Package net.i2p.router.time

Class NtpMessage

java.lang.Object
net.i2p.router.time.NtpMessage
class NtpMessage
extends Object
This class represents a NTP message, as specified in RFC 2030. The message format is compatible with all versions of NTP and SNTP. 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 = InetAddress.getByName("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()); 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

Year 2036 compliance

Prior to 0.9.50, this supported years 1900-2035. As of 0.9.50, this supports years 1968-2104 and is year-2036 compliant. All double timestamps are the actual seconds since 1900. We use a "pivot" of January 1968. NTP-format dates before 1968 are coverted to 2036+. So this code handles the last half of era 0 and the first half of era 1, i.e. 1968-2104. All math and comparisons on timestamps must be on the double values, never on the raw NTP-format byte arrays. refs: https://docs.ntpsec.org/latest/rollover.html https://www.eecis.udel.edu/~mills/y2k.html https://www.eecis.udel.edu/~mills/time.html https://tools.ietf.org/html/rfc4330 sec. 3
Since:
0.9.1 moved from net.i2p.time
Author:
Adam Buckley

  • Field Summary

    Fields 
    Modifier and Type Field Description
    byte leapIndicator
    This is a two-bit code warning of an impending leap second to be inserted/deleted in the last minute of the current day.
    byte mode
    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.
    double originateTimestamp
    This is the time at which the request departed the client for the server, in seconds since 00:00 1-Jan-1900.
    byte pollInterval
    This value indicates the maximum interval between successive messages, in seconds to the nearest power of two.
    byte precision
    This value indicates the precision of the local clock, in seconds to the nearest power of two.
    double receiveTimestamp
    This is the time at which the request arrived at the server, in seconds since 00:00 1-Jan-1900.
    byte[] referenceIdentifier
    This is a 4-byte array identifying the particular reference source.
    double referenceTimestamp
    This is the time at which the local clock was last set or corrected, in seconds since 00:00 1-Jan-1900.
    double rootDelay
    This value indicates the total roundtrip delay to the primary reference source, in seconds.
    double rootDispersion
    This value indicates the nominal error relative to the primary reference source, in seconds.
    short stratum
    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
    double transmitTimestamp
    This is the time at which the reply departed the server for the client, in seconds since 00:00 1-Jan-1900.
    byte version
    This value indicates the NTP/SNTP version number.

  • Constructor Summary

    Constructors 
    Constructor Description
    NtpMessage()
    Constructs a new NtpMessage in client -> server mode, and sets the transmit timestamp to the current time.
    NtpMessage​(byte[] array)
    Constructs a new NtpMessage from an array of bytes.

  • Method Summary

    Modifier and Type Method Description
    static void encodeTimestamp​(byte[] array, int pointer, double timestamp)
    Encodes a timestamp in the specified position in the message.
    String referenceIdentifierToString()  
    byte[] toByteArray()
    This method constructs the data bytes of a raw NTP packet.
    String toString()
    Returns a string representation of a NtpMessage

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

  • Field Details

    • leapIndicator

      public byte leapIndicator
      This is a two-bit code warning of an impending leap second to be inserted/deleted in the last minute of the current day. Its 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)

    • version

      public byte version
      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.

    • mode

      public final byte mode
      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).

    • stratum

      public short stratum
      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

    • pollInterval

      public byte pollInterval
      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).

    • precision

      public byte precision
      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.

    • rootDelay

      public double rootDelay
      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.

    • rootDispersion

      public double rootDispersion
      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.

    • referenceIdentifier

      public final byte[] referenceIdentifier
      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

    • referenceTimestamp

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

    • originateTimestamp

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

    • receiveTimestamp

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

    • transmitTimestamp

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

  • Constructor Details

    • NtpMessage

      public NtpMessage​(byte[] array)
      Constructs a new NtpMessage from an array of bytes.
      Parameters:
      array - 48 bytes minimum

    • NtpMessage

      public NtpMessage()
      Constructs a new NtpMessage in client -> server mode, and sets the transmit timestamp to the current time.

  • Method Details

    • toByteArray

      public byte[] toByteArray()
      This method constructs the data bytes of a raw NTP packet.
      Returns:
      48 bytes

    • toString

      public String toString()
      Returns a string representation of a NtpMessage
      Overrides:
      toString in class Object

    • encodeTimestamp

      public static void encodeTimestamp​(byte[] array, int pointer, double timestamp)
      Encodes a timestamp in the specified position in the message. 2036-compliant as of 0.9.50. Timestamps before 1968 will be encoded as Jan. 1968. Timestamps after Feb. 2104 will be encoded as Feb. 2104.
      Parameters:
      array - output 8 bytes starting at pointer
      pointer - the offset
      timestamp - the time to encode (since 1900, NOT Java time)

    • referenceIdentifierToString

      public String referenceIdentifierToString()
      Returns:
      non-null, "" if unset
      Since:
      0.9.29