Test ACKing deleted messages

Test that explicitly ACKs messages that have been already removed from a stream

server/jetstream_cluster_4_test.go

@@ -2872,3 +2872,135 @@ func TestJetStreamClusterConsumeWithStartSequence(t *testing.T) {
 		)
 	}
 }
+
+func TestJetStreamClusterAckDeleted(t *testing.T) {
+
+	const (
+		NumMessages         = 10
+		StreamName          = "TEST"
+		StreamSubject       = "ORDERS.*"
+		StreamSubjectPrefix = "ORDERS."
+	)
+
+	for _, ClusterSize := range []int{
+		1, // Single server
+		3, // 3-node cluster
+	} {
+		R := ClusterSize
+		t.Run(
+			fmt.Sprintf("Nodes:%d,Replicas:%d", ClusterSize, R),
+			func(t *testing.T) {
+				// Setup: start server or cluster, connect client
+				var server *Server
+				if ClusterSize == 1 {
+					server = RunBasicJetStreamServer(t)
+					defer server.Shutdown()
+				} else {
+					c := createJetStreamCluster(t, jsClusterTempl, "HUB", _EMPTY_, ClusterSize, 22020, true)
+					defer c.shutdown()
+					server = c.randomServer()
+				}
+
+				// Setup: connect
+				var nc *nats.Conn
+				var js nats.JetStreamContext
+				nc, js = jsClientConnect(t, server)
+				defer nc.Close()
+
+				// Setup: create stream
+				_, err := js.AddStream(&nats.StreamConfig{
+					Replicas:  R,
+					Name:      StreamName,
+					Subjects:  []string{StreamSubject},
+					Retention: nats.LimitsPolicy,
+					Discard:   nats.DiscardOld,
+					MaxMsgs:   1, // Only keep the latest message
+				})
+				require_NoError(t, err)
+
+				// Setup: create durable consumer and subscription
+				const Durable = "dlc"
+				c, err := js.AddConsumer(StreamName, &nats.ConsumerConfig{
+					Durable:       Durable,
+					Replicas:      R,
+					AckPolicy:     nats.AckExplicitPolicy,
+					MaxAckPending: NumMessages,
+				})
+				require_NoError(t, err)
+				defer func() {
+					require_NoError(t, js.DeleteConsumer(c.Stream, c.Name))
+				}()
+
+				// Setup: create durable consumer subscription
+				sub, err := js.PullSubscribe(
+					"",
+					"",
+					nats.Bind(StreamName, Durable),
+				)
+				require_NoError(t, err)
+				defer func() {
+					require_NoError(t, sub.Unsubscribe())
+				}()
+
+				// Collect received and non-ACKed messages
+				receivedMessages := make([]*nats.Msg, 0, NumMessages)
+
+				buf := make([]byte, 100)
+				for i := uint64(1); i <= NumMessages; i++ {
+					// Publish one message
+					msgId := nuid.Next()
+					pubAck, err := js.Publish(
+						StreamSubjectPrefix+strconv.Itoa(int(i)),
+						buf,
+						nats.MsgId(msgId),
+					)
+					require_NoError(t, err)
+					require_Equal(t, pubAck.Sequence, i)
+
+					// Consume message
+					msgs, err := sub.Fetch(1)
+					require_NoError(t, err)
+					require_Equal(t, len(msgs), 1)
+
+					// Validate message
+					msg := msgs[0]
+					require_Equal(t, msgs[0].Header.Get(nats.MsgIdHdr), msgId)
+
+					// Validate message metadata
+					msgMeta, err := msg.Metadata()
+					require_NoError(t, err)
+					// Check sequence number
+					require_Equal(t, msgMeta.Sequence.Stream, i)
+
+					// Save for ACK later
+					receivedMessages = append(receivedMessages, msg)
+				}
+
+				// Verify stream state, expecting a single message due to limits
+				streamInfo, err := js.StreamInfo(StreamName)
+				require_NoError(t, err)
+				require_Equal(t, streamInfo.State.Msgs, 1)
+
+				// Verify consumer state, expecting ack floor corresponding to messages dropped
+				consumerInfo, err := js.ConsumerInfo(StreamName, Durable)
+				require_NoError(t, err)
+				require_Equal(t, consumerInfo.NumAckPending, 1)
+				require_Equal(t, consumerInfo.AckFloor.Stream, 9)
+				require_Equal(t, consumerInfo.AckFloor.Consumer, 9)
+
+				// ACK all messages (all except last have been dropped from the stream)
+				for _, message := range receivedMessages {
+					err := message.AckSync()
+					require_NoError(t, err)
+				}
+
+				// Verify consumer state, all messages ACKed
+				consumerInfo, err = js.ConsumerInfo(StreamName, Durable)
+				require_NoError(t, err)
+				require_Equal(t, consumerInfo.NumAckPending, 0)
+				require_Equal(t, consumerInfo.AckFloor.Stream, 10)
+				require_Equal(t, consumerInfo.AckFloor.Consumer, 10)
+			},
+		)
+	}
+}