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 .…    # 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.

"""Help for building DNS wire format messages"""

import cStringIO
import struct
import random
import time

import dns.exception
import dns.tsig

QUESTION = 0
ANSWER = 1
AUTHORITY = 2
ADDITIONAL = 3

class Renderer(object):
    """Helper class for building DNS wire-format messages.

    Most applications can use the higher-level L{dns.message.Message}
    class and its to_wire() method to generate wire-format messages.
    This class is for those applications which need finer control
    over the generation of messages.

    Typical use::

        r = dns.renderer.Renderer(id=1, flags=0x80, max_size=512)
        r.add_question(qname, qtype, qclass)
        r.add_rrset(dns.renderer.ANSWER, rrset_1)
        r.add_rrset(dns.renderer.ANSWER, rrset_2)
        r.add_rrset(dns.renderer.AUTHORITY, ns_rrset)
        r.add_edns(0, 0, 4096)
        r.add_rrset(dns.renderer.ADDTIONAL, ad_rrset_1)
        r.add_rrset(dns.renderer.ADDTIONAL, ad_rrset_2)
        r.write_header()
        r.add_tsig(keyname, secret, 300, 1, 0, '', request_mac)
        wire = r.get_wire()

    @ivar output: where rendering is written
    @type output: cStringIO.StringIO object
    @ivar id: the message id
    @type id: int
    @ivar flags: the message flags
    @type flags: int
    @ivar max_size: the maximum size of the message
    @type max_size: int
    @ivar origin: the origin to use when rendering relative names
    @type origin: dns.name.Name object
    @ivar compress: the compression table
    @type compress: dict
    @ivar section: the section currently being rendered
    @type section: int (dns.renderer.QUESTION, dns.renderer.ANSWER,
    dns.renderer.AUTHORITY, or dns.renderer.ADDITIONAL)
    @ivar counts: list of the number of RRs in each section
    @type counts: int list of length 4
    @ivar mac: the MAC of the rendered message (if TSIG was used)
    @type mac: string
    """

    def __init__(self, id=None, flags=0, max_size=65535, origin=None):
        """Initialize a new renderer.

        @param id: the message id
        @type id: int
        @param flags: the DNS message flags
        @type flags: int
        @param max_size: the maximum message size; the default is 65535.
        If rendering results in a message greater than I{max_size},
        then L{dns.exception.TooBig} will be raised.
        @type max_size: int
        @param origin: the origin to use when rendering relative names
        @type origin: dns.name.Namem or None.
        """

        self.output = cStringIO.StringIO()
        if id is None:
            self.id = random.randint(0, 65535)
        else:
            self.id = id
        self.flags = flags
        self.max_size = max_size
        self.origin = origin
        self.compress = {}
        self.section = QUESTION
        self.counts = [0, 0, 0, 0]
        self.output.write('\x00' * 12)
        self.mac = ''

    def _rollback(self, where):
        """Truncate the output buffer at offset I{where}, and remove any
        compression table entries that pointed beyond the truncation
        point.

        @param where: the offset
        @type where: int
        """

        self.output.seek(where)
        self.output.truncate()
        keys_to_delete = []
        for k, v in self.compress.iteritems():
            if v >= wher