Move dnspython to third_party.

Signed-off-by: Jelmer Vernooij <jelmer@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Nov 12 22:40:53 CET 2014 on sn-devel-104

1 files changed, 1161 insertions, 0 deletions

diff --git a/third_party/dnspython/dns/resolver.py b/third_party/dnspython/dns/resolver.py
new file mode 100644
index 0000000000..90f95e8ed0
--- /dev/null
+++ b/third_party/dnspython/dns/resolver.py
@@ -0,0 +1,1161 @@
+# 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.
+
+"""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.ipv4
+import dns.ipv6
+import dns.message
+import dns.name
+import dns.query
+import dns.rcode
+import dns.rdataclass
+import dns.rdatatype
+import dns.reversename
+
+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 NoMetaqueries(dns.exception.DNSException):
+    """Metaqueries are not allowed."""
+    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)
+    @ivar canonical_name: The canonical name of the query name
+    @type canonical_name: dns.name.Name object
+    """
+    def __init__(self, qname, rdtype, rdclass, response,
+                 raise_on_no_answer=True):
+        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:
+                        if raise_on_no_answer:
+                            raise NoAnswer
+                if raise_on_no_answer:
+                    raise NoAnswer
+        if rrset is None and raise_on_no_answer:
+            raise NoAnswer
+        self.canonical_name = qname
+        self.rrset = rrset
+        if rrset is None:
+            while 1:
+                # Look for a SOA RR whose owner name is a superdomain
+                # of qname.
+                try:
+                    srrset = response.find_rrset(response.authority, qname,
+                                                rdclass, dns.rdatatype.SOA)
+                    if min_ttl == -1 or srrset.ttl < min_ttl:
+                        min_ttl = srrset.ttl
+                    if srrset[0].minimum < min_ttl:
+                        min_ttl = srrset[0].minimum
+                    break
+                except KeyError:
+                    try:
+                        qname = qname.parent()
+                    except dns.name.NoParent:
+                        break
+        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 LRUCacheNode(object):
+    """LRUCache node.
+    """
+    def __init__(self, key, value):
+        self.key = key
+        self.value = value
+        self.prev = self
+        self.next = self
+
+    def link_before(self, node):
+        self.prev = node.prev
+        self.next = node
+        node.prev.next = self
+        node.prev = self
+
+    def link_after(self, node):
+        self.prev = node
+        self.next = node.next
+        node.next.prev = self
+        node.next = self
+
+    def unlink(self):
+        self.next.prev = self.prev
+        self.prev.next = self.next
+
+class LRUCache(object):
+    """Bounded least-recently-used DNS answer cache.
+
+    This cache is better than the simple cache (above) if you're
+    running a web crawler or other process that does a lot of
+    resolutions.  The LRUCache has a maximum number of nodes, and when
+    it is full, the least-recently used node is removed to make space
+    for a new one.
+
+    @ivar data: A dictionary of cached data
+    @type data: dict
+    @ivar sentinel: sentinel node for circular doubly linked list of nodes
+    @type sentinel: LRUCacheNode object
+    @ivar max_size: The maximum number of nodes
+    @type max_size: int
+    """
+
+    def __init__(self, max_size=100000):
+        """Initialize a DNS cache.
+
+        @param max_size: The maximum number of nodes to cache; the default is
+        100000.  Must be > 1.
+        @type max_size: int
+        """
+        self.data = {}
+        self.set_max_size(max_size)
+        self.sentinel = LRUCacheNode(None, None)
+
+    def set_max_size(self, max_size):
+        if max_size < 1:
+            max_size = 1
+        self.max_size = max_size
+
+    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
+        """
+        node = self.data.get(key)
+        if node is None:
+            return None
+        # Unlink because we're either going to move the node to the front
+        # of the LRU list or we're going to free it.
+        node.unlink()
+        if node.value.expiration <= time.time():
+            del self.data[node.key]
+            return None
+        node.link_after(self.sentinel)
+        return node.value
+
+    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
+        """
+        node = self.data.get(key)
+        if not node is None:
+            node.unlink()
+            del self.data[node.key]
+        while len(self.data) >= self.max_size:
+            node = self.sentinel.prev
+            node.unlink()
+            del self.data[node.key]
+        node = LRUCacheNode(key, value)
+        node.link_after(self.sentinel)
+        self.data[key] = node
+
+    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:
+            node = self.data.get(key)
+            if not node is None:
+                node.unlink()
+                del self.data[node.key]
+        else:
+            node = self.sentinel.next
+            while node != self.sentinel:
+                next = node.next
+                node.prev = None
+                node.next = None
+                node = next
+            self.data = {}
+
+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, raise_on_no_answer=True):
+        """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
+        @param raise_on_no_answer: raise NoAnswer if there's no answer
+        (defaults is True).
+        @type raise_on_no_answer: bool
+        @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 and
+        raise_on_no_answer is True.
