path: root/tags/1.0.2/ipaddr.py

#!/usr/bin/python
#
# Copyright 2007 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""An IPv4/IPv6 manipulation library in Python.

This library is used to create/poke/manipulate IPv4 and IPv6 addresses and
prefixes.
"""

__version__ = '1.0.1'


class Error(Exception):
  """Base class for exceptions."""


class IPTypeError(Error):
  """Tried to perform a v4 action on v6 object or vice versa."""


class IPAddressExclusionError(Error):
  """An Error we should never see occurred in address exclusion."""


class IPv4IpValidationError(Error):
  """Raised when an IPv4 address is invalid."""

  def __init__(self, ip):
    Error.__init__(self)
    self.ip = ip

  def __str__(self):
    return repr(self.ip) + ' is not a valid IPv4 address'


class IPv4NetmaskValidationError(Error):
  """Raised when a netmask is invalid."""

  def __init__(self, netmask):
    Error.__init__(self)
    self.netmask = netmask

  def __str__(self):
    return repr(self.netmask) + ' is not a valid IPv4 netmask'


class IPv6IpValidationError(Error):
  """Raised when an IPv6 address is invalid."""

  def __init__(self, ip):
    Error.__init__(self)
    self.ip = ip

  def __str__(self):
    return repr(self.ip) + ' is not a valid IPv6 address'


class IPv6NetmaskValidationError(Error):
  """Raised when an IPv6 netmask is invalid."""

  def __init__(self, netmask):
    Error.__init__(self)
    self.netmask = netmask

  def __str__(self):
    return repr(self.netmask) + ' is not a valid IPv6 netmask'


class PrefixlenDiffInvalidError(Error):
  """Raised when Sub/Supernets is called with an invalid prefixlen_diff."""

  def __init__(self, error_str):
    Error.__init__(self)
    self.error_str = error_str


def IP(ipaddr):
  """Take an IP string or int and return an object of the correct type.

  Args:
    ipaddr: A string or integer, the IP address.  Either IPv4 or IPv6
      addresses may be supplied; integers less than 2**32 will be
      considered to be IPv4.

  Returns:
    An IPv4 or IPv6 object.

  Raises:
    ValueError: if the string passed isn't either a v4 or a v6 address.
  """
  force_v4 = False
  try:
    if int(ipaddr) < 2**32:
      force_v4 = True
  except (TypeError, ValueError):
    pass

  # Try v6 first because of the confusing nature of v4 in mapped in v6
  # addresses.
  if not force_v4:
    try:
      return IPv6(ipaddr)
    except (IPv6IpValidationError, IPv6NetmaskValidationError):
      pass

  try:
    return IPv4(ipaddr)
  except (IPv4IpValidationError, IPv4NetmaskValidationError):
    pass

  raise ValueError("%s doesn't appear to be an IPv4 or IPv6 address" % ipaddr)


def _CollapseAddressListRecursive(addresses):
  """Recursively loops through the addresses, collapsing concurrent netblocks.

  Example:

    ip1 = IPv4('1.1.0.0/24')
    ip2 = IPv4('1.1.1.0/24')
    ip3 = IPv4('1.1.2.0/24')
    ip4 = IPv4('1.1.3.0/24')
    ip5 = IPv4('1.1.4.0/24')
    ip6 = IPv4('1.1.0.1/22')

    _CollapseAddressListRecursive([ip1, ip2, ip3, ip4, ip5, ip6]) ->
    [IPv4('1.1.0.0/22'), IPv4('1.1.4.0/24')]

  This shouldn't be called directly; it is called via CollapseAddrList([]).

  Args:
    addresses: A list of IPv4 or IPv6 objects.

  Returns:
    A list of IPv4 or IPv6 objects depending on what we were passed.
  """
  ret_array = []
  optimized = False

  for cur_addr in addresses:
    if not ret_array:
      ret_array.append(cur_addr)
      continue
    if ret_array[-1].Contains(cur_addr):
      optimized = True
    elif cur_addr == ret_array[-1].Supernet().Subnet()[1]:
      ret_array.append(ret_array.pop().Supernet())
      optimized = True
    else:
      ret_array.append(cur_addr)

  if optimized:
    return _CollapseAddressListRecursive(ret_array)

  return ret_array


def CollapseAddrList(addresses):
  """Collapse a list of IP objects.

