fix: accept callable roots handlers (#4639)

* Accept callable roots handlers

🤖 Generated with OpenAI Codex

* fix: cover callable object roots handlers

🤖 Generated with OpenAI Codex

---------

Co-authored-by: Shuying <zsy@u.northwestern.edu>

fastmcp_slim/fastmcp/client/roots.py

@@ -37,7 +37,7 @@ def create_roots_callback(
     if isinstance(handler, list):
         # TODO(ty): remove when ty supports isinstance union narrowing
         return _create_roots_callback_from_roots(handler)  # type: ignore[arg-type]  # ty:ignore[invalid-argument-type]
-    elif inspect.isfunction(handler):
+    elif callable(handler):
         return _create_roots_callback_from_fn(handler)
     else:
         raise ValueError(f"Invalid roots handler: {handler}")

fastmcp_slim/fastmcp/server/providers/proxy.py

@@ -1327,12 +1327,7 @@ def _restore_request_context(
 
 
 def _make_restoring_handler(handler: Callable, rc_ref: list[Any]) -> Callable:
-    """Wrap a proxy handler to restore request_ctx before delegating.
-
-    The wrapper is a plain ``async def`` so it passes
-    ``inspect.isfunction()`` checks in handler registration paths
-    (e.g., ``create_roots_callback``).
-    """
+    """Wrap a proxy handler to restore request_ctx before delegating."""
 
     async def wrapper(*args: Any, **kwargs: Any) -> Any:
         _restore_request_context(rc_ref)

tests/client/test_roots.py

@@ -1,3 +1,5 @@
+import functools
+
 import pytest
 
 from fastmcp import Client, Context, FastMCP
@@ -43,3 +45,40 @@ class TestClientRoots:
                 "file://x/y/z",
                 "file://x/y/z",
             ]
+
+    async def test_bound_method_roots_handler(self, fastmcp_server: FastMCP):
+        class RootsProvider:
+            async def get_roots(self, _context: object) -> list[str]:
+                return ["file:///bound-method"]
+
+        provider = RootsProvider()
+
+        async with Client(
+            fastmcp_server, mode="legacy", roots=provider.get_roots
+        ) as client:
+            result = await client.call_tool("list_roots", {})
+
+        assert result.data == ["file:///bound-method"]
+
+    async def test_partial_roots_handler(self, fastmcp_server: FastMCP):
+        async def get_roots(prefix: str, _context: object) -> list[str]:
+            return [f"file:///{prefix}"]
+
+        handler = functools.partial(get_roots, "partial")
+
+        async with Client(fastmcp_server, mode="legacy", roots=handler) as client:
+            result = await client.call_tool("list_roots", {})
+
+        assert result.data == ["file:///partial"]
+
+    async def test_callable_object_roots_handler(self, fastmcp_server: FastMCP):
+        class RootsProvider:
+            async def __call__(self, _context: object) -> list[str]:
+                return ["file:///callable-object"]
+
+        async with Client(
+            fastmcp_server, mode="legacy", roots=RootsProvider()
+        ) as client:
+            result = await client.call_tool("list_roots", {})
+
+        assert result.data == ["file:///callable-object"]