+        @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, unicode)):
+            rdtype = dns.rdatatype.from_text(rdtype)
+        if dns.rdatatype.is_metatype(rdtype):
+            raise NoMetaqueries
+        if isinstance(rdclass, (str, unicode)):
+            rdclass = dns.rdataclass.from_text(rdclass)
+        if dns.rdataclass.is_metaclass(rdclass):
+            raise NoMetaqueries
+        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 not answer is None:
+                    if answer.rrset is None and raise_on_no_answer:
+                        raise NoAnswer
+                    else:
+                        return answer
+            request = dns.message.make_query(qname, rdtype, rdclass)
+            if not self.keyname is None:
+                request.use_tsig(self.keyring, self.keyname,
+                                 algorithm=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,
+                        raise_on_no_answer)
+        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, raise_on_no_answer=True):
+    """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,
+                                        raise_on_no_answer)
+
+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)
+            if answer.rrset.name == name:
+                return name
+            # otherwise we were CNAMEd or DNAMEd and need to look higher
+        except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
+            pass
+        try:
+            name = name.parent()
+        except dns.name.NoParent:
+            raise NoRootSOA
+
+#
+# Support for overriding the system resolver for all python code in the
+# running process.
+#
+
+_protocols_for_socktype = {
+    socket.SOCK_DGRAM : [socket.SOL_UDP],
+    socket.SOCK_STREAM : [socket.SOL_TCP],
+    }
+
+_resolver = None
+_original_getaddrinfo = socket.getaddrinfo
+_original_getnameinfo = socket.getnameinfo
+_original_getfqdn = socket.getfqdn
+_original_gethostbyname = socket.gethostbyname
+_original_gethostbyname_ex = socket.gethostbyname_ex
+_original_gethostbyaddr = socket.gethostbyaddr
+
+def _getaddrinfo(host=None, service=None, family=socket.AF_UNSPEC, socktype=0,
+                 proto=0, flags=0):
+    if flags & (socket.AI_ADDRCONFIG|socket.AI_V4MAPPED) != 0:
+        raise NotImplementedError
+    if host is None and service is None:
+        raise socket.gaierror(socket.EAI_NONAME)
+    v6addrs = []
+    v4addrs = []
+    canonical_name = None
+    try:
+        # Is host None or a V6 address literal?
+        if host is None:
+            canonical_name = 'localhost'
+            if flags & socket.AI_PASSIVE != 0:
+                v6addrs.append('::')
+                v4addrs.append('0.0.0.0')
+            else:
+                v6addrs.append('::1')
+                v4addrs.append('127.0.0.1')
+        else:
+            parts = host.split('%')
+            if len(parts) == 2:
+                ahost = parts[0]
+            else:
+                ahost = host
+            addr = dns.ipv6.inet_aton(ahost)
+            v6addrs.append(host)
+            canonical_name = host
+    except:
+        try:
+            # Is it a V4 address literal?
+            addr = dns.ipv4.inet_aton(host)
+            v4addrs.append(host)
+            canonical_name = host
+        except:
+            if flags & socket.AI_NUMERICHOST == 0:
+                try:
+                    qname = None
+                    if family == socket.AF_INET6 or family == socket.AF_UNSPEC:
+                        v6 = _resolver.query(host, dns.rdatatype.AAAA,
+                                             raise_on_no_answer=False)
+                        # Note that setting host ensures we query the same name
+                        # for A as we did for AAAA.
+                        host = v6.qname
+                        canonical_name = v6.canonical_name.to_text(True)
+                        if v6.rrset is not None:
+                            for rdata in v6.rrset:
+                                v6addrs.append(rdata.address)
+                    if family == socket.AF_INET or family == socket.AF_UNSPEC:
+                        v4 = _resolver.query(host, dns.rdatatype.A,
+                                             raise_on_no_answer=False)
+                        host = v4.qname
+                        canonical_name = v4.canonical_name.to_text(True)
+                        if v4.rrset is not None:
+                            for rdata in v4.rrset:
+                                v4addrs.append(rdata.address)
+                except dns.resolver.NXDOMAIN:
+                    raise socket.gaierror(socket.EAI_NONAME)
+                except:
+                    raise socket.gaierror(socket.EAI_SYSTEM)
+    port = None
+    try:
+        # Is it a port literal?
