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Filename : mxbase.py
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# Copyright (C) 2003-2007, 2009-2011 Nominum, Inc.
#
# Permission to use, copy, modify, and distribute this software and its
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# 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
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# OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

"""MX-like base classes."""

from io import BytesIO
import struct

import dns.exception
import dns.rdata
import dns.name


class MXBase(dns.rdata.Rdata):

    """Base class for rdata that is like an MX record.

    @ivar preference: the preference value
    @type preference: int
    @ivar exchange: the exchange name
    @type exchange: dns.name.Name object"""

    __slots__ = ['preference', 'exchange']

    def __init__(self, rdclass, rdtype, preference, exchange):
        super(MXBase, self).__init__(rdclass, rdtype)
        self.preference = preference
        self.exchange = exchange

    def to_text(self, origin=None, relativize=True, **kw):
        exchange = self.exchange.choose_relativity(origin, relativize)
        return '%d %s' % (self.preference, exchange)

    @classmethod
    def from_text(cls, rdclass, rdtype, tok, origin=None, relativize=True):
        preference = tok.get_uint16()
        exchange = tok.get_name()
        exchange = exchange.choose_relativity(origin, relativize)
        tok.get_eol()
        return cls(rdclass, rdtype, preference, exchange)

    def to_wire(self, file, compress=None, origin=None):
        pref = struct.pack("!H", self.preference)
        file.write(pref)
        self.exchange.to_wire(file, compress, origin)

    def to_digestable(self, origin=None):
        return struct.pack("!H", self.preference) + \
            self.exchange.to_digestable(origin)

    @classmethod
    def from_wire(cls, rdclass, rdtype, wire, current, rdlen, origin=None):
        (preference, ) = struct.unpack('!H', wire[current: current + 2])
        current += 2
        rdlen -= 2
        (exchange, cused) = dns.name.from_wire(wire[: current + rdlen],
                                               current)
        if cused != rdlen:
            raise dns.exception.FormError
        if origin is not None:
            exchange = exchange.relativize(origin)
        return cls(rdclass, rdtype, preference, exchange)

    def choose_relativity(self, origin=None, relativize=True):
        self.exchange = self.exchange.choose_relativity(origin, relativize)


class UncompressedMX(MXBase):

    """Base class for rdata that is like an MX record, but whose name
    is not compressed when converted to DNS wire format, and whose
    digestable form is not downcased."""

    def to_wire(self, file, compress=None, origin=None):
        super(UncompressedMX, self).to_wire(file, None, origin)

    def to_digestable(self, origin=None):
        f = BytesIO()
        self.to_wire(f, None, origin)
        return f.getvalue()


class UncompressedDowncasingMX(MXBase):

    """Base class for rdata that is like an MX record, but whose name
    is not compressed when convert to DNS wire format."""

    def to_wire(self, file, compress=None, origin=None):
        super(UncompressedDowncasingMX, self).to_wire(file, None, origin)