+ # See https://twistedmatrix.com/documents/13.1.0/api/twisted.internet.defer.html#inlineCallbacks
+ @defer.inlineCallbacks
+ def _lookup(self, name, cls, type, timeout = None):
+ try:
+ result = yield authority.BindAuthority._lookup(self, name, cls,
+ type, timeout)
+ defer.returnValue(result)
+ except dns.AuthoritativeDomainError:
+ # If we didn't find an exact match for the name we were
+ # seeking, check if it's within a subdomain we're supposed
+ # to delegate to some other DNS server.
+ while '.' in name:
+ _, name = name.split('.', 1)
+ try:
+ # BindAuthority puts the NS in the authority
+ # section automatically for us, so just return
+ # it. We override the type to NS.
+ result = yield authority.BindAuthority._lookup(self, name, cls,
+ dns.NS, timeout)
+ defer.returnValue(result)
+ except (dns.DomainError, dns.AuthoritativeDomainError):
+ pass
+ # We didn't find a delegation, so return the original
+ # NXDOMAIN.
+ raise
+
+class TypeLenientResolverChain(resolve.ResolverChain):
+ """
+ This is a ResolverChain which is more lenient in its handling of
+ queries requesting unimplemented record types.
+ """
+
+ def query(self, query, timeout = None):
+ try:
+ return self.typeToMethod[query.type](str(query.name), timeout)
+ except KeyError, e:
+ # We don't support the requested record type. Twisted would
+ # have us return SERVFAIL. Instead, we'll check whether the
+ # name exists in our zone at all and return NXDOMAIN or an empty
+ # result set with NOERROR as appropriate.
+ deferredResult = self.lookupAllRecords(str(query.name), timeout)
+ if isinstance(deferredResult.result, failure.Failure):
+ return deferredResult
+ return defer.succeed(([], [], []))
+