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편집 파일: name.py

# Copyright (C) 2001-2007, 2009-2011 Nominum, Inc.
#
# Permission to use, copy, modify, and distribute this software and its
# documentation for any purpose with or without fee is hereby granted,
# provided that the above copyright notice and this permission notice
# appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND NOMINUM DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL NOMINUM BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""DNS Names.

@var root: The DNS root name.
@type root: dns.name.Name object
@var empty: The empty DNS name.
@type empty: dns.name.Name object
"""

from io import BytesIO
import struct
import sys
import copy
import encodings.idna
try:
    import idna
    have_idna_2008 = True
except ImportError:
    have_idna_2008 = False

import dns.exception
import dns.wiredata

from ._compat import long, binary_type, text_type, unichr, maybe_decode

try:
    maxint = sys.maxint
except AttributeError:
    maxint = (1 << (8 * struct.calcsize("P"))) // 2 - 1

NAMERELN_NONE = 0
NAMERELN_SUPERDOMAIN = 1
NAMERELN_SUBDOMAIN = 2
NAMERELN_EQUAL = 3
NAMERELN_COMMONANCESTOR = 4

class EmptyLabel(dns.exception.SyntaxError):

"""A DNS label is empty."""

class BadEscape(dns.exception.SyntaxError):

"""An escaped code in a text format of DNS name is invalid."""

class BadPointer(dns.exception.FormError):

"""A DNS compression pointer points forward instead of backward."""

class BadLabelType(dns.exception.FormError):

"""The label type in DNS name wire format is unknown."""

class NeedAbsoluteNameOrOrigin(dns.exception.DNSException):

"""An attempt was made to convert a non-absolute name to
    wire when there was also a non-absolute (or missing) origin."""

class NameTooLong(dns.exception.FormError):

"""A DNS name is > 255 octets long."""

class LabelTooLong(dns.exception.SyntaxError):

"""A DNS label is > 63 octets long."""

class AbsoluteConcatenation(dns.exception.DNSException):

"""An attempt was made to append anything other than the
    empty name to an absolute DNS name."""

class NoParent(dns.exception.DNSException):

"""An attempt was made to get the parent of the root name
    or the empty name."""

class NoIDNA2008(dns.exception.DNSException):

"""IDNA 2008 processing was requested but the idna module is not
    available."""

class IDNAException(dns.exception.DNSException):

"""IDNA processing raised an exception."""

supp_kwargs = set(['idna_exception'])
    fmt = "IDNA processing exception: {idna_exception}"

class IDNACodec(object):

"""Abstract base class for IDNA encoder/decoders."""

def __init__(self):
        pass

def is_idna(self, label):
        return label.lower().startswith(b'xn--')

def is_all_ascii(self, label):
        for c in label:
            if ord(c) > 0x7f:
                return False
        return True

def encode(self, label):
        raise NotImplementedError

def decode(self, label):
        # We do not apply any IDNA policy on decode.
        if self.is_idna(label):
            try:
                label = label[4:].decode('punycode')
            except Exception as e:
                raise IDNAException(idna_exception=e)
        else:
            label = maybe_decode(label)
        return _escapify(label)

class IDNA2003Codec(IDNACodec):

"""IDNA 2003 encoder/decoder."""

def __init__(self, strict_decode=False):
        """Initialize the IDNA 2003 encoder/decoder.
        @param strict_decode: If True, then IDNA2003 checking is done when
        decoding.  This can cause failures if the name was encoded with
        IDNA2008.  The default is False.
        @type strict_decode: bool
        """
        super(IDNA2003Codec, self).__init__()
        self.strict_decode = strict_decode

def encode(self, label):
        if label == '':
            return b''
        try:
            return encodings.idna.ToASCII(label)
        except UnicodeError:
            raise LabelTooLong

def decode(self, label):
        if not self.strict_decode:
            return super(IDNA2003Codec, self).decode(label)
        if label == b'':
            return u''
        try:
            return _escapify(encodings.idna.ToUnicode(label))
        except Exception as e:
            raise IDNAException(idna_exception=e)

class IDNA2008Codec(IDNACodec):

"""IDNA 2008 encoder/decoder."""

