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# Action Cable -- Integrated websockets for Rails
# Action Cable – Integrated websockets for Rails

Action Cable seamlessly integrates websockets with the rest of your Rails application.
It allows for real-time features to be written in Ruby in the same style
Expand Down Expand Up @@ -36,29 +36,31 @@ reflections of each unit.

## A full-stack example

The first thing you must do is defined your ApplicationCable::Connection class in Ruby. This
The first thing you must do is defined your `ApplicationCable::Connection` class in Ruby. This
is the place where you do authorization of the incoming connection, and proceed to establish it
if all is well. Here's the simplest example starting with the server-side connection class:

# app/channels/application_cable/connection.rb
module ApplicationCable
class Connection < ActionCable::Connection::Base
identified_by :current_user

def connect
self.current_user = find_verified_user
end

protected
def find_verified_user
if current_user = User.find cookies.signed[:user_id]
current_user
else
reject_unauthorized_connection
end
end
```ruby
# app/channels/application_cable/connection.rb
module ApplicationCable
class Connection < ActionCable::Connection::Base
identified_by :current_user

def connect
self.current_user = find_verified_user
end

protected
def find_verified_user
if current_user = User.find cookies.signed[:user_id]
current_user
else
reject_unauthorized_connection
end
end
end
end
```

This relies on the fact that you will already have handled authentication of the user, and
that a successful authentication sets a signed cookie with the user_id. This cookie is then
Expand All @@ -69,9 +71,11 @@ potentially disconnect them all if the user is deleted or deauthorized).

The client-side needs to setup a consumer instance of this connection. That's done like so:

# app/assets/javascripts/cable.coffee
@App = {}
App.cable = Cable.createConsumer "http://cable.example.com"
```coffeescript
# app/assets/javascripts/cable.coffee
@App = {}
App.cable = Cable.createConsumer "http://cable.example.com"
```

The http://cable.example.com address must point to your set of Action Cable servers, and it
must share a cookie namespace with the rest of the application (which may live under http://example.com).
Expand All @@ -89,59 +93,63 @@ Here's a simple example of a channel that tracks whether a user is online or not

First you declare the server-side channel:

# app/channels/appearance_channel.rb
class AppearanceChannel < ApplicationCable::Channel
def subscribed
current_user.appear
end

def unsubscribed
current_user.disappear
end

def appear(data)
current_user.appear on: data['appearing_on']
end

def away
current_user.away
end
```ruby
# app/channels/appearance_channel.rb
class AppearanceChannel < ApplicationCable::Channel
def subscribed
current_user.appear
end

def unsubscribed
current_user.disappear
end

def appear(data)
current_user.appear on: data['appearing_on']
end

def away
current_user.away
end
end
```

The #subscribed callback is invoked when, as we'll show below, a client-side subscription is initiated. In this case,
The `#subscribed` callback is invoked when, as we'll show below, a client-side subscription is initiated. In this case,
we take that opportunity to say "the current user has indeed appeared". That appear/disappear API could be backed by
Redis or a database or whatever else. Here's what the client-side of that looks like:

# app/assets/javascripts/cable/subscriptions/appearance.coffee
App.appearance = App.cable.subscriptions.create "AppearanceChannel",
connected: ->
# Called once the subscription has been successfully completed

appear: ->
@perform 'appear', appearing_on: @appearingOn()

away: ->
@perform 'away'

appearingOn: ->
$('main').data 'appearing-on'

$(document).on 'page:change', ->
App.appearance.appear()

$(document).on 'click', '[data-behavior~=appear_away]', ->
App.appearance.away()
false

Simply calling App.cable.subscriptions.create will setup the subscription, which will call AppearanceChannel#subscribed,
which in turn is linked to original App.consumer -> ApplicationCable::Connection instances.

We then link App.appearance#appear to AppearanceChannel#appear(data). This is possible because the server-side
```coffeescript
# app/assets/javascripts/cable/subscriptions/appearance.coffee
App.appearance = App.cable.subscriptions.create "AppearanceChannel",
connected: ->
# Called once the subscription has been successfully completed

appear: ->
@perform 'appear', appearing_on: @appearingOn()

away: ->
@perform 'away'

appearingOn: ->
$('main').data 'appearing-on'

$(document).on 'page:change', ->
App.appearance.appear()

$(document).on 'click', '[data-behavior~=appear_away]', ->
App.appearance.away()
false
```

Simply calling `App.cable.subscriptions.create` will setup the subscription, which will call `AppearanceChannel#subscribed`,
which in turn is linked to original `App.consumer` -> `ApplicationCable::Connection` instances.

We then link `App.appearance#appear` to `AppearanceChannel#appear(data)`. This is possible because the server-side
channel instance will automatically expose the public methods declared on the class (minus the callbacks), so that these
can be reached as remote procedure calls via App.appearance#perform.
can be reached as remote procedure calls via `App.appearance#perform`.

Finally, we expose App.appearance to the machinations of the application itself by hooking the #appear call into the
Turbolinks page:change callback and allowing the user to click a data-behavior link that triggers the #away call.
Finally, we expose `App.appearance` to the machinations of the application itself by hooking the `#appear` call into the
Turbolinks `page:change` callback and allowing the user to click a data-behavior link that triggers the `#away` call.


## Channel example 2: Receiving new web notifications
Expand All @@ -153,26 +161,29 @@ action on the client.
This is a web notification channel that allows you to trigger client-side web notifications when you broadcast to the right
streams:

# app/channels/web_notifications.rb
class WebNotificationsChannel < ApplicationCable::Channel
def subscribed
stream_from "web_notifications_#{current_user.id}"
end
```ruby
# app/channels/web_notifications.rb
class WebNotificationsChannel < ApplicationCable::Channel
def subscribed
stream_from "web_notifications_#{current_user.id}"
end

# Somewhere in your app this is called, perhaps from a NewCommentJob
ActionCable.server.broadcast \
"web_notifications_1", { title: 'New things!', body: 'All shit fit for print' }

# Client-side which assumes you've already requested the right to send web notifications
App.cable.subscriptions.create "WebNotificationsChannel",
received: (data) ->
web_notification = new Notification data['title'], body: data['body']

The ActionCable.server.broadcast call places a message in the Redis' pubsub queue under the broadcasting name of "web_notifications_1".
end
```
```coffeescript
# Somewhere in your app this is called, perhaps from a NewCommentJob
ActionCable.server.broadcast \
"web_notifications_1", { title: 'New things!', body: 'All shit fit for print' }

# Client-side which assumes you've already requested the right to send web notifications
App.cable.subscriptions.create "WebNotificationsChannel",
received: (data) ->
web_notification = new Notification data['title'], body: data['body']
```

The `ActionCable.server.broadcast` call places a message in the Redis' pubsub queue under the broadcasting name of "web_notifications_1".
The channel has been instructed to stream everything that arrives at "web_notifications_1" directly to the client by invoking the
#received(data) callback. The data is the hash sent as the second parameter to the server-side broadcast call, JSON encoded for the trip
across the wire, and unpacked for the data argument arriving to #received.
`#received(data)` callback. The data is the hash sent as the second parameter to the server-side broadcast call, JSON encoded for the trip
across the wire, and unpacked for the data argument arriving to `#received`.


## Dependencies
Expand Down

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