  Example:

    CollapseAddrList([IPv4('1.1.0.0/24'), IPv4('1.1.1.0/24')]) ->
    [IPv4('1.1.0.0/23')]

  Args:
    addresses: A list of IPv4 or IPv6 objects.

  Returns:
    A list of IPv4 or IPv6 objects depending on what we were passed.
  """
  return _CollapseAddressListRecursive(sorted(addresses,
                                              cmp=BaseIP.CompareNetworks))


class BaseIP(object):
  """A generic IP object.

  This IP class contains most of the methods which are used by
  the IPv4 and IPv6 classes.
  """

  def __getitem__(self, n):
    if n >= 0:
      if self.network + n > self.broadcast:
        raise IndexError
      return self._StrFromIpInt(self.network + n)
    else:
      if self.broadcast + n < self.network:
        raise IndexError
      return self._StrFromIpInt(self.broadcast + n)

  def __eq__(self, other):
    try:
      if self.version != other.version:
        return False
    except AttributeError:
      raise NotImplementedError('%s is not an IP address' % repr(other))
    return self.ip == other.ip and self.netmask == other.netmask

  def __ne__(self, other):
    return not self.__eq__(other)

  def __cmp__(self, other):
    try:
      return (cmp(self.version, other.version) or
              cmp(self.ip, other.ip) or
              cmp(self.prefixlen, other.prefixlen) or
              0)
    except AttributeError:
      return super(BaseIP, self).__cmp__(other)

  def __repr__(self):
    return '%s(%r)' % (self.__class__.__name__, str(self))

  def AddressExclude(self, other):
    """Remove an address from a larger block.

    For example:

      addr1 = IP('10.1.1.0/24')
      addr2 = IP('10.1.1.0/26')
      addr1.AddressExclude(addr2) = [IP('10.1.1.64/26'), IP('10.1.1.128/25')]

    or IPv6:

      addr1 = IP('::1/32')
      addr2 = IP('::1/128')
      addr1.AddressExclude(addr2) = [IP('::0/128'),
                                     IP('::2/127'),
                                     IP('::4/126'),
                                     IP('::8/125'),
                                     ...
                                     IP('0:0:8000::/33')]

    Args:
      other: An IP object of the same type.

    Returns:
      A sorted list of IP objects addresses which is self minus other.

    Raises:
      IPTypeError: If self and other are of difffering address versions.
      IPAddressExclusionError: There was some unknown error in the address
        exclusion process.  This likely points to a bug elsewhere in this code.
      ValueError: If other is not completely contained by self.
    """
    if not self.version == other.version:
      raise IPTypeError("%s and %s aren't of the same version" % (
          str(self), str(other)))

    if not self.Contains(other):
      raise ValueError('%s not contained in %s' % (str(other), str(self)))

    ret_addrs = []

    # Make sure we're comparing the network of other.
    other = IP(other.network_ext + '/' + str(other.prefixlen))

    s1, s2 = self.Subnet()
    while s1 != other and s2 != other:
      if s1.Contains(other):
        ret_addrs.append(s2)
        s1, s2 = s1.Subnet()
      elif s2.Contains(other):
        ret_addrs.append(s1)
        s1, s2 = s2.Subnet()
      else:
        # If we got here, there's a bug somewhere.
        raise IPAddressExclusionError('Error performing address exclusion: '
                                      's1: %s s2: %s other: %s' %
                                      (str(s1), str(s2), str(other)))
    if s1 == other:
      ret_addrs.append(s2)
    elif s2 == other:
      ret_addrs.append(s1)
    else:
      # If we got here, there's a bug somewhere.
      raise IPAddressExclusionError('Error performing address exclusion: '
                                    's1: %s s2: %s other: %s' %
                                    (str(s1), str(s2), str(other)))

    return sorted(ret_addrs, cmp=BaseIP.CompareNetworks)

  def CompareNetworks(self, other):
    """Compare two IP objects.

    This is only concerned about the comparison of the integer
    representation of the network addresses.  This means that the host bits
    aren't considered at all in this method.  If you want to compare host
    bits, you can easily enough do a 'HostA.ip < HostB.ip'

    Args:
      other: An IP object.

