Snippet for impl rate limiter

rate_limit.rs

/// Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=7f2ff17ff7ae239924d11698d12a69f9

mod rate_limiter {
  #[test]
  fn test() {
    const MAX_REQ_ALLOWED_IN_WINDOW: usize = 2;
    const WINDOW_SIZE_MS: usize = 1000;

    #[derive(Debug, /* deep copy support */ Clone, /* deep equality support */ PartialEq)]
    enum RateLimitCheck {
      Approve,
      Reject,
    }

    fn is_ts_in_window(ts: usize, new_req_time_ms: usize) -> bool { new_req_time_ms - ts < WINDOW_SIZE_MS }

    fn check_rate_limit(new_req_ts: usize, vec_success_ts: &mut Vec<usize>) -> RateLimitCheck {
      // How many transactions have already been allowed in the last WINDOWS_SIZE_MS?
      let num_previously_allowed_in_window: usize = {
        let mut count = 0;
        for ts in vec_success_ts.iter().rev() {
          if is_ts_in_window(*ts, new_req_ts) {
            count += 1;
          }
        }
        count
      };

      // Reject or Approve?
      if num_previously_allowed_in_window < MAX_REQ_ALLOWED_IN_WINDOW {
        vec_success_ts.push(new_req_ts);
        RateLimitCheck::Approve
      } else {
        RateLimitCheck::Reject
      }
    }

    fn main() {
      let mut vec_success_ts: Vec<usize> = vec![1000, 1500, 2000];
      assert_eq!(check_rate_limit(2_100, &mut vec_success_ts), RateLimitCheck::Reject);
      assert_eq!(check_rate_limit(2_500, &mut vec_success_ts), RateLimitCheck::Approve);
    }
  }
}