def __init__(self, uts_46=False, transitional=False,
                 allow_pure_ascii=False, strict_decode=False):
        """Initialize the IDNA 2008 encoder/decoder.
        @param uts_46: If True, apply Unicode IDNA compatibility processing
        as described in Unicode Technical Standard #46
        (U{http://unicode.org/reports/tr46/}).  This parameter is only
        meaningful if IDNA 2008 is in use.  If False, do not apply
        the mapping.  The default is False
        @type uts_46: bool
        @param transitional: If True, use the "transitional" mode described
        in Unicode Technical Standard #46.  This parameter is only
        meaningful if IDNA 2008 is in use.  The default is False.
        @type transitional: bool
        @param allow_pure_ascii: If True, then a label which
        consists of only ASCII characters is allowed.  This is less strict
        than regular IDNA 2008, but is also necessary for mixed names,
        e.g. a name with starting with "_sip._tcp." and ending in an IDN
        suffixm which would otherwise be disallowed.  The default is False
        @type allow_pure_ascii: bool
        @param strict_decode: If True, then IDNA2008 checking is done when
        decoding.  This can cause failures if the name was encoded with
        IDNA2003.  The default is False.
        @type strict_decode: bool
        """
        super(IDNA2008Codec, self).__init__()
        self.uts_46 = uts_46
        self.transitional = transitional
        self.allow_pure_ascii = allow_pure_ascii
        self.strict_decode = strict_decode

def encode(self, label):
        if label == '':
            return b''
        if self.allow_pure_ascii and self.is_all_ascii(label):
            return label.encode('ascii')
        if not have_idna_2008:
            raise NoIDNA2008
        try:
            if self.uts_46:
                label = idna.uts46_remap(label, False, self.transitional)
            return idna.alabel(label)
        except idna.IDNAError as e:
            raise IDNAException(idna_exception=e)

def decode(self, label):
        if not self.strict_decode:
            return super(IDNA2008Codec, self).decode(label)
        if label == b'':
            return u''
        if not have_idna_2008:
            raise NoIDNA2008
        try:
            if self.uts_46:
                label = idna.uts46_remap(label, False, False)
            return _escapify(idna.ulabel(label))
        except idna.IDNAError as e:
            raise IDNAException(idna_exception=e)

_escaped = bytearray(b'"().;\\@$')
_escaped_text = '"().;\\@$'

IDNA_2003_Practical = IDNA2003Codec(False)
IDNA_2003_Strict = IDNA2003Codec(True)
IDNA_2003 = IDNA_2003_Practical
IDNA_2008_Practical = IDNA2008Codec(True, False, True, False)
IDNA_2008_UTS_46 = IDNA2008Codec(True, False, False, False)
IDNA_2008_Strict = IDNA2008Codec(False, False, False, True)
IDNA_2008_Transitional = IDNA2008Codec(True, True, False, False)
IDNA_2008 = IDNA_2008_Practical

def _escapify(label):
    """Escape the characters in label which need it.
    @returns: the escaped string
    @rtype: string"""
    if isinstance(label, bytes):
        # Ordinary DNS label mode.  Escape special characters and values
        # < 0x20 or > 0x7f.
        text = ''
        if isinstance(label, text_type):
            label = label.encode()
        for c in bytearray(label):
            if c in _escaped:
                text += '\\' + chr(c)
            elif c > 0x20 and c < 0x7F:
                text += chr(c)
            else:
                text += '\\%03d' % c
        return text

# Unicode label mode.  Escape only special characters and values < 0x20
    text = u''
    for c in label:
        if c in _escaped_text:
            text += '\\' + c
        elif c <= '\x20':
            text += '\\%03d' % ord(c)
        else:
            text += c
    return text

def _validate_labels(labels):
    """Check for empty labels in the middle of a label sequence,
    labels that are too long, and for too many labels.
    @raises NameTooLong: the name as a whole is too long
    @raises EmptyLabel: a label is empty (i.e. the root label) and appears
    in a position other than the end of the label sequence"""

l = len(labels)
    total = 0
    i = -1
    j = 0
    for label in labels:
        ll = len(label)
        total += ll + 1
        if ll > 63:
            raise LabelTooLong
        if i < 0 and label == b'':
            i = j
        j += 1
    if total > 255:
        raise NameTooLong
    if i >= 0 and i != l - 1:
        raise EmptyLabel

def _ensure_bytes(label):
    if isinstance(label, binary_type):
        return label
    if isinstance(label, text_type):
        return label.encode()
    raise ValueError

class Name(object):

"""A DNS name.

