Merge pull request #3016 from silkeh/improve-service-lookups
Improve handling of SRV records for federation connections
This commit is contained in:
Richard van der Hoff
GitHub
commit
664adb4236
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@ -12,8 +12,6 @@
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import socket
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from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
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from twisted.internet import defer, reactor
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from twisted.internet.error import ConnectError
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@ -33,7 +31,7 @@ SERVER_CACHE = {}
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# our record of an individual server which can be tried to reach a destination.
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#
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# "host" is actually a dotted-quad or ipv6 address string. Except when there's
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# "host" is the hostname acquired from the SRV record. Except when there's
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# no SRV record, in which case it is the original hostname.
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_Server = collections.namedtuple(
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"_Server", "priority weight host port expires"
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@ -297,20 +295,13 @@ def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=t
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payload = answer.payload
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hosts = yield _get_hosts_for_srv_record(
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dns_client, str(payload.target)
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)
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for (ip, ttl) in hosts:
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host_ttl = min(answer.ttl, ttl)
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servers.append(_Server(
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host=ip,
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port=int(payload.port),
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priority=int(payload.priority),
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weight=int(payload.weight),
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expires=int(clock.time()) + host_ttl,
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))
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servers.append(_Server(
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host=str(payload.target),
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port=int(payload.port),
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priority=int(payload.priority),
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weight=int(payload.weight),
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expires=int(clock.time()) + answer.ttl,
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))
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servers.sort()
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cache[service_name] = list(servers)
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@ -328,81 +319,3 @@ def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=t
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raise e
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defer.returnValue(servers)
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@defer.inlineCallbacks
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def _get_hosts_for_srv_record(dns_client, host):
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"""Look up each of the hosts in a SRV record
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Args:
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dns_client (twisted.names.dns.IResolver):
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host (basestring): host to look up
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Returns:
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Deferred[list[(str, int)]]: a list of (host, ttl) pairs
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"""
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ip4_servers = []
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ip6_servers = []
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def cb(res):
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# lookupAddress and lookupIP6Address return a three-tuple
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# giving the answer, authority, and additional sections of the
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# response.
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#
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# we only care about the answers.
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return res[0]
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def eb(res, record_type):
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if res.check(DNSNameError):
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return []
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logger.warn("Error looking up %s for %s: %s", record_type, host, res)
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return res
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# no logcontexts here, so we can safely fire these off and gatherResults
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d1 = dns_client.lookupAddress(host).addCallbacks(
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cb, eb, errbackArgs=("A", ))
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d2 = dns_client.lookupIPV6Address(host).addCallbacks(
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cb, eb, errbackArgs=("AAAA", ))
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results = yield defer.DeferredList(
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[d1, d2], consumeErrors=True)
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# if all of the lookups failed, raise an exception rather than blowing out
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# the cache with an empty result.
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if results and all(s == defer.FAILURE for (s, _) in results):
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defer.returnValue(results[0][1])
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for (success, result) in results:
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if success == defer.FAILURE:
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continue
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for answer in result:
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if not answer.payload:
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continue
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try:
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if answer.type == dns.A:
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ip = answer.payload.dottedQuad()
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ip4_servers.append((ip, answer.ttl))
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elif answer.type == dns.AAAA:
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ip = socket.inet_ntop(
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socket.AF_INET6, answer.payload.address,
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)
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ip6_servers.append((ip, answer.ttl))
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else:
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# the most likely candidate here is a CNAME record.
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# rfc2782 says srvs may not point to aliases.
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logger.warn(
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"Ignoring unexpected DNS record type %s for %s",
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answer.type, host,
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)
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continue
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except Exception as e:
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logger.warn("Ignoring invalid DNS response for %s: %s",
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host, e)
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continue
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# keep the ipv4 results before the ipv6 results, mostly to match historical
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# behaviour.
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defer.returnValue(ip4_servers + ip6_servers)
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@ -33,8 +33,6 @@ class DnsTestCase(unittest.TestCase):
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service_name = "test_service.example.com"
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host_name = "example.com"
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ip_address = "127.0.0.1"
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ip6_address = "::1"
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answer_srv = dns.RRHeader(
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type=dns.SRV,
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@ -43,29 +41,9 @@ class DnsTestCase(unittest.TestCase):
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)
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)
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answer_a = dns.RRHeader(
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type=dns.A,
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payload=dns.Record_A(
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address=ip_address,
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)
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)
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answer_aaaa = dns.RRHeader(
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type=dns.AAAA,
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payload=dns.Record_AAAA(
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address=ip6_address,
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)
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)
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dns_client_mock.lookupService.return_value = defer.succeed(
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([answer_srv], None, None),
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)
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dns_client_mock.lookupAddress.return_value = defer.succeed(
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([answer_a], None, None),
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)
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dns_client_mock.lookupIPV6Address.return_value = defer.succeed(
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([answer_aaaa], None, None),
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)
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cache = {}
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@ -74,13 +52,10 @@ class DnsTestCase(unittest.TestCase):
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)
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dns_client_mock.lookupService.assert_called_once_with(service_name)
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dns_client_mock.lookupAddress.assert_called_once_with(host_name)
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dns_client_mock.lookupIPV6Address.assert_called_once_with(host_name)
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self.assertEquals(len(servers), 2)
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self.assertEquals(len(servers), 1)
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self.assertEquals(servers, cache[service_name])
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self.assertEquals(servers[0].host, ip_address)
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self.assertEquals(servers[1].host, ip6_address)
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self.assertEquals(servers[0].host, host_name)
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@defer.inlineCallbacks
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def test_from_cache_expired_and_dns_fail(self):
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