Use append in case pubAck is larger than stack []byte

Signed-off-by: Derek Collison <derek@nats.io>

server/jetstream_test.go

@@ -12884,6 +12884,32 @@ func TestJetStreamExpireAllWhileServerDown(t *testing.T) {
 	}
 }
 
+func TestJetStreamLongStreamNamesAndPubAck(t *testing.T) {
+	s := RunBasicJetStreamServer()
+	defer s.Shutdown()
+
+	config := s.JetStreamConfig()
+	if config != nil {
+		defer removeDir(t, config.StoreDir)
+	}
+
+	nc, js := jsClientConnect(t, s)
+	defer nc.Close()
+
+	data := make([]byte, 256)
+	rand.Read(data)
+	stream := base64.StdEncoding.EncodeToString(data)[:256]
+
+	cfg := &nats.StreamConfig{
+		Name:     stream,
+		Subjects: []string{"foo"},
+	}
+	if _, err := js.AddStream(cfg); err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	js.Publish("foo", []byte("HELLO"))
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // Simple JetStream Benchmarks
 ///////////////////////////////////////////////////////////////////////////

server/stream.go

@@ -2594,9 +2594,8 @@ func (mset *stream) processJetStreamMsg(subject, reply string, hdr, msg []byte,
 
 	var resp = &JSPubAckResponse{}
 
-	var buf [128]byte
-	copy(buf[0:], mset.pubAck)
-	pubAck := buf[:len(mset.pubAck)]
+	var buf [256]byte
+	pubAck := append(buf[:0], mset.pubAck...)
 
 	// For clustering the lower layers will pass our expected lseq. If it is present check for that here.
 	if lseq > 0 && lseq != (mset.lseq+mset.clfs) {