NtpMessage.java

/*******************************************************************************
 * This file is part of OpenNMS(R).
 *
 * Copyright (C) 2009-2011 The OpenNMS Group, Inc.
 * OpenNMS(R) is Copyright (C) 1999-2011 The OpenNMS Group, Inc.
 *
 * OpenNMS(R) is a registered trademark of The OpenNMS Group, Inc.
 *
 * OpenNMS(R) is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published
 * by the Free Software Foundation, either version 3 of the License,
 * or (at your option) any later version.
 *
 * OpenNMS(R) 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with OpenNMS(R).  If not, see:
 *      http://www.gnu.org/licenses/
 *
 * For more information contact:
 *     OpenNMS(R) Licensing <license@opennms.org>
 *     http://www.opennms.org/
 *     http://www.opennms.com/
 *******************************************************************************/

/**
 * This class represents a NTP message, as specified in RFC 2030.  The message
 * format is compatible with all versions of NTP and SNTP.  ToDo: Is this true?
 *
 * This class does not support the optional authentication protocol, and
 * ignores the key ID and message digest fields.
 *
 * For convenience, this class exposes message values as native Java types, not
 * the NTP-specified data formats.  For example, timestamps are
 * stored as doubles (as opposed to the NTP unsigned 64-bit fixed point
 * format).
 *
 * However, the contructor NtpMessage(byte[]) and the method toByteArray()
 * allow the import and export of the raw NTP message format.
 *
 *
 * Usage example
 *
 * // Send message
 * DatagramSocket socket = new DatagramSocket();
 * InetAddress address = InetAddressUtils.addr("ntp.cais.rnp.br");
 * byte[] buf = new NtpMessage().toByteArray();
 * DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 123);
 * socket.send(packet);
 *
 * // Get response
 * socket.receive(packet);
 * System.out.println(msg.toString());
 *
 *
 * This code is copyright (c) Adam Buckley 2004
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.  A HTML version of the GNU General Public License can be
 * seen at http://www.gnu.org/licenses/gpl.html
 *
 * This program 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 General Public License for
 * more details.
 *
 *
 * Comments for member variables are taken from RFC2030 by David Mills,
 * University of Delaware.
 *
 * Number format conversion code in NtpMessage(byte[] array) and toByteArray()
 * inspired by http://www.pps.jussieu.fr/~jch/enseignement/reseaux/
 * NTPMessage.java which is copyright (c) 2003 by Juliusz Chroboczek
 *
 * @author Adam Buckley
 * @version $Id: $
 */

package org.opennms.netmgt.provision.support.ntp;

import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Random;
public class NtpMessage {
    
    private static final DecimalFormat NTP_FRACTION_FORMAT = new DecimalFormat(".000000");

    private static final SimpleDateFormat NTP_DATE_FORMAT = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss");

    /**
     * This is a two-bit code warning of an impending leap second to be
     * inserted/deleted in the last minute of the current day. It's values may
     * be as follows:
     * 
     * Value Meaning ----- ------- 0 no warning 1 last minute has 61 seconds 2
     * last minute has 59 seconds) 3 alarm condition (clock not synchronized)
     */
    public byte leapIndicator = 0;

    /**
     * This value indicates the NTP/SNTP version number. The version number is 3
     * for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI). If
     * necessary to distinguish between IPv4, IPv6 and OSI, the encapsulating
     * context must be inspected.
     */
    public byte version = 3;

    /**
     * This value indicates the mode, with values defined as follows:
     * 
     * Mode Meaning ---- ------- 0 reserved 1 symmetric active 2 symmetric
     * passive 3 client 4 server 5 broadcast 6 reserved for NTP control message
     * 7 reserved for private use
     * 
     * In unicast and anycast modes, the client sets this field to 3 (client) in
     * the request and the server sets it to 4 (server) in the reply. In
     * multicast mode, the server sets this field to 5 (broadcast).
     */
    public byte mode = 0;

    /**
     * This value indicates the stratum level of the local clock, with values
     * defined as follows:
     * 
     * Stratum Meaning ---------------------------------------------- 0
     * unspecified or unavailable 1 primary reference (e.g., radio clock) 2-15
     * secondary reference (via NTP or SNTP) 16-255 reserved
     */
    public short stratum = 0;

