Socket.IO MongoDB adapter

The @socket.io/mongo-adapter package allows broadcasting packets between multiple Socket.IO servers.

Unlike the existing socket.io-adapter-mongo package which uses tailable cursors, this package relies on change streams and thus requires a replica set or a sharded cluster.

Supported features:

Related packages:

MongoDB emitter: https://github.com/socketio/socket.io-mongo-emitter/
Redis adapter: https://github.com/socketio/socket.io-redis-adapter/
Redis emitter: https://github.com/socketio/socket.io-redis-emitter/
Postgres adapter: https://github.com/socketio/socket.io-postgres-adapter/
Postgres emitter: https://github.com/socketio/socket.io-postgres-emitter/

Table of contents

Installation
Usage
Known errors
License

Installation

npm install @socket.io/mongo-adapter mongodb

For TypeScript users, you might also need @types/mongodb.

Usage

There are two ways to clean up the documents in MongoDB:

a capped collection
a TTL index

Usage with a capped collection

const { Server } = require("socket.io");
const { createAdapter } = require("@socket.io/mongo-adapter");
const { MongoClient } = require("mongodb");

const DB = "mydb";
const COLLECTION = "socket.io-adapter-events";

const io = new Server();

const mongoClient = new MongoClient("mongodb://localhost:27017/?replicaSet=rs0", {
  useUnifiedTopology: true,
});

const main = async () => {
  await mongoClient.connect();

  try {
    await mongoClient.db(DB).createCollection(COLLECTION, {
      capped: true,
      size: 1e6
    });
  } catch (e) {
    // collection already exists
  }
  const mongoCollection = mongoClient.db(DB).collection(COLLECTION);

  io.adapter(createAdapter(mongoCollection));
  io.listen(3000);
}

main();

Usage with a TTL index

const { Server } = require("socket.io");
const { createAdapter } = require("@socket.io/mongo-adapter");
const { MongoClient } = require("mongodb");

const DB = "mydb";
const COLLECTION = "socket.io-adapter-events";

const io = new Server();

const mongoClient = new MongoClient("mongodb://localhost:27017/?replicaSet=rs0", {
  useUnifiedTopology: true,
});

const main = async () => {
  await mongoClient.connect();

  const mongoCollection = mongoClient.db(DB).collection(COLLECTION);

  await mongoCollection.createIndex(
    { createdAt: 1 },
    { expireAfterSeconds: 3600, background: true }
  );

  io.adapter(createAdapter(mongoCollection, {
    addCreatedAtField: true
  }));
  io.listen(3000);
}

main();

Known errors

MongoError: The $changeStream stage is only supported on replica sets

Change streams are only available for replica sets and sharded clusters.

More information here.

Please note that, for development purposes, you can have a single MongoDB process acting as a replica set by running rs.initiate() on the node.

TypeError: this.mongoCollection.insertOne is not a function

You probably passed a MongoDB client instead of a MongoDB collection to the createAdapter method.

License

MIT