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Filename : query.py
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# Copyright (C) 2003-2007, 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.

"""Talk to a DNS server."""

from __future__ import generators

import errno
import select
import socket
import struct
import sys
import time

import dns.exception
import dns.inet
import dns.name
import dns.message
import dns.rdataclass
import dns.rdatatype
from ._compat import long, string_types

if sys.version_info > (3,):
    select_error = OSError
else:
    select_error = select.error

# Function used to create a socket.  Can be overridden if needed in special
# situations.
socket_factory = socket.socket

class UnexpectedSource(dns.exception.DNSException):

    """A DNS query response came from an unexpected address or port."""


class BadResponse(dns.exception.FormError):

    """A DNS query response does not respond to the question asked."""


def _compute_expiration(timeout):
    if timeout is None:
        return None
    else:
        return time.time() + timeout


def _poll_for(fd, readable, writable, error, timeout):
    """Poll polling backend.
    @param fd: File descriptor
    @type fd: int
    @param readable: Whether to wait for readability
    @type readable: bool
    @param writable: Whether to wait for writability
    @type writable: bool
    @param timeout: Deadline timeout (expiration time, in seconds)
    @type timeout: float
    @return True on success, False on timeout
    """
    event_mask = 0
    if readable:
        event_mask |= select.POLLIN
    if writable:
        event_mask |= select.POLLOUT
    if error:
        event_mask |= select.POLLERR

    pollable = select.poll()
    pollable.register(fd, event_mask)

    if timeout:
        event_list = pollable.poll(long(timeout * 1000))
    else:
        event_list = pollable.poll()

    return bool(event_list)


def _select_for(fd, readable, writable, error, timeout):
    """Select polling backend.
    @param fd: File descriptor
    @type fd: int
    @param readable: Whether to wait for readability
    @type readable: bool
    @param writable: Whether to wait for writability
    @type writable: bool
    @param timeout: Deadline timeout (expiration time, in seconds)
    @type timeout: float
    @return True on success, False on timeout
    """
    rset, wset, xset = [], [], []

    if readable:
        rset = [fd]
    if writable:
        wset = [fd]
    if error:
        xset = [fd]

    if timeout is None:
        (rcount, wcount, xcount) = select.select(rset, wset, xset)
    else:
        (rcount, wcount, xcount) = select.select(rset, wset, xset, timeout)

    return bool((rcount or wcount or xcount))


def _wait_for(fd, readable, writable, error, expiration):
    done = False
    while not done:
        if expiration is None:
            timeout = None
        else:
            timeout = expiration - time.time()
            if timeout <= 0.0:
                raise dns.exception.Timeout
        try:
            if not _polling_backend(fd, readable, writable, error, timeout):
                raise dns.exception.Timeout
        except select_error as e:
            if e.args[0] != errno.EINTR:
                raise e
        done = True


def _set_polling_backend(fn):
    """
    Internal API. Do not use.
    """
    global _polling_backend

    _polling_backend = fn

if hasattr(select, 'poll'):
    # Prefer poll() on platforms that support it because it has no
    # limits on the maximum value of a file descriptor (plus it will
    # be more efficient for high values).
    _polling_backend = _poll_for
else:
    _polling_backend = _select_for


def _wait_for_readable(s, expiration):
    _wait_for(s, True, False, True, expiration)


def _wait_for_writable(s, expiration):
    _wait_for(s, False, True, True, expiration)


def _addresses_equal(af, a1, a2):
    # Convert the first value of the tuple, which is a textual format
    # address into binary form, so that we are not confused by different
    # textual representations of the same address
    n1 = dns.inet.inet_pton(af, a1[0])
    n2 = dns.inet.inet_pton(af, a2[0])
    return n1 == n2 and a1[1:] == a2[1:]


def _matches_destination(af, from_address, destination, ignore_unexpected):
    # Check that from_address is appropriate for a response to a query
    # sent to destination.
    if not destination:
        return True
    if _addresses_equal(af, from_address, destination) or (
        dns.inet.is_multicast(destination[0]) and from_address[1:] == destination[1:]
    ):
        return True
    elif ignore_unexpected:
        return False
    raise UnexpectedSource(
        f"got a response from {from_address} instead of " f"{destination}"
    )


