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✏️ Editing: edns.py

# Copyright (C) Dnspython Contributors, see LICENSE for text of ISC license

# Copyright (C) 2009-2017 Nominum, Inc.
#
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# 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.
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# 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
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# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""EDNS Options"""

import math
import socket
import struct

import dns.enum
import dns.inet
import dns.rdata

class OptionType(dns.enum.IntEnum):
    #: NSID
    NSID = 3
    #: DAU
    DAU = 5
    #: DHU
    DHU = 6
    #: N3U
    N3U = 7
    #: ECS (client-subnet)
    ECS = 8
    #: EXPIRE
    EXPIRE = 9
    #: COOKIE
    COOKIE = 10
    #: KEEPALIVE
    KEEPALIVE = 11
    #: PADDING
    PADDING = 12
    #: CHAIN
    CHAIN = 13
    #: EDE (extended-dns-error)
    EDE = 15

@classmethod
    def _maximum(cls):
        return 65535

class Option:

"""Base class for all EDNS option types."""

def __init__(self, otype):
        """Initialize an option.

*otype*, an ``int``, is the option type.
        """
        self.otype = OptionType.make(otype)

def to_wire(self, file=None):
        """Convert an option to wire format.

Returns a ``bytes`` or ``None``.

"""
        raise NotImplementedError  # pragma: no cover

@classmethod
    def from_wire_parser(cls, otype, parser):
        """Build an EDNS option object from wire format.

*otype*, an ``int``, is the option type.

*parser*, a ``dns.wire.Parser``, the parser, which should be
        restructed to the option length.

Returns a ``dns.edns.Option``.
        """
        raise NotImplementedError  # pragma: no cover

def _cmp(self, other):
        """Compare an EDNS option with another option of the same type.

Returns < 0 if < *other*, 0 if == *other*, and > 0 if > *other*.
        """
        wire = self.to_wire()
        owire = other.to_wire()
        if wire == owire:
            return 0
        if wire > owire:
            return 1
        return -1

def __eq__(self, other):
        if not isinstance(other, Option):
            return False
        if self.otype != other.otype:
            return False
        return self._cmp(other) == 0

def __ne__(self, other):
        if not isinstance(other, Option):
            return True
        if self.otype != other.otype:
            return True
        return self._cmp(other) != 0

def __lt__(self, other):
        if not isinstance(other, Option) or \
                self.otype != other.otype:
            return NotImplemented
        return self._cmp(other) < 0

def __le__(self, other):
        if not isinstance(other, Option) or \
                self.otype != other.otype:
            return NotImplemented
        return self._cmp(other) <= 0

def __ge__(self, other):
        if not isinstance(other, Option) or \
                self.otype != other.otype:
            return NotImplemented
        return self._cmp(other) >= 0

def __gt__(self, other):
        if not isinstance(other, Option) or \
                self.otype != other.otype:
            return NotImplemented
        return self._cmp(other) > 0

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

class GenericOption(Option):

"""Generic Option Class

This class is used for EDNS option types for which we have no better
    implementation.
    """

def __init__(self, otype, data):
        super().__init__(otype)
        self.data = dns.rdata.Rdata._as_bytes(data, True)

def to_wire(self, file=None):
        if file:
            file.write(self.data)
        else:
            return self.data

def to_text(self):
        return "Generic %d" % self.otype

@classmethod
    def from_wire_parser(cls, otype, parser):
        return cls(otype, parser.get_remaining())

class ECSOption(Option):
    """EDNS Client Subnet (ECS, RFC7871)"""

def __init__(self, address, srclen=None, scopelen=0):
        """*address*, a ``str``, is the client address information.

*srclen*, an ``int``, the source prefix length, which is the
        leftmost number of bits of the address to be used for the
        lookup.  The default is 24 for IPv4 and 56 for IPv6.

