s4-python: import a copy of the python dns library

This library is not installed on enough systems for us to rely
on it being available. We use the system copy if possible, and
fallback to this local copy

Pair-Programmed-With: Andrew Bartlett <abartlet@samba.org>

1 files changed, 761 insertions, 0 deletions

diff --git a/source4/scripting/python/samba_external/dnspython/dns/resolver.py b/source4/scripting/python/samba_external/dnspython/dns/resolver.py
new file mode 100644
index 0000000000..372d7d8361
--- /dev/null
+++ b/source4/scripting/python/samba_external/dnspython/dns/resolver.py
@@ -0,0 +1,761 @@
+# Copyright (C) 2003-2007, 2009, 2010 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.
+
+"""DNS stub resolver.
+
+@var default_resolver: The default resolver object
+@type default_resolver: dns.resolver.Resolver object"""
+
+import socket
+import sys
+import time
+
+import dns.exception
+import dns.message
+import dns.name
+import dns.query
+import dns.rcode
+import dns.rdataclass
+import dns.rdatatype
+
+if sys.platform == 'win32':
+    import _winreg
+
+class NXDOMAIN(dns.exception.DNSException):
+    """The query name does not exist."""
+    pass
+
+# The definition of the Timeout exception has moved from here to the
+# dns.exception module.  We keep dns.resolver.Timeout defined for
+# backwards compatibility.
+
+Timeout = dns.exception.Timeout
+
+class NoAnswer(dns.exception.DNSException):
+    """The response did not contain an answer to the question."""
+    pass
+
+class NoNameservers(dns.exception.DNSException):
+    """No non-broken nameservers are available to answer the query."""
+    pass
+
+class NotAbsolute(dns.exception.DNSException):
+    """Raised if an absolute domain name is required but a relative name
+    was provided."""
+    pass
+
+class NoRootSOA(dns.exception.DNSException):
+    """Raised if for some reason there is no SOA at the root name.
+    This should never happen!"""
+    pass
+
+
+class Answer(object):
+    """DNS stub resolver answer
+
+    Instances of this class bundle up the result of a successful DNS
+    resolution.
+
+    For convenience, the answer object implements much of the sequence
+    protocol, forwarding to its rrset.  E.g. "for a in answer" is
+    equivalent to "for a in answer.rrset", "answer[i]" is equivalent
+    to "answer.rrset[i]", and "answer[i:j]" is equivalent to
+    "answer.rrset[i:j]".
+
+    Note that CNAMEs or DNAMEs in the response may mean that answer
+    node's name might not be the query name.
+
+    @ivar qname: The query name
+    @type qname: dns.name.Name object
+    @ivar rdtype: The query type
+    @type rdtype: int
+    @ivar rdclass: The query class
+    @type rdclass: int
+    @ivar response: The response message
+    @type response: dns.message.Message object
+    @ivar rrset: The answer
+    @type rrset: dns.rrset.RRset object
+    @ivar expiration: The time when the answer expires
+    @type expiration: float (seconds since the epoch)
+    """
+    def __init__(self, qname, rdtype, rdclass, response):
+        self.qname = qname
+        self.rdtype = rdtype
+        self.rdclass = rdclass
+        self.response = response
+        min_ttl = -1
+        rrset = None
+        for count in xrange(0, 15):
+            try:
+                rrset = response.find_rrset(response.answer, qname,
+                                            rdclass, rdtype)
+                if min_ttl == -1 or rrset.ttl < min_ttl:
+                    min_ttl = rrset.ttl
+                break
+            except KeyError:
+                if rdtype != dns.rdatatype.CNAME:
+                    try:
+                        crrset = response.find_rrset(response.answer,
+                                                     qname,
+                                                     rdclass,
+                                                     dns.rdatatype.CNAME)
+                        if min_ttl == -1 or crrset.ttl < min_ttl:
+                            min_ttl = crrset.ttl
+                        for rd in crrset:
+                            qname = rd.target
+                            break
+                        continue
+                    except KeyError:
+                        raise NoAnswer
+                raise NoAnswer
+        if rrset is None:
+            raise NoAnswer
+        self.rrset = rrset
+        self.expiration = time.time() + min_ttl
+
+    def __getattr__(self, attr):
+        if attr == 'name':
+            return self.rrset.name
+        elif attr == 'ttl':
+            return self.rrset.ttl
+        elif attr == 'covers':
+            return self.rrset.covers
+        elif attr == 'rdclass':
+            return self.rrset.rdclass
+        elif attr == 'rdtype':
+            return self.rrset.rdtype
+        else:
+            raise AttributeError(attr)
+
+    def __len__(self):
+        return len(self.rrset)
+
+    def __iter__(self):
+        return iter(self.rrset)
+
+    def __getitem__(self, i):
+        return self.rrset[i]
+
+    def __delitem__(self, i):
+        del self.rrset[i]
+
+    def __getslice__(self, i, j):
+        return self.rrset[i:j]
+
+    def __delslice__(self, i, j):
+        del self.rrset[i:j]
+
+class Cache(object):
+    """Simple DNS answer cache.