def _destination_and_source(af, where, port, source, source_port):
    # Apply defaults and compute destination and source tuples
    # suitable for use in connect(), sendto(), or bind().
    if af is None:
        try:
            af = dns.inet.af_for_address(where)
        except Exception:
            af = dns.inet.AF_INET
    if af == dns.inet.AF_INET:
        destination = (where, port)
        if source is not None or source_port != 0:
            if source is None:
                source = '0.0.0.0'
            source = (source, source_port)
    elif af == dns.inet.AF_INET6:
        destination = (where, port, 0, 0)
        if source is not None or source_port != 0:
            if source is None:
                source = '::'
            source = (source, source_port, 0, 0)
    return (af, destination, source)


def udp(q, where, timeout=None, port=53, af=None, source=None, source_port=0,
        ignore_unexpected=False, one_rr_per_rrset=False, ignore_errors=False):
    """Return the response obtained after sending a query via UDP.

    @param q: the query
    @type q: dns.message.Message
    @param where: where to send the message
    @type where: string containing an IPv4 or IPv6 address
    @param timeout: The number of seconds to wait before the query times out.
    If None, the default, wait forever.
    @type timeout: float
    @param port: The port to which to send the message.  The default is 53.
    @type port: int
    @param af: the address family to use.  The default is None, which
    causes the address family to use to be inferred from the form of where.
    If the inference attempt fails, AF_INET is used.
    @type af: int
    @rtype: dns.message.Message object
    @param source: source address.  The default is the wildcard address.
    @type source: string
    @param source_port: The port from which to send the message.
    The default is 0.
    @type source_port: int
    @param ignore_unexpected: If True, ignore responses from unexpected
    sources.  The default is False.
    @type ignore_unexpected: bool
    @param one_rr_per_rrset: Put each RR into its own RRset
    @type one_rr_per_rrset: bool
    """

    wire = q.to_wire()
    (af, destination, source) = _destination_and_source(af, where, port,
                                                        source, source_port)
    s = socket_factory(af, socket.SOCK_DGRAM, 0)
    begin_time = None
    try:
        expiration = _compute_expiration(timeout)
        s.setblocking(0)
        if source is not None:
            s.bind(source)
        _wait_for_writable(s, expiration)
        begin_time = time.time()
        s.sendto(wire, destination)
        while 1:
            _wait_for_readable(s, expiration)
            (wire, from_address) = s.recvfrom(65535)
            if not _matches_destination(
                s.family, from_address, destination, ignore_unexpected
            ):
                continue

            response_time = time.time() - begin_time

            try:
                r = dns.message.from_wire(wire, keyring=q.keyring, request_mac=q.mac,
                                  one_rr_per_rrset=one_rr_per_rrset)
                r.time = response_time
            except Exception:
                if ignore_errors:
                    continue
                else:
                    raise

            if q.is_response(r):
                return r
            else:
                if ignore_errors:
                    continue
                else:
                    raise BadResponse
    finally:
        s.close()


def _net_read(sock, count, expiration):
    """Read the specified number of bytes from sock.  Keep trying until we
    either get the desired amount, or we hit EOF.
    A Timeout exception will be raised if the operation is not completed
    by the expiration time.
    """
    s = b''
    while count > 0:
        _wait_for_readable(sock, expiration)
        n = sock.recv(count)
        if n == b'':
            raise EOFError
        count = count - len(n)
        s = s + n
    return s


def _net_write(sock, data, expiration):
    """Write the specified data to the socket.
    A Timeout exception will be raised if the operation is not completed
    by the expiration time.
    """
    current = 0
    l = len(data)
    while current < l:
        _wait_for_writable(sock, expiration)
        current += sock.send(data[current:])


def _connect(s, address):
    try:
        s.connect(address)
    except socket.error:
        (ty, v) = sys.exc_info()[:2]

        if hasattr(v, 'errno'):
            v_err = v.errno
        else:
            v_err = v[0]
        if v_err not in [errno.EINPROGRESS, errno.EWOULDBLOCK, errno.EALREADY]:
            raise v


def tcp(q, where, timeout=None, port=53, af=None, source=None, source_port=0,
        one_rr_per_rrset=False):
    """Return the response obtained after sending a query via TCP.

