Method reduce

rate_limiter/src/lib.rs:162–211

Attempts to consume `tokens` from the bucket and returns whether the action succeeded. TODO (Issue #259): handle cases where a single request is larger than the full capacity for such cases we need to support partial fulfilment of requests

(&mut self, mut tokens: u64)

    // TODO (Issue #259): handle cases where a single request is larger than the full capacity
    // for such cases we need to support partial fulfilment of requests
    pub fn reduce(&mut self, mut tokens: u64) -> BucketReduction {
        // First things first: consume the one-time-burst budget.
        if self.one_time_burst > 0 {
            // We still have burst budget for *all* tokens requests.
            if self.one_time_burst >= tokens {
                self.one_time_burst -= tokens;
                self.last_update = Instant::now();
                // No need to continue to the refill process, we still have burst budget to consume from.
                return BucketReduction::Success;
            }
            // We still have burst budget for *some* of the tokens requests.
            // The tokens left unfulfilled will be consumed from current `self.budget`.
            tokens -= self.one_time_burst;
            self.one_time_burst = 0;
        }

        // Compute time passed since last refill/update.
        let time_delta = self.last_update.elapsed().as_nanos() as u64;
        self.last_update = Instant::now();

        // At each 'time_delta' nanoseconds the bucket should refill with:
        // refill_amount = (time_delta * size) / (complete_refill_time_ms * 1_000_000)
        // `processed_capacity` and `processed_refill_time` are the result of simplifying above
        // fraction formula with their greatest-common-factor.
        self.budget += (time_delta * self.processed_capacity) / self.processed_refill_time;

        if self.budget >= self.size {
            self.budget = self.size;
        }

        if tokens > self.budget {
            // This operation requests a bandwidth higher than the bucket size
            if tokens > self.size {
                error!(
                    "Consumed {} tokens from bucket of size {}",
                    tokens, self.size
                );
                // Empty the bucket and report an overconsumption of
                // (remaining tokens / size) times larger than the bucket size
                tokens -= self.budget;
                self.budget = 0;
                return BucketReduction::OverConsumption(tokens as f64 / self.size as f64);
            }
            // If not enough tokens consume() fails, return false.
            return BucketReduction::Failure;
        }

        self.budget -= tokens;
        BucketReduction::Success
    }

    /// "Manually" adds tokens to bucket.
    pub fn replenish(&mut self, tokens: u64) {