def _discoverAuthority(self, query, servers, timeout, queriesLeft):
"""
Issue a query to a server and follow a delegation if necessary.
@param query: The query to issue.
@type query: L{dns.Query}
@param servers: The servers which might have an answer for this
query.
@type servers: L{list} of L{tuple} of L{str} and L{int}
@param timeout: A C{tuple} of C{int} giving the timeout to use for this
query.
@param queriesLeft: A C{int} giving the number of queries which may
yet be attempted to answer this query before the attempt will be
abandoned.
@return: A L{Deferred} which fires with a three-tuple of lists of
L{twisted.names.dns.RRHeader} giving the response, or with a
L{Failure} if there is a timeout or response error.
"""
# Stop now if we've hit the query limit.
if queriesLeft <= 0:
return Failure(
error.ResolverError("Query limit reached without result"))
d = self._query(query, servers, timeout, False)
d.addCallback(
self._discoveredAuthority, query, timeout, queriesLeft - 1)
return d
def _discoveredAuthority(self, response, query, timeout, queriesLeft):
"""
Interpret the response to a query, checking for error codes and
following delegations if necessary.
@param response: The L{Message} received in response to issuing C{query}.
@type response: L{Message}
@param query: The L{dns.Query} which was issued.
@type query: L{dns.Query}.
@param timeout: The timeout to use if another query is indicated by
this response.
@type timeout: L{tuple} of L{int}
@param queriesLeft: A C{int} giving the number of queries which may
yet be attempted to answer this query before the attempt will be
abandoned.
@return: A L{Failure} indicating a response error, a three-tuple of
lists of L{twisted.names.dns.RRHeader} giving the response to
C{query} or a L{Deferred} which will fire with one of those.
"""
if response.rCode != dns.OK:
return Failure(self.exceptionForCode(response.rCode)(response))
# Turn the answers into a structure that's a little easier to work with.
records = {}
for answer in response.answers:
records.setdefault(answer.name, []).append(answer)
def findAnswerOrCName(name, type, cls):
cname = None
for record in records.get(name, []):
if record.cls == cls:
if record.type == type:
return record
elif record.type == dns.CNAME:
cname = record
# If there were any CNAME records, return the last one. There's
# only supposed to be zero or one, though.
return cname
seen = set()
name = query.name
record = None
while True:
seen.add(name)
previous = record
record = findAnswerOrCName(name, query.type, query.cls)
if record is None:
if name == query.name:
# If there's no answer for the original name, then this may
# be a delegation. Code below handles it.
break
else:
# Try to resolve the CNAME with another query.
d = self._discoverAuthority(
dns.Query(str(name), query.type, query.cls),
self._roots(), timeout, queriesLeft)
# We also want to include the CNAME in the ultimate result,
# otherwise this will be pretty confusing.
def cbResolved(results):
answers, authority, additional = results
answers.insert(0, previous)
return (answers, authority, additional)
d.addCallback(cbResolved)
return d
elif record.type == query.type:
return (
response.answers,
response.authority,
response.additional)
else:
# It's a CNAME record. Try to resolve it from the records
# in this response with another iteration around the loop.
if record.payload.name in seen:
raise error.ResolverError("Cycle in CNAME processing")
name = record.payload.name
# Build a map to use to convert NS names into IP addresses.
addresses = {}
for rr in response.additional:
if rr.type == dns.A:
addresses[rr.name.name] = rr.payload.dottedQuad()
hints = []
traps = []
for rr in response.authority:
if rr.type == dns.NS:
ns = rr.payload.name.name
if ns in addresses:
hints.append((addresses[ns], dns.PORT))
else:
traps.append(ns)
if hints:
return self._discoverAuthority(
query, hints, timeout, queriesLeft)
elif traps:
d = self.lookupAddress(traps[0], timeout)
def getOneAddress(results):
answers, authority, additional = results
return answers[0].payload.dottedQuad()
d.addCallback(getOneAddress)
d.addCallback(
lambda hint: self._discoverAuthority(
query, [(hint, dns.PORT)], timeout, queriesLeft - 1))
return d
else:
return Failure(error.ResolverError(
"Stuck at response without answers or delegation"))
def _discoveredAuthority(self, response, query, timeout, queriesLeft):
"""
Interpret the response to a query, following CNAMES if necessary.
@param response: The L{Message} received in response to issuing C{query}.
@type response: L{Message}
@param query: The L{dns.Query} which was issued.
@type query: L{dns.Query}.
@param timeout: The timeout to use if another query is indicated by
this response.
@type timeout: L{tuple} of L{int}
@param queriesLeft: A C{int} giving the number of queries which may
yet be attempted to answer this query before the attempt will be
abandoned.
@return: A L{Failure} indicating a response error, a three-tuple of
lists of L{twisted.names.dns.RRHeader} giving the response to
C{query} or a L{Deferred} which will fire with one of those.
"""
answers, authority, additional = response
if not answers:
return Failure(error.DomainError())
# Turn the answers into a structure that's a little easier to work with.
records = {}
for answer in answers:
records.setdefault(answer.name, []).append(answer)
def findAnswerOrCName(name, type, cls):
cname = None
for record in records.get(name, []):
if record.cls == cls:
if record.type == type:
return record
elif record.type == dns.CNAME:
cname = record
# If there were any CNAME records, return the last one. There's
# only supposed to be zero or one, though.
return cname
seen = set()
name = query.name
record = None
while True:
seen.add(name)
previous = record
record = findAnswerOrCName(name, query.type, query.cls)
if record is None:
if name == query.name:
# If there's no answer for the original name, then this may
# be a delegation. Code below handles it.
break
else:
# Try to resolve the CNAME with another query.
d = self._discoverAuthority(
dns.Query(str(name), query.type, query.cls),
timeout, queriesLeft)
# We also want to include the CNAME in the ultimate result,
# otherwise this will be pretty confusing.
def cbResolved(results):
answers, authority, additional = results
answers.insert(0, previous)
return (answers, authority, additional)
d.addCallback(cbResolved)
return d
elif record.type == query.type:
return (
answers,
authority,
additional)
else:
# It's a CNAME record. Try to resolve it from the records
# in this response with another iteration around the loop.
if record.payload.name in seen:
raise error.ResolverError("Cycle in CNAME processing")
name = record.payload.name
return Failure(error.DomainError())
