per account). This will take care of remapping the
     * username to client object mappings that were made by the Presents
     * services when the user logs on, but anything else that has had its
     * grubby mits on the username will be left to its own devices, hence
     * the care that must be exercised when using this method.
     *
     * @param ucl an entity that will (optionally) be notified when the
     * username conversion process is complete.
     */
    public void setUsername (Name username, final UserChangeListener ucl)
    {
        ClientResolutionListener clr = new ClientResolutionListener() {
            public void clientResolved (final Name username,
                    final ClientObject clobj)
            {
                // if they old client object is gone by now, they ended
                // their session while we were switching, so freak out
                if (_clobj == null) {
                    Log.warning("Client disappeared before we could " +
                                "complete the switch to a new client " +
                                "object [ousername=" + _username +
                                ", nusername=" + username + "].");
                    _cmgr.releaseClientObject(username);
                    Exception error = new Exception("Early withdrawal");
                    resolutionFailed(username, error);
                    return;
                }

                // let the client know that the rug has been yanked out
                // from under their ass
                Object[] args = new Object[] { Integer.valueOf(clobj.getOid()) };
                _clobj.postMessage(ClientObject.CLOBJ_CHANGED, args);

                // call down to any derived classes
                clientObjectWillChange(_clobj, clobj);

                // let the caller know that we've got some new business
                if (ucl != null) {
                    ucl.changeReported(clobj, new ResultListener() {
                        public void requestCompleted (Object result) {
                            finishResolved(username, clobj);
                        }

                        public void requestFailed (Exception cause) {
                            finishResolved(username, clobj);
                        }
                    });
                } else {
                    finishResolved(username, clobj);
                }
            }

            /**
             * Finish the final phase of the switch.
             */
            protected void finishResolved (Name username, ClientObject clobj)
            {
                // release our old client object; this will destroy it
                _cmgr.releaseClientObject(_username);

                // update our internal fields
                _username = username;
                _clobj = clobj;

                // call down to any derived classes
                clientObjectDidChange(_clobj);

                // let our listener know we're groovy
                if (ucl != null) {
                    ucl.changeCompleted(_clobj);
                }
            }

            public void resolutionFailed (Name username, Exception reason) {
                Log.warning("Unable to resolve new client object " +
                            "[oldname=" + _username + ", newname=" + username +
                            ", reason=" + reason + "].");
                Log.logStackTrace(reason);

                // let our listener know we're hosed
                if (ucl != null) {
                    ucl.changeFailed(reason);
                }
            }
        };

        // resolve the new client object
        _cmgr.resolveClientObject(username, clr);
    }

    /**
     * Called when {@link #setUsername} has been called and the new client
     * object is about to be applied to this client. The old client object
     * will not yet have been destroyed, so any final events can be sent
     * along prior to the new object being put into effect.
     */
    protected void clientObjectWillChange (
        ClientObject oldClobj, ClientObject newClobj)
    {
    }

    /**
     * Called after the new client object has been committed to this
     * client due to a call to {@link #setUsername}.
     */
    protected void clientObjectDidChange (ClientObject newClobj)
    {
    }

    /**
     * Returns the client object that is associated with this client.
     */
    public ClientObject getClientObject ()
    {
        return _clobj;
    }

    /**
     * Initializes this client instance with the specified username,
     * connection instance and client object and begins a client session.
     */
    protected void startSession (
        ClientManager cmgr, Credentials creds, Connection conn, Object authdata)
    {
        _cmgr = cmgr;
        _creds = creds;
        _authdata = authdata;
        setConnection(conn);

        // obtain our starting username
        assignStartingUsername();

        // resolve our client object before we get fully underway
        cmgr.resolveClientObject(_username, this);

        // make a note of our session start time
        _sessionStamp = System.currentTimeMillis();
    }