    /**
     * This value indicates the maximum interval between successive messages, in
     * seconds to the nearest power of two. The values that can appear in this
     * field presently range from 4 (16 s) to 14 (16284 s); however, most
     * applications use only the sub-range 6 (64 s) to 10 (1024 s).
     */
    public byte pollInterval = 0;

    /**
     * This value indicates the precision of the local clock, in seconds to the
     * nearest power of two. The values that normally appear in this field\
     * range from -6 for mains-frequency clocks to -20 for microsecond clocks
     * found in some workstations.
     */
    public byte precision = 0;

    /**
     * This value indicates the total roundtrip delay to the primary reference
     * source, in seconds. Note that this variable can take on both positive and
     * negative values, depending on the relative time and frequency offsets.
     * The values that normally appear in this field range from negative values
     * of a few milliseconds to positive values of several hundred milliseconds.
     */
    public double rootDelay = 0;

    /**
     * This value indicates the nominal error relative to the primary reference
     * source, in seconds. The values that normally appear in this field range
     * from 0 to several hundred milliseconds.
     */
    public double rootDispersion = 0;

    /**
     * This is a 4-byte array identifying the particular reference source. In
     * the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
     * stratum-1 (primary) servers, this is a four-character ASCII string, left
     * justified and zero padded to 32 bits. In NTP Version 3 secondary servers,
     * this is the 32-bit IPv4 address of the reference source. In NTP Version 4
     * secondary servers, this is the low order 32 bits of the latest transmit
     * timestamp of the reference source. NTP primary (stratum 1) servers should
     * set this field to a code identifying the external reference source
     * according to the following list. If the external reference is one of
     * those listed, the associated code should be used. Codes for sources not
     * listed can be contrived as appropriate.
     * 
     * Code External Reference Source ---- ------------------------- LOCL
     * uncalibrated local clock used as a primary reference for a subnet without
     * external means of synchronization PPS atomic clock or other
     * pulse-per-second source individually calibrated to national standards
     * ACTS NIST dialup modem service USNO USNO modem service PTB PTB (Germany)
     * modem service TDF Allouis (France) Radio 164 kHz DCF Mainflingen
     * (Germany) Radio 77.5 kHz MSF Rugby (UK) Radio 60 kHz WWV Ft. Collins (US)
     * Radio 2.5, 5, 10, 15, 20 MHz WWVB Boulder (US) Radio 60 kHz WWVH Kaui
     * Hawaii (US) Radio 2.5, 5, 10, 15 MHz CHU Ottawa (Canada) Radio 3330,
     * 7335, 14670 kHz LORC LORAN-C radionavigation system OMEG OMEGA
     * radionavigation system GPS Global Positioning Service GOES Geostationary
     * Orbit Environment Satellite
     */
    public byte[] referenceIdentifier = { 0, 0, 0, 0 };

    /**
     * This is the time at which the local clock was last set or corrected, in
     * seconds since 00:00 1-Jan-1900.
     */
    public double referenceTimestamp = 0;

    /**
     * This is the time at which the request departed the client for the server,
     * in seconds since 00:00 1-Jan-1900.
     */
    public double originateTimestamp = 0;

    /**
     * This is the time at which the request arrived at the server, in seconds
     * since 00:00 1-Jan-1900.
     */
    public double receiveTimestamp = 0;

    /**
     * This is the time at which the reply departed the server for the client,
     * in seconds since 00:00 1-Jan-1900.
     */
    public double transmitTimestamp = 0;

    /**
     * Constructs a new NtpMessage from an array of bytes.
     *
     * @param array an array of byte.
     */
    public NtpMessage(final byte[] array) {
        // See the packet format diagram in RFC 2030 for details
        leapIndicator = (byte) ((array[0] >> 6) & 0x3);
        version = (byte) ((array[0] >> 3) & 0x7);
        mode = (byte) (array[0] & 0x7);
        stratum = unsignedByteToShort(array[1]);
        pollInterval = array[2];
        precision = array[3];

        rootDelay = (array[4] * 256.0) + unsignedByteToShort(array[5]) + (unsignedByteToShort(array[6]) / 256.0) + (unsignedByteToShort(array[7]) / 65536.0);

        rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + unsignedByteToShort(array[9]) + (unsignedByteToShort(array[10]) / 256.0) + (unsignedByteToShort(array[11]) / 65536.0);

        referenceIdentifier[0] = array[12];
        referenceIdentifier[1] = array[13];
        referenceIdentifier[2] = array[14];
        referenceIdentifier[3] = array[15];

        referenceTimestamp = decodeTimestamp(array, 16);
        originateTimestamp = decodeTimestamp(array, 24);
        receiveTimestamp = decodeTimestamp(array, 32);
        transmitTimestamp = decodeTimestamp(array, 40);
    }

