PYTHON-2791 Ignore erroneous serviceId field for non-LB connections (#663)

(cherry picked from commit b823b95)

Author: ShaneHarvey

pymongo/pool.py

@@ -634,6 +634,8 @@ def _ismaster(self, cluster_time, topology_version,
         if self.opts.load_balanced and _MOCK_SERVICE_ID:
             process_id = doc.get('topologyVersion', {}).get('processId')
             doc.setdefault('serviceId', process_id)
+        if not self.opts.load_balanced:
+            doc.pop('serviceId', None)
         ismaster = IsMaster(doc, awaitable=awaitable)
         self.is_writable = ismaster.is_writable
         self.max_wire_version = ismaster.max_wire_version
@@ -671,6 +673,9 @@ def _next_reply(self):
         unpacked_docs = reply.unpack_response()
         response_doc = unpacked_docs[0]
         helpers._check_command_response(response_doc, self.max_wire_version)
+        # Remove after PYTHON-2712.
+        if not self.opts.load_balanced:
+            response_doc.pop('serviceId', None)
         return response_doc
 
     def command(self, dbname, spec, slave_ok=False,

pymongo/topology_description.py

@@ -361,7 +361,7 @@ def updated_topology_description(topology_description, server_description):
             topology_description._topology_settings)
 
     if topology_type == TOPOLOGY_TYPE.Unknown:
-        if server_type == SERVER_TYPE.Standalone:
+        if server_type in (SERVER_TYPE.Standalone, SERVER_TYPE.LoadBalancer):
             if len(topology_description._topology_settings.seeds) == 1:
                 topology_type = TOPOLOGY_TYPE.Single
             else:

test/test_topology.py

@@ -18,7 +18,9 @@
 
 sys.path[0:0] = [""]
 
+from bson.objectid import ObjectId
 from bson.py3compat import imap
+
 from pymongo import common
 from pymongo.read_preferences import ReadPreference, Secondary
 from pymongo.server_type import SERVER_TYPE
@@ -294,7 +296,7 @@ def test_readable_writable(self):
             'setName': 'rs',
             'hosts': ['a', 'b']})
 
-        self.assertTrue(
+        self.assertEqual(
             t.description.topology_type_name, 'ReplicaSetWithPrimary')
         self.assertTrue(t.description.has_writable_server())
         self.assertTrue(t.description.has_readable_server())
@@ -319,7 +321,7 @@ def test_readable_writable(self):
             'setName': 'rs',
             'hosts': ['a', 'b']})
 
-        self.assertTrue(
+        self.assertEqual(
             t.description.topology_type_name, 'ReplicaSetNoPrimary')
         self.assertFalse(t.description.has_writable_server())
         self.assertFalse(t.description.has_readable_server())
@@ -344,7 +346,7 @@ def test_readable_writable(self):
             'hosts': ['a', 'b'],
             'tags': {'tag': 'exists'}})
 
-        self.assertTrue(
+        self.assertEqual(
             t.description.topology_type_name, 'ReplicaSetWithPrimary')
         self.assertTrue(t.description.has_writable_server())
         self.assertTrue(t.description.has_readable_server())
@@ -680,6 +682,26 @@ def test_topology_repr(self):
             "<ServerDescription ('c', 27017) server_type: Unknown,"
             " rtt: None>]>" % (t._topology_id,))
 
+    def test_unexpected_load_balancer(self):
+        # Note: This behavior should not be reachable in practice but we
+        # should handle it gracefully nonetheless. See PYTHON-2791.
+        # Load balancers are included in topology with a single seed.
+        t = create_mock_topology(seeds=['a'])
+        mock_lb_response = {'ok': 1, 'msg': 'isdbgrid',
+                            'serviceId': ObjectId(), 'maxWireVersion': 13}
+        got_ismaster(t, ('a', 27017), mock_lb_response)
+        sds = t.description.server_descriptions()
+        self.assertIn(('a', 27017), sds)
+        self.assertEqual(sds[('a', 27017)].server_type_name, 'LoadBalancer')
+        self.assertEqual(t.description.topology_type_name, 'Single')
+        self.assertTrue(t.description.has_writable_server())
+
+        # Load balancers are removed from a topology with multiple seeds.
+        t = create_mock_topology(seeds=['a', 'b'])
+        got_ismaster(t, ('a', 27017), mock_lb_response)
+        self.assertNotIn(('a', 27017), t.description.server_descriptions())
+        self.assertEqual(t.description.topology_type_name, 'Unknown')
+
 
 def wait_for_master(topology):
     """Wait for a Topology to discover a writable server.