    /**
     * This is factored out to allow derived classes to use a different
     * starting username than the one supplied in the user's credentials.
     * Generally one only wants to munge the starting username if the user
     * will subsequently choose a "screen name" and it is desirable to
     * avoid collision between the authentication user namespace and the
     * screen namespace.
     */
    protected void assignStartingUsername ()
    {
        _username = _creds.getUsername();
    }

    // documentation inherited from interface
    public void clientResolved (Name username, ClientObject clobj)
    {
        // we'll be keeping this bad boy
        _clobj = clobj;

        // finish up our regular business
        sessionWillStart();
        sendBootstrap();
    }

    // documentation inherited from interface
    public void resolutionFailed (Name username, Exception reason)
    {
        // urk; nothing to do but complain and get the f**k out of dodge
        Log.warning("Unable to resolve client [username=" + username + "].");
        Log.logStackTrace(reason);

        // end the session now to prevent danglage
        endSession();
    }

    /**
     * Called by the client manager when a new connection arrives that
     * authenticates as this already established client. This must only be
     * called from the congmr thread.
     */
    protected void resumeSession (Connection conn)
    {
        // check to see if we've already got a connection object, in which
        // case it's probably stale
        Connection oldconn = getConnection();
        if (oldconn != null && !oldconn.isClosed()) {
            Log.info("Closing stale connection [old=" + oldconn +
                     ", new=" + conn + "].");
            // close the old connection (which results in everything being
            // properly unregistered)
            oldconn.close();
        }

        // start using the new connection
        setConnection(conn);

        // if a client connects, drops the connection and reconnects
        // within the span of a very short period of time, we'll find
        // ourselves in resumeSession() before their client object was
        // resolved from the initial connection; in such a case, we can
        // simply bail out here and let the original session establishment
        // code take care of initializing this resumed session
        if (_clobj == null) {
            Log.warning("Rapid-fire reconnect caused us to arrive in " +
                        "resumeSession() before the original session " +
                        "resolved its client object? " + this + ".");
            return;
        }

        // we need to get onto the distributed object thread so that we
        // can finalize the resumption of the session.
        PresentsServer.omgr.postRunnable(new Runnable() {
            public void run () {
                // now that we're on the dobjmgr thread we can resume our
                // session resumption
                finishResumeSession();
            }
        });
    }

    /**
     * This is called from the dobjmgr thread to complete the session
     * resumption. We call some call backs and send the bootstrap info to
     * the client.
     */
    protected void finishResumeSession ()
    {
        // let derived classes do any session resuming
        sessionWillResume();

        // send off a bootstrap notification immediately because we've
        // already got our client object
        sendBootstrap();

        Log.info("Session resumed " + this + ".");
    }

    /**
     * Forcibly terminates a client's session. This must be called from
     * the dobjmgr thread.
     */
    public void endSession ()
    {
        // queue up a request for our connection to be closed (if we have
        // a connection, that is)
        Connection conn = getConnection();
        if (conn != null) {
            // go ahead and clear out our connection now to prevent
            // funniness
            setConnection(null);
            // have the connection manager close our connection when it is
            // next convenient
            PresentsServer.conmgr.closeConnection(conn);
        }

        // if we don't have a client object, we failed to resolve in the
        // first place, in which case we have to cope as best we can
        if (_clobj != null) {
            // and clean up after ourselves
            try {
                sessionDidEnd();
            } catch (Exception e) {
                Log.warning("Choked in sessionDidEnd [client=" + this + "].");
                Log.logStackTrace(e);
            }

            // release (and destroy) our client object
            _cmgr.releaseClientObject(_username);
        }

        // let the client manager know that we're audi 5000
        _cmgr.clientDidEndSession(this);

        // clear out the client object so that we know the session is over
        _clobj = null;
    }

    /**
     * Queues up a runnable on the object manager thread where we can
     * safely end the session.
     */
    protected void safeEndSession ()
    {
        PresentsServer.omgr.postRunnable(new Runnable() {
            public void run () {
                if (getClientObject() == null) {
                    // refuse to end the session unless the client is
                    // fully resolved
                    Log.warning("Refusing logoff request from " +
                                "still-resolving client " + this + ".");
                } else {
                    // end the session in a civilized manner
                    endSession();
                }
            }
        });
    }

