add factory interface and implementations

backoff.go

@@ -43,6 +43,11 @@ func (b *ZeroBackOff) Reset() {}
 
 func (b *ZeroBackOff) NextBackOff() time.Duration { return 0 }
 
+func (b *ZeroBackOff) NewBackOff() BackOff {
+	copy := *b
+	return &copy
+}
+
 // StopBackOff is a fixed backoff policy that always returns backoff.Stop for
 // NextBackOff(), meaning that the operation should never be retried.
 type StopBackOff struct{}
@@ -51,6 +56,11 @@ func (b *StopBackOff) Reset() {}
 
 func (b *StopBackOff) NextBackOff() time.Duration { return Stop }
 
+func (b *StopBackOff) NewBackOff() BackOff {
+	copy := *b
+	return &copy
+}
+
 // ConstantBackOff is a backoff policy that always returns the same backoff delay.
 // This is in contrast to an exponential backoff policy,
 // which returns a delay that grows longer as you call NextBackOff() over and over again.
@@ -60,6 +70,10 @@ type ConstantBackOff struct {
 
 func (b *ConstantBackOff) Reset()                     {}
 func (b *ConstantBackOff) NextBackOff() time.Duration { return b.Interval }
+func (b *ConstantBackOff) NewBackOff() BackOff {
+	copy := *b
+	return &copy
+}
 
 func NewConstantBackOff(d time.Duration) *ConstantBackOff {
 	return &ConstantBackOff{Interval: d}

backoff_test.go

@@ -24,4 +24,14 @@ func TestConstantBackOff(t *testing.T) {
 	if backoff.NextBackOff() != time.Second {
 		t.Error("invalid interval")
 	}
+
+	backoffCpy := backoff.NewBackOff()
+	constant, ok := backoffCpy.(*ConstantBackOff)
+	if !ok {
+		t.Error("wrong type from NewBackOff")
+	}
+
+	if constant.Interval != backoff.Interval {
+		t.Error("invalid interval")
+	}
 }

exponential.go

@@ -156,3 +156,9 @@ func getRandomValueFromInterval(randomizationFactor, random float64, currentInte
 	// we want a 33% chance for selecting either 1, 2 or 3.
 	return time.Duration(minInterval + (random * (maxInterval - minInterval + 1)))
 }
+
+// NewBackOff implements Factory, and returns a copy of the exponential backoff
+func (b *ExponentialBackOff) NewBackOff() BackOff {
+	copy := *b
+	return &copy
+}

exponential_test.go

@@ -117,3 +117,35 @@ func assertEquals(t *testing.T, expected, value time.Duration) {
 		t.Errorf("got: %d, expected: %d", value, expected)
 	}
 }
+
+func TestNewBackOff(t *testing.T) {
+	var (
+		testInitialInterval     = 500 * time.Millisecond
+		testRandomizationFactor = 0.1
+		testMultiplier          = 2.0
+		testMaxInterval         = 5 * time.Second
+		testMaxElapsedTime      = 15 * time.Minute
+	)
+
+	exp := NewExponentialBackOff()
+	exp.InitialInterval = testInitialInterval
+	exp.RandomizationFactor = testRandomizationFactor
+	exp.Multiplier = testMultiplier
+	exp.MaxInterval = testMaxInterval
+	exp.MaxElapsedTime = testMaxElapsedTime
+	exp.Reset()
+
+	expCpy := exp.NewBackOff()
+	exp2, ok := expCpy.(*ExponentialBackOff)
+	if !ok {
+		t.Error("wrong type from NewBackoff")
+	}
+
+	if exp2 == exp {
+		t.Error("returned backoff is the same as original")
+	}
+
+	if *exp2 != *exp {
+		t.Error("backoff copy was not equal to base backoff")
+	}
+}

factory.go

@@ -0,0 +1,14 @@
+package backoff
+
+// A Factory creates and returns a new backoff policy
+type Factory interface {
+	NewBackOff() BackOff
+}
+
+// FactoryFunc is a function that returns a new backoff policy
+type FactoryFunc func() BackOff
+
+// NewBackOff implements Factory, allowing a FactoryFunc to be passed to anyywhere that accepts a Factory
+func (ff FactoryFunc) NewBackOff() BackOff {
+	return ff()
+}