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diff --git a/guides/source/action_cable_overview.md b/guides/source/action_cable_overview.md index 5cc280072e..93bcb6157a 100644 --- a/guides/source/action_cable_overview.md +++ b/guides/source/action_cable_overview.md @@ -12,41 +12,39 @@ After reading this guide, you will know: Introduction ------------ -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 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. +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. What is Pub/Sub --------------- -Pub/Sub, 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. - -What is Action Cable --------------------- - -Action Cable is a server which can handle multiple connection instances, with one -client-server connection instance established per WebSocket connection. +[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 -the cable server is accepting, a Connection object will be instantiated on the server side. -This instance 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 a consumer. An individual -user will create one consumer-connection pair per browser tab, window, or device they have open. +*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 instantiated via the `ApplicationCable::Connection` class in Ruby. -In this class, you authorize the incoming connection, and proceed to establish it -if the user can be identified. +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 @@ -78,17 +76,17 @@ create a delegate by the same name on any channel instances created off the conn 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`. +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 +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 deauthorized). ### Channels -A channel encapsulates a logical unit of work, similar to what a controller does in a +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. @@ -103,7 +101,7 @@ end ``` Then you would create your own channel classes. For example, you could have a -**ChatChannel** and an **AppearanceChannel**: +`ChatChannel` and an `AppearanceChannel`: ```ruby # app/channels/chat_channel.rb @@ -119,15 +117,15 @@ A consumer could then be subscribed to either or both of these channels. #### 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. +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 of this channel + # Called when the consumer has successfully + # become a subscriber of this channel. def subscribed end end @@ -138,7 +136,7 @@ end ### Connections Consumers require an instance of the connection on their side. This can be -established using the following Javascript, which is generated by default in Rails: +established using the following JavaScript, which is generated by default by Rails: #### Connect Consumer @@ -155,18 +153,13 @@ established using the following Javascript, which is generated by default in Rai }).call(this); ``` -This will ready a consumer that'll connect against /cable on your server by default. +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 -When a consumer is subscribed to a channel, they act as a subscriber. 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. -(remember that a physical user may have multiple consumers, one per tab/device open to your connection). - -A consumer becomes a subscriber, by creating a subscription to a given channel: +A consumer becomes a subscriber by creating a subscription to a given channel: ```coffeescript # app/assets/javascripts/cable/subscriptions/chat.coffee @@ -179,12 +172,20 @@ App.cable.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: + +```coffeescript +App.cable.subscriptions.create { channel: "ChatChannel", room: "1st Room" } +App.cable.subscriptions.create { channel: "ChatChannel", room: "2nd Room" } +``` + ## Client-Server Interactions ### Streams -Streams provide the mechanism by which channels route published content -(broadcasts) to its subscribers. +*Streams* provide the mechanism by which channels route published content +(broadcasts) to their subscribers. ```ruby # app/channels/chat_channel.rb @@ -208,21 +209,30 @@ class CommentsChannel < ApplicationCable::Channel end ``` -You can then broadcast to this channel using: `CommentsChannel.broadcast_to(@post, @comment)` +You can then broadcast to this channel like this: + +```ruby +CommentsChannel.broadcast_to(@post, @comment) +``` -### Broadcastings +### Broadcasting -A broadcasting is a pub/sub link where anything transmitted by a publisher +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. + +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' +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 @@ -231,14 +241,14 @@ 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(data)` +`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. +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. ```coffeescript # app/assets/javascripts/cable/subscriptions/chat.coffee @@ -260,10 +270,10 @@ App.cable.subscriptions.create { channel: "ChatChannel", room: "Best Room" }, """ ``` -### Passing Parameters to Channel +### Passing Parameters to Channels -You can pass parameters from the client-side to the server-side when -creating a subscription. For example: +You can pass parameters from the client side to the server side when creating a +subscription. For example: ```ruby # app/channels/chat_channel.rb @@ -274,8 +284,8 @@ class ChatChannel < ApplicationCable::Channel end ``` -Pass an object as the first argument to `subscriptions.create`, and that object -will become your params hash in your cable channel. The keyword `channel` is required. +An object passed as the first argument to `subscriptions.create` becomes the +params hash in the cable channel. The keyword `channel` is required: ```coffeescript # app/assets/javascripts/cable/subscriptions/chat.coffee @@ -297,14 +307,18 @@ App.cable.subscriptions.create { channel: "ChatChannel", room: "Best Room" }, ``` ```ruby -# Somewhere in your app this is called, perhaps from a NewCommentJob -ChatChannel.broadcast_to "chat_#{room}", sent_by: 'Paul', body: 'This is a cool chat app.' +# Somewhere in your app this is called, perhaps +# from a NewCommentJob. +ChatChannel.broadcast_to( + "chat_#{room}", + sent_by: 'Paul', + body: 'This is a cool chat app.' +) ``` +### Rebroadcasting a Message -### Rebroadcasting message - -A common use case is to rebroadcast a message sent by one client to any +A common use case is to *rebroadcast* a message sent by one client to any other connected clients. ```ruby @@ -315,7 +329,7 @@ class ChatChannel < ApplicationCable::Channel end def receive(data) - ChatChannel.broadcast_to "chat_#{params[:room]}", data + ChatChannel.broadcast_to("chat_#{params[:room]}", data) end end ``` @@ -333,20 +347,21 @@ 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 +## 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) + 1. [Setup your connection](#connection-setup). + 2. [Setup your parent channel](#parent-channel-setup). + 3. [Connect your consumer](#connect-consumer). + +### Example 1: User Appearances -### 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: +Create the server-side appearance channel: ```ruby # app/channels/appearance_channel.rb @@ -360,7 +375,7 @@ class AppearanceChannel < ApplicationCable::Channel end def appear(data) - current_user.appear on: data['appearing_on'] + current_user.appear(on: data['appearing_on']) end def away @@ -369,35 +384,34 @@ class AppearanceChannel < ApplicationCable::Channel end ``` -When `#subscribed` callback is invoked by the consumer, 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, a database, -or whatever else. +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: +Create the client-side appearance channel subscription: ```coffeescript # app/assets/javascripts/cable/subscriptions/appearance.coffee App.cable.subscriptions.create "AppearanceChannel", - # Called when the subscription is ready for use on the server + # Called when the subscription is ready for use on the server. connected: -> @install() @appear() - # Called when the WebSocket connection is closed + # Called when the WebSocket connection is closed. disconnected: -> @uninstall() - # Called when the subscription is rejected by the server + # Called when the subscription is rejected by the server. rejected: -> @uninstall() appear: -> - # Calls `AppearanceChannel#appear(data)` on the server + # Calls `AppearanceChannel#appear(data)` on the server. @perform("appear", appearing_on: $("main").data("appearing-on")) away: -> - # Calls `AppearanceChannel#away` on the server + # Calls `AppearanceChannel#away` on the server. @perform("away") @@ -419,13 +433,33 @@ App.cable.subscriptions.create "AppearanceChannel", ``` ##### Client-Server Interaction -1. **Client** establishes a connection with the **Server** via `App.cable = ActionCable.createConsumer("ws://cable.example.com")`. [*` cable.js`*] The **Server** identified this connection instance by `current_user`. -2. **Client** initiates a subscription to the `Appearance Channel` for their connection via `App.cable.subscriptions.create "AppearanceChannel"`. [*`appearance.coffee`*] -3. **Server** recognizes a new subscription has been initiated for `AppearanceChannel` channel performs the `subscribed` callback, which calls the `appear` method on the `current_user`. [*`appearance_channel.rb`*] -4. **Client** recognizes that a subscription has been established and calls `connected` [*`appearance.coffee`*] which in turn calls `@install` and `@appear`. `@appear` calls`AppearanceChannel#appear(data)` on the server, and supplies a data hash of `appearing_on: $("main").data("appearing-on")`. 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 a subscription's `perform` method. -5. **Server** receives the request for the `appear` action on the `AppearanceChannel` channel for the connection identified by `current_user`. [*`appearance_channel.rb`*] The 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 +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 +`App.cable.subscriptions.create(channel: "AppearanceChannel")`. (`appearance.coffee`) + +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.coffee`) which in turn calls `@install` and `@appear`. +`@appear` calls `AppearanceChannel#appear(data)` on the server, and supplies a +data hash of `{ appearing_on: $("main").data("appearing-on") }`. 