@coko/server/src/graphql/PostgresPubSub.js

Reusable server for use by Coko's projects

/**
 * Code courtesy of the authors in this repo:
 * https://github.com/GraphQLCollege/graphql-postgres-subscriptions/blob/master/postgres-pubsub.js
 *
 * Repo seems abandoned, so moved here to be able to keep dependencies up to date.
 */

const { PubSub } = require('graphql-subscriptions')
const { Client } = require('pg')
const pgIPC = require('pg-ipc')

const {
  eventEmitterAsyncIterator,
} = require('./event-emitter-to-async-iterator')

const defaultCommonMessageHandler = message => message

class PostgresPubSub extends PubSub {
  constructor(options = {}) {
    const { commonMessageHandler, client, ...pgOptions } = options
    super()
    this.client = client || new Client(pgOptions)

    if (!client) {
      this.client.connect()
    }

    /* eslint-disable-next-line new-cap */
    this.ee = new pgIPC(this.client)
    this.subscriptions = {}
    this.subIdCounter = 0
    this.commonMessageHandler =
      commonMessageHandler || defaultCommonMessageHandler
  }

  publish(triggerName, payload) {
    this.ee.notify(triggerName, payload)
    return true
  }

  subscribe(triggerName, onMessage) {
    const callback = message => {
      onMessage(
        message instanceof Error
          ? message
          : this.commonMessageHandler(message.payload),
      )
    }

    this.ee.on(triggerName, callback)
    this.subIdCounter += 1
    this.subscriptions[this.subIdCounter] = [triggerName, callback]
    return Promise.resolve(this.subIdCounter)
  }

  unsubscribe(subId) {
    const [triggerName, onMessage] = this.subscriptions[subId]
    delete this.subscriptions[subId]
    this.ee.removeListener(triggerName, onMessage)
  }

  asyncIterator(triggers) {
    return eventEmitterAsyncIterator(
      this.ee,
      triggers,
      this.commonMessageHandler,
    )
  }
}

module.exports = PostgresPubSub