Pub/Sub triggers

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 functions.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 onPublish() event handler:

exports.helloPubSub = functions.pubsub.topic('topic-name').onPublish((message) => {
  // ...
});

Access the pub/sub message payload {:#access-pub/sub}

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 = message.json.name;
  } catch (e) {
    functions.logger.error('PubSub message was not JSON', e);
  }
index.js

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 messageBody = message.data ? Buffer.from(message.data, 'base64').toString() : null;
index.js

Access message attributes {:#access-message}

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 = message.attributes.name;
index.js

You might notice that some basic data such as the message ID or the message publish time are not available in Message.attributes . To work around this, you can access these details in the triggering event's EventContext . For example:

exports.myFunction = functions.pubsub.topic('topic1').onPublish((message, context) => {
    console.log('The function was triggered at ', context.timestamp);
    console.log('The unique ID for the event is', context.eventId);
});