The dns.name.Name class represents a DNS name as a tuple of labels.
    Instances of the class are immutable.

@ivar labels: The tuple of labels in the name. Each label is a string of
    up to 63 octets."""

__slots__ = ['labels']

def __init__(self, labels):
        """Initialize a domain name from a list of labels.
        @param labels: the labels
        @type labels: any iterable whose values are strings
        """
        labels = [_ensure_bytes(x) for x in labels]
        super(Name, self).__setattr__('labels', tuple(labels))
        _validate_labels(self.labels)

def __setattr__(self, name, value):
        raise TypeError("object doesn't support attribute assignment")

def __copy__(self):
        return Name(self.labels)

def __deepcopy__(self, memo):
        return Name(copy.deepcopy(self.labels, memo))

def __getstate__(self):
        return {'labels': self.labels}

def __setstate__(self, state):
        super(Name, self).__setattr__('labels', state['labels'])
        _validate_labels(self.labels)

def is_absolute(self):
        """Is the most significant label of this name the root label?
        @rtype: bool
        """

return len(self.labels) > 0 and self.labels[-1] == b''

def is_wild(self):
        """Is this name wild?  (I.e. Is the least significant label '*'?)
        @rtype: bool
        """

return len(self.labels) > 0 and self.labels[0] == b'*'

def __hash__(self):
        """Return a case-insensitive hash of the name.
        @rtype: int
        """

h = long(0)
        for label in self.labels:
            for c in bytearray(label.lower()):
                h += (h << 3) + c
        return int(h % maxint)

def fullcompare(self, other):
        """Compare two names, returning a 3-tuple (relation, order, nlabels).

I{relation} describes the relation ship between the names,
        and is one of: dns.name.NAMERELN_NONE,
        dns.name.NAMERELN_SUPERDOMAIN, dns.name.NAMERELN_SUBDOMAIN,
        dns.name.NAMERELN_EQUAL, or dns.name.NAMERELN_COMMONANCESTOR

I{order} is < 0 if self < other, > 0 if self > other, and ==
        0 if self == other.  A relative name is always less than an
        absolute name.  If both names have the same relativity, then
        the DNSSEC order relation is used to order them.

I{nlabels} is the number of significant labels that the two names
        have in common.
        """

sabs = self.is_absolute()
        oabs = other.is_absolute()
        if sabs != oabs:
            if sabs:
                return (NAMERELN_NONE, 1, 0)
            else:
                return (NAMERELN_NONE, -1, 0)
        l1 = len(self.labels)
        l2 = len(other.labels)
        ldiff = l1 - l2
        if ldiff < 0:
            l = l1
        else:
            l = l2

order = 0
        nlabels = 0
        namereln = NAMERELN_NONE
        while l > 0:
            l -= 1
            l1 -= 1
            l2 -= 1
            label1 = self.labels[l1].lower()
            label2 = other.labels[l2].lower()
            if label1 < label2:
                order = -1
                if nlabels > 0:
                    namereln = NAMERELN_COMMONANCESTOR
                return (namereln, order, nlabels)
            elif label1 > label2:
                order = 1
                if nlabels > 0:
                    namereln = NAMERELN_COMMONANCESTOR
                return (namereln, order, nlabels)
            nlabels += 1
        order = ldiff
        if ldiff < 0:
            namereln = NAMERELN_SUPERDOMAIN
        elif ldiff > 0:
            namereln = NAMERELN_SUBDOMAIN
        else:
            namereln = NAMERELN_EQUAL
        return (namereln, order, nlabels)

def is_subdomain(self, other):
        """Is self a subdomain of other?

The notion of subdomain includes equality.
        @rtype: bool
        """

(nr, o, nl) = self.fullcompare(other)
        if nr == NAMERELN_SUBDOMAIN or nr == NAMERELN_EQUAL:
            return True
        return False

def is_superdomain(self, other):
        """Is self a superdomain of other?