    Returns:
      If the IP versions of self and other are the same, returns:

      -1 if self < other:
         eg: IPv4('1.1.1.0/24') < IPv4('1.1.2.0/24')
             IPv6('1080::200C:417A') < IPv6('1080::200B:417B')
       0 if self == other
         eg: IPv4('1.1.1.1/24') == IPv4('1.1.1.2/24')
             IPv6('1080::200C:417A/96') == IPv6('1080::200C:417B/96')
       1 if self > other
         eg: IPv4('1.1.1.0/24') > IPv4('1.1.0.0/24')
             IPv6('1080::1:200C:417A/112') > IPv6('1080::0:200C:417A/112')

      If the IP versions of self and other are different, returns:

      -1 if self.version < other.version
         eg: IPv4('10.0.0.1/24') < IPv6('::1/128')
       1 if self.version > other.version
         eg: IPv6('::1/128') > IPv4('255.255.255.0/24')
    """
    if self.version != other.version:
      return cmp(self.version, other.version)

    if self.network < other.network:
      return -1
    if self.network > other.network:
      return 1
    # self.network == other.network below here:
    if self.netmask < other.netmask:
      return -1
    if self.netmask > other.netmask:
      return 1
    # self.network == other.network and self.netmask == other.netmask
    return 0

  def __str__(self):
    return  '%s/%s' % (self._StrFromIpInt(self.ip), str(self.prefixlen))

  def __hash__(self):
    return hash(self.ip ^ self.netmask)

  def Contains(self, other):
    """Return True if the given IP is wholly contained by the current network.

    Args:
      other: An IP object.

    Returns:
      A boolean.
    """
    return self.network <= other.ip and self.broadcast >= other.broadcast

  __contains__ = Contains

  @property
  def ip_ext(self):
    """Dotted decimal or colon string version of the IP address."""
    return self._StrFromIpInt(self.ip)

  @property
  def ip_ext_full(self):
    return self.ip_ext

  @property
  def broadcast(self):
    """Integer representation of the broadcast address."""
    return self.ip | self.hostmask

  @property
  def broadcast_ext(self):
    """Dotted decimal or colon string version of the broadcast address."""
    return self._StrFromIpInt(self.broadcast)

  @property
  def hostmask(self):
    """Integer representation of the hostmask."""
    return self.netmask ^ self._ALL_ONES

  @property
  def hostmask_ext(self):
    """Dotted decimal or colon string representation of the hostmask."""
    return self._StrFromIpInt(self.hostmask)

  @property
  def network(self):
    """Integer representation of the network."""
    return self.ip & self.netmask

  @property
  def network_ext(self):
    """Dotted decimal or colon string representation of the network."""
    return self._StrFromIpInt(self.network)

  @property
  def netmask_ext(self):
    """Dotted decimal or colon string representation of the netmask."""
    return self._StrFromIpInt(self.netmask)

  @property
  def numhosts(self):
    """Number of hosts in the current subnet."""
    return self.broadcast - self.network + 1

  @property
  def version(self):
    raise NotImplementedError('BaseIP has no version')

  def _IpIntFromPrefixlen(self, prefixlen=None):
    """Turn the prefix length netmask into a int for easy comparison.

    Args:
      prefixlen: An integer, the prefix length.

    Returns:
      An integer.
    """
    if not prefixlen and prefixlen != 0:
      prefixlen = self.prefixlen
    return self._ALL_ONES ^ (self._ALL_ONES >> prefixlen)

  def _PrefixlenFromIpInt(self, ip_int, mask=32):
    """Return prefix length from the decimal netmask.

    Args:
      ip_int: An integer, the IP address.
      mask: The netmask.  Defaults to 32.

    Returns:
      An integer, the prefix length.
    """
    while mask:
      if ip_int & 1 == 1:
        break
      ip_int >>= 1
      mask -= 1

    return mask

  def _IpStrFromPrefixlen(self, prefixlen=None):
    """Turn a prefix length into a dotted decimal string.

    Args:
      prefixlen: The netmask prefix length.

    Returns:
      A string, the dotted decimal netmask string.
    """
    if not prefixlen:
      prefixlen = self.prefixlen
    return self._StrFromIpInt(self._IpIntFromPrefixlen(prefixlen))


class IPv4(BaseIP):
  """This class represents and manipulates 32-bit IPv4 addresses.

