Fix async pub paf id for old js API

Signed-off-by: Tomasz Pietrek <tomasz@nats.io>

js.go

@@ -227,14 +227,16 @@ type js struct {
 	opts *jsOpts
 
 	// For async publish context.
-	mu           sync.RWMutex
-	rpre         string
-	rsub         *Subscription
-	pafs         map[string]*pubAckFuture
-	stc          chan struct{}
-	dch          chan struct{}
-	rr           *rand.Rand
-	connStatusCh chan (Status)
+	mu             sync.RWMutex
+	rpre           string
+	rsub           *Subscription
+	pafs           map[string]*pubAckFuture
+	stc            chan struct{}
+	dch            chan struct{}
+	rr             *rand.Rand
+	connStatusCh   chan (Status)
+	replyPrefix    string
+	replyPrefixLen int
 }
 
 type jsOpts struct {
@@ -283,6 +285,12 @@ func (nc *Conn) JetStream(opts ...JSOpt) (JetStreamContext, error) {
 			maxpa: defaultAsyncPubAckInflight,
 		},
 	}
+	inboxPrefix := InboxPrefix
+	if js.nc.Opts.InboxPrefix != _EMPTY_ {
+		inboxPrefix = js.nc.Opts.InboxPrefix + "."
+	}
+	js.replyPrefix = inboxPrefix
+	js.replyPrefixLen = len(js.replyPrefix) + aReplyTokensize + 1
 
 	for _, opt := range opts {
 		if err := opt.configureJSContext(js.opts); err != nil {
@@ -641,7 +649,6 @@ func (paf *pubAckFuture) Msg() *Msg {
 }
 
 // For quick token lookup etc.
-const aReplyPreLen = 14
 const aReplyTokensize = 6
 
 func (js *js) newAsyncReply() string {
@@ -654,11 +661,7 @@ func (js *js) newAsyncReply() string {
 		for i := 0; i < aReplyTokensize; i++ {
 			b[i] = rdigits[int(b[i]%base)]
 		}
-		inboxPrefix := InboxPrefix
-		if js.nc.Opts.InboxPrefix != _EMPTY_ {
-			inboxPrefix = js.nc.Opts.InboxPrefix + "."
-		}
-		js.rpre = fmt.Sprintf("%s%s.", inboxPrefix, b[:aReplyTokensize])
+		js.rpre = fmt.Sprintf("%s%s.", js.replyPrefix, b[:aReplyTokensize])
 		sub, err := js.nc.Subscribe(fmt.Sprintf("%s*", js.rpre), js.handleAsyncReply)
 		if err != nil {
 			js.mu.Unlock()
@@ -767,10 +770,10 @@ func (js *js) asyncStall() <-chan struct{} {
 
 // Handle an async reply from PublishAsync.
 func (js *js) handleAsyncReply(m *Msg) {
-	if len(m.Subject) <= aReplyPreLen {
+	if len(m.Subject) <= js.replyPrefixLen {
 		return
 	}
-	id := m.Subject[aReplyPreLen:]
+	id := m.Subject[js.replyPrefixLen:]
 
 	js.mu.Lock()
 	paf := js.getPAF(id)
@@ -916,7 +919,7 @@ func (js *js) PublishMsgAsync(m *Msg, opts ...PubOpt) (PubAckFuture, error) {
 		return nil, errors.New("nats: error creating async reply handler")
 	}
 
-	id := m.Reply[aReplyPreLen:]
+	id := m.Reply[js.replyPrefixLen:]
 	paf := &pubAckFuture{msg: m, st: time.Now()}
 	numPending, maxPending := js.registerPAF(id, paf)