package chanfitness
import (
"math"
"time"
)
const (
// rateLimitScale is the number of events we allow per rate limited
// tier. Increasing this value makes our rate limiting more lenient,
// decreasing it makes us less lenient.
rateLimitScale = 200
// flapCountCooldownFactor is the factor by which we decrease a peer's
// flap count if they have not flapped for the cooldown period.
flapCountCooldownFactor = 0.95
// flapCountCooldownPeriod is the amount of time that we require a peer
// has not flapped for before we reduce their all time flap count using
// our cooldown factor.
flapCountCooldownPeriod = time.Hour * 8
)
// rateLimits is the set of rate limit tiers we apply to our peers based on
// their flap count. A peer can be placed in their tier by dividing their flap
// count by the rateLimitScale and returning the value at that index.
var rateLimits = []time.Duration{
time.Second,
time.Second * 5,
time.Second * 30,
time.Minute,
time.Minute * 30,
time.Hour,
}
// getRateLimit returns the value of the rate limited tier that we are on based
// on current flap count. If a peer's flap count exceeds the top tier, we just
// return our highest tier.
func getRateLimit(flapCount int) time.Duration {
// Figure out the tier we fall into based on our current flap count.
tier := flapCount / rateLimitScale
// If we have more events than our number of tiers, we just use the
// last tier
tierLen := len(rateLimits)
if tier >= tierLen {
tier = tierLen - 1
}
return rateLimits[tier]
}
// cooldownFlapCount takes a timestamped flap count, and returns its value
// scaled down by our cooldown factor if at least our cooldown period has
// elapsed since the peer last flapped. We do this because we store all-time
// flap count for peers, and want to allow downgrading of peers that have not
// flapped for a long time.
func cooldownFlapCount(now time.Time, flapCount int,
lastFlap time.Time) int {
// Calculate time since our last flap, and the number of times we need
// to apply our cooldown factor.
timeSinceFlap := now.Sub(lastFlap)
// If our cooldown period has not elapsed yet, we just return our flap
// count. We allow fractional cooldown periods once this period has
// elapsed, so we do not want to apply a fractional cooldown before the
// full cooldown period has elapsed.
if timeSinceFlap < flapCountCooldownPeriod {
return flapCount
}
// Get the factor by which we need to cooldown our flap count. If
// insufficient time has passed to cooldown our flap count. Use use a
// float so that we allow fractional cooldown periods.
cooldownPeriods := float64(timeSinceFlap) /
float64(flapCountCooldownPeriod)
effectiveFactor := math.Pow(flapCountCooldownFactor, cooldownPeriods)
return int(float64(flapCount) * effectiveFactor)
}