fix: detect context on callable tool objects

Author: fengjikui

src/mcp/server/mcpserver/utilities/context_injection.py

@@ -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

tests/server/mcpserver/test_tool_manager.py

@@ -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."""