modelcontextprotocol / modelcontextprotocol/python-sdk

Lazy HTTP connections seem to make error handling difficult.

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enhancement needs decision P2
Dominant language
Python
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Description

Question

When using streamablehttp_client, since HTTP connections are initialized with anyio.create_task_group, if the server is unreachable, an error will occur unexpectedly at some point later. Is this the intended behavior? If the connection is impossible, I want to wait and handle the error. However, the current behavior executes the code after the initialization and then throws an error at some point. If the error had occurred earlier, the code below it wouldn't have needed to execute. I consider this excessive optimization. Is there a reason for this design?

Additional Context
import asyncio
from langchain_mcp_adapters.tools import load_mcp_tools
from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client

async def _init_and_load(session: ClientSession):
    try:
        async with asyncio.timeout(10): # << I cannot access the server and will time out.
            await session.initialize()
            return await load_mcp_tools(session)
    except Exception as e:
        return []

async def main():
    async with streamablehttp_client(url="https://some.unreachable.domain") as client:
        async with ClientSession(client[0], client[1]) as session:
            tools = await _init_and_load(session)
            await asyncio.sleep(100) # << A httpx.ConnectTimeout exception occurred while performing the following operation!!
import asyncio
from langchain_mcp_adapters.tools import load_mcp_tools
from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client

async def _init_and_load(session: ClientSession):
    try:
        await session.initialize()
        return await load_mcp_tools(session)
    except Exception as e: # << Since the error is caused by tg, this cannot handle the error too!!
        return []

async def main():
    async with streamablehttp_client(url="https://some.unreachable.domain", timeout=10) as client:
        async with ClientSession(client[0], client[1]) as session:
            tools = await _init_and_load(session)
            await asyncio.sleep(100)

Contributor guide

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start at the streamablehttp_client entry point and its anyio.create_task_group setup; reproduce the unreachable-domain examples with asyncio.timeout and timeout=10. Trace when the httpx.ConnectTimeout is surfaced relative to session.initialize() and the surrounding context manager, then define completion as corrected or documented error timing for the shown cases.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
networking
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
30/100

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