Build reliable, real-time, stateless applications with Node.js and Redis faster than ever before

Ynez (pronounced e-nez) is a toolkit for building streaming real-time applications using Node.js, Redis Streams, WebSockets and localStorage, which aims to dramatically reduce the amount of code, cash and cognitive overhead required to write reliable, distributed, real-time applications with no single points of failure.

Ynez is two packages:

ynez, the server package

• hosts a websocket server
• connects to a Redis server supporting the new Streams feature.

ynez-client, the client package

• a browser and Node.js compatible client library
• connects to a ynez server via websocket

Example

Server

// An example server looks very much like a Socket.io example, aside from the connections to Redis.
// Everything after server.listen() is the default behavior
// if you define your own `connect` handler, it will overwrite this default.
const Ynez = require('ynez')
const server = new Ynez(['localhost:6379', 'another-server:6379'])
server.listen({ key: '...', cert: '...', port: 8080 })

server.on('connect', socket => {
  socket.on('subscribe', (channel, offset) => {
    // TODO: Filter channel permissions?
    socket.subscribe(channel, offset)
  })
  socket.on('messages', (channel, messages) => {
    // TODO: Filter messages? Side effects or triggered actions?
    socket.emit(channel, messages)
  })
  socket.on('publish', (channel, message) => {
    // TODO: Validate / Audit messages from users
    server.publish(channel, message, { maxLength: 5000 })
  })
})

Client

// A simple client example also looks very much like a traditional WebSocket:
const client = require('ynez-client')('https://ynez-api.demo:8080')
client.on('messages', messages => { doStuff(messages) }) // Read...
client.publish('myTestChannel', 'TEST_MESSAGE', { foo: 'bar' }) // Write...

// You wont receive any messages unless you subscribe to a channel:
client.subscribe('myTestChannel', { localStorage: true })

But while it may look exactly like a normal WebSocket tutorial, we get a whole lot of features out of the box:

• Ynez Servers are stateless; the state of the stream exists in Redis, not Node.js - if an instance crashes or a user reconnects to a different instance, no state is lost and the user sees no difference! Deploy socket based applications without state concerns!

• Ynez Streams are distributed; any other server (and their clients) which is subscribed to a channel will receive the messages. No need for the cluster module or other premature optimizations and complexities. Optionally add Redis Cluster for a zero SPOF infrastructure!

• Ynez Streams are replayable; past messages can be re-read from the Redis stream after they have been originally sent (up to a configurable limit).

• Ynez Streams are persistent-ish; Messages can be sent before any clients are listening, to be collected at a later point, and clients can easily store messages in localStorage for later replay. Streams also have a configurable maximum length, after which messages can be forgotten.

• State checkpoints, consumer groups, Redis Cluster support, queues and more!

Table of Contents

0. About
1. Examples
2. Messages
3. Server
   • Ynez()
   • Server Events
   • .listen()
   • .connect()
   • .publish()
   • Socket Events
   • Socket.subscribe()
   • Socket.unsubscribe()
   • Socket.emit()
4. Client
   • Client()
   • Client Events
   • .load()
   • .subscribe()
   • .unsubscribe()
   • .publish()

About

The project is named after the Santa Ynez River, where I grew up, which both feeds and is fed by many smaller creeks and streams.

Ynez is powered by brand new features in the Redis Database - Streams! Ynez uses XREAD and XADD to read and write to Redis Streams, and exposes an API that allows easy creation of real-time WebSocket services. You should read the original blog post and the official Redis docs if you're interested in learning more!

We also make use of the UNBLOCK CLIENT syntax which has only (as of writing) just landed in Redis unstable. The erulabs/redis-unstable docker image is an easy way to get started.

API Documentation

Messages

Messages events provide arrays of "Message" objects, which have the following properties:

const Message = {
  offset: string,
  key: value,
  key2: value2...
}

For example, consider the following:

// Server
socket.emit('testChannel', 'TEST_MESSAGE', { foo: 'bar' })

// Client
client.on('messages', (channel, messages) => {
  // channel === "testChannel"
  // messages === [
  //  {
  //    offset: "1518951480106-0",
  //    TEST_MESSAGE: { foo: 'bar' } }
  // ]
})

Server

Ynez(options)

Where "options" is an object with the following properties:

| Option | Required | Default | Description | | :------------ | :------: | :--------------: | ----------------------------------------- | | targets | no | ["localhost:6379"] | An array of Redis server URIs | | autoConnect | no | true | Calls .connect() on construction (connects to Redis) | | encode | no | JSON.stringify | A function for encoding published objects | | decode | no | JSON.parse | A function for decoding published objects |

const server = new Ynez({ autoConnect: false })

If the "options" argument is a string, or an array of strings, it is assumed to be the targets option.

