Exception in ClientSessionGroup if streamable_http MCP server is not available #915
Description
Describe the bug
When I use the ClientSessionGroup for a remote MCP server via remote_http for a remote server that is not running, I get exception RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
(complete output collapsed)
an error occurred during closing of asynchronous generator <async_generator object streamablehttp_client at 0xffffa53755d0>
asyncgen: <async_generator object streamablehttp_client at 0xffffa53755d0>
+ Exception Group Traceback (most recent call last):
| File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
| raise BaseExceptionGroup(
| "unhandled errors in a TaskGroup", self._exceptions
| ) from None
| BaseExceptionGroup: unhandled errors in a TaskGroup (2 sub-exceptions)
+-+---------------- 1 ----------------
| Traceback (most recent call last):
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_transports/default.py", line 101, in map_httpcore_exceptions
| yield
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_transports/default.py", line 394, in handle_async_request
| resp = await self._pool.handle_async_request(req)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_async/connection_pool.py", line 256, in handle_async_request
| raise exc from None
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_async/connection_pool.py", line 236, in handle_async_request
| response = await connection.handle_async_request(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| pool_request.request
| ^^^^^^^^^^^^^^^^^^^^
| )
| ^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_async/connection.py", line 101, in handle_async_request
| raise exc
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_async/connection.py", line 78, in handle_async_request
| stream = await self._connect(request)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_async/connection.py", line 124, in _connect
| stream = await self._network_backend.connect_tcp(**kwargs)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_backends/auto.py", line 31, in connect_tcp
| return await self._backend.connect_tcp(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ...<5 lines>...
| )
| ^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_backends/anyio.py", line 113, in connect_tcp
| with map_exceptions(exc_map):
| ~~~~~~~~~~~~~~^^^^^^^^^
| File "/usr/local/lib/python3.13/contextlib.py", line 162, in __exit__
| self.gen.throw(value)
| ~~~~~~~~~~~~~~^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpcore/_exceptions.py", line 14, in map_exceptions
| raise to_exc(exc) from exc
| httpcore.ConnectError: All connection attempts failed
|
| The above exception was the direct cause of the following exception:
|
| Traceback (most recent call last):
| File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/streamable_http.py", line 391, in handle_request_async
| await self._handle_post_request(ctx)
| File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/streamable_http.py", line 251, in _handle_post_request
| async with ctx.client.stream(
| ~~~~~~~~~~~~~~~~~^
| "POST",
| ^^^^^^^
| ...<2 lines>...
| headers=headers,
| ^^^^^^^^^^^^^^^^
| ) as response:
| ^
| File "/usr/local/lib/python3.13/contextlib.py", line 214, in __aenter__
| return await anext(self.gen)
| ^^^^^^^^^^^^^^^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_client.py", line 1583, in stream
| response = await self.send(
| ^^^^^^^^^^^^^^^^
| ...<4 lines>...
| )
| ^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_client.py", line 1629, in send
| response = await self._send_handling_auth(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ...<4 lines>...
| )
| ^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_client.py", line 1657, in _send_handling_auth
| response = await self._send_handling_redirects(
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ...<3 lines>...
| )
| ^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_client.py", line 1694, in _send_handling_redirects
| response = await self._send_single_request(request)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_client.py", line 1730, in _send_single_request
| response = await transport.handle_async_request(request)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_transports/default.py", line 393, in handle_async_request
| with map_httpcore_exceptions():
| ~~~~~~~~~~~~~~~~~~~~~~~^^
| File "/usr/local/lib/python3.13/contextlib.py", line 162, in __exit__
| self.gen.throw(value)
| ~~~~~~~~~~~~~~^^^^^^^
| File "/workspaces/test/.venv/lib/python3.13/site-packages/httpx/_transports/default.py", line 118, in map_httpcore_exceptions
| raise mapped_exc(message) from exc
| httpx.ConnectError: All connection attempts failed
+---------------- 2 ----------------
| Traceback (most recent call last):
| File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/streamable_http.py", line 492, in streamablehttp_client
| yield (
| ...<3 lines>...
| )
| GeneratorExit
+------------------------------------
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/streamable_http.py", line 464, in streamablehttp_client
async with anyio.create_task_group() as tg:
~~~~~~~~~~~~~~~~~~~~~~~^^
File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 778, in __aexit__
if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 457, in __exit__
raise RuntimeError(
...<2 lines>...
)
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
Traceback (most recent call last):
File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/streams/memory.py", line 111, in receive
return self.receive_nowait()
~~~~~~~~~~~~~~~~~~~^^
File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/streams/memory.py", line 106, in receive_nowait
raise WouldBlock
anyio.WouldBlock
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/workspaces/test.py", line 14, in <module>
asyncio.run(main())
~~~~~~~~~~~^^^^^^^^
File "/usr/local/lib/python3.13/asyncio/runners.py", line 195, in run
return runner.run(main)
~~~~~~~~~~^^^^^^
File "/usr/local/lib/python3.13/asyncio/runners.py", line 118, in run
return self._loop.run_until_complete(task)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/usr/local/lib/python3.13/asyncio/base_events.py", line 719, in run_until_complete
return future.result()
~~~~~~~~~~~~~^^
File "/workspaces/test.py", line 10, in main
await client_session_group.connect_to_server(server_params)
File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/session_group.py", line 232, in connect_to_server
server_info, session = await self._establish_session(server_params)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/session_group.py", line 267, in _establish_session
result = await session.initialize()
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/client/session.py", line 133, in initialize
result = await self.send_request(
^^^^^^^^^^^^^^^^^^^^^^^^
...<15 lines>...
)
^
File "/workspaces/test/.venv/lib/python3.13/site-packages/mcp/shared/session.py", line 283, in send_request
response_or_error = await response_stream_reader.receive()
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/streams/memory.py", line 119, in receive
await receive_event.wait()
File "/workspaces/test/.venv/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 1774, in wait
await self._event.wait()
File "/usr/local/lib/python3.13/asyncio/locks.py", line 213, in wait
await fut
asyncio.exceptions.CancelledError: Cancelled by cancel scope ffffa51c4050
To Reproduce
I tested this with this script:
import asyncio
from mcp.client.session_group import ClientSessionGroup, StreamableHttpParameters
async def main():
async with ClientSessionGroup() as client_session_group:
server_params = StreamableHttpParameters(url="http://localhost:3001/mcp/")
try:
await client_session_group.connect_to_server(server_params)
except Exception:
print("this is never reached")
if __name__ == "__main__":
asyncio.run(main())Expected behavior
I would like to be able to catch any error that happens during connect_to_server and handle it within my application code - in my case I am using the ClientSessionGroup for multiple MCP servers and want to provide the tools of the running MCP servers to the LLM.
Additional context
- I am using version
1.9.3