Event Bus

info

Wire Unchained to an Event based system

We can easily swap the default event tracker module (EventEmitter) used by unchained with out own module by implementing EventAdapter interface and registering it on EventDirector on system boot time. Both classes are exported from the core-events module.

Here is an example of redis-enabled Unchained Events:

import { createClient } from '@redis/client';
import { EmitAdapter, setEmitAdapter } from '@unchainedshop/events';

const { REDIS_PORT = 6379, REDIS_HOST = '127.0.0.1' } = process.env;

const subscribedEvents = new Set();

const RedisEventEmitter = (): EmitAdapter => {
  const redisPublisher = createClient({
    url: `redis://${REDIS_HOST}:${REDIS_PORT}`,
  });

  const redisSubscriber = createClient({
    url: `redis://${REDIS_HOST}:${REDIS_PORT}`,
  });

  return {
    publish: (eventName, payload) => redisPublisher.publish(eventName, JSON.stringify(payload)),
    subscribe: (eventName, callback) => {
      if (!subscribedEvents.has(eventName)) {
        redisSubscriber.subscribe(eventName, (payload) => {
          callback(JSON.parse(payload));
        });
        subscribedEvents.add(eventName);
      }
    },
  };
};

setEmitAdapter(RedisEventEmitter());

Register custom events:

  startPlatform({...});
  ...
  registerEvents([
      'CUSTOM_EVENT_ONE',
      'CUSTOM_EVENT_TWO',
      'CUSTOM_EVENT_THREE',
  ])

Explanation:

We have decided to use redis for event tracking. In order to do that we have to create new class extending the EventAddapter interface and implement the two functions required subscribe & publish.

in this functions we defined how redis implements the pub/sub model.

Next all we need to is register it in EventDirector class using the static function setEventAdapter.