[BUG] Client can't to connect mcp sever SSE

[ratchanonth60]

app-1 | | File "/usr/local/lib/python3.13/site-packages/mcp/shared/session.py", line 209, in aexit
app-1 | | return await self._task_group.aexit(exc_type, exc_val, exc_tb)
app-1 | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
app-1 | | File "/usr/local/lib/python3.13/site-packages/anyio/_backends/_asyncio.py", line 772, in aexit
app-1 | | raise BaseExceptionGroup(
app-1 | | "unhandled errors in a TaskGroup", self._exceptions
app-1 | | ) from None
app-1 | | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
app-1 | +-+---------------- 1 ----------------
app-1 | | Traceback (most recent call last):
app-1 | | File "/usr/local/lib/python3.13/site-packages/mcp/server/session.py", line 146, in _receive_loop
app-1 | | await super()._receive_loop()
app-1 | | File "/usr/local/lib/python3.13/site-packages/mcp/shared/session.py", line 331, in _receive_loop
app-1 | | elif isinstance(message.message.root, JSONRPCRequest):
app-1 | | ^^^^^^^^^^^^^^^
app-1 | | File "/usr/local/lib/python3.13/site-packages/pydantic/main.py", line 989, in getattr
app-1 | | raise AttributeError(f'{type(self).name!r} object has no attribute {item!r}')
app-1 | | AttributeError: 'JSONRPCMessage' object has no attribute 'message'
app-1 | +------------------------------------

[hyson666]

I had the same problem. I downgraded my mcp package to version 1.7.0. It was probably a compatibility issue with the new version: pip3 install mcp==1.7.0

[quantotto]

In the mcp/shared/session.py the code is expecting to read SessionMessage, but it actually gets JSONRPCMessage and thus anywhere it says message.message gets the above exception. I experimentally changed all the occurrences of message.message to just message and it started working.

This is the commit in the mcp python SDK that introduced the change of wrapping messages into SessionMessage:

modelcontextprotocol/python-sdk@da0cf22#diff-aaa1596dd4db91f5cd7f743c8afbe58596daf01a2ecec4a0024768f7409fb1dc

[sndp-s]

Thanks @hyson666 @quantotto

[daidi]

+1

[ierickson]

There is a PR (#137) that addresses this issue.

[xiuluoshendaren]

I had the same problem. I downgraded my mcp package to version 1.7.0. It was probably a compatibility issue with the new version: pip3 install mcp==1.7.0

Thank you very much.