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# Source code for kafka.util

    import binascii
    import collections
    import struct
    import sys
    from threading import Thread, Event

    import six

    from kafka.common import BufferUnderflowError

    def crc32(data):
        return binascii.crc32(data) & 0xffffffff

    def write_int_string(s):
        if s is not None and not isinstance(s, six.binary_type):
            raise TypeError('Expected "%s" to be bytes\n'
                            'data=%s' % (type(s), repr(s)))
        if s is None:
            return struct.pack('>i', -1)
        else:
            return struct.pack('>i%ds' % len(s), len(s), s)

    def write_short_string(s):
        if s is not None and not isinstance(s, six.binary_type):
            raise TypeError('Expected "%s" to be bytes\n'
                            'data=%s' % (type(s), repr(s)))
        if s is None:
            return struct.pack('>h', -1)
        elif len(s) > 32767 and sys.version_info < (2, 7):
            # Python 2.6 issues a deprecation warning instead of a struct error
            raise struct.error(len(s))
        else:
            return struct.pack('>h%ds' % len(s), len(s), s)

    def read_short_string(data, cur):
        if len(data) < cur + 2:
            raise BufferUnderflowError("Not enough data left")

        (strlen,) = struct.unpack('>h', data[cur:cur + 2])
        if strlen == -1:
            return None, cur + 2

        cur += 2
        if len(data) < cur + strlen:
            raise BufferUnderflowError("Not enough data left")

        out = data[cur:cur + strlen]
        return out, cur + strlen

    def read_int_string(data, cur):
        if len(data) < cur + 4:
            raise BufferUnderflowError(
                "Not enough data left to read string len (%d < %d)" %
                (len(data), cur + 4))

        (strlen,) = struct.unpack('>i', data[cur:cur + 4])
        if strlen == -1:
            return None, cur + 4

        cur += 4
        if len(data) < cur + strlen:
            raise BufferUnderflowError("Not enough data left")

        out = data[cur:cur + strlen]
        return out, cur + strlen

    def relative_unpack(fmt, data, cur):
        size = struct.calcsize(fmt)
        if len(data) < cur + size:
            raise BufferUnderflowError("Not enough data left")

        out = struct.unpack(fmt, data[cur:cur + size])
        return out, cur + size

    def group_by_topic_and_partition(tuples):
        out = collections.defaultdict(dict)
        for t in tuples:
            out[t.topic][t.partition] = t
        return out

    def kafka_bytestring(s):
        """
        Takes a string or bytes instance
        Returns bytes, encoding strings in utf-8 as necessary
        """
        if isinstance(s, six.binary_type):
            return s
        if isinstance(s, six.string_types):
            return s.encode('utf-8')
        raise TypeError(s)

    class ReentrantTimer(object):
        """
        A timer that can be restarted, unlike threading.Timer
        (although this uses threading.Timer)

        Arguments:

            t: timer interval in milliseconds
            fn: a callable to invoke
            args: tuple of args to be passed to function
            kwargs: keyword arguments to be passed to function
        """
        def __init__(self, t, fn, *args, **kwargs):

            if t <= 0:
                raise ValueError('Invalid timeout value')

            if not callable(fn):
                raise ValueError('fn must be callable')

            self.thread = None
            self.t = t / 1000.0
            self.fn = fn
            self.args = args
            self.kwargs = kwargs
            self.active = None

        def _timer(self, active):
            # python2.6 Event.wait() always returns None
            # python2.7 and greater returns the flag value (true/false)
            # we want the flag value, so add an 'or' here for python2.6
            # this is redundant for later python versions (FLAG OR FLAG == FLAG)
            while not (active.wait(self.t) or active.is_set()):
                self.fn(*self.args, **self.kwargs)

        def start(self):
            if self.thread is not None:
                self.stop()

            self.active = Event()
            self.thread = Thread(target=self._timer, args=(self.active,))
            self.thread.daemon = True  # So the app exits when main thread exits
            self.thread.start()

        def stop(self):
            if self.thread is None:
                return

            self.active.set()
            self.thread.join(self.t + 1)
            # noinspection PyAttributeOutsideInit
            self.timer = None
            self.fn = None

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