    @param q: the query
    @type q: dns.message.Message object
    @param where: where to send the message
    @type where: string containing an IPv4 or IPv6 address
    @param timeout: The number of seconds to wait before the query times out.
    If None, the default, wait forever.
    @type timeout: float
    @param port: The port to which to send the message.  The default is 53.
    @type port: int
    @param af: the address family to use.  The default is None, which
    causes the address family to use to be inferred from the form of where.
    If the inference attempt fails, AF_INET is used.
    @type af: int
    @rtype: dns.message.Message object
    @param source: source address.  The default is the wildcard address.
    @type source: string
    @param source_port: The port from which to send the message.
    The default is 0.
    @type source_port: int
    @param one_rr_per_rrset: Put each RR into its own RRset
    @type one_rr_per_rrset: bool
    """

    wire = q.to_wire()
    (af, destination, source) = _destination_and_source(af, where, port,
                                                        source, source_port)
    s = socket_factory(af, socket.SOCK_STREAM, 0)
    begin_time = None
    try:
        expiration = _compute_expiration(timeout)
        s.setblocking(0)
        begin_time = time.time()
        if source is not None:
            s.bind(source)
        _connect(s, destination)

        l = len(wire)

        # copying the wire into tcpmsg is inefficient, but lets us
        # avoid writev() or doing a short write that would get pushed
        # onto the net
        tcpmsg = struct.pack("!H", l) + wire
        _net_write(s, tcpmsg, expiration)
        ldata = _net_read(s, 2, expiration)
        (l,) = struct.unpack("!H", ldata)
        wire = _net_read(s, l, expiration)
    finally:
        if begin_time is None:
            response_time = 0
        else:
            response_time = time.time() - begin_time
        s.close()
    r = dns.message.from_wire(wire, keyring=q.keyring, request_mac=q.mac,
                              one_rr_per_rrset=one_rr_per_rrset)
    r.time = response_time
    if not q.is_response(r):
        raise BadResponse
    return r


def xfr(where, zone, rdtype=dns.rdatatype.AXFR, rdclass=dns.rdataclass.IN,
        timeout=None, port=53, keyring=None, keyname=None, relativize=True,
        af=None, lifetime=None, source=None, source_port=0, serial=0,
        use_udp=False, keyalgorithm=dns.tsig.default_algorithm):
    """Return a generator for the responses to a zone transfer.

    @param where: where to send the message
    @type where: string containing an IPv4 or IPv6 address
    @param zone: The name of the zone to transfer
    @type zone: dns.name.Name object or string
    @param rdtype: The type of zone transfer.  The default is
    dns.rdatatype.AXFR.
    @type rdtype: int or string
    @param rdclass: The class of the zone transfer.  The default is
    dns.rdataclass.IN.
    @type rdclass: int or string
    @param timeout: The number of seconds to wait for each response message.
    If None, the default, wait forever.
    @type timeout: float
    @param port: The port to which to send the message.  The default is 53.
    @type port: int
    @param keyring: The TSIG keyring to use
    @type keyring: dict
    @param keyname: The name of the TSIG key to use
    @type keyname: dns.name.Name object or string
    @param relativize: If True, all names in the zone will be relativized to
    the zone origin.  It is essential that the relativize setting matches
    the one specified to dns.zone.from_xfr().
    @type relativize: bool
    @param af: the address family to use.  The default is None, which
    causes the address family to use to be inferred from the form of where.
    If the inference attempt fails, AF_INET is used.
    @type af: int
    @param lifetime: The total number of seconds to spend doing the transfer.
    If None, the default, then there is no limit on the time the transfer may
    take.
    @type lifetime: float
    @rtype: generator of dns.message.Message objects.
    @param source: source address.  The default is the wildcard address.
    @type source: string
    @param source_port: The port from which to send the message.
    The default is 0.
    @type source_port: int
    @param serial: The SOA serial number to use as the base for an IXFR diff
    sequence (only meaningful if rdtype == dns.rdatatype.IXFR).
    @type serial: int
    @param use_udp: Use UDP (only meaningful for IXFR)
    @type use_udp: bool
    @param keyalgorithm: The TSIG algorithm to use; defaults to
    dns.tsig.default_algorithm
    @type keyalgorithm: string
    """

