Google Cloud Platform for Developers

Pull subscriptions

In the pull model of message delivery, subscribers initiate requests to the Cloud Pub/Sub API and receive queued messages in the API response. When the queue is empty, the API responds with an error code to indicate that no messages are available. In addition to the message body, attributes, and message ID, each message is returned with an acknowledgment (ack) ID. Subscribers must inform Cloud Pub/Sub that a message should be removed from the queue by making an additional API call with that message's ack ID.

Google provides Cloud Pub/Sub client libraries for many common languages. These client libraries abstract away much of the overhead of ingesting messages via the Cloud Pub/Sub APIs and should be used whenever possible. ...