Pub/Sub triggers
Stay organized with collections
Save and categorize content based on your preferences.
Google Cloud's Pub/Sub is a globally distributed message bus that automatically scales as you need it. You can trigger a function whenever a new Pub/Sub message is sent to a specific topic.
Import the required modules
To get started, import the modules required for handling Pub/Sub events:
Node.js
const{onMessagePublished}=require("firebase-functions/pubsub");
constlogger=require("firebase-functions/logger");
Python
fromfirebase_functionsimport pubsub_fn
Trigger the function
You must specify the Pub/Sub topic name that you want to trigger your function, and set the event within the event handler:
Node.js
exports.hellopubsub=onMessagePublished("topic-name",(event)=>{
Python
@pubsub_fn.on_message_published(topic="topic-name")
defhellopubsub(event: pubsub_fn.CloudEvent[pubsub_fn.MessagePublishedData]) -> None:
"""Log a message using data published to a Pub/Sub topic."""
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:
Node.js
// Get the `name` attribute of the PubSub message JSON body. letname=null; try{ name=event.data.message.json.name; }catch(e){ logger.error("PubSub message was not JSON",e); }
Python
# Get the `name` attribute of the PubSub message JSON body.
try:
data = event.data.message.json
except ValueError:
print("PubSub message was not JSON")
return
if data is None:
return
if "name" not in data:
print("No 'name' key")
return
name = data["name"]
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'
Node.js
// Decode the PubSub Message body. constmessage=event.data.message; constmessageBody=message.data? Buffer.from(message.data,"base64").toString(): null;
Python
# Decode the PubSub message body.
message_body = base64.b64decode(event.data.message.data)
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 the corresponding property of the message object:
Node.js
// Get the `name` attribute of the message. constname=event.data.message.attributes.name;
Python
# Get the `name` attribute of the message.
if "name" not in event.data.message.attributes:
print("No 'name' attribute")
return
name = event.data.message.attributes["name"]