aboutsummaryrefslogtreecommitdiffstats
path: root/guides/source/action_cable_overview.md
blob: 7a9ff96c445e7da26386fc0270d0771204d2072a (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.**

Action Cable Overview
=====================

In this guide, you will learn how Action Cable works and how to use WebSockets to
incorporate real-time features into your Rails application.

After reading this guide, you will know:

* What Action Cable is and its integration backend and frontend
* How to setup Action Cable
* How to setup channels
* Deployment and Architecture setup for running Action Cable

--------------------------------------------------------------------------------

Introduction
------------

Action Cable seamlessly integrates
[WebSockets](https://en.wikipedia.org/wiki/WebSocket) with the rest of your
Rails application. It allows for real-time features to be written in Ruby in the
same style and form as the rest of your Rails application, while still being
performant and scalable. It's a full-stack offering that provides both a
client-side JavaScript framework and a server-side Ruby framework. You have
access to your full domain model written with Active Record or your ORM of
choice.

Terminology
-----------

A single Action Cable server can handle multiple connection instances. It has one
connection instance per WebSocket connection. A single user may have multiple
WebSockets open to your application if they use multiple browser tabs or devices.
The client of a WebSocket connection is called the consumer.

Each consumer can in turn subscribe to multiple cable channels. Each channel
encapsulates a logical unit of work, similar to what a controller does in
a regular MVC setup. For example, you could have a `ChatChannel` and
an `AppearancesChannel`, and a consumer could be subscribed to either
or to both of these channels. At the very least, a consumer should be subscribed
to one channel.

When the consumer is subscribed to a channel, they act as a subscriber.
The connection between the subscriber and the channel is, surprise-surprise,
called a subscription. A consumer can act as a subscriber to a given channel
any number of times. For example, a consumer could subscribe to multiple chat rooms
at the same time. (And remember that a physical user may have multiple consumers,
one per tab/device open to your connection).

Each channel can then again be streaming zero or more broadcastings.
A broadcasting is a pubsub link where anything transmitted by the broadcaster is
sent directly to the channel subscribers who are streaming that named broadcasting.

As you can see, this is a fairly deep architectural stack. There's a lot of new
terminology to identify the new pieces, and on top of that, you're dealing
with both client and server side reflections of each unit.

What is Pub/Sub
---------------

[Pub/Sub](https://en.wikipedia.org/wiki/Publish%E2%80%93subscribe_pattern), or
Publish-Subscribe, refers to a message queue paradigm whereby senders of
information (publishers), send data to an abstract class of recipients
(subscribers), without specifying individual recipients. Action Cable uses this
approach to communicate between the server and many clients.

## Server-Side Components

### Connections

*Connections* form the foundation of the client-server relationship. For every
WebSocket accepted by the server, a connection object is instantiated. This
object becomes the parent of all the *channel subscriptions* that are created
from there on. The connection itself does not deal with any specific application
logic beyond authentication and authorization. The client of a WebSocket
connection is called the connection *consumer*. An individual user will create
one consumer-connection pair per browser tab, window, or device they have open.

Connections are instances of `ApplicationCable::Connection`. In this class, you
authorize the incoming connection, and proceed to establish it if the user can
be identified.

#### Connection Setup

```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

    private
      def find_verified_user
        if verified_user = User.find_by(id: cookies.encrypted[:user_id])
          verified_user
        else
          reject_unauthorized_connection
        end
      end
  end
end
```

Here `identified_by` is a connection identifier that can be used to find the
specific connection later. Note that anything marked as an identifier will automatically
create a delegate by the same name on any channel instances created off the connection.

This example relies on the fact that you will already have handled authentication of the user
somewhere else in your application, and that a successful authentication sets a signed
cookie with the user ID.

The cookie is then automatically sent to the connection instance when a new connection
is attempted, and you use that to set the `current_user`. By identifying the connection
by this same current user, you're also ensuring that you can later retrieve all open
connections by a given user (and potentially disconnect them all if the user is deleted
or unauthorized).

### Channels

A *channel* encapsulates a logical unit of work, similar to what a controller does in a
regular MVC setup. By default, Rails creates a parent `ApplicationCable::Channel` class
for encapsulating shared logic between your channels.

