[fix][broker] Fix non-batched null-value messages not removed during topic compaction

pulsar-broker/src/main/java/org/apache/pulsar/compaction/AbstractTwoPhaseCompactor.java

@@ -462,14 +462,22 @@ private CompletableFuture<Void> addToCompactedLedger(LedgerHandle lh, RawMessage
     return bkf;
   }
 
+  /**
+   * Extract the partition key and the payload size for a non-batch message.
+   *
+   * @return a pair of (partitionKey, payloadSize), or null if the message has no partition key.
+   */
   protected Pair<String, Integer> extractKeyAndSize(RawMessage m, MessageMetadata msgMetadata) {
-    ByteBuf headersAndPayload = m.getHeadersAndPayload();
     if (msgMetadata.hasPartitionKey()) {
-      int size = headersAndPayload.readableBytes();
+      int payloadSize;
       if (msgMetadata.hasUncompressedSize()) {
-        size = msgMetadata.getUncompressedSize();
+        payloadSize = msgMetadata.getUncompressedSize();
+      } else {
+        ByteBuf headersAndPayload = m.getHeadersAndPayload().duplicate();
+        Commands.skipMessageMetadata(headersAndPayload);
+        payloadSize = headersAndPayload.readableBytes();
       }
-      return Pair.of(msgMetadata.getPartitionKey(), size);
+      return Pair.of(msgMetadata.getPartitionKey(), payloadSize);
     } else {
       return null;
     }

pulsar-broker/src/main/java/org/apache/pulsar/compaction/EventTimeOrderCompactor.java

@@ -18,7 +18,6 @@
  */
 package org.apache.pulsar.compaction;
 
-import io.netty.buffer.ByteBuf;
 import java.io.IOException;
 import java.util.List;
 import java.util.Map;
@@ -138,17 +137,12 @@ protected boolean compactBatchMessage(String topic, Map<String, Pair<MessageId,
   }
 
   protected MessageCompactionData extractMessageCompactionData(RawMessage m, MessageMetadata metadata) {
-    ByteBuf headersAndPayload = m.getHeadersAndPayload();
-    if (metadata.hasPartitionKey()) {
-      int size = headersAndPayload.readableBytes();
-      if (metadata.hasUncompressedSize()) {
-        size = metadata.getUncompressedSize();
-      }
-      return new MessageCompactionData(m.getMessageId(), metadata.getPartitionKey(),
-          size, metadata.getEventTime());
-    } else {
+    Pair<String, Integer> keyAndSize = extractKeyAndSize(m, metadata);
+    if (keyAndSize == null) {
       return null;
     }
+    return new MessageCompactionData(m.getMessageId(), keyAndSize.getLeft(),
+        keyAndSize.getRight(), metadata.getEventTime());
   }
 
   private List<MessageCompactionData> extractMessageCompactionDataFromBatch(RawMessage msg, MessageMetadata metadata)

pulsar-broker/src/test/java/org/apache/pulsar/compaction/CompactionTest.java

@@ -640,6 +640,80 @@ public void testBatchMessageWithNullValue() throws Exception {
         assertEquals(messages.get(2).getKey(), "key5");
     }
 
+    /**
+     * Write raw non-batch entries directly to the managed ledger, simulating
+     * messages from C++/Python clients that do not set numMessagesInBatch.
+     * Verifies that null-value tombstones remove keys during compaction.
+     */
+    @Test
+    public void testNonBatchedMessageWithNullValue() throws Exception {
+        String topic = "persistent://my-tenant/my-ns/non-batched-message-with-null-value";
+
+        admin.topics().createNonPartitionedTopic(topic);
+        pulsarClient.newConsumer().topic(topic).subscriptionName("sub1")
+                .receiverQueueSize(1).readCompacted(true).subscribe().close();
+
+        PersistentTopic persistentTopic =
+                (PersistentTopic) pulsar.getBrokerService().getTopic(topic, false).join().get();
+        ManagedLedgerImpl ml = (ManagedLedgerImpl) persistentTopic.getManagedLedger();
+
+        long seqId = 0;
+
+        // key1: value then null-value tombstone
+        ml.addEntry(buildNonBatchEntry("key1", "my-message-1".getBytes(), seqId++));
+        ml.addEntry(buildNonBatchEntry("key1", null, seqId++));
+
+        // key2: value only (should survive)
+        ml.addEntry(buildNonBatchEntry("key2", "my-message-3".getBytes(), seqId++));
+
+        // key3: value then null-value tombstone
+        ml.addEntry(buildNonBatchEntry("key3", "my-message-4".getBytes(), seqId++));
+        ml.addEntry(buildNonBatchEntry("key3", null, seqId++));
+
+        // key4: value only (should survive)
+        ml.addEntry(buildNonBatchEntry("key4", "my-message-6".getBytes(), seqId++));
+
+        compact(topic);
+
+        List<Message<byte[]>> messages = new ArrayList<>();
+        try (Consumer<byte[]> consumer = pulsarClient.newConsumer().topic(topic)
+             .subscriptionName("sub1").receiverQueueSize(1).readCompacted(true).subscribe()) {
+            while (true) {
+                Message<byte[]> message = consumer.receive(5, TimeUnit.SECONDS);
+                if (message == null) {
+                    break;
+                }
+                messages.add(message);
+            }
+        }
+
+        assertEquals(messages.size(), 2);
+        assertEquals(messages.get(0).getKey(), "key2");
+        assertEquals(messages.get(1).getKey(), "key4");
+    }
+
+    private byte[] buildNonBatchEntry(String key, byte[] payload, long sequenceId) {
+        org.apache.pulsar.common.api.proto.MessageMetadata metadata =
+                new org.apache.pulsar.common.api.proto.MessageMetadata();
+        metadata.setPartitionKey(key);
+        metadata.setPublishTime(System.currentTimeMillis());
+        metadata.setProducerName("test-non-batch");
+        metadata.setSequenceId(sequenceId);
+        if (payload == null) {
+            metadata.setNullValue(true);
+        }
+        ByteBuf payloadBuf = io.netty.buffer.Unpooled.wrappedBuffer(
+                payload != null ? payload : new byte[0]);
+        ByteBuf entry = org.apache.pulsar.common.protocol.Commands.serializeMetadataAndPayload(
+                org.apache.pulsar.common.protocol.Commands.ChecksumType.Crc32c,
+                metadata, payloadBuf);
+        byte[] bytes = new byte[entry.readableBytes()];
+        entry.readBytes(bytes);
+        entry.release();
+        payloadBuf.release();
+        return bytes;
+    }
+
     @Test
     public void testWholeBatchCompactedOut() throws Exception {
         String topic = "persistent://my-tenant/my-ns/whole-batch-compacted-out";