+
+    @ivar data: A dictionary of cached data
+    @type data: dict
+    @ivar cleaning_interval: The number of seconds between cleanings.  The
+    default is 300 (5 minutes).
+    @type cleaning_interval: float
+    @ivar next_cleaning: The time the cache should next be cleaned (in seconds
+    since the epoch.)
+    @type next_cleaning: float
+    """
+
+    def __init__(self, cleaning_interval=300.0):
+        """Initialize a DNS cache.
+
+        @param cleaning_interval: the number of seconds between periodic
+        cleanings.  The default is 300.0
+        @type cleaning_interval: float.
+        """
+
+        self.data = {}
+        self.cleaning_interval = cleaning_interval
+        self.next_cleaning = time.time() + self.cleaning_interval
+
+    def maybe_clean(self):
+        """Clean the cache if it's time to do so."""
+
+        now = time.time()
+        if self.next_cleaning <= now:
+            keys_to_delete = []
+            for (k, v) in self.data.iteritems():
+                if v.expiration <= now:
+                    keys_to_delete.append(k)
+            for k in keys_to_delete:
+                del self.data[k]
+            now = time.time()
+            self.next_cleaning = now + self.cleaning_interval
+
+    def get(self, key):
+        """Get the answer associated with I{key}.  Returns None if
+        no answer is cached for the key.
+        @param key: the key
+        @type key: (dns.name.Name, int, int) tuple whose values are the
+        query name, rdtype, and rdclass.
+        @rtype: dns.resolver.Answer object or None
+        """
+
+        self.maybe_clean()
+        v = self.data.get(key)
+        if v is None or v.expiration <= time.time():
+            return None
+        return v
+
+    def put(self, key, value):
+        """Associate key and value in the cache.
+        @param key: the key
+        @type key: (dns.name.Name, int, int) tuple whose values are the
+        query name, rdtype, and rdclass.
+        @param value: The answer being cached
+        @type value: dns.resolver.Answer object
+        """
+
+        self.maybe_clean()
+        self.data[key] = value
+
+    def flush(self, key=None):
+        """Flush the cache.
+
+        If I{key} is specified, only that item is flushed.  Otherwise
+        the entire cache is flushed.
+
+        @param key: the key to flush
+        @type key: (dns.name.Name, int, int) tuple or None
+        """
+
+        if not key is None:
+            if self.data.has_key(key):
+                del self.data[key]
+        else:
+            self.data = {}
+            self.next_cleaning = time.time() + self.cleaning_interval
+
+class Resolver(object):
+    """DNS stub resolver
+
+    @ivar domain: The domain of this host
+    @type domain: dns.name.Name object
+    @ivar nameservers: A list of nameservers to query.  Each nameserver is
+    a string which contains the IP address of a nameserver.
+    @type nameservers: list of strings
+    @ivar search: The search list.  If the query name is a relative name,
+    the resolver will construct an absolute query name by appending the search
+    names one by one to the query name.
+    @type search: list of dns.name.Name objects
+    @ivar port: The port to which to send queries.  The default is 53.
+    @type port: int
+    @ivar timeout: The number of seconds to wait for a response from a
+    server, before timing out.
+    @type timeout: float
+    @ivar lifetime: The total number of seconds to spend trying to get an
+    answer to the question.  If the lifetime expires, a Timeout exception
+    will occur.
+    @type lifetime: float
+    @ivar keyring: The TSIG keyring to use.  The default is None.
+    @type keyring: dict
+    @ivar keyname: The TSIG keyname to use.  The default is None.
+    @type keyname: dns.name.Name object
+    @ivar keyalgorithm: The TSIG key algorithm to use.  The default is
+    dns.tsig.default_algorithm.