    /**
     * Constructs a new NtpMessage
     *
     * @param leapIndicator a byte.
     * @param version a byte.
     * @param mode a byte.
     * @param stratum a short.
     * @param pollInterval a byte.
     * @param precision a byte.
     * @param rootDelay a double.
     * @param rootDispersion a double.
     * @param referenceIdentifier an array of byte.
     * @param referenceTimestamp a double.
     * @param originateTimestamp a double.
     * @param receiveTimestamp a double.
     * @param transmitTimestamp a double.
     */
    public NtpMessage(final byte leapIndicator, final byte version, final byte mode, final short stratum, final byte pollInterval, final byte precision, final double rootDelay, final double rootDispersion, final byte[] referenceIdentifier, final double referenceTimestamp, final double originateTimestamp, final double receiveTimestamp, final double transmitTimestamp) {
        // ToDo: Validity checking
        this.leapIndicator = leapIndicator;
        this.version = version;
        this.mode = mode;
        this.stratum = stratum;
        this.pollInterval = pollInterval;
        this.precision = precision;
        this.rootDelay = rootDelay;
        this.rootDispersion = rootDispersion;
        this.referenceIdentifier = referenceIdentifier;
        this.referenceTimestamp = referenceTimestamp;
        this.originateTimestamp = originateTimestamp;
        this.receiveTimestamp = receiveTimestamp;
        this.transmitTimestamp = transmitTimestamp;
    }

    /**
     * Constructs a new NtpMessage in client -> server mode, and sets the
     * transmit timestamp to the current time.
     */
    public NtpMessage() {
        // Note that all the other member variables are already set with
        // appropriate default values.
        this.mode = 3;
        this.transmitTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0;
    }

    /**
     * This method constructs the data bytes of a raw NTP packet.
     *
     * @return an array of byte.
     */
    public byte[] toByteArray() {
        // All bytes are automatically set to 0
        final byte[] p = new byte[48];

        p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
        p[1] = (byte) stratum;
        p[2] = (byte) pollInterval;
        p[3] = (byte) precision;

        // root delay is a signed 16.16-bit FP, in Java an int is 32-bits
        final int l = (int) (rootDelay * 65536.0);
        p[4] = (byte) ((l >> 24) & 0xFF);
        p[5] = (byte) ((l >> 16) & 0xFF);
        p[6] = (byte) ((l >> 8) & 0xFF);
        p[7] = (byte) (l & 0xFF);

        // root dispersion is an unsigned 16.16-bit FP, in Java there are no
        // unsigned primitive types, so we use a long which is 64-bits
        final long ul = (long) (rootDispersion * 65536.0);
        p[8] = (byte) ((ul >> 24) & 0xFF);
        p[9] = (byte) ((ul >> 16) & 0xFF);
        p[10] = (byte) ((ul >> 8) & 0xFF);
        p[11] = (byte) (ul & 0xFF);

        p[12] = referenceIdentifier[0];
        p[13] = referenceIdentifier[1];
        p[14] = referenceIdentifier[2];
        p[15] = referenceIdentifier[3];

        encodeTimestamp(p, 16, referenceTimestamp);
        encodeTimestamp(p, 24, originateTimestamp);
        encodeTimestamp(p, 32, receiveTimestamp);
        encodeTimestamp(p, 40, transmitTimestamp);

        return p;
    }

    /**
     * Returns a string representation of a NtpMessage
     *
     * @return a {@link java.lang.String} object.
     */
    public String toString() {
        final String precisionStr = new DecimalFormat("0.#E0").format(Math.pow(2, precision));
        return "Leap indicator: " + leapIndicator + "\n" + "Version: " + version + "\n" + "Mode: " + mode + "\n" + "Stratum: " + stratum + "\n" + "Poll: " + pollInterval + "\n" + "Precision: " + precision + " (" + precisionStr + " seconds)\n" + "Root delay: " + new DecimalFormat("0.00").format(rootDelay * 1000) + " ms\n" + "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion * 1000) + " ms\n" + "Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + "\n" + "Reference timestamp: " + timestampToString(referenceTimestamp) + "\n" + "Originate timestamp: " + timestampToString(originateTimestamp) + "\n" + "Receive timestamp:   " + timestampToString(receiveTimestamp) + "\n" + "Transmit timestamp:  " + timestampToString(transmitTimestamp);
    }

