timesyncclientextension.java

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package org.mortbay.cometd.client.ext;

import java.util.Map;

import org.cometd.Client;
import org.cometd.Extension;
import org.cometd.Message;
import org.mortbay.util.ajax.JSON;

public class TimesyncClientExtension implements Extension
{
    volatile int _lag;
    volatile int _offset;
    
    public Message rcv(Client from, Message message)
    {
        return message;
    }

    public Message rcvMeta(Client from, Message message)
    {
        Map<String,Object> ext=message.getExt(false);
        if (ext!=null)
        {
            Map<String,Object> sync=(Map<String,Object>)ext.get("timesync");
            if (sync!=null)
            {
                long now = System.currentTimeMillis();

                final long tc=((Number)sync.get("tc")).longValue();
                final long ts=((Number)sync.get("ts")).longValue();
                final int p=((Number)sync.get("p")).intValue();
                final int a=((Number)sync.get("a")).intValue();

                int l=(int)(now-tc-p)/2-a;
                int o=(int)(ts-tc)-l;

                _lag=(_lag+l)/2;
                _offset=(_offset+o)/2;   
            }
        }
            
        return message;
    }

    public Message send(Client from, Message message)
    {
        return message;
    }

    public Message sendMeta(Client from, Message message)
    {
        Map<String,Object> ext=message.getExt(true);
        long now = System.currentTimeMillis();
        JSON.Literal timesync=new JSON.Literal("{\"tc\":"+now+",\"l\":"+_lag+",\"o\":"+_offset+"}");
        ext.put("timesync",timesync);
        return message;
    }

    public int getOffset()
    {
        return _offset;
    }

    public int getLag()
    {
        return _lag;
    }

    public long getServerTime()
    {
        return System.currentTimeMillis()+_offset;
    }
    
}