+    @type keyalgorithm: string
+    @ivar edns: The EDNS level to use.  The default is -1, no Edns.
+    @type edns: int
+    @ivar ednsflags: The EDNS flags
+    @type ednsflags: int
+    @ivar payload: The EDNS payload size.  The default is 0.
+    @type payload: int
+    @ivar cache: The cache to use.  The default is None.
+    @type cache: dns.resolver.Cache object
+    """
+    def __init__(self, filename='/etc/resolv.conf', configure=True):
+        """Initialize a resolver instance.
+
+        @param filename: The filename of a configuration file in
+        standard /etc/resolv.conf format.  This parameter is meaningful
+        only when I{configure} is true and the platform is POSIX.
+        @type filename: string or file object
+        @param configure: If True (the default), the resolver instance
+        is configured in the normal fashion for the operating system
+        the resolver is running on.  (I.e. a /etc/resolv.conf file on
+        POSIX systems and from the registry on Windows systems.)
+        @type configure: bool"""
+
+        self.reset()
+        if configure:
+            if sys.platform == 'win32':
+                self.read_registry()
+            elif filename:
+                self.read_resolv_conf(filename)
+
+    def reset(self):
+        """Reset all resolver configuration to the defaults."""
+        self.domain = \
+            dns.name.Name(dns.name.from_text(socket.gethostname())[1:])
+        if len(self.domain) == 0:
+            self.domain = dns.name.root
+        self.nameservers = []
+        self.search = []
+        self.port = 53
+        self.timeout = 2.0
+        self.lifetime = 30.0
+        self.keyring = None
+        self.keyname = None
+        self.keyalgorithm = dns.tsig.default_algorithm
+        self.edns = -1
+        self.ednsflags = 0
+        self.payload = 0
+        self.cache = None
+
+    def read_resolv_conf(self, f):
+        """Process f as a file in the /etc/resolv.conf format.  If f is
+        a string, it is used as the name of the file to open; otherwise it
+        is treated as the file itself."""
+        if isinstance(f, str) or isinstance(f, unicode):
+            try:
+                f = open(f, 'r')
+            except IOError:
+                # /etc/resolv.conf doesn't exist, can't be read, etc.
+                # We'll just use the default resolver configuration.
+                self.nameservers = ['127.0.0.1']
+                return
+            want_close = True
+        else:
+            want_close = False
+        try:
+            for l in f:
+                if len(l) == 0 or l[0] == '#' or l[0] == ';':
+                    continue
+                tokens = l.split()
+                if len(tokens) == 0:
+                    continue
+                if tokens[0] == 'nameserver':
+                    self.nameservers.append(tokens[1])
+                elif tokens[0] == 'domain':
+                    self.domain = dns.name.from_text(tokens[1])
+                elif tokens[0] == 'search':
+                    for suffix in tokens[1:]:
+                        self.search.append(dns.name.from_text(suffix))
+        finally:
+            if want_close:
+                f.close()
+        if len(self.nameservers) == 0:
+            self.nameservers.append('127.0.0.1')
+
+    def _determine_split_char(self, entry):
+        #
+        # The windows registry irritatingly changes the list element
+        # delimiter in between ' ' and ',' (and vice-versa) in various
+        # versions of windows.
+        #
+        if entry.find(' ') >= 0:
+            split_char = ' '
+        elif entry.find(',') >= 0:
+            split_char = ','
+        else:
+            # probably a singleton; treat as a space-separated list.
+            split_char = ' '
+        return split_char
+
+    def _config_win32_nameservers(self, nameservers):
+        """Configure a NameServer registry entry."""
+        # we call str() on nameservers to convert it from unicode to ascii
+        nameservers = str(nameservers)
+        split_char = self._determine_split_char(nameservers)
+        ns_list = nameservers.split(split_char)
+        for ns in ns_list:
+            if not ns in self.nameservers:
+                self.nameservers.append(ns)
+
+    def _config_win32_domain(self, domain):
+        """Configure a Domain registry entry."""
+        # we call str() on domain to convert it from unicode to ascii
+        self.domain = dns.name.from_text(str(domain))
+
+    def _config_win32_search(self, search):
+        """Configure a Search registry entry."""
