McpToolset does not handle MCP server restart #3321
Description
Describe the bug
If a ClientSession is created by an McpToolset, that session will be reused for any request with the same headers. However, if the MCP server suddenly restarts, the session is not marked as disconnected (MCPSessionManager._is_session_disconnected() still returns False), so the toolset will try to use it again on subsequent requests, resulting in a Session Terminated error.
ERROR: Exception in ASGI application
Traceback (most recent call last):
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\uvicorn\protocols\http\h11_impl.py", line 403, in run_asgi
result = await app( # type: ignore[func-returns-value]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
self.scope, self.receive, self.send
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\uvicorn\middleware\proxy_headers.py", line 60, in __call__
return await self.app(scope, receive, send)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\fastapi\applications.py", line 1134, in __call__
await super().__call__(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\applications.py", line 113, in __call__
await self.middleware_stack(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\middleware\errors.py", line 186, in __call__
raise exc
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\middleware\errors.py", line 164, in __call__
await self.app(scope, receive, _send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\middleware\exceptions.py", line 63, in __call__
await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\_exception_handler.py", line 53, in wrapped_app
raise exc
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\_exception_handler.py", line 42, in wrapped_app
await app(scope, receive, sender)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\fastapi\middleware\asyncexitstack.py", line 18, in __call__
await self.app(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\routing.py", line 716, in __call__
await self.middleware_stack(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\routing.py", line 736, in app
await route.handle(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\routing.py", line 290, in handle
await self.app(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\fastapi\routing.py", line 124, in app
await wrap_app_handling_exceptions(app, request)(scope, receive, send)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\_exception_handler.py", line 53, in wrapped_app
raise exc
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\starlette\_exception_handler.py", line 42, in wrapped_app
await app(scope, receive, sender)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\fastapi\routing.py", line 110, in app
response = await f(request)
^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\fastapi\routing.py", line 390, in app
raw_response = await run_endpoint_function(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...<3 lines>...
)
^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\fastapi\routing.py", line 289, in run_endpoint_function
return await dependant.call(**values)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\cli\adk_web_server.py", line 1387, in run_agent
events = [event async for event in agen]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\runners.py", line 442, in run_async
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\runners.py", line 426, in _run_with_trace
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\runners.py", line 652, in _exec_with_plugin
async for event in agen:
...<9 lines>...
yield (modified_event if modified_event else event)
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\runners.py", line 415, in execute
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\agents\base_agent.py", line 294, in run_async
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\agents\llm_agent.py", line 408, in _run_async_impl
async for event in agen:
...<3 lines>...
return
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 356, in run_async
async for event in agen:
last_event = event
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 429, in _run_one_step_async
async for event in agen:
...<3 lines>...
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 531, in _postprocess_async
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 689, in _postprocess_handle_function_calls_async
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\agents\base_agent.py", line 294, in run_async
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\agents\llm_agent.py", line 408, in _run_async_impl
async for event in agen:
...<3 lines>...
return
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 356, in run_async
async for event in agen:
last_event = event
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 375, in _run_one_step_async
async for event in agen:
yield event
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\flows\llm_flows\base_llm_flow.py", line 472, in _preprocess_async
tools = await _convert_tool_union_to_tools(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...<4 lines>...
)
^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\agents\llm_agent.py", line 160, in _convert_tool_union_to_tools
return await tool_union.get_tools_with_prefix(ctx)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\tools\base_toolset.py", line 114, in get_tools_with_prefix
tools = await self.get_tools(readonly_context)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\tools\mcp_tool\mcp_session_manager.py", line 128, in wrapper
return await func(self, *args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\google\adk\tools\mcp_tool\mcp_toolset.py", line 180, in get_tools
tools_response: ListToolsResult = await session.list_tools()
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\mcp\client\session.py", line 482, in list_tools
result = await self.send_request(
^^^^^^^^^^^^^^^^^^^^^^^^
...<2 lines>...
)
^
File "d:\workdir\xff\adk-testing\.venv\Lib\site-packages\mcp\shared\session.py", line 286, in send_request
raise McpError(response_or_error.error)
mcp.shared.exceptions.McpError: Session terminated
To Reproduce
- Have an agent execute a tool call provided by an McpToolset.
- Restart the MCP server.
- Send a message to the same agent. When it tries to list tools in the McpToolset, it will reuse the same (now terminated) session, resulting in the error.
Expected behavior
If the session was terminated, a new session should be started.
Desktop:
- Windows
- Python 3.13.2
- google-adk 1.17.0