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67 lines
1.9 KiB
67 lines
1.9 KiB
package waiter
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import (
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"fmt"
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"math"
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"time"
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"github.com/aws/smithy-go/rand"
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)
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// ComputeDelay computes delay between waiter attempts. The function takes in a current attempt count,
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// minimum delay, maximum delay, and remaining wait time for waiter as input. The inputs minDelay and maxDelay
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// must always be greater than 0, along with minDelay lesser than or equal to maxDelay.
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//
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// Returns the computed delay and if next attempt count is possible within the given input time constraints.
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// Note that the zeroth attempt results in no delay.
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func ComputeDelay(attempt int64, minDelay, maxDelay, remainingTime time.Duration) (delay time.Duration, err error) {
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// zeroth attempt, no delay
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if attempt <= 0 {
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return 0, nil
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}
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// remainingTime is zero or less, no delay
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if remainingTime <= 0 {
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return 0, nil
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}
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// validate min delay is greater than 0
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if minDelay == 0 {
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return 0, fmt.Errorf("minDelay must be greater than zero when computing Delay")
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}
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// validate max delay is greater than 0
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if maxDelay == 0 {
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return 0, fmt.Errorf("maxDelay must be greater than zero when computing Delay")
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}
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// Get attempt ceiling to prevent integer overflow.
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attemptCeiling := (math.Log(float64(maxDelay/minDelay)) / math.Log(2)) + 1
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if attempt > int64(attemptCeiling) {
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delay = maxDelay
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} else {
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// Compute exponential delay based on attempt.
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ri := 1 << uint64(attempt-1)
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// compute delay
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delay = minDelay * time.Duration(ri)
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}
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if delay != minDelay {
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// randomize to get jitter between min delay and delay value
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d, err := rand.CryptoRandInt63n(int64(delay - minDelay))
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if err != nil {
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return 0, fmt.Errorf("error computing retry jitter, %w", err)
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}
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delay = time.Duration(d) + minDelay
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}
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// check if this is the last attempt possible and compute delay accordingly
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if remainingTime-delay <= minDelay {
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delay = remainingTime - minDelay
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}
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return delay, nil
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}
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