fix: MCP tools/call fails with missing 'request' positional argument#669
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gambletan wants to merge 2 commits intoLightning-AI:mainfrom
Open
fix: MCP tools/call fails with missing 'request' positional argument#669gambletan wants to merge 2 commits intoLightning-AI:mainfrom
gambletan wants to merge 2 commits intoLightning-AI:mainfrom
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The `_call_handler` function assumed MCP arguments would be keyed by
the endpoint handler's parameter name (e.g. `request`), but MCP clients
send the model's fields directly as flat arguments. When there is no
key matching the parameter name, `bind_partial` produces empty bindings
and the handler call raises:
endpoint_handler() missing 1 required positional argument: 'request'
Fix: detect single-parameter handlers whose parameter is a BaseModel
subclass and construct the model from the flat MCP arguments when
the arguments are not already wrapped under the parameter name.
Fixes Lightning-AI#560
Signed-off-by: Tan <alvinttang@gmail.com>
gambletan
requested review from
Abdul-0x4A,
KaelanDt,
andyland,
aniketmaurya,
dmitsf,
ethanwharris,
justusschock,
k223kim,
lantiga and
tchaton
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Summary
Fixes #560
_call_handlerassumed MCP arguments would be keyed by the endpoint handler's parameter name (e.g.request), but MCP clients send the model's fields directly as flat keyword arguments. When no key matches the parameter name,bind_partialproduces empty bindings and the call raisesendpoint_handler() missing 1 required positional argument: 'request'.BaseModelsubclass and construct the model instance from the flat MCP arguments. Also handles the case where arguments are already wrapped under the parameter name.test_call_handler_with_flat_mcp_argumentscovering both flat and wrapped argument styles.Test plan
tests/unit/test_mcp.py)name="Alice", age=30) and wrapped args (request={"name": "Bob", "age": 25}) resolve correctly