+        if service is None:
+            port = 0
+        else:
+            port = int(service)
+    except:
+        if flags & socket.AI_NUMERICSERV == 0:
+            try:
+                port = socket.getservbyname(service)
+            except:
+                pass
+    if port is None:
+        raise socket.gaierror(socket.EAI_NONAME)
+    tuples = []
+    if socktype == 0:
+        socktypes = [socket.SOCK_DGRAM, socket.SOCK_STREAM]
+    else:
+        socktypes = [socktype]
+    if flags & socket.AI_CANONNAME != 0:
+        cname = canonical_name
+    else:
+        cname = ''
+    if family == socket.AF_INET6 or family == socket.AF_UNSPEC:
+        for addr in v6addrs:
+            for socktype in socktypes:
+                for proto in _protocols_for_socktype[socktype]:
+                    tuples.append((socket.AF_INET6, socktype, proto,
+                                   cname, (addr, port, 0, 0)))
+    if family == socket.AF_INET or family == socket.AF_UNSPEC:
+        for addr in v4addrs:
+            for socktype in socktypes:
+                for proto in _protocols_for_socktype[socktype]:
+                    tuples.append((socket.AF_INET, socktype, proto,
+                                   cname, (addr, port)))
+    if len(tuples) == 0:
+        raise socket.gaierror(socket.EAI_NONAME)
+    return tuples
+
+def _getnameinfo(sockaddr, flags=0):
+    host = sockaddr[0]
+    port = sockaddr[1]
+    if len(sockaddr) == 4:
+        scope = sockaddr[3]
+        family = socket.AF_INET6
+    else:
+        scope = None
+        family = socket.AF_INET
+    tuples = _getaddrinfo(host, port, family, socket.SOCK_STREAM,
+                          socket.SOL_TCP, 0)
+    if len(tuples) > 1:
+        raise socket.error('sockaddr resolved to multiple addresses')
+    addr = tuples[0][4][0]
+    if flags & socket.NI_DGRAM:
+        pname = 'udp'
+    else:
+        pname = 'tcp'
+    qname = dns.reversename.from_address(addr)
+    if flags & socket.NI_NUMERICHOST == 0:
+        try:
+            answer = _resolver.query(qname, 'PTR')
+            hostname = answer.rrset[0].target.to_text(True)
+        except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
+            if flags & socket.NI_NAMEREQD:
+                raise socket.gaierror(socket.EAI_NONAME)
+            hostname = addr
+            if scope is not None:
+                hostname += '%' + str(scope)
+    else:
+        hostname = addr
+        if scope is not None:
+            hostname += '%' + str(scope)
+    if flags & socket.NI_NUMERICSERV:
+        service = str(port)
+    else:
+        service = socket.getservbyport(port, pname)
+    return (hostname, service)
+
+def _getfqdn(name=None):
+    if name is None:
+        name = socket.gethostname()
+    return _getnameinfo(_getaddrinfo(name, 80)[0][4])[0]
+
+def _gethostbyname(name):
+    return _gethostbyname_ex(name)[2][0]
+
+def _gethostbyname_ex(name):
+    aliases = []
+    addresses = []
+    tuples = _getaddrinfo(name, 0, socket.AF_INET, socket.SOCK_STREAM,
+                         socket.SOL_TCP, socket.AI_CANONNAME)
+    canonical = tuples[0][3]
+    for item in tuples:
+        addresses.append(item[4][0])
+    # XXX we just ignore aliases
+    return (canonical, aliases, addresses)
+
+def _gethostbyaddr(ip):
+    try:
+        addr = dns.ipv6.inet_aton(ip)
+        sockaddr = (ip, 80, 0, 0)
+        family = socket.AF_INET6
+    except:
+        sockaddr = (ip, 80)
+        family = socket.AF_INET
+    (name, port) = _getnameinfo(sockaddr, socket.NI_NAMEREQD)
+    aliases = []
+    addresses = []
+    tuples = _getaddrinfo(name, 0, family, socket.SOCK_STREAM, socket.SOL_TCP,
+                          socket.AI_CANONNAME)
+    canonical = tuples[0][3]
+    for item in tuples:
+        addresses.append(item[4][0])
+    # XXX we just ignore aliases
+    return (canonical, aliases, addresses)
+
+def override_system_resolver(resolver=None):
+    """Override the system resolver routines in the socket module with
+    versions which use dnspython's resolver.
+
+    This can be useful in testing situations where you want to control
+    the resolution behavior of python code without having to change
+    the system's resolver settings (e.g. /etc/resolv.conf).
+
+    The resolver to use may be specified; if it's not, the default
+    resolver will be used.
+
+    @param resolver: the resolver to use
+    @type resolver: dns.resolver.Resolver object or None
+    """
+    if resolver is None:
+        resolver = get_default_resolver()
+    global _resolver
+    _resolver = resolver
+    socket.getaddrinfo = _getaddrinfo
+    socket.getnameinfo = _getnameinfo
+    socket.getfqdn = _getfqdn
+    socket.gethostbyname = _gethostbyname
+    socket.gethostbyname_ex = _gethostbyname_ex
+    socket.gethostbyaddr = _gethostbyaddr
+
+def restore_system_resolver():
+    """Undo the effects of override_system_resolver().
+    """
+    global _resolver
+    _resolver = None
+    socket.getaddrinfo = _original_getaddrinfo
+    socket.getnameinfo = _original_getnameinfo
+    socket.getfqdn = _original_getfqdn
+    socket.gethostbyname = _original_gethostbyname
+    socket.gethostbyname_ex = _original_gethostbyname_ex
+    socket.gethostbyaddr = _original_gethostbyaddr