[Bug]: Using with Langchain MultiServerMCPClient aync contextmanager does not exit

[shivaang14]

Version

latest

App

• Cursor
• Windsurf
• VSCode
• VSCode Insiders
• Claude Desktop
• Other

Affected Models (if applicable)

• Claude 3.5 Sonnet
• Claude 3.7 Sonnet
• GPT-4a
• o4-mini
• Other

Bug Description

I am using following python script

import asyncio
from langchain_mcp_adapters.client import MultiServerMCPClient
from langchain_mcp_adapters.tools import load_mcp_tools

async def main():
    client = MultiServerMCPClient(
        {
            "mongodb": {
                "transport": "stdio",
                "command": "npx",
                "args": [
                    "-y",
                    "mongodb-mcp-server@latest",
                    "--readOnly"
                ],
                "env": {
                    "MDB_MCP_CONNECTION_STRING": "mongodb://localhost:27017"
                }
            }
        }
    )

    async with client.session("mongodb") as session:
        tools = await load_mcp_tools(session)
        print(f"Loaded {len(tools)} tools:")
        for tool in tools:
            print(f"  - {tool.name}")


asyncio.run(main())

Output

Loaded 17 tools:
  - aggregate
  - collection-indexes
  - collection-schema
  - collection-storage-size
  - connect
  - count
  - db-stats
  - explain
  - export
  - find
  - list-collections
  - list-databases
  - mongodb-logs
  - atlas-local-connect-deployment
  - atlas-local-list-deployments
  - list-knowledge-sources
  - search-knowledge

And it is stuck here.

I am using

• Python 3.12.11
• langchain-mcp-adapters == 0.2.1

[github-actions]

Thanks for opening this issue. The ticket MCP-440 was created for internal tracking.

[nirinchev]

Is this a problem with the MongoDB MCP server though? It appears like your script is successfully loading it and printing the available tools.

[shrutimantri]

I have added a PR that handles closing the connection. However, note that closing the connection leads to anyio.BrokenResourceError as expected (the resource connection is now broken). Hence, the python code will need to change to handle this broken connection error as follows:

import asyncio
from langchain_mcp_adapters.client import MultiServerMCPClient
from langchain_mcp_adapters.tools import load_mcp_tools

async def main():
    client = MultiServerMCPClient(
        {
            "mongodb": {
                "transport": "stdio",
                "command": "npx",
                "args": [
                    "-y",
                    "mongodb-mcp-server@latest",
                    "--readOnly"
                ],
                "env": {
                    "MDB_MCP_CONNECTION_STRING": "mongodb://localhost:27017"
                }
            }
        }
    )

    async with client.session("mongodb") as session:
        tools = await load_mcp_tools(session)
        print(f"Loaded {len(tools)} tools:")
        for tool in tools:
            print(f"  - {tool.name}")

if __name__ == "__main__":
    import anyio
    try:
        asyncio.run(main())
    except* anyio.BrokenResourceError:
        pass

[shivaang14]

@shrutimantri Thanks for the PR and solution.