    /**
     * This is called when the server is shut down in the middle of a
     * client session. In this circumstance, {@link #endSession} will
     * <em>not</em> be called and so any persistent data that might
     * normally be flushed at the end of a client's session should likely
     * be flushed here.
     */
    public void shutdown  ()
    {
        // if the client is connected, we need to fake the computation of
        // their final connect time because we won't be closing their
        // socket normally
        if (getConnection() != null) {
            long now = System.currentTimeMillis();
            _connectTime += ((now - _networkStamp) / 1000);
        }
    }

    /**
     * Makes a note that this client is subscribed to this object so that
     * we can clean up after ourselves if and when the client goes
     * away. This is called by the client internals and needn't be called
     * by code outside the client.
     */
    public synchronized void mapSubscrip (DObject object)
    {
        _subscrips.put(object.getOid(), object);
    }

    /**
     * Makes a note that this client is no longer subscribed to this
     * object. The subscription map is used to clean up after the client
     * when it goes away. This is called by the client internals and
     * needn't be called by code outside the client.
     */
    public synchronized void unmapSubscrip (int oid)
    {
        DObject object = _subscrips.remove(oid);
        if (object != null) {
            object.removeSubscriber(this);
        } else {
            Log.warning("Requested to unmap non-existent subscription " +
                        "[oid=" + oid + "].");
        }
    }

    /**
     * Clears out the tracked client subscriptions. Called when the client
     * goes away and shouldn't be called otherwise.
     */
    protected void clearSubscrips (boolean verbose)
    {
        for (DObject object : _subscrips.values()) {
            if (verbose) {
                Log.info("Clearing subscription [client=" + this +
                         ", obj=" + object.getOid() + "].");
            }
            object.removeSubscriber(this);
        }
        _subscrips.clear();
    }

    /**
     * Called when the client session is first started. The client object
     * has been created at this point and after this method is executed,
     * the bootstrap information will be sent to the client which will
     * trigger the start of the session. Derived classes that override
     * this method should be sure to call
     * <code>super.sessionWillStart</code>.
     *
     * <p><em>Note:</em> This function will be called on the dobjmgr
     * thread which means that object manipulations are OK, but client
     * instance manipulations must done carefully.
     */
    protected void sessionWillStart ()
    {
    }

    /**
     * Called when the client resumes a session (after having disconnected
     * and reconnected). After this method is executed, the bootstrap
     * information will be sent to the client which will trigger the
     * resumption of the session. Derived classes that override this
     * method should be sure to call <code>super.sessionWillResume</code>.
     *
     * <p><em>Note:</em> This function will be called on the dobjmgr
     * thread which means that object manipulations are OK, but client
     * instance manipulations must done carefully.
     */
    protected void sessionWillResume ()
    {
    }

    /**
     * Called when the client session ends (either because the client
     * logged off or because the server forcibly terminated the session).
     * Derived classes that override this method should be sure to call
     * <code>super.sessionDidEnd</code>.
     *
     * <p><em>Note:</em> This function will be called on the dobjmgr
     * thread which means that object manipulations are OK, but client
     * instance manipulations must done carefully.
     */
    protected void sessionDidEnd ()
    {
        // clear out our subscriptions so that we don't get a complaint
        // about inability to forward the object destroyed event we're
        // about to generate
        clearSubscrips(false);
    }

    /**
     * This is called once we have a handle on the client distributed
     * object. It sends a bootstrap notification to the client with all
     * the information it will need to interact with the server.
     */
    protected void sendBootstrap ()
    {
//         Log.info("Sending bootstrap " + this + ".");

        // create and populate our bootstrap data
        BootstrapData data = createBootstrapData();
        populateBootstrapData(data);