  Attributes: [examples for IPv4('1.2.3.4/27')]
    .ip: 16909060
    .ip_ext: '1.2.3.4'
    .ip_ext_full: '1.2.3.4'
    .network: 16909056L
    .network_ext: '1.2.3.0'
    .hostmask: 31L (0x1F)
    .hostmask_ext: '0.0.0.31'
    .broadcast: 16909087L (0x102031F)
    .broadcast_ext: '1.2.3.31'
    .netmask: 4294967040L (0xFFFFFFE0)
    .netmask_ext: '255.255.255.224'
    .prefixlen: 27
  """

  # Equivalent to 255.255.255.255 or 32 bits of 1's.
  _ALL_ONES = (2**32) - 1

  def __init__(self, ipaddr):
    """Instantiate a new IPv4 object.

    Args:
      ipaddr: A string or integer representing the IP [ & network ].
        '192.168.1.1/32'
        '192.168.1.1/255.255.255.255'
        '192.168.1.1/0.0.0.255'
        '192.168.1.1'
        are all functionally the same in IPv4. That is to say, failing to
        provide a subnetmask will create an object with a mask of /32.
        A netmask of '255.255.255.255' is assumed to be /32 and
        '0.0.0.0' is assumed to be /0, even though other netmasks can be
        expressed both as host- and net-masks.  (255.0.0.0 == 0.255.255.255)

        Additionally, an integer can be passed, so
        IPv4('192.168.1.1') == IPv4(3232235777).
        or, more generally
        IPv4(IPv4('192.168.1.1').ip) == IPv4('192.168.1.1')

    Raises:
      IPv4IpValidationError: If ipaddr isn't a valid IPv4 address.
      IPv4NetmaskValidationError: If the netmask isn't valid for an IPv4
        address.
    """
    BaseIP.__init__(self)
    self._version = 4

    # Efficient constructor from integer.
    if isinstance(ipaddr, int) or isinstance(ipaddr, long):
      self.ip = ipaddr
      self.prefixlen = 32
      self.netmask = self._ALL_ONES
      if ipaddr < 0 or ipaddr > self._ALL_ONES:
        raise IPv4IpValidationError(ipaddr)
      return

    # Assume input argument to be string or any object representation
    # which converts into a formatted IP prefix string.
    addr = str(ipaddr).split('/')

    if len(addr) > 2:
      raise IPv4IpValidationError(ipaddr)

    if not self._IsValidIp(addr[0]):
      raise IPv4IpValidationError(addr[0])

    self.ip = self._IpIntFromStr(addr[0])

    if len(addr) == 2:
      mask = addr[1].split('.')
      if len(mask) == 4:
        # We have dotted decimal netmask.
        if not self._IsValidNetmask(addr[1]):
          raise IPv4NetmaskValidationError(addr[1])
        if self._IsHostMask(addr[1]):
          self.netmask = self._IpIntFromStr(addr[1]) ^ self._ALL_ONES
        else:
          self.netmask = self._IpIntFromStr(addr[1])
        self.prefixlen = self._PrefixlenFromIpInt(self.netmask)
      else:
        # We have a netmask in prefix length form.
        if not self._IsValidNetmask(addr[1]):
          raise IPv4NetmaskValidationError(addr[1])
        self.prefixlen = int(addr[1])
        self.netmask = self._IpIntFromPrefixlen(self.prefixlen)
    else:
      self.prefixlen = 32
      self.netmask = self._IpIntFromPrefixlen(self.prefixlen)

  def SetPrefix(self, prefixlen):
    """Change the prefix length.

    Args:
      prefixlen: An integer, the new prefix length.

    Raises:
      IPv4NetmaskValidationError: If prefixlen is out of bounds.
    """
    if not 0 <= prefixlen <= 32:
      raise IPv4NetmaskValidationError(prefixlen)
    self.prefixlen = prefixlen
    self.netmask = self._IpIntFromPrefixlen(self.prefixlen)

  def Subnet(self, prefixlen_diff=1):
    """The subnets which join to make the current subnet.

    In the case that self contains only one IP (self.prefixlen == 32),
    return a list with just ourself.

    Args:
      prefixlen_diff: An integer, the amount the prefix length should be
        increased by.  Given a /24 network and a prefixlen_diff of 3,
        for example, 8 subnets of size /27 will be returned.  The default
        value of 1 splits the current network into two halves.

