Refactor and bugfix for resove_service (#4427)

synapse/http/endpoint.py

@@ -12,30 +12,18 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-import collections
 import logging
 import random
 import re
-import time
 
 from twisted.internet import defer
 from twisted.internet.endpoints import HostnameEndpoint, wrapClientTLS
 from twisted.internet.error import ConnectError
-from twisted.names import client, dns
-from twisted.names.error import DNSNameError, DomainError
+
+from synapse.http.federation.srv_resolver import Server, resolve_service
 
 logger = logging.getLogger(__name__)
 
-SERVER_CACHE = {}
-
-# our record of an individual server which can be tried to reach a destination.
-#
-# "host" is the hostname acquired from the SRV record. Except when there's
-# no SRV record, in which case it is the original hostname.
-_Server = collections.namedtuple(
-    "_Server", "priority weight host port expires"
-)
-
 
 def parse_server_name(server_name):
     """Split a server name into host/port parts.
@@ -165,12 +153,9 @@ class SRVClientEndpoint(object):
         self.service_name = "_%s._%s.%s" % (service, protocol, domain)
 
         if default_port is not None:
-            self.default_server = _Server(
+            self.default_server = Server(
                 host=domain,
                 port=default_port,
-                priority=0,
-                weight=0,
-                expires=0,
             )
         else:
             self.default_server = None
@@ -240,57 +225,3 @@ class SRVClientEndpoint(object):
         )
         connection = yield endpoint.connect(protocolFactory)
         defer.returnValue(connection)
-
-
-@defer.inlineCallbacks
-def resolve_service(service_name, dns_client=client, cache=SERVER_CACHE, clock=time):
-    cache_entry = cache.get(service_name, None)
-    if cache_entry:
-        if all(s.expires > int(clock.time()) for s in cache_entry):
-            servers = list(cache_entry)
-            defer.returnValue(servers)
-
-    servers = []
-
-    try:
-        try:
-            answers, _, _ = yield dns_client.lookupService(service_name)
-        except DNSNameError:
-            defer.returnValue([])
-
-        if (len(answers) == 1
-                and answers[0].type == dns.SRV
-                and answers[0].payload
-                and answers[0].payload.target == dns.Name(b'.')):
-            raise ConnectError("Service %s unavailable" % service_name)
-
-        for answer in answers:
-            if answer.type != dns.SRV or not answer.payload:
-                continue
-
-            payload = answer.payload
-
-            servers.append(_Server(
-                host=str(payload.target),
-                port=int(payload.port),
-                priority=int(payload.priority),
-                weight=int(payload.weight),
-                expires=int(clock.time()) + answer.ttl,
-            ))
-
-        servers.sort()
-        cache[service_name] = list(servers)
-    except DomainError as e:
-        # We failed to resolve the name (other than a NameError)
-        # Try something in the cache, else rereaise
-        cache_entry = cache.get(service_name, None)
-        if cache_entry:
-            logger.warn(
-                "Failed to resolve %r, falling back to cache. %r",
-                service_name, e
-            )
-            servers = list(cache_entry)
-        else:
-            raise e
-
-    defer.returnValue(servers)