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