The notion of subdomain includes equality.
        @rtype: bool
        """

(nr, o, nl) = self.fullcompare(other)
        if nr == NAMERELN_SUPERDOMAIN or nr == NAMERELN_EQUAL:
            return True
        return False

def canonicalize(self):
        """Return a name which is equal to the current name, but is in
        DNSSEC canonical form.
        @rtype: dns.name.Name object
        """

return Name([x.lower() for x in self.labels])

def __eq__(self, other):
        if isinstance(other, Name):
            return self.fullcompare(other)[1] == 0
        else:
            return False

def __ne__(self, other):
        if isinstance(other, Name):
            return self.fullcompare(other)[1] != 0
        else:
            return True

def __lt__(self, other):
        if isinstance(other, Name):
            return self.fullcompare(other)[1] < 0
        else:
            return NotImplemented

def __le__(self, other):
        if isinstance(other, Name):
            return self.fullcompare(other)[1] <= 0
        else:
            return NotImplemented

def __ge__(self, other):
        if isinstance(other, Name):
            return self.fullcompare(other)[1] >= 0
        else:
            return NotImplemented

def __gt__(self, other):
        if isinstance(other, Name):
            return self.fullcompare(other)[1] > 0
        else:
            return NotImplemented

def __repr__(self):
        return '<DNS name ' + self.__str__() + '>'

def __str__(self):
        return self.to_text(False)

def to_text(self, omit_final_dot=False):
        """Convert name to text format.
        @param omit_final_dot: If True, don't emit the final dot (denoting the
        root label) for absolute names.  The default is False.
        @rtype: string
        """

if len(self.labels) == 0:
            return maybe_decode(b'@')
        if len(self.labels) == 1 and self.labels[0] == b'':
            return maybe_decode(b'.')
        if omit_final_dot and self.is_absolute():
            l = self.labels[:-1]
        else:
            l = self.labels
        s = '.'.join(map(_escapify, l))
        return s

def to_unicode(self, omit_final_dot=False, idna_codec=None):
        """Convert name to Unicode text format.

IDN ACE labels are converted to Unicode.

@param omit_final_dot: If True, don't emit the final dot (denoting the
        root label) for absolute names.  The default is False.
        @type omit_final_dot: bool
        @param idna_codec: IDNA encoder/decoder.  If None, the
        IDNA_2003_Practical encoder/decoder is used.  The IDNA_2003_Practical
        decoder does not impose any policy, it just decodes punycode, so if
        you don't want checking for compliance, you can use this decoder for
        IDNA2008 as well.
        @type idna_codec: dns.name.IDNA
        @rtype: string
        """

if len(self.labels) == 0:
            return u'@'
        if len(self.labels) == 1 and self.labels[0] == b'':
            return u'.'
        if omit_final_dot and self.is_absolute():
            l = self.labels[:-1]
        else:
            l = self.labels
        if idna_codec is None:
            idna_codec = IDNA_2003_Practical
        return u'.'.join([idna_codec.decode(x) for x in l])

def to_digestable(self, origin=None):
        """Convert name to a format suitable for digesting in hashes.

The name is canonicalized and converted to uncompressed wire format.

@param origin: If the name is relative and origin is not None, then
        origin will be appended to it.
        @type origin: dns.name.Name object
        @raises NeedAbsoluteNameOrOrigin: All names in wire format are
        absolute.  If self is a relative name, then an origin must be supplied;
        if it is missing, then this exception is raised
        @rtype: string
        """

def to_wire(self, file=None, compress=None, origin=None):
        """Convert name to wire format, possibly compressing it.

@param file: the file where the name is emitted (typically
        a BytesIO file).  If None, a string containing the wire name
        will be returned.
        @type file: file or None
        @param compress: The compression table.  If None (the default) names
        will not be compressed.
        @type compress: dict
        @param origin: If the name is relative and origin is not None, then
        origin will be appended to it.
        @type origin: dns.name.Name object
        @raises NeedAbsoluteNameOrOrigin: All names in wire format are
        absolute.  If self is a relative name, then an origin must be supplied;
        if it is missing, then this exception is raised
        """

if file is None:
            file = BytesIO()
            want_return = True
        else:
            want_return = False

