ntpmessage.java

ntp服务器测试代码,采用Java实现！内含两个实例代码

        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
     */
    public NtpMessage(byte leapIndicator, byte version, byte mode, short stratum, byte pollInterval, byte precision, double rootDelay, double rootDispersion, byte[] referenceIdentifier, double referenceTimestamp, double originateTimestamp, double receiveTimestamp, 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.
     */
    public byte[] toByteArray() {
        // All bytes are automatically set to 0
        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
        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
        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
     */
    public String toString() {
        String precisionStr = new DecimalFormat("0.#E0").format(Math.pow(2, precision));
        return "Leap indicator: " + leapIndicator + " " + "Version: " + version + " " + "Mode: " + mode + " " + "Stratum: " + stratum + " " + "Poll: " + pollInterval + " " + "Precision: " + precision + " (" + precisionStr + " seconds) " + "Root delay: " + new DecimalFormat("0.00").format(rootDelay * 1000) + " ms " + "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion * 1000) + " ms " + "Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + " " + "Reference timestamp: " + timestampToString(referenceTimestamp) + " " + "Originate timestamp: " + timestampToString(originateTimestamp) + " " + "Receive timestamp:   " + timestampToString(receiveTimestamp) + " " + "Transmit timestamp:  " + timestampToString(transmitTimestamp);
    }

    /** *//**
     * Converts an unsigned byte to a short. By default, Java assumes that a
     * byte is signed.
     */
    public static short unsignedByteToShort(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.
     */
    public static double decodeTimestamp(byte[] array, 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
     */
    public static void encodeTimestamp(byte[] array, 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
            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) (Math.random() * 255.0);
    }

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

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

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

        // date/time
        String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms));

        // fraction
        double fraction = timestamp - ((long) timestamp);
        String fractionSting = new DecimalFormat(".000000").format(fraction);

        return date + fractionSting;
    }

    /** *//**
     * Returns a string representation of a reference identifier according to
     * the rules set out in RFC 2030.
     */
    public static String referenceIdentifierToString(byte[] ref, short stratum, 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 "";
    }
}