Capturing Message IDs from Google Pub/Sub on write

I wanted to clarify the difference between how message IDs are retrieved when publishing to a Google Cloud Pub/Sub topic using a "Future" (which is effectively what we want), versus how the current script provided retrieves them via subscription.

When we publish a message, the Publisher.publish() method returns an future in Python, which represents the asynchronous result of the publish operation. By calling future.result(), we can retrieve the message ID assigned by Pub/Sub at the moment it has successfully published working as a sort of Acknowledgement.

For Example, in Python you can do the following:

future = publisher.publish(topic_path, b"Hello world")
message_id = future.result()
print(f"Published message ID: {message_id}")

What we want is to use the above-mentioned method due to tracking or logging the message ID immediately after publishing and received by the Topic.

However, in the Groovy script provided, we're not publishing but rather it pulling messages from a subscription. In this case, we receive a ReceivedMessage object, which includes:

message.getMessageId() - ID assigned at publish time

receivedMessage.getAckId() - Ack ID generated when the message is delivered to the subscription

So instead of using a Future, the current script is retrieving the message ID after the message has been published and delivered to a subscriber which is not what we are interested in currently.

Our goal is to capture the message ID at publish time, we would need a script to have a publishing step and use the future returned by the publisher client.

If you have any further question please do let me know.