        // create a send bootstrap notification
        postMessage(new BootstrapNotification(data));
    }

    /**
     * Derived client classes can override this member to create derived
     * bootstrap data classes that contain extra bootstrap information, if
     * desired.
     */
    protected BootstrapData createBootstrapData ()
    {
        return new BootstrapData();
    }

    /**
     * Derived client classes can override this member to populate the
     * bootstrap data with additional information. They should be sure to
     * call <code>super.populateBootstrapData</code> before doing their
     * own populating, however.
     *
     * <p><em>Note:</em> This function will be called on the dobjmgr
     * thread which means that object manipulations are OK, but client
     * instance manipulations must be done carefully.
     */
    protected void populateBootstrapData (BootstrapData data)
    {
        // give them the client object id
        data.clientOid = _clobj.getOid();

        // fill in the list of bootstrap services
        data.services = PresentsServer.invmgr.bootlist;
    }

    /**
     * Called by the connection manager when this client's connection is
     * unmapped. That may be because of a connection failure (in which
     * case this call will be followed up by a call to
     * <code>connectionFailed</code>) or it may be because of an orderly
     * closing of the connection. In either case, the client can deal with
     * its lack of a connection in this method. This is invoked by the
     * conmgr thread and should behave accordingly.
     */
    protected void wasUnmapped ()
    {
        // clear out our connection reference
        setConnection(null);

        // clear out our subscriptions. we need to do this on the dobjmgr
        // thread. it is important that we do this *after* we clear out
        // our connection reference. once the connection ref is null, no
        // more subscriptions will be processed (even those that were
        // queued up before the connection went away)
        PresentsServer.omgr.postRunnable(new Runnable() {
            public void run () {
                sessionConnectionClosed();
            }
        });
    }

    /**
     * Called on the dobjmgr thread when the connection associated with
     * this session has been closed and unmapped. If the user logged off
     * before closing their connection, this will be preceded by a call to
     * {@link #sessionDidEnd}.
     */
    protected void sessionConnectionClosed ()
    {
        // clear out our dobj subscriptions in case they weren't cleared
        // by a call to sessionDidEnd
        clearSubscrips(false);
    }

    /**
     * Called by the connection manager when this client's connection
     * fails. This is invoked on the conmgr thread and should behave
     * accordingly.
     */
    protected void connectionFailed (IOException fault)
    {
        // nothing to do here presently. the client manager already
        // complained about the failed connection
    }

    /**
     * Sets our connection reference in a thread safe way. Also
     * establishes the back reference to us as the connection's message
     * handler.
     */
    protected synchronized void setConnection (Connection conn)
    {
        // if our connection is being cleared out, record the amount of
        // time we were connected to our total connected time
        long now = System.currentTimeMillis();
        if (_conn != null && conn == null) {
            _connectTime += ((now - _networkStamp) / 1000);
        }

        // keep a handle to the new connection
        _conn = conn;

        // tell the connection to pass messages on to us (if we're setting
        // a connection rather than clearing one out)
        if (_conn != null) {
            _conn.setMessageHandler(this);

            // configure any active custom class loader
            if (_loader != null) {
                _conn.setClassLoader(_loader);
            }
        }

        // make a note that our network status changed
        _networkStamp = now;
    }

    /**
     * The connection instance must be accessed via this member function
     * because it is read from both the dobjmgr and conmgr threads and is
     * modified by the conmgr thread.
     *
     * @return The connection instance associated with this client or null
     * if the client is not currently connected.
     */
    protected synchronized Connection getConnection ()
    {
        return _conn;
    }

    // documentation inherited from interface
    public void handleMessage (UpstreamMessage message)
    {
        _messagesIn++; // count 'em up!

