File Overview

The file extra adds CachedFileEnforcerProvider - a ready-made enforcer_provider for model.conf + policy.csv setups.

It loads the Casbin enforcer once, keeps it cached in memory, and hot-reloads automatically when either file changes on disk.

Install

pip install "casbin-fastapi-decorator[file]"

Import

from casbin_fastapi_decorator_file import CachedFileEnforcerProvider

Why use it?

Compared to a plain dependency that calls casbin.Enforcer(...) on every request, CachedFileEnforcerProvider:

• avoids re-reading model.conf and policy.csv on every request
• keeps a single cached enforcer in memory
• reloads automatically when either file changes
• fits directly into FastAPI dependency injection

Setup

1. Create the provider

from casbin_fastapi_decorator_file import CachedFileEnforcerProvider

enforcer_provider = CachedFileEnforcerProvider(
    model_path="casbin/model.conf",
    policy_path="casbin/policy.csv",
)

2. Pass it to PermissionGuard

from casbin_fastapi_decorator import PermissionGuard
from fastapi import HTTPException

guard = PermissionGuard(
    user_provider=get_current_user,
    enforcer_provider=enforcer_provider,
    error_factory=lambda *_: HTTPException(403, "Forbidden"),
)

3. Start the watcher in FastAPI lifespan

from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from fastapi import FastAPI

@asynccontextmanager
async def lifespan(_app: FastAPI) -> AsyncIterator[None]:
    async with enforcer_provider:
        yield

app = FastAPI(lifespan=lifespan)

Without the context manager the provider still caches the enforcer, but it will not watch the files for changes.

Constructor parameters

CachedFileEnforcerProvider(
    model_path: str,
    policy_path: str,
)

Parameter	Type	Description
model_path	str	Path to the Casbin model file
policy_path	str	Path to the Casbin policy file

Reload behavior

• changes to model.conf mark the cached enforcer as stale
• changes to policy.csv do the same
• the provider rebuilds the enforcer lazily on the next request
• no application restart is required

Full example

See the File Hot-Reload Example for a complete app that exposes /policy and demonstrates live updates while the server is running.