[BUG] When using this tool to do a mcp svr, the client will hang when encountering problems, and it will not continue to execute further, nor will it reach the exception.

[daidi]

my client:

try:
                    result = await self._session.call_tool("plan_recall", {"query": query})
except Exception as e:
                    logger.exception(e)

and sometime it got errors like:

ERROR    [mcp.client.sse] Error parsing server message: 1 validation error for JSONRPCMessage
  Invalid JSON: EOF while parsing a string at line 1 column 76684 [type=json_invalid, input_value='{"jsonrpc":"2.0","id":9,...', input_type=str]
    For further information visit https://errors.pydantic.dev/2.10/v/json_invalid

but my client did't catch the error,so the code hangs....

I guess it might be related to the svr implementation? For example, the error message returned by the sse of the mcp svr received by the fastapi svr, but it didn't disconnect it?

[shahar4499]

Hey @daidi , can you share more about your implementation of the client?
And do you have clear reproduction steps? Does it happen consistently?
Thanks!

[shira-ayal]

Closing as it is quite outdated, there is a new version, and we didn't see much response on this bug.
@daidi please re-open if it happens with the new version too!