        // if the client has been getting crazy with the cheeze whiz,
        // stick a fork in them; the first time through we end our
        // session, subsequently _throttle is null and we just drop any
        // messages that come in until we've fully shutdown
        if (_throttle == null) {
//             Log.info("Dropping message from force-quit client " +
//                      "[conn=" + _conn +
//                      ", msg=" + message + "].");
            return;
        } else if (_throttle.throttleOp(message.received)) {
            Log.warning("Client sent more than 100 messages in 10 seconds, " +
                        "forcing disconnect " + this + ".");
            safeEndSession();
            _throttle = null;
        }

        // we dispatch to a message dispatcher that is specialized for the
        // particular class of message that we received
        MessageDispatcher disp = _disps.get(message.getClass());
        if (disp == null) {
            Log.warning("No dispatcher for message [msg=" + message + "].");
            return;
        }

        // otherwise pass the message on to the dispatcher
        disp.dispatch(this, message);
    }

    // documentation inherited from interface
    public void objectAvailable (DObject object)
    {
        if (postMessage(new ObjectResponse(object))) {
            // make a note of this new subscription
            mapSubscrip(object);
        } else {
            // if we failed to send the object response, unsubscribe
            object.removeSubscriber(this);
        }
    }

    // documentation inherited from interface
    public void requestFailed (int oid, ObjectAccessException cause)
    {
        postMessage(new FailureResponse(oid));
    }

    // documentation inherited from interface
    public void eventReceived (DEvent event)
    {
        if (event instanceof PresentsDObjectMgr.AccessObjectEvent) {
            Log.warning("Ignoring event that shouldn't be forwarded " +
                        event + ".");
            Thread.dumpStack();
        } else {
            postMessage(new EventNotification(event));
        }
    }

    /** Callable from non-dobjmgr thread, this queues up a runnable on the
     * dobjmgr thread to post the supplied message to this client. */
    protected final void safePostMessage (final DownstreamMessage msg)
    {
        PresentsServer.omgr.postRunnable(new Runnable() {
            public void run () {
                postMessage(msg);
            }
        });
    }

    /** Queues a message for delivery to the client. */
    protected final boolean postMessage (DownstreamMessage msg)
    {
        Connection conn = getConnection();
        if (conn != null) {
            conn.postMessage(msg);
            _messagesOut++; // count 'em up!
            return true;
        }

        // don't log dropped messages unless we're dropping a lot of them
        // (meaning something is still queueing messages up for this dead
        // client even though it shouldn't be)
        if (++_messagesDropped % 50 == 0) {
            Log.warning("Dropping many messages? [client=" + this +
                        ", count=" + _messagesDropped + "].");
        }

        // make darned sure we don't have any remaining subscriptions
        if (_subscrips.size() > 0) {
//             Log.warning("Clearing stale subscriptions [client=" + this +
//                         ", subscrips=" + _subscrips.size() + "].");
            clearSubscrips(_messagesDropped > 10);
        }
        return false;
    }

    /**
     * Generates a string representation of this instance.
     */
    public String toString ()
    {
        StringBuilder buf = new StringBuilder("[");
        toString(buf);
        return buf.append("]").toString();
    }

    /**
     * Derived classes override this to augment stringification.
     */
    protected void toString (StringBuilder buf)
    {
        buf.append("username=").append(_username);
        buf.append(", conn=").append(_conn);
        buf.append(", cloid=").append(
            (_clobj == null) ? -1 : _clobj.getOid());
        buf.append(", in=").append(_messagesIn);
        buf.append(", out=").append(_messagesOut);
    }

    /**
     * Message dispatchers are used to dispatch each different type of
     * upstream message. We can look the dispatcher up in a table and
     * invoke it through an overloaded member which is faster (so we
     * think) than doing a bunch of instanceofs.
     */
    protected static interface MessageDispatcher
    {
        /**
         * Dispatch the supplied message for the specified client.
         */
        public void dispatch (PresentsClient client, UpstreamMessage mge);
    }

    /**
     * Processes subscribe requests.
     */
    protected static class SubscribeDispatcher implements MessageDispatcher
    {
        public void dispatch (PresentsClient client, UpstreamMessage msg)
        {
            SubscribeRequest req = (SubscribeRequest)msg;
//              Log.info("Subscribing [client=" + client +
//                       ", oid=" + req.getOid() + "].");

