This node receives a message that has been published to a topic. During configuration, the property called Subscription is used to name the GCP Subscription that we are watching.
This is an event generating node and as such has no inputs. When a message is received, the flowing msg will contain a payload property corresponding to a GCP Pub/Sub message data payload. In addition, the msg.message will contain a read-only copy of the original message properties. This is described here. The message is auto acknowledged.
If we know that the incoming message contains a data payload that is JSON encoded, a configuration option called Assume JSON can be selected. When selected, the content of the message is parsed from a JSON string to an object representation and stored at msg.payload.