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fix: detect context on callable tool objects #2817

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fix: detect context on callable tool objects #2817

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6 changes: 5 additions & 1 deletion src/mcp/server/mcpserver/utilities/context_injection.py
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Original file line number Diff line number Diff line change
Expand Up @@ -22,9 +22,13 @@ def find_context_parameter(fn: Callable[..., Any]) -> str | None:
Returns:
The name of the context parameter, or None if not found
"""
target = fn
if not inspect.isfunction(fn) and not inspect.ismethod(fn):
target = fn.__call__

# Get type hints to properly resolve string annotations
try:
hints = typing.get_type_hints(fn)
hints = typing.get_type_hints(target)
except Exception: # pragma: lax no cover
# If we can't resolve type hints, we can't find the context parameter
return None
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34 changes: 34 additions & 0 deletions tests/server/mcpserver/test_tool_manager.py
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Expand Up @@ -328,6 +328,40 @@ def something(a: int, ctx: Context) -> int: # pragma: no cover
assert "ctx" not in tool.fn_metadata.arg_model.model_fields


def test_context_arg_excluded_from_callable_object_schema():
class MyTool:
def __init__(self):
self.__name__ = "MyTool"

async def __call__(self, query: str, ctx: Context) -> str: # pragma: no cover
return query

manager = ToolManager()
tool = manager.add_tool(MyTool())

assert tool.context_kwarg == "ctx"
assert "ctx" not in json.dumps(tool.parameters)
assert "Context" not in json.dumps(tool.parameters)
assert "ctx" not in tool.fn_metadata.arg_model.model_fields


@pytest.mark.anyio
async def test_context_injected_into_callable_object():
class MyTool:
def __init__(self):
self.__name__ = "MyTool"

async def __call__(self, query: str, ctx: Context) -> str:
assert isinstance(ctx, Context)
return query

manager = ToolManager()
manager.add_tool(MyTool())

result = await manager.call_tool("MyTool", {"query": "hello"}, context=Context())
assert result == "hello"


class TestContextHandling:
"""Test context handling in the tool manager."""

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