[fix][broker] Correctly set byte and message out totals per topic.

Fixes apache#15819

The existing code calculates the pulsar_out_bytes_total and pulsar_out_messages_total
per subscription metrics by adding the values from the currently connected consumers.
This produces incorrect values as soon as one or more of the consumers disconnects
from the subscription.

This changes these two metrics to directly use the subscription stats for these
values, and match the output of `pulsar-admin topic stats`.

Signed-off-by: Paul Gier <paul.gier@datastax.com>

pulsar-broker/src/main/java/org/apache/pulsar/broker/stats/prometheus/NamespaceStatsAggregator.java

@@ -115,6 +115,8 @@ private static void aggregateTopicStats(TopicStats stats, SubscriptionStatsImpl
                                             AggregatedSubscriptionStats subsStats) {
         stats.subscriptionsCount++;
         stats.msgBacklog += subscriptionStats.msgBacklog;
+        subsStats.bytesOutCounter = subscriptionStats.bytesOutCounter;
+        subsStats.msgOutCounter = subscriptionStats.msgOutCounter;
         subsStats.msgBacklog = subscriptionStats.msgBacklog;
         subsStats.msgDelayed = subscriptionStats.msgDelayed;
         subsStats.msgRateExpired = subscriptionStats.msgRateExpired;
@@ -133,8 +135,6 @@ private static void aggregateTopicStats(TopicStats stats, SubscriptionStatsImpl
             subsStats.msgRateOut += cStats.msgRateOut;
             subsStats.messageAckRate += cStats.messageAckRate;
             subsStats.msgThroughputOut += cStats.msgThroughputOut;
-            subsStats.bytesOutCounter += cStats.bytesOutCounter;
-            subsStats.msgOutCounter += cStats.msgOutCounter;
             if (!subsStats.blockedSubscriptionOnUnackedMsgs && cStats.blockedConsumerOnUnackedMsgs) {
                 subsStats.blockedSubscriptionOnUnackedMsgs = true;
             }

pulsar-broker/src/test/java/org/apache/pulsar/broker/stats/PrometheusMetricsTest.java

@@ -352,6 +352,88 @@ public void testPerTopicStats() throws Exception {
         c2.close();
     }
 
+    /**
+     * Test that the total message and byte counts for a topic are not reset when a consumer disconnects.
+     *
+     * @throws Exception
+     */
+    @Test
+    public void testPerTopicStatsReconnect() throws Exception {
+        Producer<byte[]> p1 = pulsarClient.newProducer().topic("persistent://my-property/use/my-ns/my-topic1").create();
+
+        Consumer<byte[]> c1 = pulsarClient.newConsumer()
+                .topic("persistent://my-property/use/my-ns/my-topic1")
+                .subscriptionName("test")
+                .subscribe();
+
+        final int messages = 5;
+        final int pulsarMessageOverhead = 31; // Number of extra bytes pulsar adds to each message
+        final int messageSizeBytes = "my-message-n".getBytes().length + pulsarMessageOverhead;
+
+        for (int i = 0; i < messages; i++) {
+            String message = "my-message-" + i;
+            p1.send(message.getBytes());
+        }
+
+        for (int i = 0; i < messages; i++) {
+            c1.acknowledge(c1.receive());
+        }
+
+        c1.close();
+
+        for (int i = 0; i < messages; i++) {
+            String message = "my-message-" + i;
+            p1.send(message.getBytes());
+        }
+
+        Consumer<byte[]> c2 = pulsarClient.newConsumer()
+                .topic("persistent://my-property/use/my-ns/my-topic1")
+                .subscriptionName("test")
+                .subscribe();
+
+        for (int i = 0; i < messages; i++) {
+            c2.acknowledge(c2.receive());
+        }
+
+        p1.close();
+        c2.close();
+
+        ByteArrayOutputStream statsOut = new ByteArrayOutputStream();
+        PrometheusMetricsGenerator.generate(pulsar, true, false, false, statsOut);
+        String metricsStr = statsOut.toString();
+        Multimap<String, Metric> metrics = parseMetrics(metricsStr);
+
+        metrics.entries().forEach(e -> {
+            System.out.println(e.getKey() + ": " + e.getValue());
+        });
+
+        List<Metric> cm = (List<Metric>) metrics.get("pulsar_in_bytes_total");
+        assertEquals(cm.size(), 1);
+        assertEquals(cm.get(0).value, (messageSizeBytes * messages * 2));
+        assertEquals(cm.get(0).tags.get("topic"), "persistent://my-property/use/my-ns/my-topic1");
+        assertEquals(cm.get(0).tags.get("namespace"), "my-property/use/my-ns");
+
+        cm = (List<Metric>) metrics.get("pulsar_in_messages_total");
+        assertEquals(cm.size(), 1);
+        assertEquals(cm.get(0).value, (messages * 2));
+        assertEquals(cm.get(0).tags.get("topic"), "persistent://my-property/use/my-ns/my-topic1");
+        assertEquals(cm.get(0).tags.get("namespace"), "my-property/use/my-ns");
+
+        cm = (List<Metric>) metrics.get("pulsar_out_bytes_total");
+        assertEquals(cm.size(), 1);
+        assertEquals(cm.get(0).value, (messageSizeBytes * messages * 2));
+        assertEquals(cm.get(0).tags.get("topic"), "persistent://my-property/use/my-ns/my-topic1");
+        assertEquals(cm.get(0).tags.get("namespace"), "my-property/use/my-ns");
+        assertEquals(cm.get(0).tags.get("subscription"), "test");
+
+        cm = (List<Metric>) metrics.get("pulsar_out_messages_total");
+        assertEquals(cm.size(), 1);
+        assertEquals(cm.get(0).value, (messages * 2));
+        assertEquals(cm.get(0).tags.get("topic"), "persistent://my-property/use/my-ns/my-topic1");
+        assertEquals(cm.get(0).tags.get("namespace"), "my-property/use/my-ns");
+        assertEquals(cm.get(0).tags.get("subscription"), "test");
+    }
+
     @Test
     public void testPerTopicExpiredStat() throws Exception {
         String ns = "prop/ns-abc1";