06_custom_cache

Custom Cache — TTL Wrapper

Compose a TTL layer on top of any existing FileCache impl. Pattern: the wrapper itself satisfies FileCache, so it can be passed to create_app(cache=...) like any built-in.

The protocol

class FileCache(Protocol):
    async def try_get(self, cache_key: str, file_path: str) -> bytes | None: ...
    async def set(self, cache_key: str, file_path: str, data: bytes) -> None: ...
    async def remove(self, file_path: str) -> None: ...

What this example does

TTLCache keeps an in-memory map of (file_path, cache_key) → timestamp. On try_get it checks freshness; on set it records the timestamp and forwards. On remove it drops timestamps for the file.

The inner cache is InMemoryCache here, but it could equally be LocalFileCache or RedisCache — TTLCache doesn't care.

Run

pip install groupdocs-viewer-net-ui uvicorn
python main.py
# → http://127.0.0.1:8080/viewer/

Render a page — second request hits the cache. Wait 5 minutes, render again — re-renders.

When to use this

When source documents can change underneath the viewer and you want the cache to invalidate eventually even without an explicit remove(file_path) call. For documents that never change, a plain LocalFileCache is simpler.