mxbase.py

# Copyright (C) 2003-2007, 2009-2011 Nominum, Inc.
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"""MX-like base classes."""

import cStringIO
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)

    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)
        rd = dns.rdata.with_comment(tok, cls(rdclass, rdtype, preference, exchange))
        tok.get_eol()
        return rd

    from_text = classmethod(from_text)

    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)

    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 not origin is None:
            exchange = exchange.relativize(origin)
        return cls(rdclass, rdtype, preference, exchange)

    from_wire = classmethod(from_wire)

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

    def _cmp(self, other):
        sp = struct.pack("!H", self.preference)
        op = struct.pack("!H", other.preference)
        v = cmp(sp, op)
        if v == 0:
            v = cmp(self.exchange, other.exchange)
        return v

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 = cStringIO.StringIO()
        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)