+        # we call str() on search to convert it from unicode to ascii
+        search = str(search)
+        split_char = self._determine_split_char(search)
+        search_list = search.split(split_char)
+        for s in search_list:
+            if not s in self.search:
+                self.search.append(dns.name.from_text(s))
+
+    def _config_win32_fromkey(self, key):
+        """Extract DNS info from a registry key."""
+        try:
+            servers, rtype = _winreg.QueryValueEx(key, 'NameServer')
+        except WindowsError:
+            servers = None
+        if servers:
+            self._config_win32_nameservers(servers)
+            try:
+                dom, rtype = _winreg.QueryValueEx(key, 'Domain')
+                if dom:
+                    self._config_win32_domain(dom)
+            except WindowsError:
+                pass
+        else:
+            try:
+                servers, rtype = _winreg.QueryValueEx(key, 'DhcpNameServer')
+            except WindowsError:
+                servers = None
+            if servers:
+                self._config_win32_nameservers(servers)
+                try:
+                    dom, rtype = _winreg.QueryValueEx(key, 'DhcpDomain')
+                    if dom:
+                        self._config_win32_domain(dom)
+                except WindowsError:
+                    pass
+        try:
+            search, rtype = _winreg.QueryValueEx(key, 'SearchList')
+        except WindowsError:
+            search = None
+        if search:
+            self._config_win32_search(search)
+
+    def read_registry(self):
+        """Extract resolver configuration from the Windows registry."""
+        lm = _winreg.ConnectRegistry(None, _winreg.HKEY_LOCAL_MACHINE)
+        want_scan = False
+        try:
+            try:
+                # XP, 2000
+                tcp_params = _winreg.OpenKey(lm,
+                                             r'SYSTEM\CurrentControlSet'
+                                             r'\Services\Tcpip\Parameters')
+                want_scan = True
+            except EnvironmentError:
+                # ME
+                tcp_params = _winreg.OpenKey(lm,
+                                             r'SYSTEM\CurrentControlSet'
+                                             r'\Services\VxD\MSTCP')
+            try:
+                self._config_win32_fromkey(tcp_params)
+            finally:
+                tcp_params.Close()
+            if want_scan:
+                interfaces = _winreg.OpenKey(lm,
+                                             r'SYSTEM\CurrentControlSet'
+                                             r'\Services\Tcpip\Parameters'
+                                             r'\Interfaces')
+                try:
+                    i = 0
+                    while True:
+                        try:
+                            guid = _winreg.EnumKey(interfaces, i)
+                            i += 1
+                            key = _winreg.OpenKey(interfaces, guid)
+                            if not self._win32_is_nic_enabled(lm, guid, key):
+                                continue
+                            try:
+                                self._config_win32_fromkey(key)
+                            finally:
+                                key.Close()
+                        except EnvironmentError:
+                            break
+                finally:
+                    interfaces.Close()
+        finally:
+            lm.Close()
+
+    def _win32_is_nic_enabled(self, lm, guid, interface_key):
+         # Look in the Windows Registry to determine whether the network
+         # interface corresponding to the given guid is enabled.
+         #
+         # (Code contributed by Paul Marks, thanks!)
+         #
+         try:
+             # This hard-coded location seems to be consistent, at least
+             # from Windows 2000 through Vista.
+             connection_key = _winreg.OpenKey(
+                 lm,
+                 r'SYSTEM\CurrentControlSet\Control\Network'
+                 r'\{4D36E972-E325-11CE-BFC1-08002BE10318}'
+                 r'\%s\Connection' % guid)
+
+             try:
+                 # The PnpInstanceID points to a key inside Enum
+                 (pnp_id, ttype) = _winreg.QueryValueEx(
+                     connection_key, 'PnpInstanceID')
+
+                 if ttype != _winreg.REG_SZ:
+                     raise ValueError
+
+                 device_key = _winreg.OpenKey(
+                     lm, r'SYSTEM\CurrentControlSet\Enum\%s' % pnp_id)
+
+                 try:
+                     # Get ConfigFlags for this device
+                     (flags, ttype) = _winreg.QueryValueEx(
+                         device_key, 'ConfigFlags')
+
+                     if ttype != _winreg.REG_DWORD:
+                         raise ValueError
+
+                     # Based on experimentation, bit 0x1 indicates that the
+                     # device is disabled.
