PYTHON-4007 Stop sending exhaustAllowed to Serverless/load balanced clusters unless configured (#1405)

doc/changelog.rst

@@ -28,6 +28,8 @@ PyMongo 4.6 brings a number of improvements including:
 - :meth:`~pymongo.uri_parser.parse_uri` now considers the delimiting slash (``/``)
   between hosts and connection options optional. For example,
   "mongodb://example.com?tls=true" is now a valid URI.
+- Fixed a bug where PyMongo would incorrectly promote all cursors to exhaust cursors
+  when connected to load balanced MongoDB clusters or Serverless clusters.
 
 Changes in Version 4.5
 ----------------------

pymongo/message.py

@@ -565,7 +565,7 @@ class _GetMore:
 
         if use_cmd:
             spec = self.as_command(conn, apply_timeout=True)[0]
-            if self.conn_mgr:
+            if self.conn_mgr and self.exhaust:
                 flags = _OpMsg.EXHAUST_ALLOWED
             else:
                 flags = 0

test/mockupdb/test_cursor.py

@@ -0,0 +1,61 @@
+# Copyright 2023-present MongoDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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.
+
+"""Test PyMongo cursor does not set exhaustAllowed automatically (PYTHON-4007)."""
+from __future__ import annotations
+
+import unittest
+
+from mockupdb import MockupDB, OpMsg, going
+
+from bson.objectid import ObjectId
+from pymongo import MongoClient
+
+
+class TestCursor(unittest.TestCase):
+    def test_getmore_load_balanced(self):
+        server = MockupDB()
+        server.autoresponds(
+            "hello",
+            isWritablePrimary=True,
+            msg="isdbgrid",
+            minWireVersion=0,
+            maxWireVersion=20,
+            helloOk=True,
+            serviceId=ObjectId(),
+        )
+        server.run()
+        self.addCleanup(server.stop)
+
+        client = MongoClient(server.uri, loadBalanced=True)
+        self.addCleanup(client.close)
+        collection = client.db.coll
+        cursor = collection.find()
+        with going(next, cursor):
+            request = server.receives(OpMsg({"find": "coll"}))
+            self.assertEqual(request.flags, 0, "exhaustAllowed should not be set")
+            # Respond with a different namespace.
+            request.reply({"cursor": {"id": 123, "firstBatch": [{}]}})
+
+        # 3 batches, check exhaustAllowed on all getMores.
+        for i in range(1, 3):
+            with going(next, cursor):
+                request = server.receives(OpMsg({"getMore": 123}))
+                self.assertEqual(request.flags, 0, "exhaustAllowed should not be set")
+                cursor_id = 123 if i < 2 else 0
+                request.replies({"cursor": {"id": cursor_id, "nextBatch": [{}]}})
+
+
+if __name__ == "__main__":
+    unittest.main()