d9fdff0839
* Add constants (enumlike) for stanza types * NewIQ, NewMessage and NewPresence are now initialized with the Attrs struct * Update examples * Do not export backoff code. For now, we do not need to expose backoff in the documentation * Make presence priority an int8
102 lines
2.7 KiB
Go
102 lines
2.7 KiB
Go
/*
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Interesting reference on backoff:
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- Exponential Backoff And Jitter (AWS Blog):
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https://www.awsarchitectureblog.com/2015/03/backoff.html
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We use Jitter as a default for exponential backoff, as the goal of
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this module is not to provide precise 'ticks', but good behaviour to
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implement retries that are helping the server to recover faster in
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case of congestion.
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It can be used in several ways:
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- Using duration to get next sleep time.
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- Using ticker channel to trigger callback function on tick
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The functions for Backoff are not threadsafe, but you can:
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- Keep the attempt counter on your end and use durationForAttempt(int)
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- Use lock in your own code to protect the Backoff structure.
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TODO: Implement Backoff Ticker channel
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TODO: Implement throttler interface. Throttler could be used to implement various reconnect strategies.
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*/
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package xmpp
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import (
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"math"
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"math/rand"
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"time"
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)
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const (
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defaultBase int = 20 // Backoff base, in ms
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defaultFactor int = 2
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defaultCap int = 180000 // 3 minutes
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)
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// backoff provides increasing duration with the number of attempt
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// performed. The structure is used to support exponential backoff on
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// connection attempts to avoid hammering the server we are connecting
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// to.
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type backoff struct {
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NoJitter bool
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Base int
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Factor int
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Cap int
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lastDuration int
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attempt int
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}
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// duration returns the duration to apply to the current attempt.
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func (b *backoff) duration() time.Duration {
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d := b.durationForAttempt(b.attempt)
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b.attempt++
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return d
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}
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// wait sleeps for backoff duration for current attempt.
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func (b *backoff) wait() {
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time.Sleep(b.duration())
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}
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// durationForAttempt returns a duration for an attempt number, in a stateless way.
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func (b *backoff) durationForAttempt(attempt int) time.Duration {
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b.setDefault()
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expBackoff := math.Min(float64(b.Cap), float64(b.Base)*math.Pow(float64(b.Factor), float64(b.attempt)))
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d := int(math.Trunc(expBackoff))
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if !b.NoJitter {
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d = rand.Intn(d)
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}
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return time.Duration(d) * time.Millisecond
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}
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// reset sets back the number of attempts to 0. This is to be called after a successful operation has been performed,
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// to reset the exponential backoff interval.
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func (b *backoff) reset() {
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b.attempt = 0
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}
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func (b *backoff) setDefault() {
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if b.Base == 0 {
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b.Base = defaultBase
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}
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if b.Cap == 0 {
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b.Cap = defaultCap
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}
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if b.Factor == 0 {
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b.Factor = defaultFactor
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}
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}
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/*
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We use full jitter as default for now as it seems to provide good behaviour for reconnect.
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Base is the default interval between attempts (if backoff Factor was equal to 1)
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Attempt is the number of retry for operation. If we start attempt at 0, first sleep equals base.
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Cap is the maximum sleep time duration we tolerate between attempts
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*/
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