+                     return not (flags & 0x1)
+
+                 finally:
+                     device_key.Close()
+             finally:
+                 connection_key.Close()
+         except (EnvironmentError, ValueError):
+             # Pre-vista, enabled interfaces seem to have a non-empty
+             # NTEContextList; this was how dnspython detected enabled
+             # nics before the code above was contributed.  We've retained
+             # the old method since we don't know if the code above works
+             # on Windows 95/98/ME.
+             try:
+                 (nte, ttype) = _winreg.QueryValueEx(interface_key,
+                                                     'NTEContextList')
+                 return nte is not None
+             except WindowsError:
+                 return False
+
+    def _compute_timeout(self, start):
+        now = time.time()
+        if now < start:
+            if start - now > 1:
+                # Time going backwards is bad.  Just give up.
+                raise Timeout
+            else:
+                # Time went backwards, but only a little.  This can
+                # happen, e.g. under vmware with older linux kernels.
+                # Pretend it didn't happen.
+                now = start
+        duration = now - start
+        if duration >= self.lifetime:
+            raise Timeout
+        return min(self.lifetime - duration, self.timeout)
+
+    def query(self, qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN,
+              tcp=False, source=None):
+        """Query nameservers to find the answer to the question.
+
+        The I{qname}, I{rdtype}, and I{rdclass} parameters may be objects
+        of the appropriate type, or strings that can be converted into objects
+        of the appropriate type.  E.g. For I{rdtype} the integer 2 and the
+        the string 'NS' both mean to query for records with DNS rdata type NS.
+
+        @param qname: the query name
+        @type qname: dns.name.Name object or string
+        @param rdtype: the query type
+        @type rdtype: int or string
+        @param rdclass: the query class
+        @type rdclass: int or string
+        @param tcp: use TCP to make the query (default is False).
+        @type tcp: bool
+        @param source: bind to this IP address (defaults to machine default IP).
+        @type source: IP address in dotted quad notation
+        @rtype: dns.resolver.Answer instance
+        @raises Timeout: no answers could be found in the specified lifetime
+        @raises NXDOMAIN: the query name does not exist
+        @raises NoAnswer: the response did not contain an answer
+        @raises NoNameservers: no non-broken nameservers are available to
+        answer the question."""
+
+        if isinstance(qname, (str, unicode)):
+            qname = dns.name.from_text(qname, None)
+        if isinstance(rdtype, str):
+            rdtype = dns.rdatatype.from_text(rdtype)
+        if isinstance(rdclass, str):
+            rdclass = dns.rdataclass.from_text(rdclass)
+        qnames_to_try = []
+        if qname.is_absolute():
+            qnames_to_try.append(qname)
+        else:
+            if len(qname) > 1:
+                qnames_to_try.append(qname.concatenate(dns.name.root))
+            if self.search:
+                for suffix in self.search:
+                    qnames_to_try.append(qname.concatenate(suffix))
+            else:
+                qnames_to_try.append(qname.concatenate(self.domain))
+        all_nxdomain = True
+        start = time.time()
+        for qname in qnames_to_try:
+            if self.cache:
+                answer = self.cache.get((qname, rdtype, rdclass))
+                if answer:
+                    return answer
+            request = dns.message.make_query(qname, rdtype, rdclass)
+            if not self.keyname is None:
+                request.use_tsig(self.keyring, self.keyname, self.keyalgorithm)
+            request.use_edns(self.edns, self.ednsflags, self.payload)
+            response = None
+            #
+            # make a copy of the servers list so we can alter it later.
+            #
+            nameservers = self.nameservers[:]
+            backoff = 0.10
+            while response is None:
+                if len(nameservers) == 0:
+                    raise NoNameservers
+                for nameserver in nameservers[:]:
+                    timeout = self._compute_timeout(start)
+                    try:
+                        if tcp:
+                            response = dns.query.tcp(request, nameserver,
+                                                     timeout, self.port,
+                                                     source=source)
+                        else:
+                            response = dns.query.udp(request, nameserver,
+                                                     timeout, self.port,
+                                                     source=source)
+                    except (socket.error, dns.exception.Timeout):
+                        #
+                        # Communication failure or timeout.  Go to the
+                        # next server
+                        #
+                        response = None
+                        continue
+                    except dns.query.UnexpectedSource:
+                        #
+                        # Who knows?  Keep going.
+                        #
+                        response = None
+                        continue
+                    except dns.exception.FormError:
+                        #
+                        # We don't understand what this server is
+                        # saying.  Take it out of the mix and
+                        # continue.
