From 9211f4ce8cc6d918df314d6a2ff13da2e0ef35fa Mon Sep 17 00:00:00 2001
From: Shangjie Chen <deanchen@google.com>
Date: Fri, 14 Nov 2025 15:21:56 -0800
Subject: [PATCH] fix: Use `async for` to loop through event iterator to get
 all events in vertex_ai_session_service

Fix https://github.com/google/adk-python/issues/3559

Co-authored-by: Shangjie Chen <deanchen@google.com>
PiperOrigin-RevId: 832476367
---
 .../adk/sessions/vertex_ai_session_service.py |  2 +-
 .../test_vertex_ai_session_service.py         | 63 ++++++++++++++++++-
 2 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/src/google/adk/sessions/vertex_ai_session_service.py b/src/google/adk/sessions/vertex_ai_session_service.py
index 571ae53a..252a69e0 100644
--- a/src/google/adk/sessions/vertex_ai_session_service.py
+++ b/src/google/adk/sessions/vertex_ai_session_service.py
@@ -178,7 +178,7 @@ class VertexAiSessionService(BaseSessionService):
     )
     session.events += [
         _from_api_event(event)
-        for event in events_iterator
+        async for event in events_iterator
         if event.timestamp.timestamp() <= update_timestamp
     ]
 
diff --git a/tests/unittests/sessions/test_vertex_ai_session_service.py b/tests/unittests/sessions/test_vertex_ai_session_service.py
index 29c3c74c..fa80dc9a 100644
--- a/tests/unittests/sessions/test_vertex_ai_session_service.py
+++ b/tests/unittests/sessions/test_vertex_ai_session_service.py
@@ -11,8 +11,8 @@
 # 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 copy
+import datetime
 import re
 import types
 from typing import Any
@@ -130,6 +130,36 @@ MOCK_SESSION_JSON_PAGE2 = {
     'user_id': 'user_with_pages',
 }
 
+MOCK_SESSION_JSON_5 = {
+    'name': (
+        'projects/test-project/locations/test-location/'
+        'reasoningEngines/123/sessions/5'
+    ),
+    'update_time': '2024-12-12T12:15:12.123456Z',
+    'user_id': 'user_with_many_events',
+}
+
+
+def _generate_mock_events_for_session_5(num_events):
+  events = []
+  start_time = isoparse('2024-12-12T12:12:12.123456Z')
+  for i in range(num_events):
+    event_time = start_time + datetime.timedelta(microseconds=i * 1000)
+    events.append({
+        'name': (
+            'projects/test-project/locations/test-location/'
+            f'reasoningEngines/123/sessions/5/events/{i}'
+        ),
+        'invocation_id': f'invocation_{i}',
+        'author': 'user_with_many_events',
+        'timestamp': event_time.isoformat().replace('+00:00', 'Z'),
+    })
+  return events
+
+
+MANY_EVENTS_COUNT = 200
+MOCK_EVENTS_JSON_5 = _generate_mock_events_for_session_5(MANY_EVENTS_COUNT)
+
 MOCK_SESSION = Session(
     app_name='123',
     user_id='user',
@@ -228,6 +258,11 @@ def _convert_to_object(data):
     return data
 
 
+async def to_async_iterator(data):
+  for item in data:
+    yield item
+
+
 class MockAsyncClient:
   """Mocks the API Client."""
 
@@ -330,7 +365,7 @@ class MockAsyncClient:
             for event in events
             if isoparse(event['timestamp']) >= after_timestamp
         ]
-    return [_convert_to_object(event) for event in events]
+    return to_async_iterator([_convert_to_object(event) for event in events])
 
   async def _append_event(
       self,
@@ -496,6 +531,22 @@ async def test_get_session_with_after_timestamp_filter():
   assert session.events[0].id == '456'
 
 
+@pytest.mark.asyncio
+@pytest.mark.usefixtures('mock_get_api_client')
+async def test_get_session_with_many_events(mock_api_client_instance):
+  mock_api_client_instance.session_dict['5'] = MOCK_SESSION_JSON_5
+  mock_api_client_instance.event_dict['5'] = (
+      copy.deepcopy(MOCK_EVENTS_JSON_5),
+      None,
+  )
+  session_service = mock_vertex_ai_session_service()
+  session = await session_service.get_session(
+      app_name='123', user_id='user_with_many_events', session_id='5'
+  )
+  assert session is not None
+  assert len(session.events) == MANY_EVENTS_COUNT
+
+
 @pytest.mark.asyncio
 @pytest.mark.usefixtures('mock_get_api_client')
 async def test_list_sessions():
@@ -524,7 +575,13 @@ async def test_list_sessions_all_users():
   session_service = mock_vertex_ai_session_service()
   sessions = await session_service.list_sessions(app_name='123', user_id=None)
   assert len(sessions.sessions) == 5
-  assert {s.id for s in sessions.sessions} == {'1', '2', '3', 'page1', 'page2'}
+  assert {s.id for s in sessions.sessions} == {
+      '1',
+      '2',
+      '3',
+      'page1',
+      'page2',
+  }
 
 
 @pytest.mark.asyncio