narya/src/java/com/threerings/presents/net/PongResponse.java

//
// $Id$
//
// Narya library - tools for developing networked games
// Copyright (C) 2002-2007 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.net;

import java.io.IOException;

import com.threerings.io.ObjectInputStream;
import com.threerings.io.ObjectOutputStream;

import static com.threerings.presents.Log.log;

/**
 * Let's the client know the server heard its ping (and that the server and connection are still
 * alive).
 */
public class PongResponse extends DownstreamMessage
{
    /**
     * Zero argument constructor used when unserializing an instance.
     */
    public PongResponse ()
    {
        super();
    }

    /**
     * Constructs a pong response which will use the supplied ping time to establish the end-to-end
     * processing delay introduced by the server.
     */
    public PongResponse (long pingStamp, Transport transport)
    {
        // save this for when we are serialized in preparation for delivery over the network
        _pingStamp = pingStamp;
        _transport = transport;
    }

    /**
     * Returns the time at which this packet was packed for delivery in the time frame of the
     * server that sent the packet.
     */
    public long getPackStamp ()
    {
        return _packStamp;
    }

    /**
     * Returns the number of milliseconds that elapsed between the time that the ping which
     * instigated this pong was read from the network and the time that this pong was written to
     * the network.
     */
    public int getProcessDelay ()
    {
        return _processDelay;
    }

    /**
     * Returns a timestamp that was obtained when this packet was decoded by the low-level
     * networking code.
     */
    public long getUnpackStamp ()
    {
        return _unpackStamp;
    }

    /**
     * Writes our custom streamable fields.
     */
    public void writeObject (ObjectOutputStream out)
        throws IOException
    {
        // make a note of the time at which we were packed
        _packStamp = System.currentTimeMillis();

        // the time spent between unpacking the ping and packing the pong is the processing delay
        if (_pingStamp == 0L) {
            log.warning("Pong response written that was not constructed " +
                        "with a valid ping stamp [rsp=" + this + "].");
            _processDelay = 0;
        } else {
            _processDelay = (int)(_packStamp - _pingStamp);
        }

        out.defaultWriteObject();
    }

    /**
     * Reads our custom streamable fields.
     */
    public void readObject (ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
        // grab a timestamp noting when we were decoded from a raw buffer after being received over
        // the network
        _unpackStamp = System.currentTimeMillis();

        in.defaultReadObject();
    }

    @Override // documentation inherited
    public void setTransport (Transport transport)
    {
        _transport = transport;
    }

    @Override // documentation inherited
    public Transport getTransport ()
    {
        return _transport;
    }

    @Override
    public String toString ()
    {
        return "[type=PONG, msgid=" + messageId + ", transport=" + _transport + "]";
    }

    /** The ping unpack stamp provided at construct time to this pong response; only valid on the
     * sending process, not the receiving process. */
    protected transient long _pingStamp;

    /** The timestamp obtained immediately before this packet was sent out over the network. */
    protected long _packStamp;

    /** The delay in milliseconds between the time that the ping request was read from the network
     * and the time the pong response was written to the network. */
    protected int _processDelay;

    /** A time stamp obtained when we unserialize this object (the intent is to get a timestamp as
     * close as possible to when the packet was received on the network). */
    protected transient long _unpackStamp;

    /** The transport parameters. */
    protected transient Transport _transport = Transport.DEFAULT;
}