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Go Circuit Breaker Pattern

Simple circuit breaker for outbound HTTP calls in Go — open, closed, half-open states.

type State int
const (Closed State = iota; Open; HalfOpen)

type CircuitBreaker struct {
    failures, threshold int
    state               State
    openAt              time.Time
}

func (cb *CircuitBreaker) Call(fn func() error) error {
    if cb.state == Open && time.Since(cb.openAt) < 30*time.Second {
        return errors.New("circuit open")
    }
    if err := fn(); err != nil {
        cb.failures++
        if cb.failures >= cb.threshold { cb.state = Open; cb.openAt = time.Now() }
        return err
    }
    cb.failures = 0; cb.state = Closed
    return nil
}