if not self.is_absolute():
            if origin is None or not origin.is_absolute():
                raise NeedAbsoluteNameOrOrigin
            labels = list(self.labels)
            labels.extend(list(origin.labels))
        else:
            labels = self.labels
        i = 0
        for label in labels:
            n = Name(labels[i:])
            i += 1
            if compress is not None:
                pos = compress.get(n)
            else:
                pos = None
            if pos is not None:
                value = 0xc000 + pos
                s = struct.pack('!H', value)
                file.write(s)
                break
            else:
                if compress is not None and len(n) > 1:
                    pos = file.tell()
                    if pos <= 0x3fff:
                        compress[n] = pos
                l = len(label)
                file.write(struct.pack('!B', l))
                if l > 0:
                    file.write(label)
        if want_return:
            return file.getvalue()

def __len__(self):
        """The length of the name (in labels).
        @rtype: int
        """

return len(self.labels)

def __getitem__(self, index):
        return self.labels[index]

def __add__(self, other):
        return self.concatenate(other)

def __sub__(self, other):
        return self.relativize(other)

def split(self, depth):
        """Split a name into a prefix and suffix at depth.

@param depth: the number of labels in the suffix
        @type depth: int
        @raises ValueError: the depth was not >= 0 and <= the length of the
        name.
        @returns: the tuple (prefix, suffix)
        @rtype: tuple
        """

l = len(self.labels)
        if depth == 0:
            return (self, dns.name.empty)
        elif depth == l:
            return (dns.name.empty, self)
        elif depth < 0 or depth > l:
            raise ValueError(
                'depth must be >= 0 and <= the length of the name')
        return (Name(self[: -depth]), Name(self[-depth:]))

def concatenate(self, other):
        """Return a new name which is the concatenation of self and other.
        @rtype: dns.name.Name object
        @raises AbsoluteConcatenation: self is absolute and other is
        not the empty name
        """

if self.is_absolute() and len(other) > 0:
            raise AbsoluteConcatenation
        labels = list(self.labels)
        labels.extend(list(other.labels))
        return Name(labels)

def relativize(self, origin):
        """If self is a subdomain of origin, return a new name which is self
        relative to origin.  Otherwise return self.
        @rtype: dns.name.Name object
        """

if origin is not None and self.is_subdomain(origin):
            return Name(self[: -len(origin)])
        else:
            return self

def derelativize(self, origin):
        """If self is a relative name, return a new name which is the
        concatenation of self and origin.  Otherwise return self.
        @rtype: dns.name.Name object
        """

if not self.is_absolute():
            return self.concatenate(origin)
        else:
            return self

def choose_relativity(self, origin=None, relativize=True):
        """Return a name with the relativity desired by the caller.  If
        origin is None, then self is returned.  Otherwise, if
        relativize is true the name is relativized, and if relativize is
        false the name is derelativized.
        @rtype: dns.name.Name object
        """

if origin:
            if relativize:
                return self.relativize(origin)
            else:
                return self.derelativize(origin)
        else:
            return self

def parent(self):
        """Return the parent of the name.
        @rtype: dns.name.Name object
        @raises NoParent: the name is either the root name or the empty name,
        and thus has no parent.
        """
        if self == root or self == empty:
            raise NoParent
        return Name(self.labels[1:])

root = Name([b''])
empty = Name([])

def from_unicode(text, origin=root, idna_codec=None):
    """Convert unicode text into a Name object.

Labels are encoded in IDN ACE form.

@param text: The text to convert into a name.
    @type text: Unicode string
    @param origin: The origin to append to non-absolute names.
    @type origin: dns.name.Name
    @param idna_codec: IDNA encoder/decoder.  If None, the default IDNA 2003
    encoder/decoder is used.
    @type idna_codec: dns.name.IDNA
    @rtype: dns.name.Name object
    """

