[I] Expose isReplicated() / getReplicatedFrom() on the public Message API [pulsar-client-cpp]

["graham-macdonald-simplisafe (via GitHub)" <gi...@apache.org>]

graham-macdonald-simplisafe opened a new issue, #569:
URL: https://github.com/apache/pulsar-client-cpp/issues/569

   ## Feature Request
   
   Expose replication-origin metadata on the public `Message` class so consumer logic can detect whether a received message was produced locally or geo-replicated from a remote cluster.
   
   ### Requested API additions to `include/pulsar/Message.h`
   
   ```cpp
   /**
    * Check if this message was geo-replicated from another cluster.
    *
    * @return true if the message was replicated from a remote cluster,
    *         false if it was produced locally
    */
   bool isReplicated() const;
   
   /**
    * Get the name of the cluster this message was replicated from.
    *
    * @return the source cluster name, or an empty string if the message
    *         was produced locally (i.e. isReplicated() == false)
    */
   const std::string& getReplicatedFrom() const;
   ```
   
   ### Why this is straightforward to implement
   
   `MessageImpl` already holds `proto::MessageMetadata metadata` (see `lib/MessageImpl.h`), which contains the `replicated_from` optional string field from the Pulsar binary protocol. The implementation would simply wrap:
   
   ```cpp
   bool Message::isReplicated() const {
       return impl_->metadata.has_replicated_from() &&
              !impl_->metadata.replicated_from().empty();
   }
   
   const std::string& Message::getReplicatedFrom() const {
       return impl_->metadata.replicated_from();
   }
   ```
   
   The Java client already exposes both methods on `Message`. This brings the C++ client to parity.
   
   ### Use case: active-active geo-replication consumer routing
   
   In a geo-replicated active-active topology with a single replicated topic, consumers use `isReplicated()` as the routing signal for nack-based deferral:
   
   ```cpp
   if (!message.isReplicated()) {
       // Locally produced — process immediately
       process(message);
       consumer.acknowledge(message);
   } else if (message.getRedeliveryCount() == 0) {
       // Replicated from remote — defer; let the home-cluster consumer handle it.
       // If the home-cluster consumer is healthy, the replicated subscription cursor
       // sync will resolve this message before the delay expires.
       consumer.negativeAcknowledge(message);  // ~1s redelivery delay
   } else {
       // Home cluster is down — take over
       process(message);
       consumer.acknowledge(message);
   }
   ```
   
   Without `isReplicated()`, the only alternative is a dual-topic pattern (one topic per cluster), which doubles topic count and requires cluster-aware producer logic. Exposing `isReplicated()` enables a simpler single-topic topology.
   
   ### Related
   
   - The Node.js client (`pulsar-client-node`) wraps the C++ client and will be able to surface this once it is available here.
   - `replicateSubscriptionState` is also not yet surfaced in the Node.js client: apache/pulsar-client-node#478


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Re: [I] Expose isReplicated() / getReplicatedFrom() on the public Message API [pulsar-client-cpp]

["BewareMyPower (via GitHub)" <gi...@apache.org>]

BewareMyPower closed issue #569: Expose isReplicated() / getReplicatedFrom() on the public Message API
URL: https://github.com/apache/pulsar-client-cpp/issues/569


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