fixing bug - possible overflow in overflow branch of FibonacciBackoff::Next

fibonacci/fibonacci.go

@@ -34,20 +34,23 @@ func (f *FibonacciBackoff) Next() time.Duration {
 	if multiplier <= 0 {
 		multiplier = DefaultMultiplier
 	}
-	pause := time.Duration(Fibonacci(f.Iteration))
+	var pause time.Duration
+	for {
+		pause = time.Duration(Fibonacci(f.Iteration))
 		if product, overflows := utilities.ProductWouldOverflowInt64(pause.Nanoseconds(), multiplier.Nanoseconds()); overflows {
-		// cowardly refusal to overflow - return time.Duration(math.MaxInt64)
-		// we can't calculate jitter, because that could overflow.
+			// cowardly refusal to overflow - decrement Iteration until multiplication is safe.
 			// realistically, this should never happen, we're talking about almost 300 years.
 			f.foundMax = f.Iteration - 1
 			f.Iteration = f.foundMax
-		pause = time.Duration(Fibonacci(f.Iteration)) * multiplier
+			continue
 		} else if f.MaxPause > 0 && time.Duration(product) > f.MaxPause {
 			f.foundMax = f.Iteration
 			pause = f.MaxPause
 		} else {
 			pause = time.Duration(product)
 		}
+		break
+	}
 
 	// increment f.Iteration if appropriate
 	maxIteration := int64(len(TheFibonacciSequence) - 1)