Merge pull request #25282 from prathamesh-sonpatki/trim-ac-readme
Trim Action Cable README [ci skip]
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Kasper Timm Hansen
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@ -7,7 +7,6 @@ and scalable. It's a full-stack offering that provides both a client-side
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JavaScript framework and a server-side Ruby framework. You have access to your full
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domain model written with Active Record or your ORM of choice.
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## Terminology
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A single Action Cable server can handle multiple connection instances. It has one
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@ -300,165 +299,15 @@ The rebroadcast will be received by all connected clients, _including_ the clien
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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 how to add channels.
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## Download and installation
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## Configuration
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The latest version of Action Cable can be installed with RubyGems:
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Action Cable has three required configurations: a subscription adapter, allowed request origins, and the cable server URL (which can optionally be set on the client side).
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$ gem install actioncable
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### Redis
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Source code can be downloaded as part of the Rails project on GitHub
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By default, `ActionCable::Server::Base` will look for a configuration file in `Rails.root.join('config/cable.yml')`.
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This file must specify an adapter and a URL for each Rails environment. It may use the following format:
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```yaml
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production: &production
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adapter: redis
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url: redis://10.10.3.153:6381
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development: &development
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adapter: redis
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url: redis://localhost:6379
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test: *development
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```
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You can also change the location of the Action Cable config file in a Rails initializer with something like:
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```ruby
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Rails.application.paths.add "config/cable", with: "somewhere/else/cable.yml"
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```
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### Allowed Request Origins
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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 match will be performed.
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```ruby
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Rails.application.config.action_cable.allowed_request_origins = ['http://rubyonrails.com', /http:\/\/ruby.*/]
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```
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When running in the development environment, this defaults to "http://localhost:3000".
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To disable and allow requests from any origin:
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```ruby
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Rails.application.config.action_cable.disable_request_forgery_protection = true
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```
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### Consumer Configuration
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Once you have decided how to run your cable server (see below), you must provide the server URL (or path) to your client-side setup.
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There are two ways you can do this.
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The first is to simply pass it in when creating your consumer. For a standalone server,
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this would be something like: `App.cable = ActionCable.createConsumer("ws://example.com:28080")`, and for an in-app server,
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something like: `App.cable = ActionCable.createConsumer("/cable")`.
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The second option is to pass the server URL through the `action_cable_meta_tag` in your layout.
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This uses a URL or path typically set via `config.action_cable.url` in the environment configuration files, or defaults to "/cable".
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This method is especially useful if your WebSocket URL might change between environments. If you host your production server via https, you will need to use the wss scheme
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for your Action Cable server, but development might remain http and use the ws scheme. You might use localhost in development and your
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domain in production.
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In any case, to vary the WebSocket URL between environments, add the following configuration to each environment:
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```ruby
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config.action_cable.url = "ws://example.com:28080"
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```
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Then add the following line to your layout before your JavaScript tag:
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```erb
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<%= action_cable_meta_tag %>
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```
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And finally, create your consumer like so:
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```coffeescript
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App.cable = ActionCable.createConsumer()
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```
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### Other Configurations
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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:
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```ruby
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Rails.application.config.action_cable.log_tags = [
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-> request { request.env['bc.account_id'] || "no-account" },
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:action_cable,
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-> request { request.uuid }
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]
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```
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For a full list of all configuration options, see the `ActionCable::Server::Configuration` class.
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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 4, so that means you have to make at least that available. You can change that in `config/database.yml` through the `pool` attribute.
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## Running the cable server
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### Standalone
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The cable server(s) is separated from your normal application server. It's still a Rack application, but it is its own Rack
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application. The recommended basic setup is as follows:
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```ruby
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# cable/config.ru
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require ::File.expand_path('../../config/environment', __FILE__)
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Rails.application.eager_load!
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run ActionCable.server
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```
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Then you start the server using a binstub in bin/cable ala:
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```sh
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#!/bin/bash
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bundle exec puma -p 28080 cable/config.ru
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```
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The above will start a cable server on port 28080.
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### In app
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If you are using a server that supports the [Rack socket hijacking API](http://www.rubydoc.info/github/rack/rack/file/SPEC#Hijacking), 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`:
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```ruby
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# config/application.rb
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class Application < Rails::Application
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config.action_cable.mount_path = '/websocket'
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end
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```
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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.
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### Notes
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Beware that currently, the cable server will _not_ auto-reload any changes in the framework. As we've discussed, long-running cable connections mean long-running objects. We don't yet have a way of reloading the classes of those objects in a safe manner. So when you change your channels, or the model your channels use, you must restart the cable server.
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We'll get all this abstracted properly when the framework is integrated into Rails.
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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](http://www.rubytutorial.io/actioncable-devise-authentication).
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## Dependencies
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Action Cable provides a subscription adapter interface to process its pubsub internals. By default, asynchronous, inline, PostgreSQL, evented Redis, and non-evented Redis adapters are included. The default adapter in new Rails applications is the asynchronous (`async`) adapter. To create your own adapter, you can look at `ActionCable::SubscriptionAdapter::Base` for all methods that must be implemented, and any of the adapters included within Action Cable as example implementations.
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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).
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## Deployment
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Action Cable is powered by a combination of WebSockets and threads. All of the
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connection management is handled internally by utilizing Ruby’s native thread
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support, which means you can use all your regular Rails models with no problems
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as long as you haven’t committed any thread-safety sins.
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The Action Cable server does _not_ need to be a multi-threaded application server.
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This is because Action Cable uses the [Rack socket hijacking API](http://www.rubydoc.info/github/rack/rack/file/SPEC#Hijacking)
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to take over control of connections from the application server. Action Cable
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then manages connections internally, in a multithreaded manner, regardless of
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whether the application server is multi-threaded or not. So Action Cable works
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with all the popular application servers -- Unicorn, Puma and Passenger.
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Action Cable does not work with WEBrick, because WEBrick does not support the
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Rack socket hijacking API.
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* https://github.com/rails/rails/tree/master/actioncable
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## License
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