PubSub Multi

Multiple implementations of Publish-Subscribe.

• In-memory
• HTTP EventSource and POST as transport

Both implementations share the same contract tests, allowing them to be used interchangeably.

The API for publishing is simple:

// publisher is an instance of MemoryPublisher
await publisher.publish('some-signal')

The API for publishing too:

// publisher is an instance of MemoryPublisher or EventSourcePubSub
const subscriber = publisher.makeSubscriber()
await subscriber.subscribe('some-signal', async () => {
  console.log('received some-signal')
})

HTTP

To use this over HTTP, mount the express middleware in your express app:

const express = require('express')
const bodyParser = require('body-parser')
const { MemoryPublisher, pubSubRouter } = require('pubsub-multi')
 
const publisher = new MemoryPublisher() // Implements both pub and sub interface
 
const app = express()
app.use(bodyParser.json())
app.use(bodyParser.text())
app.use(pubSubRouter({ publisher }))

To publish, you would use publisher.publish as described above. The pubSubRouter then sends signals to subscribers using Server-Sent Events as the transport.

Clients are configured as follows:

const { EventSourcePubSub } = require('pubsub-multi')
const Fetch22 = require('fetch-22') // Tiny lib that simplifies HTTP
const fetch = window.fetch.bind(window)
const baseUrl = 'http://host.com'
const fetch22 = new Fetch22({ baseUrl, fetch })
const eventSource = new EventSource(`${baseUrl}/pubsub`)
 
const publisher = new EventSourcePubSub({ fetch22, eventSource })
const subscriber = publisher.makeSubscriber()

To subscribe, you would use subscriber.subscribe as described above. The EventSourcePubSub registers subscriptions on the server with HTTP POST.