stdio_client not starting in windows: getting NotImplementedError #359
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bug
Something isn't working
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Hmmm... I think we need to choose the spawn mode somewhere... |
9 tasks
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NotImplementedError in asyncio subprocess_exec when using MCP client on Windows with Python 3.12 #369 |
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@saqadri #372 PR still giving me the same error in windows: NotImplementedError |
@JexinSam I'll investigate - is there anything special about your setup. For example are you running in a Jupyter notebook or regular Python script? A snippet and repro steps would be super helpful. |
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I am trying to run mcp client in fastapi server. Here is a sample code: mcp-server-config.json {
"mcpServers": {
"mysql": {
"command": "python",
"args": ["path/to/mcp-host/mysql-server"],
"env": {},
"transport": "stdio"
}
}
}app.py from mcp import ClientSession, StdioServerParameters, types
from typing import List
from mcp.client.stdio import stdio_client
import os, json
from fastapi import FastAPI, HTTPException
app = FastAPI()
CONFIG_FILE = 'mcp-server-config.json'
def load_server_config() -> dict:
# Load server configuration from the config file
if os.path.exists(CONFIG_FILE):
with open(CONFIG_FILE, "r", encoding="utf-8") as f:
return json.load(f) # Load server configuration
raise FileNotFoundError(f"Could not find config file {CONFIG_FILE}")
def create_server_parameters(server_config: dict) -> List[StdioServerParameters]:
"""Create server parameters from the server configuration."""
server_parameters = []
# Create server parameters for each server configuration
for config in server_config["mcpServers"].values():
server_parameter = StdioServerParameters(
command=config["command"],
args=config.get("args", []),
env={**config.get("env", {}), "PATH": os.getenv("PATH")}
)
# Add environment variables from the system if not provided
for key, value in server_parameter.env.items():
if len(value) == 0 and key in os.environ:
server_parameter.env[key] = os.getenv(key)
server_parameters.append(server_parameter)
return server_parameters
async def get_mcp_tools(server_param: StdioServerParameters) -> List:
"""Asynchronously retrieves and converts tools from a server using specified parameters"""
mcp_tools = []
async with stdio_client(server_param) as (read, write):
async with ClientSession(read, write) as session:
await session.initialize() # Initialize the session
tools: types.ListToolsResult = await session.list_tools() # Retrieve tools from the server
for tool_data in tools.tools:
mcp_tools.append(tool_data.__dict__)
return mcp_tools
@app.get("/api/mcp-tools")
async def get_mcp_tools_api():
"""API endpoint to retrieve MCP tools."""
server_config = load_server_config() # Load server configuration
server_params = create_server_parameters(server_config)
tools = await get_mcp_tools(server_params[0]) # Get tools from the first server
return {"tools": tools} |
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@JexinSam thanks for the repro steps. I can try looking into this later today. In the meantime, can you please try setting this to see if it helps? It is a hunch, but I noticed this issue in windows when using streamlit and jupyter as well, and at least for the streamlit case having the above resolved the issue. |
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Yes the issue is related to asyncio in windows. But the above code doesn't solve it for me. Turns out it happens only when --reload is enabled in fastapi. |
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anyio.open_process in stdio_client not working in windows. It raises NotImplementedError.
It gives out error:
Is there a solution to this?
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