    /**
     * Converts an unsigned byte to a short. By default, Java assumes that a
     * byte is signed.
     *
     * @param b a byte.
     * @return a short.
     */
    public static short unsignedByteToShort(final byte b) {
        if ((b & 0x80) == 0x80) {
            return (short) (128 + (b & 0x7f));
        } else {
            return (short) b;
        }
    }

    /**
     * Will read 8 bytes of a message beginning at <code>pointer</code> and
     * return it as a double, according to the NTP 64-bit timestamp format.
     *
     * @param array an array of byte.
     * @param pointer a int.
     * @return a double.
     */
    public static double decodeTimestamp(final byte[] array, final int pointer) {
        double r = 0.0;

        for (int i = 0; i < 8; i++) {
            r += unsignedByteToShort(array[pointer + i]) * Math.pow(2, (3 - i) * 8);
        }

        return r;
    }

    /**
     * Encodes a timestamp in the specified position in the message
     *
     * @param array an array of byte.
     * @param pointer a int.
     * @param timestamp a double.
     */
    public static void encodeTimestamp(final byte[] array, final int pointer, double timestamp) {
        // Converts a double into a 64-bit fixed point
        for (int i = 0; i < 8; i++) {
            // 2^24, 2^16, 2^8, .. 2^-32
            final double base = Math.pow(2, (3 - i) * 8);

            // Capture byte value
            array[pointer + i] = (byte) (timestamp / base);

            // Subtract captured value from remaining total
            timestamp = timestamp - (double) (unsignedByteToShort(array[pointer + i]) * base);
        }

        // From RFC 2030: It is advisable to fill the non-significant
        // low order bits of the timestamp with a random, unbiased
        // bitstring, both to avoid systematic roundoff errors and as
        // a means of loop detection and replay detection.
        array[7] = (byte) ((new Random()).nextInt(255));
    }

    /**
     * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
     * formatted date/time string.
     *
     * @param timestamp a double.
     * @return a {@link java.lang.String} object.
     */
    public static String timestampToString(final double timestamp) {
        if (timestamp == 0) return "0";

        // timestamp is relative to 1900, utc is used by Java and is relative
        // to 1970
        final double utc = timestamp - (2208988800.0);

        // milliseconds
        final long ms = (long) (utc * 1000.0);

        // date/time
        final String date = NTP_DATE_FORMAT.format(new Date(ms));

        // fraction
        final double fraction = timestamp - ((long) timestamp);
        final String fractionSting = NTP_FRACTION_FORMAT.format(fraction);

        return date + fractionSting;
    }

    /**
     * Returns a string representation of a reference identifier according to
     * the rules set out in RFC 2030.
     *
     * @param ref an array of byte.
     * @param stratum a short.
     * @param version a byte.
     * @return a {@link java.lang.String} object.
     */
    public static String referenceIdentifierToString(final byte[] ref, final short stratum, final byte version) {
        // From the RFC 2030:
        // In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
        // or stratum-1 (primary) servers, this is a four-character ASCII
        // string, left justified and zero padded to 32 bits.
        if (stratum == 0 || stratum == 1) {
            return new String(ref);
        }

        // In NTP Version 3 secondary servers, this is the 32-bit IPv4
        // address of the reference source.
        else if (version == 3) {
            return unsignedByteToShort(ref[0]) + "." + unsignedByteToShort(ref[1]) + "." + unsignedByteToShort(ref[2]) + "." + unsignedByteToShort(ref[3]);
        }

        // In NTP Version 4 secondary servers, this is the low order 32 bits
        // of the latest transmit timestamp of the reference source.
        else if (version == 4) {
            return "" + ((unsignedByteToShort(ref[0]) / 256.0) + (unsignedByteToShort(ref[1]) / 65536.0) + (unsignedByteToShort(ref[2]) / 16777216.0) + (unsignedByteToShort(ref[3]) / 4294967296.0));
        }

        return "";
    }

}