[added] option to not create durable on subscribe

js.go

@@ -147,6 +147,9 @@ type js struct {
 	stc  chan struct{}
 	dch  chan struct{}
 	rr   *rand.Rand
+
+	// Assumes underlying objects exist and prevents additional lookups
+	bound bool
 }
 
 type jsOpts struct {
@@ -166,8 +169,9 @@ const (
 	defaultAccountCheck = 20 * time.Second
 )
 
-// JetStream returns a JetStreamContext for messaging and stream management.
-func (nc *Conn) JetStream(opts ...JSOpt) (JetStreamContext, error) {
+// BindJetStream returns a JetStreamContext for messaging and stream management that will NOT create
+// underlying objects like stream or durable. It assumes they exist already.
+func (nc *Conn) jetStream(opts ...JSOpt) (*js, error) {
 	js := &js{
 		nc: nc,
 		opts: &jsOpts{
@@ -181,9 +185,28 @@ func (nc *Conn) JetStream(opts ...JSOpt) (JetStreamContext, error) {
 			return nil, err
 		}
 	}
+	return js, nil
+}
+
+// BindJetStream returns a JetStreamContext for messaging and stream management that will NOT create
+// underlying objects like stream or durable. It assumes they exist already.
+func (nc *Conn) BindJetStream(opts ...JSOpt) (JetStreamContext, error) {
+	js, err := nc.jetStream(opts...)
+	if err != nil {
+		return nil, err
+	}
+	js.bound = true
+	return js, nil
+}
 
+// JetStream returns a JetStreamContext for messaging and stream management.
+func (nc *Conn) JetStream(opts ...JSOpt) (JetStreamContext, error) {
+	js, err := nc.jetStream(opts...)
+	if err != nil {
+		return nil, err
+	}
 	// If we have check recently we can avoid another account lookup here.
-	// We want these to be lighweight and created at will.
+	// We want these to be lightweight and created at will.
 	nc.mu.Lock()
 	now := time.Now()
 	checkAccount := now.Sub(nc.jsLastCheck) > defaultAccountCheck
@@ -1030,6 +1053,9 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync
 
 	// Find the stream mapped to the subject if not bound to a stream already.
 	if o.stream == _EMPTY_ {
+		if js.bound {
+			return nil, fmt.Errorf("nats: a bound JS requires a stream name")
+		}
 		stream, err = js.lookupStreamBySubject(subj)
 		if err != nil {
 			return nil, err
@@ -1041,15 +1067,20 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync
 	// With an explicit durable name, then can lookup
 	// the consumer to which it should be attaching to.
 	consumer = o.cfg.Durable
-	if consumer != _EMPTY_ {
+	if consumer == _EMPTY_ && js.bound {
+		return nil, fmt.Errorf("nats: a bound JS requires a durable name")
+	} else if consumer != _EMPTY_ && !js.bound {
 		// Only create in case there is no consumer already.
 		info, err = js.ConsumerInfo(stream, consumer)
 		if err != nil && err.Error() != "nats: consumer not found" {
 			return nil, err
 		}
 	}
 
-	if info != nil {
+	if js.bound {
+		attached = true
+		deliver = subj
+	} else if info != nil {
 		// Attach using the found consumer config.
 		ccfg = &info.Config
 		attached = true

test/js_test.go

@@ -2252,7 +2252,7 @@ func TestJetStreamImportDirectOnly(t *testing.T) {
 	}
 	defer ncm.Close()
 
-	jsm, err := ncm.JetStream()
+	jsm, err := ncm.BindJetStream()
 	if err != nil {
 		t.Fatal(err)
 	}