#### Parent Channel Setup

```ruby
# app/channels/application_cable/channel.rb
module ApplicationCable
  class Channel < ActionCable::Channel::Base
  end
end
```

Then you would create your own channel classes. For example, you could have a
`ChatChannel` and an `AppearanceChannel`:

```ruby
# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
end

# app/channels/appearance_channel.rb
class AppearanceChannel < ApplicationCable::Channel
end
```

A consumer could then be subscribed to either or both of these channels.

#### Subscriptions

Consumers subscribe to channels, acting as *subscribers*. Their connection is
called a *subscription*. Produced messages are then routed to these channel
subscriptions based on an identifier sent by the cable consumer.

```ruby
# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
  # Called when the consumer has successfully
  # become a subscriber to this channel.
  def subscribed
  end
end
```

## Client-Side Components

### Connections

Consumers require an instance of the connection on their side. This can be
established using the following JavaScript, which is generated by default by Rails:

#### Connect Consumer

```js
// app/javascript/channels/consumer.js
// Action Cable provides the framework to deal with WebSockets in Rails.
// You can generate new channels where WebSocket features live using the `rails generate channel` command.

import { createConsumer } from "@rails/actioncable"

export default createConsumer()
```

This will ready a consumer that'll connect against `/cable` on your server by default.
The connection won't be established until you've also specified at least one subscription
you're interested in having.

#### Subscriber

A consumer becomes a subscriber by creating a subscription to a given channel:

```js
// app/javascript/channels/chat_channel.js
import consumer from "./consumer"

consumer.subscriptions.create({ channel: "ChatChannel", room: "Best Room" })

// app/javascript/channels/appearance_channel.js
import consumer from "./consumer"

consumer.subscriptions.create({ channel: "AppearanceChannel" })
```

While this creates the subscription, the functionality needed to respond to
received data will be described later on.

A consumer can act as a subscriber to a given channel any number of times. For
example, a consumer could subscribe to multiple chat rooms at the same time:

```js
// app/javascript/channels/chat_channel.js
import consumer from "./consumer"

consumer.subscriptions.create({ channel: "ChatChannel", room: "1st Room" })
consumer.subscriptions.create({ channel: "ChatChannel", room: "2nd Room" })
```

## Client-Server Interactions

### Streams

*Streams* provide the mechanism by which channels route published content
(broadcasts) to their subscribers.

```ruby
# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
  def subscribed
    stream_from "chat_#{params[:room]}"
  end
end
```

If you have a stream that is related to a model, then the broadcasting used
can be generated from the model and channel. The following example would
subscribe to a broadcasting like `comments:Z2lkOi8vVGVzdEFwcC9Qb3N0LzE`

```ruby
class CommentsChannel < ApplicationCable::Channel
  def subscribed
    post = Post.find(params[:id])
    stream_for post
  end
end
```

You can then broadcast to this channel like this:

```ruby
CommentsChannel.broadcast_to(@post, @comment)
```

### Broadcasting

A *broadcasting* is a pub/sub link where anything transmitted by a publisher
is routed directly to the channel subscribers who are streaming that named
broadcasting. Each channel can be streaming zero or more broadcastings.

Broadcastings are purely an online queue and time-dependent. If a consumer is
not streaming (subscribed to a given channel), they'll not get the broadcast
should they connect later.

Broadcasts are called elsewhere in your Rails application:

```ruby
WebNotificationsChannel.broadcast_to(
  current_user,
  title: 'New things!',
  body: 'All the news fit to print'
)
```

The `WebNotificationsChannel.broadcast_to` call places a message in the current
subscription adapter's pubsub queue under a separate broadcasting name for each user.
The default pubsub queue for Action Cable is `redis` in production and `async` in development and
test environments. For a user with an ID of 1, the broadcasting name would be `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`
callback.