            // forward the subscribe request to the omgr for processing
            PresentsServer.omgr.subscribeToObject(req.getOid(), client);
        }
    }

    /**
     * Processes unsubscribe requests.
     */
    protected static class UnsubscribeDispatcher implements MessageDispatcher
    {
        public void dispatch (PresentsClient client, UpstreamMessage msg)
        {
            UnsubscribeRequest req = (UnsubscribeRequest)msg;
            int oid = req.getOid();
//             Log.info("Unsubscribing " + client + " [oid=" + oid + "].");

            // forward the unsubscribe request to the omgr for processing
            PresentsServer.omgr.unsubscribeFromObject(oid, client);
            // update our subscription tracking table
            client.unmapSubscrip(oid);

            // post a response to the client letting them know that we
            // will no longer send them events regarding this object
            client.safePostMessage(new UnsubscribeResponse(oid));
        }
    }

    /**
     * Processes forward event requests.
     */
    protected static class ForwardEventDispatcher implements MessageDispatcher
    {
        public void dispatch (PresentsClient client, UpstreamMessage msg)
        {
            ForwardEventRequest req = (ForwardEventRequest)msg;
            DEvent fevt = req.getEvent();

            // fill in the proper source oid
            fevt.setSourceOid(client.getClientObject().getOid());

//              Log.info("Forwarding event [client=" + client +
//                       ", event=" + fevt + "].");

            // forward the event to the omgr for processing
            PresentsServer.omgr.postEvent(fevt);
        }
    }

    /**
     * Processes ping requests.
     */
    protected static class PingDispatcher implements MessageDispatcher
    {
        public void dispatch (PresentsClient client, UpstreamMessage msg)
        {
            // send a pong response
            PingRequest req = (PingRequest)msg;
            client.safePostMessage(new PongResponse(req.getUnpackStamp()));
        }
    }

    /**
     * Processes logoff requests.
     */
    protected static class LogoffDispatcher implements MessageDispatcher
    {
        public void dispatch (final PresentsClient client, UpstreamMessage msg)
        {
            Log.debug("Client requested logoff " + client + ".");
            client.safeEndSession();
        }
    }

    protected ClientManager _cmgr;
    protected Credentials _creds;
    protected Object _authdata;
    protected Name _username;
    protected Connection _conn;
    protected ClientObject _clobj;
    protected HashIntMap<DObject> _subscrips = new HashIntMap<DObject>();
    protected ClassLoader _loader;

    /** The time at which this client started their session. */
    protected long _sessionStamp;

    /** The time at which this client most recently connected or
     * disconnected. */
    protected long _networkStamp;

    /** The total number of seconds for which the user was connected to
     * the server in this session. */
    protected int _connectTime;

    /** Prevent the client from sending too many messages too frequently.
     * 100 messages in 10 seconds and you're audi. */
    protected Throttle _throttle = new Throttle(100, 10 * 1000L);

    // keep these for kicks and giggles
    protected int _messagesIn;
    protected int _messagesOut;
    protected int _messagesDropped;

    /** A mapping of message dispatchers. */
    protected static HashMap<Class<?>,MessageDispatcher> _disps =
        new HashMap<Class<?>,MessageDispatcher>();

    /** The amount of time after disconnection a user is allowed before
     * their session is forcibly ended. */
    protected static final long FLUSH_TIME = 7 * 60 * 1000L;

    // register our message dispatchers
    static {
        _disps.put(SubscribeRequest.class, new SubscribeDispatcher());
        _disps.put(UnsubscribeRequest.class, new UnsubscribeDispatcher());
        _disps.put(ForwardEventRequest.class, new ForwardEventDispatcher());
        _disps.put(PingRequest.class, new PingDispatcher());
        _disps.put(LogoffRequest.class, new LogoffDispatcher());
    }
}