Server API

In this guide we dive deeper into channels, authentication and exchanging real time messages.

Registering Channels

WebSocket channels are registered in the start/socket.js file:

start/socket.js
const Ws = use('Ws')

Ws.channel('news', ({ socket }) => {
  console.log('a new subscription for news topic')
})

Channel handlers receive a context object, similar to HTTP route handlers.

By default, channel context objects contain socket and request properties (with more added by optional middleware like Auth, Session, etc).

Once a subscription is made, use the socket instance to exchange messages:

socket.on('message', (data) => {
})

// emit events
socket.emit('message', 'Hello world')
socket.emit('typing', true)

Dynamic Topics

Channels can be registered to accept dynamic topic subscriptions:

Ws.channel('chat:*', ({ socket }) => {
  console.log(socket.topic)
})

In the example above, * sets the channel to accept any subscriptions to topics beginning with chat: (e.g. chat:watercooler, chat:intro, etc).

Subscriptions to dynamic topics are made via the Client API:

const watercooler = ws.subscribe('chat:watercooler')
const intro = ws.subscribe('chat:intro')
const news = ws.subscribe('chat:news')

In the example above, our different topic subscriptions all point to the same channel, but when topic specific events are emitted, they will be delivered to their specific topic subscribers only.

Registering Middleware

Middleware is registered inside the start/wsKernel.js file:

start/wsKernel.js
const globalMiddleware = [
  'Adonis/Middleware/Session',
  'Adonis/Middleware/AuthInit'
]

const namedMiddleware = {
  auth: 'Adonis/Middleware/Auth'
}

Named middleware is applied per channel in the start/socket.js file:

start/socket.js
Ws
  .channel('chat', 'ChatController')
  .middleware(['auth'])

Creating Middleware

WebSocket middleware required a wsHandle method.

You can share HTTP and WebSocket middleware by ensuring both handle (for HTTP requests) and wsHandle methods are defined on your middleware class:

app/Middleware/CustomMiddleware.js
'use strict'

class CustomMiddleware {
  // for HTTP
  async handle (ctx, next) {
  }

  // for WebSocket
  async wsHandle (ctx, next) {
  }
}

module.exports = CustomMiddleware

Broadcast Anywhere

As pre-registered WebSocket channels can be accessed from anywhere inside your application, WebSocket communication isn’t limited to the socket lifecycle.

Emit WebSocket events during the HTTP lifecycle like so:

app/Controllers/Http/UserController.js
const Ws = use('Ws')

class UserController {
  async register () {
    // ...

    Ws
      .getChannel('subscriptions')
      .topic('subscriptions')
      .broadcast('new:user')
  }
}

In the example above, we:

  1. Select the channel via the getChannel(name) method

  2. Select the channel topic via the topic(name) method

  3. Broadcast to topic subscribers via the broadcast(event) message

topic() returns an object containing the following methods:

const chat = Ws.getChannel('chat:*')
const { broadcast, emitTo } = chat.topic('chat:watercooler')

// broadcast: send to everyone (except the caller)
// emitTo: send to selected socket ids
For more info, see the list of socket methods below.

Socket API

Events

The following events are reserved and must not be emitted.

error

Invoked when an error is received:

socket.on('error', () => {
})

close

Invoked when a subscription is closed:

socket.on('close', () => {
})

Methods

The following methods can be called on the socket instance.

emit(event, data, [ackCallback])

Emit event to the connected client:

socket.emit('id', socket.id)
This method only sends a message to your own connection.

emitTo(event, data, socketIds[])

Emit event to an array of socket ids:

socket.emitTo('greeting', 'hello', [someIds])

broadcast(event, data)

Emit event to everyone except yourself:

socket.broadcast('message', 'hello everyone!')

broadcastToAll(event, data)

Emit event to everyone including yourself:

socket.broadcastToAll('message', 'hello everyone!')

close()

Forcefully close a subscription from the server:

socket.close()

Properties

The following read-only properties can be accessed on the socket instance.

id

Socket unique id:

socket.id

topic

Topic under which the subscription socket was created:

socket.topic

connection

Reference to the TCP connection (shared across multiple sockets for a single client for multiplexing):

socket.connection