Server Events

• ready - Connected to Redis
• connect - A new socket has connected
• error - An error has been encountered (connection to Redis failed, etc)

Server.listen(options)

Where "options" is an object with the following properties:

| Option | type | Required | Default | Description | | :----- | :--------: | :------: | :-----: | -------------------------------------------------- | | key | string | yes | - | SSL key | | cert | string | yes | - | SSL certificate | | port | number | no | 8080 | Port number to listen on for websocket connections |

const server = new Ynez({ autoConnect: false })

Server.connect()

Connects to redis - Is called automatically if autoConnect (on the Ynez constructor) is false.

async Server.publish(channel, ...)

Send data upstream to the Redis service. Like Client.publish(), this follows the rules of XADD. The number of arguments after the channel must be even, and objects will be encoded automatically.

await server.publish('myChannel', 'some', { foo: 'data' })
// returns with locally loaded messages and most recent offset

Socket Events

• disconnect - A socket has disconnected
• subscribe - A socket has requested a subscription to a channel
• unsubscribe - A socket no long wants messages from a channel
• publish - A socket has a message to publish for a channel
• messages - Messages have arrived from a subscribed channel

Socket.subscribe(channel, offset)

| Argument | type | Required | Default | Description | | :-------- | :--------: | :------: | :-----: | ---------------------- | | channel | string | yes | - | Channel identifier key | | offset | string | no | $ | Redis stream offset |

Socket.unsubscribe(channel)

Unsubscribes a socket from a given channel. This is called automatically when a socket disconnects, if there is no existing disconnect handler defined.

| Argument | type | Required | Default | Description | | :-------- | :--------: | :------: | :-----: | --------------------------- | | channel | string | yes | - | Channel to unsubscribe from |

Socket.emit(channel, messages)

Send data to a connected socket

Client

Client(options)

Where "options" is an object with the following properties:

| Option | Required | Default | Description | | :------------- | :------: | :--------------: | ----------------------------------------- | | targets | yes | - | An array of Ynez server URIs | | encode | no | JSON.stringify | A function for encoding published objects | | decode | no | JSON.parse | A function for decoding published objects | | localStorage | no | true | Automatically store retrieved messages |

Client Events

• connect - Socket is connected to the server
• disconnect - Socket has been disconnected from the server
• messages - Messages have arrived from a subscribed channel
• error - An error has been received from the server

async Client.load(channel)

| Argument | type | Required | Default | Description | | :-------- | :--------: | :------: | :-----: | ------------------------------------------ | | channel | string | yes | - | Channel to load locally stored message for |

const { messages, lastOffset } = await client.load('myChannel')
// returns with locally loaded messages and most recent offset

async Client.subscribe(channel, offset)

| Argument | type | Required | Default | Description | | :-------- | :--------: | :------: | :-----: | ------------------------------------------ | | channel | string | yes | - | Channel to load locally stored message for | | offset | string | no | $ | Redis stream offset |

await client.subscribe('myChannel')
// returns true if subscribe message sent successfully

async Client.unsubscribe(channel)

| Argument | type | Required | Default | Description | | :-------- | :--------: | :------: | :-----: | --------------------------- | | channel | string | yes | - | Channel to unsubscribe from |

await client.unsubscribe('myChannel')
// returns true if unsubscribe message sent successfully

async Client.publish(channel, ...)

| Argument | type | Required | Default | Description | | :-------- | :--------: | :------: | :-----: | ------------------------------ | | channel | string | yes | - | Channel to publish messages to |

The rest of the arguments are considered key-value pairs, to be used during the Redis Stream XADD. This means that the number of arguments after channel must be an even number. For example:

// Examples of Client Publish
await client.publish('test', 'foo', 'bar') // Success! Returns with new message offset
await client.publish('test', 'foo') // Error! Invalid argument count!
await client.publish('test', 'foo', { bar: "baz" }) // Note that object arguments are stringified automatically
await client.publish('test', 'foo', 'bar', 'baz', 'bam', 'words', 'things') // Success!