[fix][broker] Copy proto command fields into final variables in Serve…

…rCnx (apache#18987)

### Motivation

In the `PulsarDecoder`, we use a single `BaseCommand` object and overwrite it for each incoming protocol message. As a result, it is not safe to publish any references to a proto command to other threads.

Here is the single `BaseCommand`:

https://github.com/apache/pulsar/blob/82237d3684fe506bcb6426b3b23f413422e6e4fb/pulsar-common/src/main/java/org/apache/pulsar/common/protocol/PulsarDecoder.java#L99

Here is the method call that resets the object:

https://github.com/apache/pulsar/blob/82237d3684fe506bcb6426b3b23f413422e6e4fb/pulsar-common/src/main/java/org/apache/pulsar/common/protocol/PulsarDecoder.java#L114

Note that the call to `parseFrom` first calls `clear()`, which resets all values on the object.

This PR copies relevant values or objects into other variables.

### Modifications

* Replace `command` with `tcId` since the latter is a final variable meant to be published to another thread.
* Move logic to copy certain command fields to earlier in method for `handleSubscribe`
* Copy `ack` object to new `CommandAck` when there is a broker interceptor. Note that copying this command is likely somewhat costly, so we only do it when there is an interceptor configured.

### Verifying this change

This is a trivial change that is already covered by tests.

### Documentation

- [x] `doc-not-needed` 

This is an internal change.

### Matching PR in forked repository

PR in forked repository: michaeljmarshall#8

pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java

@@ -1027,6 +1027,9 @@ protected void handleSubscribe(final CommandSubscribe subscribe) {
         final KeySharedMeta keySharedMeta = subscribe.hasKeySharedMeta()
               ? new KeySharedMeta().copyFrom(subscribe.getKeySharedMeta())
               : emptyKeySharedMeta;
+        final long consumerEpoch = subscribe.hasConsumerEpoch() ? subscribe.getConsumerEpoch() : DEFAULT_CONSUMER_EPOCH;
+        final Optional<Map<String, String>> subscriptionProperties = SubscriptionOption.getPropertiesMap(
+                subscribe.getSubscriptionPropertiesList());
 
         if (log.isDebugEnabled()) {
             log.debug("Topic name = {}, subscription name = {}, schema is {}", topicName, subscriptionName,
@@ -1091,14 +1094,6 @@ protected void handleSubscribe(final CommandSubscribe subscribe) {
                     return null;
                 }
 
-                final long consumerEpoch;
-                if (subscribe.hasConsumerEpoch()) {
-                    consumerEpoch = subscribe.getConsumerEpoch();
-                } else {
-                    consumerEpoch = DEFAULT_CONSUMER_EPOCH;
-                }
-                Optional<Map<String, String>> subscriptionProperties = SubscriptionOption.getPropertiesMap(
-                        subscribe.getSubscriptionPropertiesList());
                 service.isAllowAutoTopicCreationAsync(topicName.toString())
                         .thenApply(isAllowed -> forceTopicCreation && isAllowed)
                         .thenCompose(createTopicIfDoesNotExist ->
@@ -1636,6 +1631,7 @@ protected void handleAck(CommandAck ack) {
         final boolean hasRequestId = ack.hasRequestId();
         final long requestId = hasRequestId ? ack.getRequestId() : 0;
         final long consumerId = ack.getConsumerId();
+        final CommandAck finalAck = getBrokerService().getInterceptor() != null ? new CommandAck().copyFrom(ack) : null;
 
         if (consumerFuture != null && consumerFuture.isDone() && !consumerFuture.isCompletedExceptionally()) {
             Consumer consumer = consumerFuture.getNow(null);
@@ -1644,7 +1640,7 @@ protected void handleAck(CommandAck ack) {
                             ctx.writeAndFlush(Commands.newAckResponse(
                                     requestId, null, null, consumerId));
                         }
-                getBrokerService().getInterceptor().messageAcked(this, consumer, ack);
+                getBrokerService().getInterceptor().messageAcked(this, consumer, finalAck);
             }).exceptionally(e -> {
                         if (hasRequestId) {
                             ctx.writeAndFlush(Commands.newAckResponse(requestId,
@@ -2333,7 +2329,7 @@ protected void handleNewTxn(CommandNewTxn command) {
                     if (log.isDebugEnabled()) {
                         log.debug("Send response {} for new txn request {}", tcId.getId(), requestId);
                     }
-                    commandSender.sendNewTxnResponse(requestId, txnID, command.getTcId());
+                    commandSender.sendNewTxnResponse(requestId, txnID, tcId.getId());
                 } else {
                     if (ex instanceof CoordinatorException.ReachMaxActiveTxnException) {
                         // if new txn throw ReachMaxActiveTxnException, don't return any response to client,