js: Add option to skip consumer lookup on subscribe

Signed-off-by: Waldemar Quevedo <wally@nats.io>

js.go

@@ -1468,6 +1468,7 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 		isDurable     = o.cfg.Durable != _EMPTY_
 		consumerBound = o.bound
 		ctx           = o.ctx
+		skipCInfo     = o.skipCInfo
 		notFoundErr   bool
 		lookupErr     bool
 		nc            = js.nc
@@ -1542,7 +1543,7 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 	// With an explicit durable name, we can lookup the consumer first
 	// to which it should be attaching to.
 	// If bind to ordered consumer is true, skip the lookup.
-	if consumer != _EMPTY_ {
+	if consumer != _EMPTY_ && !o.skipCInfo {
 		info, err = js.ConsumerInfo(stream, consumer)
 		notFoundErr = errors.Is(err, ErrConsumerNotFound)
 		lookupErr = err == ErrJetStreamNotEnabled || err == ErrTimeout || err == context.DeadlineExceeded
@@ -1563,6 +1564,19 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 		if !(isPullMode && lookupErr && consumerBound) {
 			return nil, err
 		}
+	case skipCInfo:
+		// When skipping consumer info, need to rely on the manually passed sub options
+		// to match the expected behavior from the subscription.
+		hasFC, hbi = o.cfg.FlowControl, o.cfg.Heartbeat
+		hasHeartbeats = hbi > 0
+		maxap = o.cfg.MaxAckPending
+		deliver = o.cfg.DeliverSubject
+		if consumerBound {
+			break
+		}
+
+		// When not bound to a consumer already, proceeed to create.
+		fallthrough
 	default:
 		// Attempt to create consumer if not found nor using Bind.
 		shouldCreate = true
@@ -1572,7 +1586,6 @@ func (js *js) subscribe(subj, queue string, cb MsgHandler, ch chan *Msg, isSync,
 			deliver = nc.NewInbox()
 			cfg.DeliverSubject = deliver
 		}
-
 		// Do filtering always, server will clear as needed.
 		cfg.FilterSubject = subj
 
@@ -2151,6 +2164,16 @@ type subOpts struct {
 	// For an ordered consumer.
 	ordered bool
 	ctx     context.Context
+
+	// To disable calling ConsumerInfo
+	skipCInfo bool
+}
+
+func SkipConsumerInfo() SubOpt {
+	return subOptFn(func(opts *subOpts) error {
+		opts.skipCInfo = true
+		return nil
+	})
 }
 
 // OrderedConsumer will create a FIFO direct/ephemeral consumer for in order delivery of messages.