A simple PubSub factory method exposing a listen-emit pattern

PubSub

This is a generic PubSub Factory exposing a listen and a emit method.

NOTE: Today, only Google Cloud PubSub has been added.

Installation

npm install --save @algoan/pubsub

Usage

Google Cloud PubSub

Run tests

To run tests or to try the PubSubFactory class, you need to have a google account and have installed gcloud sdk.

Then, to install the Google PubSub simulator, run:

gcloud components install pubsub-emulator
gcloud components update

Start tests running:

npm test

It will launch a Google PubSub emulator thanks to the google-pubsub-emulator library.

Example

To create a PubSub instance using Google Cloud:

import { EmittedMessage, GCPubSub, PubSubFactory, Transport } from '@algoan/pubsub'

const pubSub: GCPubSub = PubSubFactory.create({
  transport: Transport.GOOGLE_PUBSUB,
  options: {
    projectId: 'test',
    // And all other Google PubSub properties
  }
});
const topicName: string = 'some_topic';

await pubsub.listen(topicName, {
  autoAck: true,
  onMessage: (data: EmittedMessage<{foo: string}>) => {
    console.log(data.parsedData); // { foo: 'bar', time: {Date.now}, _eventName: 'some_topic' }
    // do whatever you want. The message has already been acknowledged
  },
  onError: (error: Error) => {
    // Handle error as you wish
  }
});

await pubsub.emit(topicName, { foo: 'bar' });

Contribution

This module uses semantic-release, please follow these instructions to contribute to the project or use npm run commit.

API

PubSubFactory.create({ transport, options })

The only static method from the PubSubFactory class. It initiates a new PubSub instance depending on the transport. By default, it connects to Google Cloud PubSub.

• transport: PubSub technology to use. Only GOOGLE_PUBSUB is available for now.
• options: Options related to the transport.
  • If transport === Transport.GOOGLE_PUBSUB, then have a look at the Google Cloud PubSub config client.
  • debug: Display logs if it is set to true. It uses a pino logger and pino-pretty if NODE_ENV is not equal to production.
  • pinoOptions: If debug is set to true, set the pino logger options. Default to level: debug and prettyPrint: true if NODE_ENV is not equal to production.
  • topicsPrefix: Add a prefix to all created topics. Example: topicsPrefix: 'my-topic', all topics will begin with my-topic+{your topic name}.
  • subscriptionsPrefix: Add a prefix to all created subscriptions. Example: subscriptionsPrefix: 'my-sub', all topics will begin with my-sub%{your topic name}.
  • namespace: Add a namespace property to Message attributes when publishing on a topic.
  • environment: Add a environment property to Message attributes when publishing on a topic.

pubsub.listen(event, opts)

Listen to a specific event.

NOTE: It only uses the Google Cloud subscription pull delivery for now.

• event: Name of the event.
• opts: Options related to the Listener method
  • onMessage: Method called when receiving a message
  • onError: Method called when an error occurs
  • options: Option related to the chosen transport

If the chosen transport is Google Cloud PubSub, then options would be:

• autoAck: Automatically ACK an event as soon as it is received (default to true)
• subscriptionOptions: Options related to the created Subscription:
  • get: Options applied to the getSubscription method (have a look at Subscription options)
  • sub: Options applied to the subscription instance (see also setOptions method)
• topicOptions: Options applied to the created topic (have a look at Topic options)

pubsub.emit(event, payload, opts)

Emit a specific event with a payload. It added attributes in the message if you have added a namespace or an environment when setting the PubSubFactory class. It also adds an _eventName and a time property in the emitted payload.

• event: Name of the event to emit.
• payload: Payload to send. It will be buffered by Google, and then parsed by the listen method.
• opts: Options related to the Emit method
  • metadata: Custom metadata added to the message
  • options: Option related to the chosen transport

If the chosen transport is Google Cloud PubSub, then options would be:

• topicOptions: Options applied to the created topic (have a look at Topic options)

Download Details:

Author: algoan

Source Code: https://github.com/algoan/pubsub

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