### Subscriptions

When a consumer is subscribed to a channel, they act as a subscriber. This
connection is called a subscription. Incoming messages are then routed to
these channel subscriptions based on an identifier sent by the cable consumer.

```js
// app/javascript/channels/chat_channel.js
// Assumes you've already requested the right to send web notifications
import consumer from "./consumer"

consumer.subscriptions.create({ channel: "ChatChannel", room: "Best Room" }, {
  received(data) {
    this.appendLine(data)
  },

  appendLine(data) {
    const html = this.createLine(data)
    const element = document.querySelector("[data-chat-room='Best Room']")
    element.insertAdjacentHTML("beforeend", html)
  },

  createLine(data) {
    return `
      <article class="chat-line">
        <span class="speaker">${data["sent_by"]}</span>
        <span class="body">${data["body"]}</span>
      </article>
    `
  }
})
```

### Passing Parameters to Channels

You can pass parameters from the client side to the server side when creating a
subscription. For example:

```ruby
# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
  def subscribed
    stream_from "chat_#{params[:room]}"
  end
end
```

An object passed as the first argument to `subscriptions.create` becomes the
params hash in the cable channel. The keyword `channel` is required:

```js
// app/javascript/channels/chat_channel.js
import consumer from "./consumer"

consumer.subscriptions.create({ channel: "ChatChannel", room: "Best Room" }, {
  received(data) {
    this.appendLine(data)
  },

  appendLine(data) {
    const html = this.createLine(data)
    const element = document.querySelector("[data-chat-room='Best Room']")
    element.insertAdjacentHTML("beforeend", html)
  },

  createLine(data) {
    return `
      <article class="chat-line">
        <span class="speaker">${data["sent_by"]}</span>
        <span class="body">${data["body"]}</span>
      </article>
    `
  }
})
```

```ruby
# Somewhere in your app this is called, perhaps
# from a NewCommentJob.
ActionCable.server.broadcast(
  "chat_#{room}",
  sent_by: 'Paul',
  body: 'This is a cool chat app.'
)
```

### Rebroadcasting a Message

A common use case is to *rebroadcast* a message sent by one client to any
other connected clients.

```ruby
# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
  def subscribed
    stream_from "chat_#{params[:room]}"
  end

  def receive(data)
    ActionCable.server.broadcast("chat_#{params[:room]}", data)
  end
end
```

```js
// app/javascript/channels/chat_channel.js
import consumer from "./consumer"

const chatChannel = consumer.subscriptions.create({ channel: "ChatChannel", room: "Best Room" }, {
  received(data) {
    // data => { sent_by: "Paul", body: "This is a cool chat app." }
  }
}

chatChannel.send({ sent_by: "Paul", body: "This is a cool chat app." })
```

The rebroadcast will be received by all connected clients, _including_ the
client that sent the message. Note that params are the same as they were when
you subscribed to the channel.

## Full-Stack Examples

The following setup steps are common to both examples:

  1. [Setup your connection](#connection-setup).
  2. [Setup your parent channel](#parent-channel-setup).
  3. [Connect your consumer](#connect-consumer).

### Example 1: User Appearances

Here's a simple example of a channel that tracks whether a user is online or not
and what page they're on. (This is useful for creating presence features like showing
a green dot next to a user name if they're online).

Create the server-side appearance channel:

```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
```

When a subscription is initiated the `subscribed` callback gets fired and we
take that opportunity to say "the current user has indeed appeared". That
appear/disappear API could be backed by Redis, a database, or whatever else.

Create the client-side appearance channel subscription:

```js
// app/javascript/channels/appearance_channel.js
import consumer from "./consumer"

consumer.subscriptions.create("AppearanceChannel", {
  // Called once when the subscription is created.
  initialized() {
    this.update = this.update.bind(this)
  },

  // Called when the subscription is ready for use on the server.
  connected() {
    this.install()
    this.update()
  },

  // Called when the WebSocket connection is closed.
  disconnected() {
    this.uninstall()
  },

  // Called when the subscription is rejected by the server.
  rejected() {
    this.uninstall()
  },

  update() {
    this.documentIsActive ? this.appear() : this.away()
  },

  appear() {
    // Calls `AppearanceChannel#appear(data)` on the server.
    this.perform("appear", { appearing_on: this.appearingOn })
  },

  away() {
    // Calls `AppearanceChannel#away` on the server.
    this.perform("away")
  },

  install() {
    window.addEventListener("focus", this.update)
    window.addEventListener("blur", this.update)
    document.addEventListener("turbolinks:load", this.update)
    document.addEventListener("visibilitychange", this.update)
  },

  uninstall() {
    window.removeEventListener("focus", this.update)
    window.removeEventListener("blur", this.update)
    document.removeEventListener("turbolinks:load", this.update)
    document.removeEventListener("visibilitychange", this.update)
  },

  get documentIsActive() {
    return document.visibilityState == "visible" && document.hasFocus()
  },

  get appearingOn() {
    const element = document.querySelector("[data-appearing-on]")
    return element ? element.getAttribute("data-appearing-on") : null
  }
})
```

