Mongopubsub

Mongopubsub is a pub/sub implementation for Node.js and MongoDB. It utilizes Mongo's capped collections and tailable cursors to notify subscribers of inserted documents that match a given query.

Example

import { MubSub } from 'mongopubsub';
import mongoose from 'mongoose';
import { Db } from 'mongodb';

const {
    MONGODB_URI = 'mongodb://localhost:27017/mongopubsub_example'
} = process.env; 

let mubsub: MubSub;
let mongoDb: Db;

const init = async () => {
  return new Promise(async (resolve, reject) => {
    try {
      await mongoose.connect(MONGODB_URI);
      console.log('🎉 Connected to database successfully');
      mongoDb = mongoose.connections[0].db;
      mubsub = new MubSub({
        mongoDb
      });
      mubsub.on(`error`, (error) => {
        console.error(`Mubsub Error`, error);
      });
      mubsub.once(`ready`, (error) => {
        console.log(`Mubsub Ready`, `Mubsub is ready to publish and subscribe`);
        resolve();
      });
    } catch (error) {
      console.error(`Mongoose connect() error`, error);
      reject(error);
    }
  });
}

const run = async () => {
  await init();
  const event = `foo`;
  const callback = (message) => {
    console.log(`Event[${event}] Message received`, { message });
  };
  const subscription = mubsub.subscribe({ event, callback });
  
  mubsub.publish({event, message: { hello: `world`}})
};

await run();

Usage

Instantiate

You pass a Db instance in the constructure options

import { MubSub } from 'mongopubsub';
import mongoose from 'mongoose';

await mongoose.connect(MONGODB_URI);
const mongoDb = mongoose.connections[0].db;
const mubsub = new MubSub({
  mongoDb
});

Channels

A channel maps one-to-one with a capped collection (Mongopubsub will create these if they do not already exist in the database). Optionally specify the byte size of the collection and/or the max number of documents in the collection when creating a channel.

WARNING: You should not create lots of channels because Mongopubsub will poll from the cursor position.

var mubsub = new MubSub('foo', {
  size: 100000,
  max: 500
});

Options:

• size max size of the collection in bytes, default is 5mb
• max max amount of documents in the collection

WARNING: Don't remove collections with running publishers. It's possible for mongod to recreate the collection on the next insert (before Mubsub has the chance to do so). If this happens the collection will be recreated as a normal, uncapped collection.

Subscribe

var subscription = mubsub.subscribe({
  event,
  callback
});

Subscriptions register a callback to be called whenever a document matching the specified event is inserted (published) into the collection (channel). You can omit the event to match all inserted documents. To later unsubscribe a particular callback, call unsubscribe on the returned subscription object:

subscription.unsubscribe();

Publish

mubsub.publish({
  event,
  message
});

Publishing a document simply inserts the document into the channel's capped collection. A callback is optional.

Listen to events

The following events will be emitted:

// The given event was published
mubsub.on('myevent', console.log);

// Any event was published
mubsub.on('message', console.log);

// mongopubsub is ready to receive new documents
mubsub.on('ready', console.log);

// Channel error
mubsub.on('error', console.log);

// Tailable cursor error
mubsub.on('cursor-error', console.log);

// Tailable cursor ended
mubsub.on('cursor-end', console.log);

// Tailable cursor closed
mubsub.on('cursor-close', console.log);

Close

mubsub.close();

Closes the MongoDB connection.

Install

npm install mongopubsub

Tests

npm run test

You can optionally specify the MongoDB URI to be used for tests:

MONGODB_URI=mongodb://localhost:27017/mongopubsub_tests npm run test