GCP Pub Sub support for Node.js

Introduction

Google Cloud Platform Pub/Sub is a messaging service in the cloud that can be used to publish and subscribe to events. CAST supports only the API methods relevant for the modelization of message publishing and message reception.

Objects

This extension, when the Node.js client library for Google Pub/Sub is found in the source code, may create the following objects representing message publishers and message receivers:

Icon	Description
	NodeJS GCP Pub/Sub Publisher
	NodeJS GCP Unknown Pub/Sub Publisher
	NodeJS GCP Pub/Sub Receiver
	NodeJS GCP Unknown Pub/Sub Receiver

API methods

Publisher

The supported “publish” API methods are:

API method	Object created	Link from caller
Topic.publish	NodeJS GCP (Unknown) Pub/Sub Publisher	callLink
Topic.publishJSON	NodeJS GCP (Unknown) Pub/Sub Publisher	callLink
Topic.publishMessage	NodeJS GCP (Unknown) Pub/Sub Publisher	callLink
Topic.resumePublishing	NodeJS GCP (Unknown) Pub/Sub Publisher	callLink
PublisherClient.publish	NodeJS GCP (Unknown) Pub/Sub Publisher	callLink

When one of the supported API methods for message publishing is found, this extension evaluates the topic name and creates a NodeJS GCP Pub/Sub Publisher named as the topic. When the topic name cannot be resolved, an Unknown Publisher object is created named Unknown.

Receiver

The supported “reception” API methods are:

API method	Object created	Link to handler (if resolved) from Receiver	Handler	Remarks
Subscription.on	NodeJS GCP (Unknown) Pub/Sub Receiver	callLink	Callback method passed as argument.	Only object created when first parameter is equal to ‘message’.
SubscriberClient.pull	NodeJS GCP (Unknown) Pub/Sub Receiver	callLink	Parent of the object calling the API method
SubscriberClient.streamingPull	NodeJS GCP Unknown Pub/Sub Receiver	callLink	Parent of the object calling the API method	Limited support: only Unknown objects are created because of complexity to analyze this low-level API.
SubscriberClient.subscriptionPath	N/A	N/A	N/A	Method used to provide subscription ids to the pull request. N/A: Not applicable.

When one of the supported API methods for message reception is found, this extension evaluates the subscription name and creates a NodeJS GCP Pub/Sub Receiver named as the subscription. When the subscription name cannot be resolved, an Unknown Receiver object is created named Unknown.

Subscription

The supported “subscription” API methods are:

API method	Object created	Remarks
Topic.subscription	NodeJS GCP Pub/Sub Subscription	Contains a list of topics in “Topics subscribed to” property.
Topic.createSubscription	NodeJS GCP Pub/Sub Subscription	As above
PubSub.subscription	NodeJS GCP Pub/Sub Subscription	As above
PubSub.createSubscription	NodeJS GCP Pub/Sub Subscription	As above

This extension evaluates the subscription name as well as the name of the topic to which the subscription is made. This information is used by the com.castsoftware.wbslinker extension to link publishers with matching receivers.

Topic evaluation

For topic evaluation, both for Subscriptions and Publishers, the following API methods are supported:

API methods	Remarks
Pubsub.createTopic	Used for evaluation of publishing/subscription topics.
PubSub.topic	As above
PublisherClient.topicPath	As above

Example

The JavaScript code below publishes a message on topic my-topic:

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
const topic = pubsub.topic('my-topic');

const data = Buffer.from('Hello, world!');

const callback = (err, messageId) => {
  if (err) {
    // Error handling omitted.
  }
};

topic.publishMessage({data}, callback);  // this results in a Publisher object

The code below shows a subscription to the same my-topic topic and the reception of the messages via the Subscription.on() API method:

const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();

const topic = pubsub.topic('my-topic');
const subscription = topic.subscription('my-subscription');

const callback = function(message) {};

subscription.on('message', callback);    // this results in a Receiver object and the link to the callback function

The resulting objects created by the Node.js extension are shown below with the respective links from the JavaScript caller to the CPG Pub/Sub Publisher and from the GCP Pub/Sub Receiver to the callback function (NONAME):

The synchronicity of the links from JavaScript to Publisher and from Receiver to JavaScript objects will be denoted by the property “Is the call asynchronous”. Note that a call to an asynchronous API with an await is considered as a synchronous call. The links between Publisher/Receiver objects are created during the application-level analysis step, even in the case they pertain to the same technology as in the present example.