"""DNS module."""
import logging
import dns
from spicerack.exceptions import SpicerackError
logger = logging.getLogger(__name__) # pylint: disable=invalid-name
[docs]class DnsError(SpicerackError):
"""Custom exception class for errors of the Dns class."""
[docs]class DnsNotFound(DnsError):
"""Custom exception class to indicate the record was not found.
One or more resource records exist for this domain but there isn’t a record matching the resource record type.
"""
[docs]class Dns:
"""Class to interact with the DNS."""
def __init__(self, *, nameserver_address=None):
"""Initialize the instance.
Arguments:
nameserver_address (str, optional): the nameserver address to use, if not set uses the OS configuration.
"""
if nameserver_address:
self._resolver = dns.resolver.Resolver(configure=False)
self._resolver.nameservers = [nameserver_address]
else:
self._resolver = dns.resolver.Resolver()
[docs] def resolve_ipv4(self, name):
"""Perform a DNS lookup for an A record for the given name.
Arguments:
name (str): the name to resolve.
Returns:
list: the list of IPv4 addresses as strings returned by the DNS response.
"""
return self._resolve_addresses(name, 'A')
[docs] def resolve_ipv6(self, name):
"""Perform a DNS lookup for an AAAA record for the given name.
Arguments:
name (str): the name to resolve.
Returns:
list: the list of IPv6 addresses as strings returned by the DNS response.
"""
return self._resolve_addresses(name, 'AAAA')
[docs] def resolve_ips(self, name):
"""Perform a DNS lookup for A and AAAA records for the given name.
Arguments:
name (str): the name to resolve.
Returns:
list: the list of IPv4 and IPv6 addresses as strings returned by the DNS response.
Raises:
spicerack.dns.DnsNotFound: when no address is found.
"""
addresses = []
for func in ('resolve_ipv4', 'resolve_ipv6'):
try:
addresses += getattr(self, func)(name)
except DnsNotFound:
pass # Allow single stack answers
if not addresses:
raise DnsNotFound('Record A or AAAA not found for {name}'.format(name=name))
return addresses
[docs] def resolve_ptr(self, address):
"""Perform a DNS lookup for PTR record for the given address.
Arguments:
address (str): the IPv4 or IPv6 address to resolve.
Returns:
list: the list of absolute target PTR records as strings, without the trailing dot.
"""
response = self.resolve(dns.reversename.from_address(address), 'PTR')
return self._parse_targets(response.rrset)
[docs] def resolve_cname(self, name):
"""Perform a DNS lookup for CNAME record for the given name.
Arguments:
name (str): the name to resolve.
Returns:
str: the absolute target name for this CNAME, without the trailing dot.
"""
targets = self._parse_targets(self.resolve(name, 'CNAME').rrset)
if len(targets) != 1:
raise DnsError('Found multiple CNAMEs target for {name}: {targets}'.format(name=name, targets=targets))
return targets[0]
[docs] def resolve(self, qname, record_type):
"""Perform a DNS lookup for the given qname and record type.
Arguments:
qname (str): the name or address to resolve.
record_type (str): the DNS record type to lookup for, like 'A', 'AAAA', 'PTR', etc.
Returns:
dns.resolver.Answer: the DNS response.
Raises:
spicerack.dns.DnsNotFound: if there are no records for the given record type but the qname has records for
different record type(s).
spicerack.dns.DnsError: on generic error.
"""
try:
response = self._resolver.query(qname, record_type)
logger.debug('Resolved %s record for %s: %s', record_type, qname, response.rrset)
except (dns.resolver.NoAnswer, dns.resolver.NXDOMAIN) as e:
raise DnsNotFound('Record {record_type} not found for {qname}'.format(
record_type=record_type, qname=qname)) from e
except dns.exception.DNSException as e:
raise DnsError('Unable to resolve {record_type} record for {qname}'.format(
record_type=record_type, qname=qname)) from e
return response
def _resolve_addresses(self, name, record_type):
"""Extract and return all the matching addresses for the given name and record type.
Arguments:
name (str): the name to resolve.
record_type (str): the DNS record type to lookup for, like 'A' and 'AAAA'.
Returns:
list: the list of IPv4 or IPv6 addresses as strings returned by the DNS response.
"""
return [rdata.address for rdata in self.resolve(name, record_type).rrset]
@staticmethod
def _parse_targets(rrset):
"""Extract and return all the matching names from the given rrset without the trailing dot.
Arguments:
rrset (dns.rrset.RRset): the RRset to parse.
Returns:
list: the list of absolute target record names as strings without the trailing dot.
Raises:
spicerack.dns.DnsError: if a relative record is found.
"""
targets = []
for rdata in rrset:
target = rdata.target.to_text()
if target[-1] != '.':
raise DnsError('Unsupported relative target {target} found'.format(target=target))
targets.append(target[:-1])
return targets