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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