# Copyright (C) 2003-2017 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.rcode
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."""


class TransferError(dns.exception.DNSException):
    """A zone transfer response got a non-zero rcode."""

    def __init__(self, rcode):
        message = 'Zone transfer error: %s' % dns.rcode.to_text(rcode)
        super(TransferError, self).__init__(message)
        self.rcode = rcode


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

# This module can use either poll() or select() as the "polling backend".
#
# A backend function takes an fd, bools for readability, writablity, and
# error detection, and a timeout.

def _poll_for(fd, readable, writable, error, timeout):
    """Poll polling backend."""

    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."""

    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):
    # Use the selected polling backend to wait for any of the specified
    # events.  An "expiration" absolute time is converted into a relative
    # timeout.

    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
    try:
        n1 = dns.inet.inet_pton(af, a1[0])
        n2 = dns.inet.inet_pton(af, a2[0])
    except dns.exception.SyntaxError:
        return False
    return n1 == n2 and a1[1:] == a2[1:]


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 send_udp(sock, what, destination, expiration=None):
    """Send a DNS message to the specified UDP socket.

    *sock*, a ``socket``.

    *what*, a ``binary`` or ``dns.message.Message``, the message to send.

    *destination*, a destination tuple appropriate for the address family
    of the socket, specifying where to send the query.

    *expiration*, a ``float`` or ``None``, the absolute time at which
    a timeout exception should be raised.  If ``None``, no timeout will
    occur.

    Returns an ``(int, float)`` tuple of bytes sent and the sent time.
    """

    if isinstance(what, dns.message.Message):
        what = what.to_wire()
    _wait_for_writable(sock, expiration)
    sent_time = time.time()
    n = sock.sendto(what, destination)
    return (n, sent_time)


def receive_udp(sock, destination, expiration=None,
                ignore_unexpected=False, one_rr_per_rrset=False,
                keyring=None, request_mac=b''):
    """Read a DNS message from a UDP socket.

    *sock*, a ``socket``.

    *destination*, a destination tuple appropriate for the address family
    of the socket, specifying where the associated query was sent.

    *expiration*, a ``float`` or ``None``, the absolute time at which
    a timeout exception should be raised.  If ``None``, no timeout will
    occur.

    *ignore_unexpected*, a ``bool``.  If ``True``, ignore responses from
    unexpected sources.

    *one_rr_per_rrset*, a ``bool``.  If ``True``, put each RR into its own
    RRset.

    *keyring*, a ``dict``, the keyring to use for TSIG.

    *request_mac*, a ``binary``, the MAC of the request (for TSIG).

    Raises if the message is malformed, if network errors occur, of if
    there is a timeout.

    Returns a ``dns.message.Message`` object.
    """

    wire = b''
    while 1:
        _wait_for_readable(sock, expiration)
        (wire, from_address) = sock.recvfrom(65535)
        if _addresses_equal(sock.family, from_address, destination) or \
           (dns.inet.is_multicast(destination[0]) and
            from_address[1:] == destination[1:]):
            break
        if not ignore_unexpected:
            raise UnexpectedSource('got a response from '
                                   '%s instead of %s' % (from_address,
                                                         destination))
    received_time = time.time()
    r = dns.message.from_wire(wire, keyring=keyring, request_mac=request_mac,
                              one_rr_per_rrset=one_rr_per_rrset)
    return (r, received_time)

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

    *q*, a ``dns.message.message``, the query to send

    *where*, a ``text`` containing an IPv4 or IPv6 address,  where
    to send the message.

    *timeout*, a ``float`` or ``None``, the number of seconds to wait before the
    query times out.  If ``None``, the default, wait forever.

    *port*, an ``int``, the port send the message to.  The default is 53.

    *af*, an ``int``, 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.  This
    parameter is historical; you need never set it.

    *source*, a ``text`` containing an IPv4 or IPv6 address, specifying
    the source address.  The default is the wildcard address.

    *source_port*, an ``int``, the port from which to send the message.
    The default is 0.

    *ignore_unexpected*, a ``bool``.  If ``True``, ignore responses from
    unexpected sources.

    *one_rr_per_rrset*, a ``bool``.  If ``True``, put each RR into its own
    RRset.

    Returns a ``dns.message.Message``.
    """

    wire = q.to_wire()
    (af, destination, source) = _destination_and_source(af, where, port,
                                                        source, source_port)
    s = socket_factory(af, socket.SOCK_DGRAM, 0)
    received_time = None
    sent_time = None
    try:
        expiration = _compute_expiration(timeout)
        s.setblocking(0)
        if source is not None:
            s.bind(source)
        (_, sent_time) = send_udp(s, wire, destination, expiration)
        (r, received_time) = receive_udp(s, destination, expiration,
                                         ignore_unexpected, one_rr_per_rrset,
                                         q.keyring, q.mac)
    finally:
        if sent_time is None or received_time is None:
            response_time = 0
        else:
            response_time = received_time - sent_time
        s.close()
    r.time = response_time
    if not q.is_response(r):
        raise BadResponse
    return r


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 send_tcp(sock, what, expiration=None):
    """Send a DNS message to the specified TCP socket.

