Only initialize ddb client if none is provided (#106)

go.mod

@@ -19,3 +19,5 @@ require (
 	google.golang.org/appengine v1.6.1 // indirect
 	gopkg.in/redis.v5 v5.2.9 // indirect
 )
+
+go 1.13

store/ddb/ddb.go

@@ -39,12 +39,10 @@ func WithRetryer(r Retryer) Option {
 
 // New returns a checkpoint that uses DynamoDB for underlying storage
 func New(appName, tableName string, opts ...Option) (*Checkpoint, error) {
-	client := dynamodb.New(session.New(aws.NewConfig()))
 
 	ck := &Checkpoint{
 		tableName:   tableName,
 		appName:     appName,
-		client:      client,
 		maxInterval: time.Duration(1 * time.Minute),
 		done:        make(chan struct{}),
 		mu:          &sync.Mutex{},
@@ -56,6 +54,15 @@ func New(appName, tableName string, opts ...Option) (*Checkpoint, error) {
 		opt(ck)
 	}
 
+	// default client
+	if ck.client == nil {
+		newSession, err := session.NewSession(aws.NewConfig())
+		if err != nil {
+			return nil, err
+		}
+		ck.client = dynamodb.New(newSession)
+	}
+
 	go ck.loop()
 
 	return ck, nil