[FIXED] Consumer MaxDeliver underflow (#7216)

A `MaxDeliver` of `-1`/infinite would result in an underflow when doing
`uint64(cfg.MaxDeliver)`. This didn't result in any issues per se, only
the `o.hasMaxDeliveries` code path couldn't short-circuit if `o.maxdc ==
0`.

Signed-off-by: Maurice van Veen <[email protected]>

Author: neilalexander

server/consumer.go

@@ -1120,7 +1120,7 @@ func (mset *stream) addConsumerWithAssignment(config *ConsumerConfig, oname stri
 		uch:       make(chan struct{}, 1),
 		mch:       make(chan struct{}, 1),
 		sfreq:     int32(sampleFreq),
-		maxdc:     uint64(config.MaxDeliver),
+		maxdc:     uint64(max(config.MaxDeliver, 0)), // MaxDeliver is negative (-1) when infinite.
 		maxp:      config.MaxAckPending,
 		retention: cfg.Retention,
 		created:   time.Now().UTC(),
@@ -2335,7 +2335,8 @@ func (o *consumer) updateConfig(cfg *ConsumerConfig) error {
 	}
 	// Set MaxDeliver if changed
 	if cfg.MaxDeliver != o.cfg.MaxDeliver {
-		o.maxdc = uint64(cfg.MaxDeliver)
+		// MaxDeliver is negative (-1) when infinite.
+		o.maxdc = uint64(max(cfg.MaxDeliver, 0))
 	}
 	// Set InactiveThreshold if changed.
 	if val := cfg.InactiveThreshold; val != o.cfg.InactiveThreshold {

server/jetstream_consumer_test.go

@@ -10241,3 +10241,47 @@ func TestJetStreamConsumerPrioritized(t *testing.T) {
 		require_NotNil(t, msg)
 	})
 }
+
+func TestJetStreamConsumerMaxDeliverUnderflow(t *testing.T) {
+	s := RunBasicJetStreamServer(t)
+	defer s.Shutdown()
+
+	nc, js := jsClientConnect(t, s)
+	defer nc.Close()
+
+	_, err := js.AddStream(&nats.StreamConfig{Name: "TEST", Subjects: []string{"foo"}})
+	require_NoError(t, err)
+
+	cfg := &nats.ConsumerConfig{Durable: "CONSUMER", MaxDeliver: -1}
+	_, err = js.AddConsumer("TEST", cfg)
+	require_NoError(t, err)
+
+	mset, err := s.globalAccount().lookupStream("TEST")
+	require_NoError(t, err)
+	o := mset.lookupConsumer("CONSUMER")
+	require_NotNil(t, o)
+
+	// Infinite MaxDeliver should be zero.
+	o.mu.RLock()
+	maxdc := o.maxdc
+	o.mu.RUnlock()
+	require_Equal(t, maxdc, 0)
+
+	// Finite MaxDeliver should be reported the same.
+	cfg.MaxDeliver = 1
+	_, err = js.UpdateConsumer("TEST", cfg)
+	require_NoError(t, err)
+	o.mu.RLock()
+	maxdc = o.maxdc
+	o.mu.RUnlock()
+	require_Equal(t, maxdc, 1)
+
+	// Infinite MaxDeliver should be zero.
+	cfg.MaxDeliver = -1
+	_, err = js.UpdateConsumer("TEST", cfg)
+	require_NoError(t, err)
+	o.mu.RLock()
+	maxdc = o.maxdc
+	o.mu.RUnlock()
+	require_Equal(t, maxdc, 0)
+}