    Returns:
      A list of IPv4 objects.

    Raises:
      PrefixlenDiffInvalidError: The prefixlen_diff is too small or too large.
    """
    if self.prefixlen == 32:
      return [self]

    if prefixlen_diff < 0:
      raise PrefixlenDiffInvalidError('prefix length diff must be > 0')
    new_prefixlen = self.prefixlen + prefixlen_diff

    if not self._IsValidNetmask(str(new_prefixlen)):
      raise PrefixlenDiffInvalidError(
          'prefix length diff %d is invalid for netblock %s' % (
              new_prefixlen, str(self)))

    first = IPv4(
        self._StrFromIpInt(self.network) + '/' + str(self.prefixlen +
                                                     prefixlen_diff))
    subnets = [first]
    current = first
    while True:
      broadcast = current.broadcast
      if broadcast == self.broadcast:
        break
      current = IPv4(self._StrFromIpInt(broadcast + 1) + '/' +
                     str(new_prefixlen))
      subnets.append(current)

    return subnets

  def Supernet(self, prefixlen_diff=1):
    """The supernet containing the current network.

    Args:
      prefixlen_diff: An integer, the amount the prefix length of the network
        should be decreased by.  For example, given a /24 network and a
        prefixlen_diff of 3, a supernet with a /21 netmask is returned.

    Returns:
      An IPv4 object.

    Raises:
      PrefixlenDiffInvalidError: If self.prefixlen - prefixlen_diff < 0. I.e.,
        you have a negative prefix length.
    """
    if self.prefixlen == 0:
      return self
    if self.prefixlen - prefixlen_diff < 0:
      raise PrefixlenDiffInvalidError(
          'current prefixlen is %d, cannot have a prefixlen_diff of %d' % (
              self.prefixlen, prefixlen_diff))
    return IPv4(self.ip_ext + '/' + str(self.prefixlen - prefixlen_diff))

  def IsRFC1918(self):
    """Test if the IPv4 address is reserved per RFC1918.

    Returns:
      A boolean, True if the address is reserved.
    """
    return (IPv4('10.0.0.0/8').Contains(self) or
            IPv4('172.16.0.0/12').Contains(self) or
            IPv4('192.168.0.0/16').Contains(self))

  def IsMulticast(self):
    """Test if the address is reserved for multicast use.

    Returns:
      A boolean, True if the address is multicast.
    """
    return IPv4('224.0.0.0/4').Contains(self)

  def IsLoopback(self):
    """Test if the address is a loopback adddress.

    Returns:
      A boolean, True if the address is a loopback.
    """
    return IPv4('127.0.0.0/8').Contains(self)

  def IsLinkLocal(self):
    """Test if the address is reserved for LinkLocal.

    Returns:
      A boolean, True if the address is link local.
    """
    return IPv4('169.254.0.0/16').Contains(self)

  @property
  def version(self):
    return self._version

  def _IsHostMask(self, ip_str):
    """Test if the IP string is a hostmask (rather than a netmask).

    Args:
      ip_str: A string, the potential hostmask.

    Returns:
      A boolean, True if the IP string is a hostmask.
    """
    parts = [int(x) for x in ip_str.split('.')]
    if parts[0] < parts[-1]:
      return True
    return False

  def _IpIntFromStr(self, ip_str):
    """Turn the given dotted decimal string into an integer for easy comparison.

    Args:
      ip_str: A string, the IP address.

    Returns:
      The IP address as an integer.
    """
    packed_ip = 0
    for oc in ip_str.split('.'):
      packed_ip = (packed_ip << 8) | int(oc)
    return packed_ip

  def _StrFromIpInt(self, ip_int):
    """Turns a 32-bit integer into dotted decimal notation.

    Args:
      ip_int: An integer, the IP address.

    Returns:
      The IP address as a string in dotted decimal notation.
    """
    octets = []
    for _ in xrange(4):
      octets.insert(0, str(ip_int & 0xFF))
      ip_int >>= 8
    return '.'.join(octets)

  def _IsValidIp(self, ip_str):
    """Validate the dotted decimal notation IP/netmask string.

    Args:
      ip_str: A string, the IP address.

