Resource templates with wildcards not working when mounted as server

[Querela]

What happened?

When mounting a FastMCP server, resource templates with wildcards do not work anymore. Static resources are fine, resources with a single parameter (not wildcard) are also fine. Only if there is a wildcards parameter, the substitution for e.g. resource://file/{path*} will only contain the value {path*} as path parameter instead of the provided value. This does not happen, when using the root FastMCP server, only in the mounted sub-server.

Example Code

from fastmcp import FastMCP
from fastmcp.server.transforms import ResourcesAsTools


mcp_sub = FastMCP("sub")

@mcp_sub.resource("resource://res")
def resource_single() -> str:
    """Resource.

    Returns:
        The resource
    """
    return "ress"

@mcp_sub.resource("resource://single/{extra}")
def resource_single(extra: str) -> str:
    """Resource template with placeholder.

    Args:
        extra: a single value

    Returns:
        The provided value
    """
    return extra


@mcp_sub.resource("resource://multi/{extra*}")
def resource_single(extra: str) -> str:
    """Resource template with wildcard

    Args:
        extra: the extra content

    Returns:
        The provided extra content.
    """
    return extra


mcp = FastMCP("main")

@mcp.resource("resource2://multi2/{extra*}")
def resource_single2(extra: str) -> str:
    """Resource template with wildcard

    Args:
        extra: the extra content

    Returns:
        The provided extra content.
    """
    return extra


mcp.mount(mcp_sub, namespace="sub")
# mcp.mount(mcp_sub)  # also doesn't work

# mcp.add_transform(ResourcesAsTools(mcp))  # no change

Version Information

FastMCP version:                                                                                 3.2.3
MCP version:                                                                                    1.27.0
Python version:                                                                                3.10.12
Platform:                                 Linux-6.6.87.2-microsoft-standard-WSL2-x86_64-with-glibc2.35
FastMCP root path:                        /<path>/.venv/lib/python3.10/site-packages

[Querela]

To reproduce with the snippet above:

uv run fastmcp list test.py --resources
# --> resource://sub/res
# NOTE: only lists resources, not resource templates! (intended?)

# -----------------------------------------
## call on root server

# works on root!
uv run fastmcp call test.py resource2://multi2/abc
# --> abc
uv run fastmcp call test.py resource2://multi2/abc/def
# --> abc/def

# -----------------------------------------
## call on sub server

# static resource, fine
uv run fastmcp call test.py resource://sub/res
# --> ress

# single parameter, fine
uv run fastmcp call test.py resource://sub/single/abc
# --> abc
uv run fastmcp call test.py resource://sub/single/abc/def
# --> expected: Error: Resource not found: Unknown resource: 'resource://sub/single/abc/dev'

# wildcard parameter, fails
uv run fastmcp call test.py resource://sub/multi/abc
# --> {extra*}
uv run fastmcp call test.py resource://sub/multi/abc/def
# --> {extra*}

# -----------------------------------------
## call on sub server (without namespace)

# same behaviour even if not mounted with namespace
uv run fastmcp call test.py resource://multi/abc/def
# --> {extra*}

[Querela]

Untested with the mcp.import_server() mainly due to async stuff. Might have the same issue?