if not isinstance(text, text_type):
        raise ValueError("input to from_unicode() must be a unicode string")
    if not (origin is None or isinstance(origin, Name)):
        raise ValueError("origin must be a Name or None")
    labels = []
    label = u''
    escaping = False
    edigits = 0
    total = 0
    if idna_codec is None:
        idna_codec = IDNA_2003
    if text == u'@':
        text = u''
    if text:
        if text == u'.':
            return Name([b''])        # no Unicode "u" on this constant!
        for c in text:
            if escaping:
                if edigits == 0:
                    if c.isdigit():
                        total = int(c)
                        edigits += 1
                    else:
                        label += c
                        escaping = False
                else:
                    if not c.isdigit():
                        raise BadEscape
                    total *= 10
                    total += int(c)
                    edigits += 1
                    if edigits == 3:
                        escaping = False
                        label += unichr(total)
            elif c in [u'.', u'\u3002', u'\uff0e', u'\uff61']:
                if len(label) == 0:
                    raise EmptyLabel
                labels.append(idna_codec.encode(label))
                label = u''
            elif c == u'\\':
                escaping = True
                edigits = 0
                total = 0
            else:
                label += c
        if escaping:
            raise BadEscape
        if len(label) > 0:
            labels.append(idna_codec.encode(label))
        else:
            labels.append(b'')

if (len(labels) == 0 or labels[-1] != b'') and origin is not None:
        labels.extend(list(origin.labels))
    return Name(labels)

def from_text(text, origin=root, idna_codec=None):
    """Convert text into a Name object.

@param text: The text to convert into a name.
    @type text: string
    @param origin: The origin to append to non-absolute names.
    @type origin: dns.name.Name
    @param idna_codec: IDNA encoder/decoder.  If None, the default IDNA 2003
    encoder/decoder is used.
    @type idna_codec: dns.name.IDNA
    @rtype: dns.name.Name object
    """

if isinstance(text, text_type):
        return from_unicode(text, origin, idna_codec)
    if not isinstance(text, binary_type):
        raise ValueError("input to from_text() must be a string")
    if not (origin is None or isinstance(origin, Name)):
        raise ValueError("origin must be a Name or None")
    labels = []
    label = b''
    escaping = False
    edigits = 0
    total = 0
    if text == b'@':
        text = b''
    if text:
        if text == b'.':
            return Name([b''])
        for c in bytearray(text):
            byte_ = struct.pack('!B', c)
            if escaping:
                if edigits == 0:
                    if byte_.isdigit():
                        total = int(byte_)
                        edigits += 1
                    else:
                        label += byte_
                        escaping = False
                else:
                    if not byte_.isdigit():
                        raise BadEscape
                    total *= 10
                    total += int(byte_)
                    edigits += 1
                    if edigits == 3:
                        escaping = False
                        label += struct.pack('!B', total)
            elif byte_ == b'.':
                if len(label) == 0:
                    raise EmptyLabel
                labels.append(label)
                label = b''
            elif byte_ == b'\\':
                escaping = True
                edigits = 0
                total = 0
            else:
                label += byte_
        if escaping:
            raise BadEscape
        if len(label) > 0:
            labels.append(label)
        else:
            labels.append(b'')
    if (len(labels) == 0 or labels[-1] != b'') and origin is not None:
        labels.extend(list(origin.labels))
    return Name(labels)

def from_wire(message, current):
    """Convert possibly compressed wire format into a Name.
    @param message: the entire DNS message
    @type message: string
    @param current: the offset of the beginning of the name from the start
    of the message
    @type current: int
    @raises dns.name.BadPointer: a compression pointer did not point backwards
    in the message
    @raises dns.name.BadLabelType: an invalid label type was encountered.
    @returns: a tuple consisting of the name that was read and the number
    of bytes of the wire format message which were consumed reading it
    @rtype: (dns.name.Name object, int) tuple
    """

if not isinstance(message, binary_type):
        raise ValueError("input to from_wire() must be a byte string")
    message = dns.wiredata.maybe_wrap(message)
    labels = []
    biggest_pointer = current
    hops = 0
    count = message[current]
    current += 1
    cused = 1
    while count != 0:
        if count < 64:
            labels.append(message[current: current + count].unwrap())
            current += count
            if hops == 0:
                cused += count
        elif count >= 192:
            current = (count & 0x3f) * 256 + message[current]
            if hops == 0:
                cused += 1
            if current >= biggest_pointer:
                raise BadPointer
            biggest_pointer = current
            hops += 1
        else:
            raise BadLabelType
        count = message[current]
        current += 1
        if hops == 0:
            cused += 1
    labels.append('')
    return (Name(labels), cused)