Google Cloud's Pub/Sub is a
globally distributed message bus that automatically scales as you need it. You
can create a function that handles Pub/Sub events by using
pubsub
.
Trigger a pub/sub function
You can trigger a function whenever a new Pub/Sub message is sent
to a specific topic. You must specify the Pub/Sub topic name that
you want to trigger your function, and set the event within the
onMessagePublished()
event handler:
exports.hellopubsub = onMessagePublished("topic-name", (event) => { // ... });
Access the pub/sub message payload
The payload for the Pub/Sub message is accessible from the
Message
object returned
to your function. For messages with JSON in the Pub/Sub message
body, the Firebase SDK for Cloud Functions has a helper property to decode the message. For
example, here is a message published with a simple JSON payload:
gcloud pubsub topics publish topic-name --message '{"name":"Xenia"}'
You can access a JSON data payload like this via the
json
property:
// Get the `name` attribute of the PubSub message JSON body. let name = null; try { name = event.data.message.json.name; } catch (e) { logger.error("PubSub message was not JSON", e); }
Other, non-JSON payloads are contained in the Pub/Sub message as base64 encoded strings in the message object. To read a message like the following, you must decode the base64 encoded string as shown:
gcloud pubsub topics publish topic-name --message 'MyMessage'
// Decode the PubSub Message body. const message = event.data.message; const messageBody = message.data ? Buffer.from(message.data, "base64").toString() : null;
Access message attributes
Pub/Sub message can be sent with data attributes set in the
publish command. For example, you could publish a message with a name
attribute:
gcloud pubsub topics publish topic-name --attribute name=Xenia
You can read such attributes from
Message.attributes
:
// Get the `name` attribute of the message. const name = event.data.message.attributes.name;