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FastMCP server with SSE transport fails to shut down on a signal #514
Description
Activity
I think uvicorn is waiting for close opened sse connection.
But I've no idea how to do it with fastmcp.Can anyone help?
It’s unclear if there’s a manual way to disconnect from the session. The session gets created when you attempt to connect using an MCP client, and even the MCP Inspector doesn’t terminate the session when "Disconnect" is clicked.
deleted previous message as thought it was raised on my project! - i have been scratching my head on this one...! would be good to get fixed.
... I would also like to add that if the MCP server has at least one real established connection, it fails to shut down even with forced Ctrl-C. The only way is to kill the process.
I'm experiencing the same issue. Initially, I suspected it might be caused by the Auto Forward Ports feature of the VS Code Remote plugin. However, after disabling automatic port forwarding, the problem persists.
so this issue has been resolved?
Also an automatic timeout would be a useful feature. If the client has connected, but is no longer actively sending messages, then terminate the connection after specified time.
for @pranftw 's suggestion of adding automatic timeout, I think we should add timeout_graceful_shutdown=3 to run_streamable_http_async()?
So it will become:-
config = uvicorn.Config( starlette_app, host=self.settings.host, port=self.settings.port, log_level=self.settings.log_level.lower(), timeout_graceful_shutdown=3 , # Force shutdown after 3 seconds )- ref.: uvicorn settings: https://www.uvicorn.org/settings/#timeouts
- "--timeout-graceful-shutdown - Maximum number of seconds to wait for graceful shutdown. After this timeout, the server will start terminating requests."
- ref.: uvicorn settings: https://www.uvicorn.org/settings/#timeouts
Still experiencing this issue with:
Name: mcp
Version: 1.14.0
Summary: Model Context Protocol SDKCursor is holding the connection and not letting go.. Repeated attempts to Ctrl+C does not help.
for @pranftw 's suggestion of adding automatic timeout, I think we should add timeout_graceful_shutdown=3 to run_streamable_http_async()?
So it will become:-
config = uvicorn.Config( starlette_app, host=self.settings.host, port=self.settings.port, log_level=self.settings.log_level.lower(), timeout_graceful_shutdown=3 , # Force shutdown after 3 seconds )-
ref.: uvicorn settings: https://www.uvicorn.org/settings/#timeouts
- "--timeout-graceful-shutdown - Maximum number of seconds to wait for graceful shutdown. After this timeout, the server will start terminating requests."
@lanstonchu Thanks!!!
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Hi! I'd like to work on this issue.
I reviewed #612 and the earlier attempts in #518, #582, and #586. #612 handles a client disconnect, while #514 is about server shutdown while an SSE connection remains active. My plan is to reproduce that remaining case against the current codebase, add a focused regression test, and implement the smallest transport-scoped fix. I will avoid a global forced-shutdown timeout and won't require a dependency upgrade.
Could a maintainer assign #514 to me if this direction matches the expected scope?
A very simple server fails to shut down on a signal if it processed at least one request:
The expected behaviour would be:
Here is the code for both the server and the client.
What do I miss?
the server
import click import sys from pydantic import Field from mcp.server.fastmcp import FastMCP @click.command() @click.option("--port", default=8085, help="Port to listen", type=int) def main(port: int): mcp = FastMCP( "mcp-echo-tool", debug=True, log_level="INFO", port=port, ) @mcp.tool(name="echo") async def echo_tool(string: str = Field(description="A string to echo back")) -> str: """Echoes back the input string""" return string mcp.run(transport='sse') return 0 if __name__ == "__main__": sys.exit(main())and the client
import asyncio import click import sys from mcp.client.session import ClientSession from mcp.client.sse import sse_client async def client(url, string): async with sse_client(url) as (read, write): async with ClientSession(read, write) as session: await session.initialize() result = await session.call_tool("echo", {"string": string}) print(result.content) @click.command() @click.option('--url', default='http://localhost:8085', help='MCP Server URL', type=str) @click.argument('string', type=str) def main(url: str, string: str): asyncio.run(client(url, string)) if __name__ == "__main__": sys.exit(main())