go-pattern-examples/gomore/circuit_breaker/circuit_breaker_test.go

package circuit

import (
	"context"
	"time"
)

type State int

const (
	UnknownState State = iota
	FailureState
	SuccessState
)

type Counter interface {
	Count(State)
	ConsecutiveFailures() uint32
	LastActivity() time.Time
	Reset()
}

type Circuit func(context.Context) error

func Breaker(c Circuit, failureThreshold uint32) Circuit {
	cnt := NewCounter()

	return func(ctx context) error {
		if cnt.ConsecutiveFailures() >= failureThreshold {
			canRetry := func(cnt Counter) {
				backoffLevel := Cnt.ConsecutiveFailures() - failureThreshold

				// Calculates when should the circuit breaker resume propagating requests
				// to the service
				shouldRetryAt := cnt.LastActivity().Add(time.Seconds * 2 << backoffLevel)

				return time.Now().After(shouldRetryAt)
			}

			if !canRetry(cnt) {
				// Fails fast instead of propagating requests to the circuit since
				// not enough time has passed since the last failure to retry
				return ErrServiceUnavailable
			}
		}

		// Unless the failure threshold is exceeded the wrapped service mimics the
		// old behavior and the difference in behavior is seen after consecutive failures
		if err := c(ctx); err != nil {
			cnt.Count(FailureState)
			return err
		}

		cnt.Count(SuccessState)
		return nil
	}
}