[QUESTION] how to use until_ready/until_n_ready

[inconspicuous99]

        println!("waiting");
        ratelimit.until_n_ready(api_cost).await.unwrap();

        println!("trying");
        if let Ok(_) = ratelimit.check_n(api_cost) {

this is the correct usage right?

[Andreas Fuchs]

The usage of until_n_ready looks right - it's fallible because api_cost could be greater than the rate limiter's burst capacity (e.g. trying to get 6 elements through a limiter that allows 5 elements per second), so unwrap() or other error-handling methods are necessary. If the api cost fits into burst capacity, until_n_ready will wait until the request can proceed.

The usage of check_n needs more special-casing though: Since there are two possible Err cases (one, saying it's not ready yet, the other saying it can never be ready). I'd suggest something like (rust syntax not checked, sorry):

match ratelimit.check_n(api_cost) {
  Ok(_) => (), // proceed
  Err(NegativeMultiDecision::BatchNonConforming(_, not_until)) => ..., // We are blocked for now, but can retry later
  Err(NegativeMultiDecision::InsufficientCapacity(_)) => panic!("Programming error: this API call can never succeed"),
}

Hope that helps - I'll close this issue, but if you need more help with the API, feel free to reopen.