*scopelen*, an ``int``, the scope prefix length.  This value
        must be 0 in queries, and should be set in responses.
        """

super().__init__(OptionType.ECS)
        af = dns.inet.af_for_address(address)

if af == socket.AF_INET6:
            self.family = 2
            if srclen is None:
                srclen = 56
            address = dns.rdata.Rdata._as_ipv6_address(address)
            srclen = dns.rdata.Rdata._as_int(srclen, 0, 128)
            scopelen = dns.rdata.Rdata._as_int(scopelen, 0, 128)
        elif af == socket.AF_INET:
            self.family = 1
            if srclen is None:
                srclen = 24
            address = dns.rdata.Rdata._as_ipv4_address(address)
            srclen = dns.rdata.Rdata._as_int(srclen, 0, 32)
            scopelen = dns.rdata.Rdata._as_int(scopelen, 0, 32)
        else:  # pragma: no cover   (this will never happen)
            raise ValueError('Bad address family')

self.address = address
        self.srclen = srclen
        self.scopelen = scopelen

addrdata = dns.inet.inet_pton(af, address)
        nbytes = int(math.ceil(srclen / 8.0))

# Truncate to srclen and pad to the end of the last octet needed
        # See RFC section 6
        self.addrdata = addrdata[:nbytes]
        nbits = srclen % 8
        if nbits != 0:
            last = struct.pack('B',
                               ord(self.addrdata[-1:]) & (0xff << (8 - nbits)))
            self.addrdata = self.addrdata[:-1] + last

def to_text(self):
        return "ECS {}/{} scope/{}".format(self.address, self.srclen,
                                           self.scopelen)

@staticmethod
    def from_text(text):
        """Convert a string into a `dns.edns.ECSOption`

*text*, a `str`, the text form of the option.

Returns a `dns.edns.ECSOption`.

Examples:

>>> import dns.edns
        >>>
        >>> # basic example
        >>> dns.edns.ECSOption.from_text('1.2.3.4/24')
        >>>
        >>> # also understands scope
        >>> dns.edns.ECSOption.from_text('1.2.3.4/24/32')
        >>>
        >>> # IPv6
        >>> dns.edns.ECSOption.from_text('2001:4b98::1/64/64')
        >>>
        >>> # it understands results from `dns.edns.ECSOption.to_text()`
        >>> dns.edns.ECSOption.from_text('ECS 1.2.3.4/24/32')
        """
        optional_prefix = 'ECS'
        tokens = text.split()
        ecs_text = None
        if len(tokens) == 1:
            ecs_text = tokens[0]
        elif len(tokens) == 2:
            if tokens[0] != optional_prefix:
                raise ValueError('could not parse ECS from "{}"'.format(text))
            ecs_text = tokens[1]
        else:
            raise ValueError('could not parse ECS from "{}"'.format(text))
        n_slashes = ecs_text.count('/')
        if n_slashes == 1:
            address, srclen = ecs_text.split('/')
            scope = 0
        elif n_slashes == 2:
            address, srclen, scope = ecs_text.split('/')
        else:
            raise ValueError('could not parse ECS from "{}"'.format(text))
        try:
            scope = int(scope)
        except ValueError:
            raise ValueError('invalid scope ' +
                             '"{}": scope must be an integer'.format(scope))
        try:
            srclen = int(srclen)
        except ValueError:
            raise ValueError('invalid srclen ' +
                             '"{}": srclen must be an integer'.format(srclen))
        return ECSOption(address, srclen, scope)

def to_wire(self, file=None):
        value = (struct.pack('!HBB', self.family, self.srclen, self.scopelen) +
                 self.addrdata)
        if file:
            file.write(value)
        else:
            return value

@classmethod
    def from_wire_parser(cls, otype, parser):
        family, src, scope = parser.get_struct('!HBB')
        addrlen = int(math.ceil(src / 8.0))
        prefix = parser.get_bytes(addrlen)
        if family == 1:
            pad = 4 - addrlen
            addr = dns.ipv4.inet_ntoa(prefix + b'\x00' * pad)
        elif family == 2:
            pad = 16 - addrlen
            addr = dns.ipv6.inet_ntoa(prefix + b'\x00' * pad)
        else:
            raise ValueError('unsupported family')

return cls(addr, src, scope)

