mirror of
https://github.com/crazybber/go-pattern-examples.git
synced 2024-11-29 06:56:03 +03:00
92 lines
1.7 KiB
Go
92 lines
1.7 KiB
Go
package circuit
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import (
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"context"
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"errors"
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"time"
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)
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var (
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ErrServiceUnavailable = errors.New("Service Unavailable")
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)
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type State int
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const (
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UnknownState State = iota
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FailureState
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SuccessState
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)
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//Counter interface
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type Counter interface {
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Count(State)
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ConsecutiveFailures() uint32
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LastActivity() time.Time
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Reset()
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}
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type counters struct {
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state State
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lastActivity time.Time
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}
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func (c *counters) Count(State) {
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}
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func (c *counters) ConsecutiveFailures() uint32 {
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return 0
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}
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func (c *counters) LastActivity() time.Time {
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return c.lastActivity
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}
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func (c *counters) Reset() {
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}
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func NewCounter() Counter {
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var i Counter
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return i
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}
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type Circuit func(context.Context) error
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func Breaker(c Circuit, failureThreshold uint32) Circuit {
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cnt := NewCounter()
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return func(ctx context.Context) error {
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if cnt.ConsecutiveFailures() >= failureThreshold {
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canRetry := func(cnt Counter) bool {
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backoffLevel := cnt.ConsecutiveFailures() - failureThreshold
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// Calculates when should the circuit breaker resume propagating requests
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// to the service
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shouldRetryAt := cnt.LastActivity().Add(time.Second * 2 << backoffLevel)
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return time.Now().After(shouldRetryAt)
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}
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if !canRetry(cnt) {
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// Fails fast instead of propagating requests to the circuit since
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// not enough time has passed since the last failure to retry
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return ErrServiceUnavailable
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}
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}
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// Unless the failure threshold is exceeded the wrapped service mimics the
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// old behavior and the difference in behavior is seen after consecutive failures
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if err := c(ctx); err != nil {
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cnt.Count(FailureState)
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return err
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}
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cnt.Count(SuccessState)
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return nil
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}
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}
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