templates.py•2.87 kB
"""Resource template functionality."""
import inspect
import re
from typing import Any, Callable
from pydantic import BaseModel, Field, TypeAdapter, validate_call
from mcp.server.fastmcp.resources.types import FunctionResource, Resource
class ResourceTemplate(BaseModel):
"""A template for dynamically creating resources."""
uri_template: str = Field(
description="URI template with parameters (e.g. weather://{city}/current)"
)
name: str = Field(description="Name of the resource")
description: str | None = Field(description="Description of what the resource does")
mime_type: str = Field(
default="text/plain", description="MIME type of the resource content"
)
fn: Callable = Field(exclude=True)
parameters: dict = Field(description="JSON schema for function parameters")
@classmethod
def from_function(
cls,
fn: Callable,
uri_template: str,
name: str | None = None,
description: str | None = None,
mime_type: str | None = None,
) -> "ResourceTemplate":
"""Create a template from a function."""
func_name = name or fn.__name__
if func_name == "<lambda>":
raise ValueError("You must provide a name for lambda functions")
# Get schema from TypeAdapter - will fail if function isn't properly typed
parameters = TypeAdapter(fn).json_schema()
# ensure the arguments are properly cast
fn = validate_call(fn)
return cls(
uri_template=uri_template,
name=func_name,
description=description or fn.__doc__ or "",
mime_type=mime_type or "text/plain",
fn=fn,
parameters=parameters,
)
def matches(self, uri: str) -> dict[str, Any] | None:
"""Check if URI matches template and extract parameters."""
# Convert template to regex pattern
pattern = self.uri_template.replace("{", "(?P<").replace("}", ">[^/]+)")
match = re.match(f"^{pattern}$", uri)
if match:
return match.groupdict()
return None
async def create_resource(self, uri: str, params: dict[str, Any]) -> Resource:
"""Create a resource from the template with the given parameters."""
try:
# Call function and check if result is a coroutine
result = self.fn(**params)
if inspect.iscoroutine(result):
result = await result
return FunctionResource(
uri=uri, # type: ignore
name=self.name,
description=self.description,
mime_type=self.mime_type,
fn=lambda: result, # Capture result in closure
)
except Exception as e:
raise ValueError(f"Error creating resource from template: {e}")