class EDECode(dns.enum.IntEnum):
    OTHER = 0
    UNSUPPORTED_DNSKEY_ALGORITHM = 1
    UNSUPPORTED_DS_DIGEST_TYPE = 2
    STALE_ANSWER = 3
    FORGED_ANSWER = 4
    DNSSEC_INDETERMINATE = 5
    DNSSEC_BOGUS = 6
    SIGNATURE_EXPIRED = 7
    SIGNATURE_NOT_YET_VALID = 8
    DNSKEY_MISSING = 9
    RRSIGS_MISSING = 10
    NO_ZONE_KEY_BIT_SET = 11
    NSEC_MISSING = 12
    CACHED_ERROR = 13
    NOT_READY = 14
    BLOCKED = 15
    CENSORED = 16
    FILTERED = 17
    PROHIBITED = 18
    STALE_NXDOMAIN_ANSWER = 19
    NOT_AUTHORITATIVE = 20
    NOT_SUPPORTED = 21
    NO_REACHABLE_AUTHORITY = 22
    NETWORK_ERROR = 23
    INVALID_DATA = 24

@classmethod
    def _maximum(cls):
        return 65535

class EDEOption(Option):
    """Extended DNS Error (EDE, RFC8914)"""

def __init__(self, code, text=None):
        """*code*, a ``dns.edns.EDECode`` or ``str``, the info code of the
        extended error.

*text*, a ``str`` or ``None``, specifying additional information about
        the error.
        """

super().__init__(OptionType.EDE)

self.code = EDECode.make(code)
        if text is not None and not isinstance(text, str):
            raise ValueError('text must be string or None')

self.code = code
        self.text = text

def to_text(self):
        output = f'EDE {self.code}'
        if self.text is not None:
            output += f': {self.text}'
        return output

def to_wire(self, file=None):
        value = struct.pack('!H', self.code)
        if self.text is not None:
            value += self.text.encode('utf8')

if file:
            file.write(value)
        else:
            return value

@classmethod
    def from_wire_parser(cls, otype, parser):
        code = parser.get_uint16()
        text = parser.get_remaining()

if text:
            if text[-1] == 0:  # text MAY be null-terminated
                text = text[:-1]
            text = text.decode('utf8')
        else:
            text = None

return cls(code, text)

_type_to_class = {
    OptionType.ECS: ECSOption,
    OptionType.EDE: EDEOption,
}

def get_option_class(otype):
    """Return the class for the specified option type.

The GenericOption class is used if a more specific class is not
    known.
    """

cls = _type_to_class.get(otype)
    if cls is None:
        cls = GenericOption
    return cls

def option_from_wire_parser(otype, parser):
    """Build an EDNS option object from wire format.

*otype*, an ``int``, is the option type.

*parser*, a ``dns.wire.Parser``, the parser, which should be
    restricted to the option length.

Returns an instance of a subclass of ``dns.edns.Option``.
    """
    cls = get_option_class(otype)
    otype = OptionType.make(otype)
    return cls.from_wire_parser(otype, parser)

def option_from_wire(otype, wire, current, olen):
    """Build an EDNS option object from wire format.

*otype*, an ``int``, is the option type.

*wire*, a ``bytes``, is the wire-format message.

*current*, an ``int``, is the offset in *wire* of the beginning
    of the rdata.

*olen*, an ``int``, is the length of the wire-format option data

Returns an instance of a subclass of ``dns.edns.Option``.
    """
    parser = dns.wire.Parser(wire, current)
    with parser.restrict_to(olen):
        return option_from_wire_parser(otype, parser)

def register_type(implementation, otype):
    """Register the implementation of an option type.

*implementation*, a ``class``, is a subclass of ``dns.edns.Option``.

*otype*, an ``int``, is the option type.
    """

_type_to_class[otype] = implementation

### BEGIN generated OptionType constants

NSID = OptionType.NSID
DAU = OptionType.DAU
DHU = OptionType.DHU
N3U = OptionType.N3U
ECS = OptionType.ECS
EXPIRE = OptionType.EXPIRE
COOKIE = OptionType.COOKIE
KEEPALIVE = OptionType.KEEPALIVE
PADDING = OptionType.PADDING
CHAIN = OptionType.CHAIN
EDE = OptionType.EDE

### END generated OptionType constants

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