    Returns:
      A boolean, True if the string is a valid dotted decimal IP string.
    """
    octets = ip_str.split('.')
    if len(octets) == 1:
      # We have an integer rather than a dotted decimal IP.
      try:
        return int(ip_str) >= 0 and int(ip_str) <= self._ALL_ONES
      except ValueError:
        return False

    if len(octets) != 4:
      return False

    for octet in octets:
      if not 0 <= int(octet) <= 255:
        return False
    return True

  def _IsValidNetmask(self, netmask):
    """Validates the netmask is in the bounds of acceptable IPv4 netmasks.

    Args:
      netmask: A string, either a prefix length or dotted decimal netmask.

    Returns:
      A boolean, True if the prefix length represents a valid IPv4 netmask.
    """
    if len(netmask.split('.')) == 4:
      return self._IsValidIp(netmask)
    try:
      netmask = int(netmask)
    except ValueError:
      return False
    return 0 <= netmask <= 32


class IPv6(BaseIP):
  """This class respresents and manipulates 128-bit IPv6 addresses.

  Attributes: [examples for IPv6('2001:658:22A:CAFE:200::1/64')]
    .ip: 42540616829182469433547762482097946625L
    .ip_ext: '2001:658:22a:cafe:200::1'
    .ip_ext_full: '2001:0658:022a:cafe:0200:0000:0000:0001'
    .network: 42540616829182469433403647294022090752L
    .network_ext: '2001:658:22a:cafe::'
    .hostmask: 18446744073709551615L
    .hostmask_ext: '::ffff:ffff:ffff:ffff'
    .broadcast: 42540616829182469451850391367731642367L
    .broadcast_ext: '2001:658:22a:cafe:ffff:ffff:ffff:ffff'
    .netmask: 340282366920938463444927863358058659840L
    .netmask_ext: 64
    .prefixlen: 64
  """
  _ALL_ONES = (2**128) - 1

  def __init__(self, ipaddr):
    """Instantiate a new IPv6 object.

    Args:
      ipaddr: A string or integer representing the IP or the IP and netmask.
        '2001:4860::/128'
        '2001:4860:0000:0000:0000:0000:0000:0000/128'
        '2001:4860::'
        are all functionally the same in IPv6.  That is to say, failing to
        provide a subnetmask will create an object with a mask of /128.

        Additionally, an integer can be passed, so
        IPv6('2001:4860::') == IPv6(42541956101370907050197289607612071936L).
        or, more generally
        IPv6(IPv6('2001:4860::').ip) == IPv6('2001:4860::')

    Raises:
      IPv6IpValidationError: If ipaddr isn't a valid IPv6 address.
      IPv6NetmaskValidationError: If the netmask isn't valid for an IPv6
        address.
    """
    BaseIP.__init__(self)
    self._version = 6

    # Efficient constructor from integer.
    if isinstance(ipaddr, long) or isinstance(ipaddr, int):
      self.ip = ipaddr
      self.prefixlen = 128
      self.netmask = self._ALL_ONES
      if ipaddr < 0 or ipaddr > self._ALL_ONES:
        raise IPv6IpValidationError(ipaddr)
      return

    # Assume input argument to be string or any object representation
    # which converts into a formatted IP prefix string.
    addr = str(ipaddr).split('/')
    if len(addr) > 1:
      if self._IsValidNetmask(addr[1]):
        self.prefixlen = int(addr[1])
      else:
        raise IPv6NetmaskValidationError(addr[1])
    else:
      self.prefixlen = 128

    self.netmask = self._IpIntFromPrefixlen(self.prefixlen)

    if not self._IsValidIp(addr[0]):
      raise IPv6IpValidationError(addr[0])

    self.ip = self._IpIntFromStr(addr[0])

  @property
  def ip_ext_full(self):
    """Returns the expanded version of the IPv6 string."""
    return self._ExplodeShortHandIpStr(self.ip_ext)

  def SetPrefix(self, prefixlen):
    """Change the prefix length.

    Args:
      prefixlen: An integer, the new prefix length.

    Raises:
      IPv6NetmaskValidationError: If prefixlen is out of bounds.
    """
    if not 0 <= prefixlen <= 128:
      raise IPv6NetmaskValidationError(prefixlen)
    self.prefixlen = prefixlen
    self.netmask = self._IpIntFromPrefixlen(self.prefixlen)

  def Subnet(self, prefixlen_diff=1):
    """The subnets which join to make the current subnet.

