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
021package org.apache.directory.server.ntp.io;
022
023
024import java.nio.ByteBuffer;
025import java.nio.charset.StandardCharsets;
026
027import org.apache.directory.server.ntp.messages.LeapIndicatorType;
028import org.apache.directory.server.ntp.messages.ModeType;
029import org.apache.directory.server.ntp.messages.NtpMessage;
030import org.apache.directory.server.ntp.messages.NtpMessageModifier;
031import org.apache.directory.server.ntp.messages.NtpTimeStamp;
032import org.apache.directory.server.ntp.messages.ReferenceIdentifier;
033import org.apache.directory.server.ntp.messages.StratumType;
034
035
036/**
037 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
038 */
039public 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, StandardCharsets.UTF_8 ) );
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}