Add test case for concurrent expected last subject sequence

server/jetstream_test.go

@@ -20282,3 +20282,86 @@ func TestJetStreamMaxBytesIgnored(t *testing.T) {
 	require_NoError(t, err)
 	require_True(t, si.State.Bytes <= 10*1024*1024)
 }
+
+func TestJetStreamLastSequenceBySubjectConcurrent(t *testing.T) {
+	for _, st := range []StorageType{FileStorage, MemoryStorage} {
+		t.Run(st.String(), func(t *testing.T) {
+			c := createJetStreamClusterExplicit(t, "JSC", 3)
+			defer c.shutdown()
+
+			nc0, js0 := jsClientConnect(t, c.randomServer())
+			defer nc0.Close()
+
+			nc1, js1 := jsClientConnect(t, c.randomServer())
+			defer nc1.Close()
+
+			cfg := StreamConfig{
+				Name:     "KV",
+				Subjects: []string{"kv.>"},
+				Storage:  st,
+				Replicas: 3,
+			}
+
+			req, err := json.Marshal(cfg)
+			if err != nil {
+				t.Fatalf("Unexpected error: %v", err)
+			}
+			// Do manually for now.
+			m, err := nc0.Request(fmt.Sprintf(JSApiStreamCreateT, cfg.Name), req, time.Second)
+			require_NoError(t, err)
+			si, err := js0.StreamInfo("KV")
+			if err != nil {
+				t.Fatalf("Unexpected error: %v, respmsg: %q", err, string(m.Data))
+			}
+			if si == nil || si.Config.Name != "KV" {
+				t.Fatalf("StreamInfo is not correct %+v", si)
+			}
+
+			pub := func(js nats.JetStreamContext, subj, data, seq string) {
+				t.Helper()
+				m := nats.NewMsg(subj)
+				m.Data = []byte(data)
+				m.Header.Set(JSExpectedLastSubjSeq, seq)
+				js.PublishMsg(m)
+			}
+
+			ready := make(chan struct{})
+			wg := &sync.WaitGroup{}
+			wg.Add(2)
+
+			go func() {
+				<-ready
+				pub(js0, "kv.foo", "0-0", "0")
+				pub(js0, "kv.foo", "0-1", "1")
+				pub(js0, "kv.foo", "0-2", "2")
+				wg.Done()
+			}()
+
+			go func() {
+				<-ready
+				pub(js1, "kv.foo", "1-0", "0")
+				pub(js1, "kv.foo", "1-1", "1")
+				pub(js1, "kv.foo", "1-2", "2")
+				wg.Done()
+			}()
+
+			time.Sleep(50 * time.Millisecond)
+			close(ready)
+			wg.Wait()
+
+			// Read the messages.
+			sub, err := js0.PullSubscribe(_EMPTY_, _EMPTY_, nats.BindStream("KV"))
+			require_NoError(t, err)
+			msgs, err := sub.Fetch(10)
+			require_NoError(t, err)
+			if len(msgs) != 3 {
+				t.Errorf("Expected 3 messages, got %d", len(msgs))
+			}
+			for i, m := range msgs {
+				if m.Header.Get(JSExpectedLastSubjSeq) != fmt.Sprint(i) {
+					t.Errorf("Expected %d for last sequence, got %q", i, m.Header.Get(JSExpectedLastSubjSeq))
+				}
+			}
+		})
+	}
+}

server/stream.go

@@ -3838,7 +3838,7 @@ func (mset *stream) processJetStreamMsg(subject, reply string, hdr, msg []byte,
 		}
 		// Expected last sequence per subject.
 		// If we are clustered we have prechecked seq > 0.
-		if seq, exists := getExpectedLastSeqPerSubject(hdr); exists && (!isClustered || seq == 0) {
+		if seq, exists := getExpectedLastSeqPerSubject(hdr); exists {
 			// TODO(dlc) - We could make a new store func that does this all in one.
 			var smv StoreMsg
 			var fseq uint64