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Description
Describe the bug
I write a multi streamable http server example according to your readme doc, but only the mcp server which pass the session_manager.run() to FastAPI works right
To Reproduce
mcp python sdk ver 1.8.1
mcp server code
from fastapi import FastAPI
import uvicorn
from mcp.server.fastmcp import FastMCP
echo_mcp = FastMCP(name="EchoServer", stateless_http=True)
@echo_mcp.tool(description="A simple echo tool")
def echo(message: str) -> str:
return f"Echo: {message}"
math_mcp = FastMCP(name="MathServer", stateless_http=True)
@math_mcp.tool(description="A simple add tool")
def add_two(m: int, n: int) -> int:
return m + n
app = FastAPI(lifespan=lambda app: echo_mcp.session_manager.run())
app.mount("/echo", echo_mcp.streamable_http_app())
app.mount("/math", math_mcp.streamable_http_app())
if __name__ == "__main__":
uvicorn.run(app, host="127.0.0.1", port=8000)mcp client code
import asyncio
from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client
async def main():
server_url = "http://127.0.0.1:8000/math/mcp"
async with streamablehttp_client(server_url) as (read, write, _):
async with ClientSession(read, write) as session:
await session.initialize()
tools = await session.list_tools()
tools = tools.tools
print(f"found {len(tools)} tools:")
if __name__ == "__main__":
asyncio.run(main())Expected behavior
Every mcp server works right.
Error Stack
/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/bin/python /Users/karsalina/PycharmProjects/playGround/script/http_server.py
INFO: Started server process [44368]
INFO: Waiting for application startup.
[05/14/25 16:21:02] INFO StreamableHTTP streamable_http_manager.py:109
session manager
started
INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO: 127.0.0.1:49685 - "POST /math/mcp HTTP/1.1" 307 Temporary Redirect
INFO: 127.0.0.1:49687 - "POST /math/mcp/ HTTP/1.1" 500 Internal Server Error
ERROR: Exception in ASGI application
Traceback (most recent call last):
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/uvicorn/protocols/http/httptools_impl.py", line 411, in run_asgi
result = await app( # type: ignore[func-returns-value]
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/uvicorn/middleware/proxy_headers.py", line 69, in __call__
return await self.app(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/fastapi/applications.py", line 1054, in __call__
await super().__call__(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/applications.py", line 112, in __call__
await self.middleware_stack(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 187, in __call__
raise exc
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 165, in __call__
await self.app(scope, receive, _send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
raise exc
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
await app(scope, receive, sender)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 714, in __call__
await self.middleware_stack(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 734, in app
await route.handle(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 460, in handle
await self.app(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/applications.py", line 112, in __call__
await self.middleware_stack(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 187, in __call__
raise exc
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/errors.py", line 165, in __call__
await self.app(scope, receive, _send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
raise exc
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
await app(scope, receive, sender)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 714, in __call__
await self.middleware_stack(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 734, in app
await route.handle(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/starlette/routing.py", line 460, in handle
await self.app(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/mcp/server/fastmcp/server.py", line 782, in handle_streamable_http
await self.session_manager.handle_request(scope, receive, send)
File "/Users/karsalina/Library/Caches/pypoetry/virtualenvs/playground-p-gXMEVB-py3.10/lib/python3.10/site-packages/mcp/server/streamable_http_manager.py", line 137, in handle_request
raise RuntimeError("Task group is not initialized. Make sure to use run().")
RuntimeError: Task group is not initialized. Make sure to use run().