##### Client-Server Interaction

1. **Client** connects to the **Server** via `App.cable =
ActionCable.createConsumer("ws://cable.example.com")`. (`cable.js`). The
**Server** identifies this connection by `current_user`.

2. **Client** subscribes to the appearance channel via
`consumer.subscriptions.create({ channel: "AppearanceChannel" })`. (`appearance_channel.js`)

3. **Server** recognizes a new subscription has been initiated for the
appearance channel and runs its `subscribed` callback, calling the `appear`
method on `current_user`. (`appearance_channel.rb`)

4. **Client** recognizes that a subscription has been established and calls
`connected` (`appearance_channel.js`) which in turn calls `install` and `appear`.
`appear` calls `AppearanceChannel#appear(data)` on the server, and supplies a
data hash of `{ appearing_on: this.appearingOn }`. This is
possible because the server-side channel instance automatically exposes all
public methods declared on the class (minus the callbacks), so that these can be
reached as remote procedure calls via a subscription's `perform` method.

5. **Server** receives the request for the `appear` action on the appearance
channel for the connection identified by `current_user`
(`appearance_channel.rb`). **Server** retrieves the data with the
`:appearing_on` key from the data hash and sets it as the value for the `:on`
key being passed to `current_user.appear`.

### Example 2: Receiving New Web Notifications

The appearance example was all about exposing server functionality to
client-side invocation over the WebSocket connection. But the great thing
about WebSockets is that it's a two-way street. So now let's show an example
where the server invokes an 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:

Create the server-side web notifications channel:

```ruby
# app/channels/web_notifications_channel.rb
class WebNotificationsChannel < ApplicationCable::Channel
  def subscribed
    stream_for current_user
  end
end
```

Create the client-side web notifications channel subscription:

```js
// app/javascript/channels/web_notifications_channel.js
// Client-side which assumes you've already requested
// the right to send web notifications.
import consumer from "./consumer"

consumer.subscriptions.create("WebNotificationsChannel", {
  received(data) {
    new Notification(data["title"], body: data["body"])
  }
})
```

Broadcast content to a web notification channel instance from elsewhere in your
application:

```ruby
# Somewhere in your app this is called, perhaps from a NewCommentJob
WebNotificationsChannel.broadcast_to(
  current_user,
  title: 'New things!',
  body: 'All the news fit to print'
)
```

The `WebNotificationsChannel.broadcast_to` call places a message in the current
subscription adapter's pubsub queue under a separate broadcasting name for each
user. For a user with an ID of 1, the broadcasting name would be
`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`
callback. The data passed as argument 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 as `received`.

### More Complete Examples

See the [rails/actioncable-examples](https://github.com/rails/actioncable-examples)
repository for a full example of how to setup Action Cable in a Rails app and adding channels.

## Configuration

Action Cable has two required configurations: a subscription adapter and allowed request origins.

### Subscription Adapter

By default, Action Cable looks for a configuration file in `config/cable.yml`.
The file must specify an adapter for each Rails environment. See the
[Dependencies](#dependencies) section for additional information on adapters.

```yaml
development:
  adapter: async

test:
  adapter: async

production:
  adapter: redis
  url: redis://10.10.3.153:6381
  channel_prefix: appname_production
```
#### Adapter Configuration

Below is a list of the subscription adapters available for end users.

##### Async Adapter

The async adapter is intended for development/testing and should not be used in production.

##### Redis Adapter

The Redis adapter requires users to provide a URL pointing to the Redis server.
Additionally, a `channel_prefix` may be provided to avoid channel name collisions
when using the same Redis server for multiple applications. See the [Redis PubSub documentation](https://redis.io/topics/pubsub#database-amp-scoping) for more details.

