fix: treat SQLite database update time as UTC for session's last update time

src/google/adk/sessions/database_session_service.py

@@ -15,6 +15,7 @@
 
 import copy
 from datetime import datetime
+from datetime import timezone
 import json
 import logging
 from typing import Any
@@ -144,6 +145,21 @@ class StorageSession(Base):
   def __repr__(self):
     return f"<StorageSession(id={self.id}, update_time={self.update_time})>"
 
+  @property
+  def _dialect_name(self) -> Optional[str]:
+    session = inspect(self).session
+    return session.bind.dialect.name if session else None
+
+  @property
+  def update_timestamp_tz(self) -> datetime:
+    """Returns the time zone aware update timestamp."""
+    if self._dialect_name == "sqlite":
+      # SQLite does not support timezone. SQLAlchemy returns a naive datetime
+      # object without timezone information. We need to convert it to UTC
+      # manually.
+      return self.update_time.replace(tzinfo=timezone.utc).timestamp()
+    return self.update_time.timestamp()
+
 
 class StorageEvent(Base):
   """Represents an event stored in the database."""
@@ -412,7 +428,7 @@ async def create_session(
           user_id=str(storage_session.user_id),
           id=str(storage_session.id),
           state=merged_state,
-          last_update_time=storage_session.update_time.timestamp(),
+          last_update_time=storage_session.update_timestamp_tz,
       )
       return session
 
@@ -473,7 +489,7 @@ async def get_session(
           user_id=user_id,
           id=session_id,
           state=merged_state,
-          last_update_time=storage_session.update_time.timestamp(),
+          last_update_time=storage_session.update_timestamp_tz,
       )
       session.events = [e.to_event() for e in reversed(storage_events)]
     return session
@@ -496,7 +512,7 @@ async def list_sessions(
             user_id=user_id,
             id=storage_session.id,
             state={},
-            last_update_time=storage_session.update_time.timestamp(),
+            last_update_time=storage_session.update_timestamp_tz,
         )
         sessions.append(session)
       return ListSessionsResponse(sessions=sessions)
@@ -529,13 +545,13 @@ async def append_event(self, session: Session, event: Event) -> Event:
           StorageSession, (session.app_name, session.user_id, session.id)
       )
 
-      if storage_session.update_time.timestamp() > session.last_update_time:
+      if storage_session.update_timestamp_tz > session.last_update_time:
         raise ValueError(
             "The last_update_time provided in the session object"
             f" {datetime.fromtimestamp(session.last_update_time):'%Y-%m-%d %H:%M:%S'} is"
             " earlier than the update_time in the storage_session"
-            f" {storage_session.update_time:'%Y-%m-%d %H:%M:%S'}. Please check"
-            " if it is a stale session."
+            f" {datetime.fromtimestamp(storage_session.update_timestamp_tz):'%Y-%m-%d %H:%M:%S'}."
+            " Please check if it is a stale session."
         )
 
       # Fetch states from storage
@@ -577,7 +593,7 @@ async def append_event(self, session: Session, event: Event) -> Event:
       session_factory.refresh(storage_session)
 
       # Update timestamp with commit time
-      session.last_update_time = storage_session.update_time.timestamp()
+      session.last_update_time = storage_session.update_timestamp_tz
 
     # Also update the in-memory session
     await super().append_event(session=session, event=event)

tests/unittests/sessions/test_session_service.py

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from datetime import datetime
+from datetime import timezone
 import enum
 
 from google.adk.events import Event
@@ -66,10 +68,17 @@ async def test_create_get_session(service_type):
   assert session.id
   assert session.state == state
   assert (
-      await session_service.get_session(
-          app_name=app_name, user_id=user_id, session_id=session.id
-      )
-      == session
+      session.last_update_time
+      <= datetime.now().astimezone(timezone.utc).timestamp()
+  )
+
+  got_session = await session_service.get_session(
+      app_name=app_name, user_id=user_id, session_id=session.id
+  )
+  assert got_session == session
+  assert (
+      got_session.last_update_time
+      <= datetime.now().astimezone(timezone.utc).timestamp()
   )
 
   session_id = session.id