001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one
003     *  or more contributor license agreements.  See the NOTICE file
004     *  distributed with this work for additional information
005     *  regarding copyright ownership.  The ASF licenses this file
006     *  to you under the Apache License, Version 2.0 (the
007     *  "License"); you may not use this file except in compliance
008     *  with the License.  You may obtain a copy of the License at
009     *  
010     *    http://www.apache.org/licenses/LICENSE-2.0
011     *  
012     *  Unless required by applicable law or agreed to in writing,
013     *  software distributed under the License is distributed on an
014     *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     *  KIND, either express or implied.  See the License for the
016     *  specific language governing permissions and limitations
017     *  under the License. 
018     *  
019     */
020    
021    package org.apache.directory.server.ntp.io;
022    
023    
024    import java.nio.ByteBuffer;
025    
026    import org.apache.directory.server.ntp.messages.LeapIndicatorType;
027    import org.apache.directory.server.ntp.messages.ModeType;
028    import org.apache.directory.server.ntp.messages.NtpMessage;
029    import org.apache.directory.server.ntp.messages.NtpMessageModifier;
030    import org.apache.directory.server.ntp.messages.NtpTimeStamp;
031    import org.apache.directory.server.ntp.messages.ReferenceIdentifier;
032    import org.apache.directory.server.ntp.messages.StratumType;
033    
034    
035    /**
036     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
037     * @version $Rev: 547539 $, $Date: 2007-06-15 08:08:06 +0200 (Fri, 15 Jun 2007) $
038     */
039    public class NtpMessageDecoder
040    {
041        /**
042         * Decodes the {@link ByteBuffer} into an {@link NtpMessage}.
043         *
044         * @param request
045         * @return The {@link NtpMessage}.
046         */
047        public NtpMessage decode( ByteBuffer request )
048        {
049            NtpMessageModifier modifier = new NtpMessageModifier();
050    
051            byte header = request.get();
052            modifier.setLeapIndicator( parseLeapIndicator( header ) );
053            modifier.setVersionNumber( parseVersionNumber( header ) );
054            modifier.setMode( parseMode( header ) );
055            modifier.setStratum( parseStratum( request ) );
056            modifier.setPollInterval( parsePollInterval( request ) );
057            modifier.setPrecision( parsePrecision( request ) );
058            modifier.setRootDelay( parseRootDelay( request ) );
059            modifier.setRootDispersion( parseRootDispersion( request ) );
060            modifier.setReferenceIdentifier( parseReferenceIdentifier( request ) );
061            modifier.setReferenceTimestamp( new NtpTimeStamp( request ) );
062            modifier.setOriginateTimestamp( new NtpTimeStamp( request ) );
063    
064            byte[] unneededBytes = new byte[8];
065            request.get( unneededBytes );
066    
067            modifier.setReceiveTimestamp( new NtpTimeStamp() );
068            modifier.setTransmitTimestamp( new NtpTimeStamp( request ) );
069    
070            return modifier.getNtpMessage();
071        }
072    
073    
074        private LeapIndicatorType parseLeapIndicator( byte header )
075        {
076            return LeapIndicatorType.getTypeByOrdinal( ( header & 0xc0 ) >>> 6 );
077        }
078    
079    
080        private int parseVersionNumber( byte header )
081        {
082            return ( header & 0x38 ) >>> 3;
083        }
084    
085    
086        private ModeType parseMode( byte header )
087        {
088            return ModeType.getTypeByOrdinal( header & 0x07 );
089        }
090    
091    
092        private StratumType parseStratum( ByteBuffer request )
093        {
094            return StratumType.getTypeByOrdinal( request.get() );
095        }
096    
097    
098        private byte parsePollInterval( ByteBuffer bytes )
099        {
100            return ( byte ) Math.round( Math.pow( 2, bytes.get() ) );
101        }
102    
103    
104        private byte parsePrecision( ByteBuffer bytes )
105        {
106            return ( byte ) ( 1000 * Math.pow( 2, bytes.get() ) );
107        }
108    
109    
110        private ReferenceIdentifier parseReferenceIdentifier( ByteBuffer request )
111        {
112            byte[] nextFourBytes = new byte[4];
113            request.get( nextFourBytes );
114            return ReferenceIdentifier.getTypeByName( new String( nextFourBytes ) );
115        }
116    
117    
118        private int parseRootDelay( ByteBuffer bytes )
119        {
120            int temp = 256 * ( 256 * ( 256 * bytes.get() + bytes.get() ) + bytes.get() ) + bytes.get();
121            return 1000 * ( temp / 0x10000 );
122        }
123    
124    
125        private int parseRootDispersion( ByteBuffer bytes )
126        {
127            int temp = 256 * ( 256 * ( 256 * bytes.get() + bytes.get() ) + bytes.get() ) + bytes.get();
128            return 1000 * ( temp / 0x10000 );
129        }
130    }