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 @@ -435,7 +469,7 @@ 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: +Create the server-side web notifications channel: ```ruby # app/channels/web_notifications_channel.rb @@ -446,34 +480,41 @@ class WebNotificationsChannel < ApplicationCable::Channel end ``` -#### Create the client-side Web Notifications Channel subscription: +Create the client-side web notifications channel subscription: + ```coffeescript # app/assets/javascripts/cable/subscriptions/web_notifications.coffee -# Client-side which assumes you've already requested the right to send web notifications +# Client-side which assumes you've already requested +# the right to send web notifications. App.cable.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 +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' +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 (Redis by default)'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`. +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(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`. +"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 to `received`. -### More complete examples +### 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. @@ -484,26 +525,20 @@ Action Cable has two required configurations: a subscription adapter and allowed ### Subscription Adapter -By default, `ActionCable::Server::Base` will look for a configuration file -in `Rails.root.join('config/cable.yml')`. The file must specify an adapter -and a URL for each Rails environment. See the "Dependencies" section for -additional information on adapters. +By default, Action Cable looks for a configuration file in `config/cable.yml`. +The file must specify an adapter and a URL for each Rails environment. See the +[Dependencies](#dependencies) section for additional information on adapters. ```yaml -production: &production - adapter: redis - url: redis://10.10.3.153:6381 -development: &development +development: adapter: async -test: *development -``` -This format allows you to specify one configuration per Rails environment. -You can also change the location of the Action Cable config file in -a Rails initializer with something like: +test: + adapter: async -```ruby -Rails.application.paths.add "config/redis/cable", with: "somewhere/else/cable.yml" +production: + adapter: redis + url: redis://10.10.3.153:6381 ``` ### Allowed Request Origins @@ -513,44 +548,46 @@ passed to the server config as an array. The origins can be instances of strings or regular expressions, against which a check for match will be performed. ```ruby -Rails.application.config.action_cable.allowed_request_origins = ['http://rubyonrails.com', /http:\/\/ruby.*/] +config.action_cable.allowed_request_origins = ['http://rubyonrails.com', %r{http://ruby.*}] ``` To disable and allow requests from any origin: ```ruby -Rails.application.config.action_cable.disable_request_forgery_protection = true +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. +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. ### Other Configurations -The other common option to configure is the log tags applied to the per-connection logger. Here's close to what we're using in Basecamp: +The other common option to configure is the log tags applied to the +per-connection logger. Here's close to what we're using in Basecamp: ```ruby -Rails.application.config.action_cable.log_tags = [ +config.action_cable.log_tags = [ -> request { request.env['bc.account_id'] || "no-account" }, :action_cable, -> request { request.uuid } ] ``` -For a full list of all configuration options, see the `ActionCable::Server::Configuration` class. +For a full list of all configuration options, see the +`ActionCable::Server::Configuration` class. -Also note that your server must provide at least the same number of -database connections as you have workers. The default worker pool is -set to 100, so that means you have to make at least that available. -You can change that in `config/database.yml` through the `pool` attribute. +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 100, so +that means you have to make at least that available. You can change that in +`config/database.yml` through the `pool` attribute. -## Running standalone cable servers +## Running Standalone Cable Servers ### In App @@ -565,30 +602,30 @@ class Application < Rails::Application end ``` -You can use `App.cable = ActionCable.createConsumer()` to connect to the -cable server if `action_cable_meta_tag` is included in the layout. A custom -path is specified as first argument to `createConsumer` -(e.g. `App.cable = ActionCable.createConsumer("/websocket")`). +You can use `App.cable = ActionCable.createConsumer()` to connect to the cable +server if `action_cable_meta_tag` is invoked in the layout. A custom path is +specified as first argument to `createConsumer` (e.g. `App.cable = +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 ActionCable, -but the use of Redis keeps messages synced across connections. +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: +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 ::File.expand_path('../../config/environment', __FILE__) +require_relative 'config/environment' Rails.application.eager_load! run ActionCable.server ``` -Then you start the server using a binstub in bin/cable ala: +Then you start the server using a binstub in `bin/cable` ala: ``` #!/bin/bash @@ -624,4 +661,5 @@ 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 all the popular application servers -- Unicorn, Puma and Passenger. +Accordingly, Action Cable works with popular servers like Unicorn, Puma, and +Passenger. |