    In the case that self contains only one IP (self.prefixlen == 128),
    return a list with just ourself.

    Args:
      prefixlen_diff: An integer, the amount the prefix length should be
        increased by.

    Returns:
      A list of IPv6 objects.

    Raises:
      PrefixlenDiffInvalidError: The prefixlen_diff is too small or too large.
    """
    # Preserve original functionality (return [self] if self.prefixlen == 128).
    if self.prefixlen == 128:
      return [self]

    if prefixlen_diff < 0:
      raise PrefixlenDiffInvalidError('Prefix length diff must be > 0')
    new_prefixlen = self.prefixlen + prefixlen_diff
    if not self._IsValidNetmask(str(new_prefixlen)):
      raise PrefixlenDiffInvalidError(
          'Prefix length diff %d is invalid for netblock %s' % (
              new_prefixlen, str(self)))
    first = IPv6(
        self._StrFromIpInt(self.network) + '/' + str(self.prefixlen +
                                                     prefixlen_diff))
    subnets = [first]
    current = first
    while True:
      broadcast = current.broadcast
      if current.broadcast == self.broadcast:
        break
      current = IPv6(self._StrFromIpInt(broadcast + 1) + '/' +
                     str(new_prefixlen))
      subnets.append(current)

    return subnets

  def Supernet(self, prefixlen_diff=1):
    """The supernet containing the current network.

    Args:
      prefixlen_diff: int - Amount the prefix length of the network should be
        decreased by.  For example, given a /24 network and a prefixlen_diff of
        3, a supernet with a /21 netmask is returned.

    Returns:
      an IPv6 object.

    Raises:
      PrefixlenDiffInvalidError: If self.prefixlen - prefixlen_diff < 0. I.e.,
        you have a negative prefix length.
    """
    if self.prefixlen == 0:
      return self
    if self.prefixlen - prefixlen_diff < 0:
      raise PrefixlenDiffInvalidError(
          'current prefixlen is %d, cannot have a prefixlen_diff of %d' % (
              self.prefixlen, prefixlen_diff))
    return IPv6(self.ip_ext + '/' + str(self.prefixlen - prefixlen_diff))

  @property
  def version(self):
    return self._version

  def _IsShortHandIp(self, ip_str=None):
    """Determine if the address is shortened.

    Args:
      ip_str: A string, the IPv6 address.

    Returns:
      A boolean, True if the address is shortened.
    """
    if ip_str.count('::') == 1:
      return True
    return False

  def _ExplodeShortHandIpStr(self, ip_str):
    """Expand a shortened IPv6 address.

    Args:
      ip_str: A string, the IPv6 address.

    Returns:
      A string, the expanded IPv6 address.
    """
    if self._IsShortHandIp(ip_str):
      new_ip = []
      hextet = ip_str.split('::')
      sep = len(hextet[0].split(':')) + len(hextet[1].split(':'))
      new_ip = hextet[0].split(':')

      for _ in xrange(8 - sep):
        new_ip.append('0000')
      new_ip += hextet[1].split(':')

      # Now need to make sure every hextet is 4 lower case characters.
      # If a hextet is < 4 characters, we've got missing leading 0's.
      ret_ip = []
      for hextet in new_ip:
        ret_ip.append(('0' * (4 - len(hextet)) + hextet).lower())
      return ':'.join(ret_ip)
    # We've already got a longhand ip_str.
    return ip_str

  def _IsValidIp(self, ip_str=None):
    """Ensure we have a valid IPv6 address.

    Probably not as exhaustive as it should be.

    Args:
      ip_str: A string, the IPv6 address.

    Returns:
      A boolean, True if this is a valid IPv6 address.
    """
    if not ip_str:
      ip_str = self.ip_ext

    # We need to have at least one ':'.
    if ':' not in ip_str:
      return False

    # We can only have one '::' shortener.
    if ip_str.count('::') > 1:
      return False

    # If we have no concatenation, we need to have 8 fields with 7 ':'.
    if '::' not in ip_str and ip_str.count(':') != 7:
      # We might have an IPv4 mapped address.
      if ip_str.count('.') != 3:
        return False

    ip_str = self._ExplodeShortHandIpStr(ip_str)

    # Now that we have that all squared away, let's check that each of the
    # hextets are between 0x0 and 0xFFFF.
    for hextet in ip_str.split(':'):
      if hextet.count('.') == 3:
        # If we have an IPv4 mapped address, the IPv4 portion has to be
        # at the end of the IPv6 portion.
        if not ip_str.split(':')[-1] == hextet:
          return False
        try:
          IPv4(hextet)
        except IPv4IpValidationError:
          return False
      elif int(hextet, 16) < 0x0 or int(hextet, 16) > 0xFFFF:
        return False
    return True

  def _IsValidNetmask(self, prefixlen):
    """Validates the netmask is in the bounds of acceptable IPv6 netmasks.

