stdio_client context manager hangs

[hwaxxer]

Describe the bug
When using the stdio_client context manager, the process is never cleaned up.

To Reproduce
Steps to reproduce the behavior:

import asyncio

from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client


async def run():
    server_params = StdioServerParameters(
        command="claude",
        args=["mcp", "serve"],
    )
    async with stdio_client(server_params) as (read, write):   
        async with ClientSession(read, write) as _:
            pass
        print("exit ClientSession")
    print("exit stdio_client")

if __name__ == "__main__":
    asyncio.run(run())

Expected behavior
The program would print:

exit ClientSession
exit stdio_client

But it never exits the stdio_client context.

[mroch]

stdio_server seems to have a similar problem:

import asyncio

from mcp.server.stdio import stdio_server


async def run():
    async with stdio_server() as (read_stream, write_stream):
        print("inside")
    print("outside")


if __name__ == "__main__":
    asyncio.run(run())

this prints inside and never exits.

[hwaxxer]

One could argue that's per design since stdio_server is built to run indefinitely. For the stdio_client however, I think it makes sense to be able to start up the server, run a discrete task and then exit.

[dsp-ant]

Can you check with most recent master if it's fixed. I think #325 already addresses the issue

[hwaxxer]

@dsp-ant Same problem still.

[hwaxxer]

The proposed fix #361 still works fwiw, but I understand it's a bit of a workaround and not addressing the underlying issue.

[mroch]

One could argue that's per design since stdio_server is built to run indefinitely. For the stdio_client however, I think it makes sense to be able to start up the server, run a discrete task and then exit.

I disagree, but can move that discussion to a different issue. For example, the server might want to exit if it gets an uncaught exception (the current bug I'm facing), but even in normal circumstances, it could be checked into your repo and you switch commits, so it needs to restart a different version. For the LSP, vscode-languageclient respawns the server when it exits.

[mroch]

#372 probably fixed this. it also adds a process.terminate() like #361