fix: exit connection cleanly on expected GoAway signal in bidi streaming

Receive the GoAway signal from the Gemini Live API, set a flag on the InvocationContext indicating reconnection is requested, and exit the receive generator cleanly instead of raising a ConnectionClosed exception. This avoids throwing expected session-recycling exceptions into custom client wrappers, which helps prevent false alarms in custom client log monitors.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 937586604
Change-Id: Ic8d85ecadfd50647c9349dcb4c1a4d53518a7621

Author: wukath

src/google/adk/flows/llm_flows/base_llm_flow.py

@@ -57,6 +57,11 @@
 # Prefix used by toolset auth credential IDs
 TOOLSET_AUTH_CREDENTIAL_ID_PREFIX = '_adk_toolset_auth_'
 
+
+class _ReconnectSentinel(Event):
+  """Internal sentinel event to signal a silent reconnection request."""
+
+
 if TYPE_CHECKING:
   from ...agents.llm_agent import LlmAgent
   from ...models.base_llm import BaseLlm
@@ -577,6 +582,7 @@ async def run_live(
               self._send_to_model(llm_connection, invocation_context)
           )
 
+          should_reconnect = False
           try:
             async with Aclosing(
                 self._receive_from_model(
@@ -587,6 +593,9 @@ async def run_live(
                 )
             ) as agen:
               async for event in agen:
+                if isinstance(event, _ReconnectSentinel):
+                  should_reconnect = True
+                  break
                 # Empty event means the queue is closed.
                 if not event:
                   break
@@ -667,6 +676,9 @@ async def run_live(
               await send_task
             except asyncio.CancelledError:
               pass
+        if should_reconnect:
+          continue
+        break
       except (ConnectionClosed, ConnectionClosedOK) as e:
         # If we have a session resumption handle, we attempt to reconnect.
         # This handle is updated dynamically during the session.
@@ -805,9 +817,9 @@ def get_author_for_event(llm_response: LlmResponse) -> str:
           if llm_response.go_away:
             logger.info(f'Received go away signal: {llm_response.go_away}')
             # The server signals that it will close the connection soon.
-            # We proactively raise ConnectionClosed to trigger the reconnection
-            # logic in run_live, which will use the latest session handle.
-            raise ConnectionClosed(None, None)
+            # We yield a sentinel event to request reconnection internally.
+            yield _ReconnectSentinel(author='system')
+            return
 
           model_response_event = Event(
               id=Event.new_id(),

tests/unittests/flows/llm_flows/test_base_llm_flow.py

@@ -22,6 +22,7 @@
 from google.adk.agents.run_config import RunConfig
 from google.adk.events.event import Event
 from google.adk.flows.llm_flows.base_llm_flow import _handle_after_model_callback
+from google.adk.flows.llm_flows.base_llm_flow import _ReconnectSentinel
 from google.adk.flows.llm_flows.base_llm_flow import BaseLlmFlow
 from google.adk.models.google_llm import Gemini
 from google.adk.models.google_llm import GoogleLLMVariant
@@ -728,15 +729,23 @@ async def mock_receive_2():
     ) as mock_connect:
       mock_connect.return_value.__aenter__ = mock_aenter
 
+      yielded_events = []
       try:
-        async for _ in flow.run_live(invocation_context):
-          pass
+        async for event in flow.run_live(invocation_context):
+          yielded_events.append(event)
       except StopError:
         pass
 
       # Verify that we attempted to connect twice (initial + reconnect after go_away).
       assert mock_connect.call_count == 2
 
+      # Verify that the internal _ReconnectSentinel is not leaked/yielded to the caller.
+      assert not any(isinstance(e, _ReconnectSentinel) for e in yielded_events)
+
+      # Verify we yielded the expected response after reconnection.
+      assert len(yielded_events) == 1
+      assert yielded_events[0].content.parts[0].text == 'hi'
+
 
 @pytest.mark.asyncio
 async def test_run_live_no_reconnect_without_handle():