    if isinstance(zone, string_types):
        zone = dns.name.from_text(zone)
    if isinstance(rdtype, string_types):
        rdtype = dns.rdatatype.from_text(rdtype)
    q = dns.message.make_query(zone, rdtype, rdclass)
    if rdtype == dns.rdatatype.IXFR:
        rrset = dns.rrset.from_text(zone, 0, 'IN', 'SOA',
                                    '. . %u 0 0 0 0' % serial)
        q.authority.append(rrset)
    if keyring is not None:
        q.use_tsig(keyring, keyname, algorithm=keyalgorithm)
    wire = q.to_wire()
    (af, destination, source) = _destination_and_source(af, where, port,
                                                        source, source_port)
    if use_udp:
        if rdtype != dns.rdatatype.IXFR:
            raise ValueError('cannot do a UDP AXFR')
        s = socket_factory(af, socket.SOCK_DGRAM, 0)
    else:
        s = socket_factory(af, socket.SOCK_STREAM, 0)
    s.setblocking(0)
    if source is not None:
        s.bind(source)
    expiration = _compute_expiration(lifetime)
    _connect(s, destination)
    l = len(wire)
    if use_udp:
        _wait_for_writable(s, expiration)
        s.send(wire)
    else:
        tcpmsg = struct.pack("!H", l) + wire
        _net_write(s, tcpmsg, expiration)
    done = False
    delete_mode = True
    expecting_SOA = False
    soa_rrset = None
    if relativize:
        origin = zone
        oname = dns.name.empty
    else:
        origin = None
        oname = zone
    tsig_ctx = None
    first = True
    while not done:
        mexpiration = _compute_expiration(timeout)
        if mexpiration is None or \
           (expiration is not None and mexpiration > expiration):
            mexpiration = expiration
        if use_udp:
            _wait_for_readable(s, expiration)
            (wire, from_address) = s.recvfrom(65535)
        else:
            ldata = _net_read(s, 2, mexpiration)
            (l,) = struct.unpack("!H", ldata)
            wire = _net_read(s, l, mexpiration)
        is_ixfr = (rdtype == dns.rdatatype.IXFR)
        r = dns.message.from_wire(wire, keyring=q.keyring, request_mac=q.mac,
                                  xfr=True, origin=origin, tsig_ctx=tsig_ctx,
                                  multi=True, first=first,
                                  one_rr_per_rrset=is_ixfr)
        tsig_ctx = r.tsig_ctx
        first = False
        answer_index = 0
        if soa_rrset is None:
            if not r.answer or r.answer[0].name != oname:
                raise dns.exception.FormError(
                    "No answer or RRset not for qname")
            rrset = r.answer[0]
            if rrset.rdtype != dns.rdatatype.SOA:
                raise dns.exception.FormError("first RRset is not an SOA")
            answer_index = 1
            soa_rrset = rrset.copy()
            if rdtype == dns.rdatatype.IXFR:
                if soa_rrset[0].serial <= serial:
                    #
                    # We're already up-to-date.
                    #
                    done = True
                else:
                    expecting_SOA = True
        #
        # Process SOAs in the answer section (other than the initial
        # SOA in the first message).
        #
        for rrset in r.answer[answer_index:]:
            if done:
                raise dns.exception.FormError("answers after final SOA")
            if rrset.rdtype == dns.rdatatype.SOA and rrset.name == oname:
                if expecting_SOA:
                    if rrset[0].serial != serial:
                        raise dns.exception.FormError(
                            "IXFR base serial mismatch")
                    expecting_SOA = False
                elif rdtype == dns.rdatatype.IXFR:
                    delete_mode = not delete_mode
                #
                # If this SOA RRset is equal to the first we saw then we're
                # finished. If this is an IXFR we also check that we're seeing
                # the record in the expected part of the response.
                #
                if rrset == soa_rrset and \
                        (rdtype == dns.rdatatype.AXFR or
                         (rdtype == dns.rdatatype.IXFR and delete_mode)):
                    done = True
            elif expecting_SOA:
                #
                # We made an IXFR request and are expecting another
                # SOA RR, but saw something else, so this must be an
                # AXFR response.
                #
                rdtype = dns.rdatatype.AXFR
                expecting_SOA = False
        if done and q.keyring and not r.had_tsig:
            raise dns.exception.FormError("missing TSIG")
        yield r
    s.close()