ntp_packet.py

import struct
import time

class NTPShort(object):

    seconds = 0
    fraction = 0

    def __init__(self, seconds, fraction):
        self.seconds = long(seconds)
        self.fraction = long(fraction)

    @staticmethod
    def from_bytes(data):
        if len(data) != 4:
            raise ValueError('data must contain 8 bytes')
        seconds, fraction = struct.unpack(b'>HH', data)
        return NTPShort(seconds, fraction)

    @staticmethod
    def from_float(value):
        seconds = long(value)
        fraction = long(round( (value - seconds) * 0x10000 ))
        if fraction > 0xffffL:
            seconds += 1
            fraction = 0
        return NTPShort(seconds, fraction)

    def to_bytes(self):
        return struct.pack(b'>HH', self.seconds, self.fraction)

    def to_float(self):
        return self.seconds + float(self.fraction) / 65536.0

    def __repr__(self):
        return 'NTPShort({seconds}, {fraction})'.format(seconds=repr(self.seconds), fraction=repr(self.fraction))

    def __str__(self):
        return str(self.to_float())

NTPShort.ZERO = NTPShort(0, 0)


class NTPTimestamp(object):

    seconds = 0
    fraction = 0

    def __init__(self, seconds, fraction):
        self.seconds = long(seconds)
        self.fraction = long(fraction)

    @staticmethod
    def from_bytes(data):
        if len(data) != 8:
            raise ValueError('data must contain 8 bytes')
        seconds, fraction = struct.unpack(b'>II', data)
        return NTPTimestamp(seconds, fraction)

    @staticmethod
    def from_unix_timestamp(timestamp):
        seconds = long(timestamp)
        fraction = long(round( (timestamp - seconds) * 0x100000000L ))
        if fraction > 0xffffffffL:
            fraction = 0xffffffffL
        seconds += 0x83aa7e80L
        seconds = (seconds & 0xffffffffL)
        return NTPTimestamp(seconds, fraction)

    def to_bytes(self):
        return struct.pack(b'>II', self.seconds, self.fraction)

    def to_unix_timestamp(self):
        return self.seconds - 0x83aa7e80 + float(self.fraction) / 0x100000000

    def __repr__(self):
        return 'NTPTimestamp({seconds}, {fraction})'.format(seconds=repr(self.seconds), fraction=repr(self.fraction))

    def __str__(self):
        ts = self.to_unix_timestamp()
        secs = long(ts)
        frac = long(round( (ts - secs) * 1000000 ))
        if frac >= 1000000:
            secs += 1
            frac = 0
        return time.strftime('%Y-%m-%dT%H:%M:%S', time.gmtime(secs)) + '.{:06d}Z'.format(frac)

NTPTimestamp.ZERO = NTPTimestamp(0, 0)


class NTPPacket(object):

    leap_indicator = 0
    version = 3
    mode = 3
    stratum = 0
    poll = 0
    precision = 0
    root_delay = NTPShort.ZERO
    root_dispersion = NTPShort.ZERO
    reference_identifier = b"\x00\x00\x00\x00"
    reference_timestamp = NTPTimestamp.ZERO
    origin_timestamp = NTPTimestamp.ZERO
    receive_timestamp = NTPTimestamp.ZERO
    transmit_timestamp = NTPTimestamp.ZERO

    @staticmethod
    def from_bytes(data):
        if len(data) < 48 and len(data) != 68:
            raise ValueError('packet too short')
        packet = NTPPacket()
        (b1, packet.stratum, packet.poll, packet.precision) = struct.unpack(b'>BBbb', data[0:4])
        packet.leap_indicator = (b1 >> 6) & 0x3
        packet.version = (b1 >> 3) & 0x7
        packet.mode = b1 & 0x7
        packet.root_delay = NTPShort.from_bytes(data[4:8])
        packet.root_dispersion = NTPShort.from_bytes(data[8:12])
        packet.reference_identifier = data[12:16]
        packet.reference_timestamp = NTPTimestamp.from_bytes(data[16:24])
        packet.origin_timestamp = NTPTimestamp.from_bytes(data[24:32])
        packet.receive_timestamp = NTPTimestamp.from_bytes(data[32:40])
        packet.transmit_timestamp = NTPTimestamp.from_bytes(data[40:48])
        return packet

    def to_bytes(self):
        b1 = self.leap_indicator << 6 | self.version << 3 | self.mode
        data = struct.pack(b'>BBbb', b1, self.stratum, self.poll, self.precision)
        data += self.root_delay.to_bytes()
        data += self.root_dispersion.to_bytes()
        data += self.reference_identifier
        data += self.reference_timestamp.to_bytes()
        data += self.origin_timestamp.to_bytes()
        data += self.receive_timestamp.to_bytes()
        data += self.transmit_timestamp.to_bytes()
        return data

    def __repr__(self):
        fields = (
            'leap_indicator',
            'version',
            'mode',
            'stratum',
            'poll',
            'precision',
            'root_delay',
            'root_dispersion',
            'reference_identifier',
            'reference_timestamp',
            'origin_timestamp',
            'receive_timestamp',
            'transmit_timestamp',
            )
        return 'NTPPacket(' + ', '.join([ field + '=' + repr(getattr(self, field)) for field in fields ]) + ')'