+                        #
+                        nameservers.remove(nameserver)
+                        response = None
+                        continue
+                    rcode = response.rcode()
+                    if rcode == dns.rcode.NOERROR or \
+                           rcode == dns.rcode.NXDOMAIN:
+                        break
+                    #
+                    # We got a response, but we're not happy with the
+                    # rcode in it.  Remove the server from the mix if
+                    # the rcode isn't SERVFAIL.
+                    #
+                    if rcode != dns.rcode.SERVFAIL:
+                        nameservers.remove(nameserver)
+                    response = None
+                if not response is None:
+                    break
+                #
+                # All nameservers failed!
+                #
+                if len(nameservers) > 0:
+                    #
+                    # But we still have servers to try.  Sleep a bit
+                    # so we don't pound them!
+                    #
+                    timeout = self._compute_timeout(start)
+                    sleep_time = min(timeout, backoff)
+                    backoff *= 2
+                    time.sleep(sleep_time)
+            if response.rcode() == dns.rcode.NXDOMAIN:
+                continue
+            all_nxdomain = False
+            break
+        if all_nxdomain:
+            raise NXDOMAIN
+        answer = Answer(qname, rdtype, rdclass, response)
+        if self.cache:
+            self.cache.put((qname, rdtype, rdclass), answer)
+        return answer
+
+    def use_tsig(self, keyring, keyname=None,
+                 algorithm=dns.tsig.default_algorithm):
+        """Add a TSIG signature to the query.
+
+        @param keyring: The TSIG keyring to use; defaults to None.
+        @type keyring: dict
+        @param keyname: The name of the TSIG key to use; defaults to None.
+        The key must be defined in the keyring.  If a keyring is specified
+        but a keyname is not, then the key used will be the first key in the
+        keyring.  Note that the order of keys in a dictionary is not defined,
+        so applications should supply a keyname when a keyring is used, unless
+        they know the keyring contains only one key.
+        @param algorithm: The TSIG key algorithm to use.  The default
+        is dns.tsig.default_algorithm.
+        @type algorithm: string"""
+        self.keyring = keyring
+        if keyname is None:
+            self.keyname = self.keyring.keys()[0]
+        else:
+            self.keyname = keyname
+        self.keyalgorithm = algorithm
+
+    def use_edns(self, edns, ednsflags, payload):
+        """Configure Edns.
+
+        @param edns: The EDNS level to use.  The default is -1, no Edns.
+        @type edns: int
+        @param ednsflags: The EDNS flags
+        @type ednsflags: int
+        @param payload: The EDNS payload size.  The default is 0.
+        @type payload: int"""
+
+        if edns is None:
+            edns = -1
+        self.edns = edns
+        self.ednsflags = ednsflags
+        self.payload = payload
+
+default_resolver = None
+
+def get_default_resolver():
+    """Get the default resolver, initializing it if necessary."""
+    global default_resolver
+    if default_resolver is None:
+        default_resolver = Resolver()
+    return default_resolver
+
+def query(qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN,
+          tcp=False, source=None):
+    """Query nameservers to find the answer to the question.
+
+    This is a convenience function that uses the default resolver
+    object to make the query.
+    @see: L{dns.resolver.Resolver.query} for more information on the
+    parameters."""
+    return get_default_resolver().query(qname, rdtype, rdclass, tcp, source)
+
+def zone_for_name(name, rdclass=dns.rdataclass.IN, tcp=False, resolver=None):
+    """Find the name of the zone which contains the specified name.
+
+    @param name: the query name
+    @type name: absolute dns.name.Name object or string
+    @param rdclass: The query class
+    @type rdclass: int
+    @param tcp: use TCP to make the query (default is False).
+    @type tcp: bool
+    @param resolver: the resolver to use
+    @type resolver: dns.resolver.Resolver object or None
+    @rtype: dns.name.Name"""
+
+    if isinstance(name, (str, unicode)):
+        name = dns.name.from_text(name, dns.name.root)
+    if resolver is None:
+        resolver = get_default_resolver()
+    if not name.is_absolute():
+        raise NotAbsolute(name)
+    while 1:
+        try:
+            answer = resolver.query(name, dns.rdatatype.SOA, rdclass, tcp)
+            return name
+        except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
+            try:
+                name = name.parent()
+            except dns.name.NoParent:
+                raise NoRootSOA