Change backoff semantics in case of initialBackoff (#186)

Co-authored-by: Will Deuschle <[email protected]>

retry/retry.go

@@ -124,6 +124,7 @@ func WithMaxAttempts(maxAttempts int) Option {
 // WithInitialBackoff sets initial backoff.
 //
 // If initial backoff option is not used, then default value of 50 milliseconds is used.
+// If initial backoff is larger than max backoff, it takes precedence.
 func WithInitialBackoff(initialBackoff time.Duration) Option {
 	return func(o *options) {
 		o.initialBackoff = initialBackoff
@@ -180,6 +181,8 @@ func Start(ctx context.Context, opts ...Option) Retrier {
 	for _, option := range opts {
 		option(&r.options)
 	}
+	// If initial backoff is larger than max backoff, it takes precedence.
+	r.options.maxBackoff = max(r.options.maxBackoff, r.options.initialBackoff)
 	r.Reset()
 	return r
 }
@@ -259,3 +262,10 @@ func (r retrier) retryIn() time.Duration {
 func (r retrier) CurrentAttempt() int {
 	return r.currentAttempt
 }
+
+func max(a, b time.Duration) time.Duration {
+	if a > b {
+		return a
+	}
+	return b
+}

retry/retry_test.go

@@ -78,6 +78,25 @@ func TestRetrier_Next_WithMaxBackoff(t *testing.T) {
 	}
 }
 
+func TestRetrier_Next_WithInitialBackoffLargerThanMax(t *testing.T) {
+	const initialBackoff = time.Second * 5
+	const maxBackoff = time.Second * 2
+
+	options := []Option{
+		WithInitialBackoff(initialBackoff),
+		WithMaxBackoff(maxBackoff),
+		WithMultiplier(2),
+		WithMaxAttempts(11),
+		WithRandomizationFactor(0),
+	}
+
+	r := Start(context.Background(), options...).(*retrier)
+	d := r.retryIn()
+	if d != initialBackoff {
+		t.Fatalf("expected initial backoff to be used: %s vs %s", d, initialBackoff)
+	}
+}
+
 func TestRetrier_Next_WithMaxAttempts(t *testing.T) {
 	const maxAttempts = 2