    Args:
      prefixlen: A string, the netmask in prefix length format.

    Returns:
      A boolean, True if the prefix length represents a valid IPv6 netmask.
    """
    try:
      prefixlen = int(prefixlen)
    except ValueError:
      return False
    return 0 <= prefixlen <= 128

  def _IpIntFromStr(self, ip_str=None):
    """Turn an IPv6 address into an integer.

    Args:
      ip_str: A string, the IPv6 address.

    Returns:
      A long, the IPv6 address.
    """
    if not ip_str:
      ip_str = self.ip_ext

    ip_int = 0

    fields = self._ExplodeShortHandIpStr(ip_str).split(':')

    # Do we have an IPv4 mapped (::ffff:a.b.c.d) or compact (::a.b.c.d) address?
    if fields[-1].count('.') == 3:
      ipv4_string = fields.pop()
      ipv4_int = IPv4(ipv4_string).ip
      octets = []
      for _ in xrange(2):
        octets.append(hex(ipv4_int & 0xFFFF).lstrip('0x').rstrip('L'))
        ipv4_int >>= 16
      fields.extend(octets)

    for field in fields:
      ip_int = (ip_int << 16) + int(field, 16)

    return ip_int

  def _CompressHextets(self, hextets):
    """Compresses a list of hextets.

    Compresses a list of strings, replacing the longest continuous sequence of
    "0" in the list with "" and adding empty strings at the beginning or at the
    end of the string such that subsequently calling ":".join(hextets) will
    produce the compressed version of the IPv6 address.

    Args:
      hextets: The list of strings to compress.

    Returns:
      A list of strings.
    """
    best_doublecolon_start = -1
    best_doublecolon_len = 0
    doublecolon_start = -1
    doublecolon_len = 0
    for index in range(len(hextets)):
      if hextets[index] == '0':
        doublecolon_len += 1
        if doublecolon_start == -1:
          # Start of a sequence of zeros.
          doublecolon_start = index
        if doublecolon_len > best_doublecolon_len:
          # This is the longest sequence of zeros so far.
          best_doublecolon_len = doublecolon_len
          best_doublecolon_start = doublecolon_start
      else:
        doublecolon_len = 0
        doublecolon_start = -1

    if best_doublecolon_len > 1:
      best_doublecolon_end = best_doublecolon_start + best_doublecolon_len
      # For zeros at the end of the address.
      if best_doublecolon_end == len(hextets):
        hextets += ['']
      hextets[best_doublecolon_start:best_doublecolon_end] = ['']
      # For zeros at the beginning of the address.
      if best_doublecolon_start == 0:
        hextets = [''] + hextets

    return hextets

  def _StrFromIpInt(self, ip_int=None):
    """Turns a 128-bit integer into hexadecimal notation.

    Args:
      ip_int: An integer, the IP address.

    Returns:
      A string, the hexadecimal representation of the address.

    Raises:
      ValueError: The address is bigger than 128 bits of all ones.
    """
    if not ip_int and ip_int != 0:
      ip_int = self.ip

    if ip_int > self._ALL_ONES:
      raise ValueError('IPv6 address is too large')

    hex_str = '%032x' % ip_int
    hextets = []
    for x in range(0, 32, 4):
      hextets.append('%x' % int(hex_str[x:x+4], 16))

    hextets = self._CompressHextets(hextets)
    return ':'.join(hextets)

  @property
  def netmask_ext(self):
    """IPv6 extended netmask.

    We don't deal with netmasks in IPv6 like we do in IPv4.  This is here
    strictly for IPv4 compatibility.  We simply return the prefix length.

    Returns:
      An integer.
    """
    return self.prefixlen