    *sock*, a ``socket``.

    *what*, a ``binary`` or ``dns.message.Message``, the message to send.

    *expiration*, a ``float`` or ``None``, the absolute time at which
    a timeout exception should be raised.  If ``None``, no timeout will
    occur.

    Returns an ``(int, float)`` tuple of bytes sent and the sent time.
    """

    if isinstance(what, dns.message.Message):
        what = what.to_wire()
    l = len(what)
    # 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) + what
    _wait_for_writable(sock, expiration)
    sent_time = time.time()
    _net_write(sock, tcpmsg, expiration)
    return (len(tcpmsg), sent_time)

def receive_tcp(sock, expiration=None, one_rr_per_rrset=False,
                keyring=None, request_mac=b''):
    """Read a DNS message from a TCP socket.

    *sock*, a ``socket``.

    *expiration*, a ``float`` or ``None``, the absolute time at which
    a timeout exception should be raised.  If ``None``, no timeout will
    occur.

    *one_rr_per_rrset*, a ``bool``.  If ``True``, put each RR into its own
    RRset.

    *keyring*, a ``dict``, the keyring to use for TSIG.

    *request_mac*, a ``binary``, the MAC of the request (for TSIG).

    Raises if the message is malformed, if network errors occur, of if
    there is a timeout.

    Returns a ``dns.message.Message`` object.
    """

    ldata = _net_read(sock, 2, expiration)
    (l,) = struct.unpack("!H", ldata)
    wire = _net_read(sock, l, expiration)
    received_time = time.time()
    r = dns.message.from_wire(wire, keyring=keyring, request_mac=request_mac,
                              one_rr_per_rrset=one_rr_per_rrset)
    return (r, received_time)

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.

    *q*, a ``dns.message.message``, the query to send

    *where*, a ``text`` containing an IPv4 or IPv6 address,  where
    to send the message.

    *timeout*, a ``float`` or ``None``, the number of seconds to wait before the
    query times out.  If ``None``, the default, wait forever.

    *port*, an ``int``, the port send the message to.  The default is 53.

    *af*, an ``int``, 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.  This
    parameter is historical; you need never set it.

    *source*, a ``text`` containing an IPv4 or IPv6 address, specifying
    the source address.  The default is the wildcard address.

    *source_port*, an ``int``, the port from which to send the message.
    The default is 0.

    *one_rr_per_rrset*, a ``bool``.  If ``True``, put each RR into its own
    RRset.

    Returns a ``dns.message.Message``.
    """

    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
    received_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)
        send_tcp(s, wire, expiration)
        (r, received_time) = receive_tcp(s, expiration, one_rr_per_rrset,
                                         q.keyring, q.mac)
    finally:
        if begin_time is None or received_time is None:
            response_time = 0
        else:
            response_time = received_time - begin_time
        s.close()
    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.

    *where*.  If the inference attempt fails, AF_INET is used.  This
    parameter is historical; you need never set it.

    *zone*, a ``dns.name.Name`` or ``text``, the name of the zone to transfer.

    *rdtype*, an ``int`` or ``text``, the type of zone transfer.  The
    default is ``dns.rdatatype.AXFR``.  ``dns.rdatatype.IXFR`` can be
    used to do an incremental transfer instead.

    *rdclass*, an ``int`` or ``text``, the class of the zone transfer.
    The default is ``dns.rdataclass.IN``.

    *timeout*, a ``float``, the number of seconds to wait for each
    response message.  If None, the default, wait forever.

    *port*, an ``int``, the port send the message to.  The default is 53.

    *keyring*, a ``dict``, the keyring to use for TSIG.

    *keyname*, a ``dns.name.Name`` or ``text``, the name of the TSIG
    key to use.

    *relativize*, a ``bool``.  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()`` if using this generator to make a zone.

    *af*, an ``int``, 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.  This
    parameter is historical; you need never set it.

    *lifetime*, a ``float``, 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.

    *source*, a ``text`` containing an IPv4 or IPv6 address, specifying
    the source address.  The default is the wildcard address.

    *source_port*, an ``int``, the port from which to send the message.
    The default is 0.

    *serial*, an ``int``, the SOA serial number to use as the base for
    an IXFR diff sequence (only meaningful if *rdtype* is
    ``dns.rdatatype.IXFR``).

    *use_udp*, a ``bool``.  If ``True``, use UDP (only meaningful for IXFR).

    *keyalgorithm*, a ``dns.name.Name`` or ``text``, the TSIG algorithm to use.

    Raises on errors, and so does the generator.

    Returns a generator of ``dns.message.Message`` objects.
    """

    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 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)
        rcode = r.rcode()
        if rcode != dns.rcode.NOERROR:
            raise TransferError(rcode)
        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()