##### PostgreSQL Adapter

The PostgreSQL adapter uses Active Record's connection pool, and thus the
application's `config/database.yml` database configuration, for its connection.
This may change in the future. [#27214](https://github.com/rails/rails/issues/27214)

### Allowed Request Origins

Action Cable will only accept requests from specified origins, which are
passed to the server config as an array. The origins can be instances of
strings or regular expressions, against which a check for the match will be performed.

```ruby
config.action_cable.allowed_request_origins = ['http://rubyonrails.com', %r{http://ruby.*}]
```

To disable and allow requests from any origin:

```ruby
config.action_cable.disable_request_forgery_protection = true
```

By default, Action Cable allows all requests from localhost:3000 when running
in the development environment.

### Consumer Configuration

To configure the URL, add a call to `action_cable_meta_tag` in your HTML layout
HEAD. This uses a URL or path typically set via `config.action_cable.url` in the
environment configuration files.

### Worker Pool Configuration

The worker pool is used to run connection callbacks and channel actions in
isolation from the server's main thread. Action Cable allows the application
to configure the number of simultaneously processed threads in the worker pool.

```ruby
config.action_cable.worker_pool_size = 4
```

Also, note that your server must provide at least the same number of database
connections as you have workers. The default worker pool size is set to 4, so
that means you have to make at least 4 database connections available.
 You can change that in `config/database.yml` through the `pool` attribute.

### Other Configurations

The other common option to configure is the log tags applied to the
per-connection logger. Here's an example that uses
the user account id if available, else "no-account" while tagging:

```ruby
config.action_cable.log_tags = [
  -> request { request.env['user_account_id'] || "no-account" },
  :action_cable,
  -> request { request.uuid }
]
```

For a full list of all configuration options, see the
`ActionCable::Server::Configuration` class.

## Running Standalone Cable Servers

### In App

Action Cable can run alongside your Rails application. For example, to
listen for WebSocket requests on `/websocket`, specify that path to
`config.action_cable.mount_path`:

```ruby
# config/application.rb
class Application < Rails::Application
  config.action_cable.mount_path = '/websocket'
end
```

You can use `ActionCable.createConsumer()` to connect to the cable
server if `action_cable_meta_tag` is invoked in the layout. Otherwise, A path is
specified as first argument to `createConsumer` (e.g. `ActionCable.createConsumer("/websocket")`).

For every instance of your server you create and for every worker your server
spawns, you will also have a new instance of Action Cable, but the use of Redis
keeps messages synced across connections.

### Standalone

The cable servers can be separated from your normal application server. It's
still a Rack application, but it is its own Rack application. The recommended
basic setup is as follows:

```ruby
# cable/config.ru
require_relative '../config/environment'
Rails.application.eager_load!

run ActionCable.server
```

Then you start the server using a binstub in `bin/cable` ala:

```
#!/bin/bash
bundle exec puma -p 28080 cable/config.ru
```

The above will start a cable server on port 28080.

### Notes

The WebSocket server doesn't have access to the session, but it has
access to the cookies. This can be used when you need to handle
authentication. You can see one way of doing that with Devise in this [article](https://greg.molnar.io/blog/actioncable-devise-authentication/).

## Dependencies

Action Cable provides a subscription adapter interface to process its
pubsub internals. By default, asynchronous, inline, PostgreSQL, and Redis
adapters are included. The default adapter
in new Rails applications is the asynchronous (`async`) adapter.

The Ruby side of things is built on top of [websocket-driver](https://github.com/faye/websocket-driver-ruby),
[nio4r](https://github.com/celluloid/nio4r), and [concurrent-ruby](https://github.com/ruby-concurrency/concurrent-ruby).

## Deployment

Action Cable is powered by a combination of WebSockets and threads. Both the
framework plumbing and user-specified channel work are handled internally by
utilizing Ruby's native thread support. This means you can use all your regular
Rails models with no problem, as long as you haven't committed any thread-safety sins.

The Action Cable server implements the Rack socket hijacking API,
thereby allowing the use of a multithreaded pattern for managing connections
internally, irrespective of whether the application server is multi-threaded or not.

Accordingly, Action Cable works with popular servers like Unicorn, Puma, and
Passenger.

## Testing

You can find detailed instructions on how to test your Action Cable functionality in the
[testing guide](testing.html#testing-action-cable).