RuntimeError: Received request before initialization was complete

[world520ai]

ERROR: Exception in ASGI application
Traceback (most recent call last):
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
result = await app( # type: ignore[func-returns-value]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in call
return await self.app(scope, receive, send)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/applications.py", line 112, in call
await self.middleware_stack(scope, receive, send)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 187, in call
raise exc
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 165, in call
await self.app(scope, receive, _send)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 62, in call
await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
raise exc
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
await app(scope, receive, sender)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 714, in call
await self.middleware_stack(scope, receive, send)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 734, in app
await route.handle(scope, receive, send)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 460, in handle
await self.app(scope, receive, send)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/server/sse.py", line 175, in handle_post_message
await writer.send(message)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/anyio/streams/memory.py", line 242, in send
self.send_nowait(item)
File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/anyio/streams/memory.py", line 213, in send_nowait
raise BrokenResourceError
anyio.BrokenResourceError
ERROR: Exception in ASGI application

• Exception Group Traceback (most recent call last):
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
  | result = await app( # type: ignore[func-returns-value]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in call
  | return await self.app(scope, receive, send)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/applications.py", line 112, in call
  | await self.middleware_stack(scope, receive, send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 187, in call
  | raise exc
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 165, in call
  | await self.app(scope, receive, _send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 62, in call
  | await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  | raise exc
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
  | await app(scope, receive, sender)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 714, in call
  | await self.middleware_stack(scope, receive, send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 734, in app
  | await route.handle(scope, receive, send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 288, in handle
  | await self.app(scope, receive, send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 76, in app
  | await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
  | raise exc
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
  | await app(scope, receive, sender)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/starlette/routing.py", line 73, in app
  | response = await f(request)
  | ^^^^^^^^^^^^^^^^
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/fastmcp/server/server.py", line 717, in handle_sse
  | async with sse.connect_sse(
  | ^^^^^^^^^^^^^^^^
  | File "/Users/lucas/.local/share/uv/python/cpython-3.12.9-macos-aarch64-none/lib/python3.12/contextlib.py", line 231, in aexit
  | await self.gen.athrow(value)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/server/sse.py", line 123, in connect_sse
  | async with anyio.create_task_group() as tg:
  | ^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 772, in aexit
  | raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
  | Exception Group Traceback (most recent call last):
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/server/sse.py", line 131, in connect_sse
  | yield (read_stream, write_stream)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/fastmcp/server/server.py", line 722, in handle_sse
  | await self._mcp_server.run(
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/server/lowlevel/server.py", line 483, in run
  | async with AsyncExitStack() as stack:
  | ^^^^^^^^^^^^^^^^
  | File "/Users/lucas/.local/share/uv/python/cpython-3.12.9-macos-aarch64-none/lib/python3.12/contextlib.py", line 754, in aexit
  | raise exc_details[1]
  | File "/Users/lucas/.local/share/uv/python/cpython-3.12.9-macos-aarch64-none/lib/python3.12/contextlib.py", line 737, in aexit
  | cb_suppress = await cb(*exc_details)
  | ^^^^^^^^^^^^^^^^^^^^^^
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/shared/session.py", line 210, in aexit
  | return await self._task_group.aexit(exc_type, exc_val, exc_tb)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 772, in aexit
  | raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
  | Traceback (most recent call last):
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/shared/session.py", line 324, in _receive_loop
  | await self._received_request(responder)
  | File "/Users/lucas/IdeaProjects/mcp_servers_ops/.venv/lib/python3.12/site-packages/mcp/server/session.py", line 163, in _received_request
  | raise RuntimeError(
  | RuntimeError: Received request before initialization was complete
  +------------------------------------
  INFO: 127.0.0.1:62923 - "GET /sse HTTP/1.1" 200 OK
  INFO: 127.0.0.1:62938 - "POST /messages/?session_id=fb7f7269ad3a4e93b67768c2fed4bd3c HTTP/1.1" 202 Accepted

[world520ai]

what is the problem? when i run the fastmcp app as server then restart it again, when i access from client, I had got the error like above comment.

[strawgate]

The client must reconnect after server restart.

The MCP Server starts a new "Server" for every session. When you restart the server there is no longer an active session with that client.

[world520ai]

If that's the case, if I restart the production environment, then all users will have to close the client and reconnect once again, doesn't that seem a bit unfriendly?

[jlowin]

Can you describe the behavior and expected behavior as an MRE please?

[world520ai]

Can you describe the behavior and expected behavior as an MRE please?

for example, if i used cline( a AI agent plugin for visual studio code) to run a task, when i paused the task and rerun it after a time duration(the MCP SSE server already restarted), it will be get error cause by above connection error.

[silverspace]

I suspect this is related to this issue and can be solved with this workaround

[jlowin]

I believe this race condition is fixed by modelcontextprotocol/python-sdk#1478