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Diffstat (limited to 'dns/resolver.py')
| -rw-r--r-- | dns/resolver.py | 589 |
1 files changed, 589 insertions, 0 deletions
diff --git a/dns/resolver.py b/dns/resolver.py new file mode 100644 index 0000000..2e3ca20 --- /dev/null +++ b/dns/resolver.py @@ -0,0 +1,589 @@ +# Copyright (C) 2003, 2004 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. + +# $Id: resolver.py,v 1.22 2004/03/19 00:17:27 halley Exp $ + +"""DNS stub resolver. + +@var default_resolver: The default resolver object +@type default_resolver: dns.resolver.Resolver object""" + +import socket +import sys +import time +import types + +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 Answer(object): + """DNS stub resolver answer + + Instances of this class bundle up the result of a successful DNS + resolution. + + For convenience, the answer is iterable. "for a in answer" is + equivalent to "for a in answer.rrset". + + 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) + +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 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.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): + f = open(f, 'r') + 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 _config_win32_nameservers(self, nameservers, split_char=','): + """Configure a NameServer registry entry.""" + # we call str() on nameservers to convert it from unicode to ascii + ns_list = str(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_list = str(search).split(',') + 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(servers) + except WindowsError: + pass + else: + try: + servers, rtype = _winreg.QueryValueEx(key, 'DhcpNameServer') + except WindowsError: + servers = None + if servers: + # Annoyingly, the DhcpNameServer list is apparently space + # separated instead of comma separated like NameServer. + self._config_win32_nameservers(servers, ' ') + try: + dom, rtype = _winreg.QueryValueEx(key, 'DhcpDomain') + if dom: + self._config_win32_domain(servers) + except WindowsError: + pass + try: + search, rtype = _winreg.QueryValueEx(key, 'SearchList') + except WindowsError: + search = None + if search: + self._config_win32_search(servers) + + 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) + try: + # enabled interfaces seem to have a non-empty + # NTEContextList + try: + (nte, ttype) = _winreg.QueryValueEx(key, + 'NTEContextList') + except WindowsError: + nte = None + if nte: + self._config_win32_fromkey(key) + finally: + key.Close() + except EnvironmentError: + break + finally: + interfaces.Close() + finally: + lm.Close() + + def query(self, qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN, + tcp=False): + """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 + @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): + 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) + 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[:] + while response is None: + if len(nameservers) == 0: + raise NoNameservers + for nameserver in nameservers: + now = time.time() + if now < start: + # Time going backwards is bad. Just give up. + raise Timeout + duration = now - start + if duration >= self.lifetime: + raise Timeout + timeout = min(self.lifetime - duration, self.timeout) + try: + if tcp: + response = dns.query.tcp(request, nameserver, + timeout, self.port) + else: + response = dns.query.udp(request, nameserver, + timeout, self.port) + except socket.error: + # + # 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 + response = None + 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): + """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.""" + self.keyring = keyring + if keyname is None: + self.keyname = self.keyring.keys()[0] + else: + self.keyname = keyname + + 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 query(qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN, + tcp=False): + """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.""" + global default_resolver + if default_resolver is None: + default_resolver = Resolver() + return default_resolver.query(qname, rdtype, rdclass, tcp) |