Idempotency that works with Litestar

[violetta98]

Hello everyone!

I got tired of rewriting idempotency in every service and getting it slightly wrong, so I packaged it. Posting here because the core is plain ASGI, not FastAPI-specific like most Python options.

from idemkit import idempotent, RedisBackend, MethodConfig

@idempotent(
    backend=RedisBackend.from_url("redis://localhost:6379"),
    config=MethodConfig(key_fields=["order_id"]),
)
async def charge(*, order_id: str, amount: int):
    return await payments.charge(order_id, amount)

Call it twice with the same order_id and the charge happens once. A concurrent duplicate waits for the first call and gets its result rather than an error.

Under the hood it's an atomic claim rather than check-then-act, a lease that expires on the storage server's clock, and a fencing token so a stalled worker can't overwrite a newer result.

There's also HTTP middleware that replays the first response for retries with the same Idempotency-Key. It's raw ASGI so it should slot into middleware=[...], but I've only tested it on Starlette and FastAPI. If you try it on Litestar and it misbehaves, tell me and I'll add a proper adapter.

https://github.com/idemkit/idemkit, Apache-2.0

If you find it useful, I'd appreciate a star. It's new, so visibility helps a lot right now.