Class: ActionCable::Channel::Base

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain: self, `::ActiveSupport::DescendantsTracker`
Instance Chain: self, `::ActiveSupport::Rescuable`, `Broadcasting`, `Naming`, `Streams`, `PeriodicTimers`, `Callbacks`, `::ActiveSupport::Callbacks`
Inherits:	Object
Defined in:	actioncable/lib/action_cable/channel/base.rb

Overview

The channel provides the basic structure of grouping behavior into logical units when communicating over the WebSocket connection. You can think of a channel like a form of controller, but one that’s capable of pushing content to the subscriber in addition to simply responding to the subscriber’s direct requests.

::ActionCable::Channel instances are long-lived. A channel object will be instantiated when the cable consumer becomes a subscriber, and then lives until the consumer disconnects. This may be seconds, minutes, hours, or even days. That means you have to take special care not to do anything silly in a channel that would balloon its memory footprint or whatever. The references are forever, so they won’t be released as is normally the case with a controller instance that gets thrown away after every request.

Long-lived channels (and connections) also mean you’re responsible for ensuring that the data is fresh. If you hold a reference to a user record, but the name is changed while that reference is held, you may be sending stale data if you don’t take precautions to avoid it.

The upside of long-lived channel instances is that you can use instance variables to keep reference to objects that future subscriber requests can interact with. Here’s a quick example:

class ChatChannel < ApplicationCable::Channel
  def subscribed
    @room = Chat::Room[params[:room_number]]
  end

  def speak(data)
    @room.speak data, user: current_user
  end
end

The #speak action simply uses the Chat::Room object that was created when the channel was first subscribed to by the consumer when that subscriber wants to say something in the room.

Action processing

Unlike subclasses of ::ActionController::Base, channels do not follow a RESTful constraint form for their actions. Instead, Action Cable operates through a remote-procedure call model. You can declare any public method on the channel (optionally taking a data argument), and this method is automatically exposed as callable to the client.

Example:

class AppearanceChannel < ApplicationCable::Channel
  def subscribed
    @connection_token = generate_connection_token
  end

  def unsubscribed
    current_user.disappear @connection_token
  end

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

  def away
    current_user.away @connection_token
  end

  private
    def generate_connection_token
      SecureRandom.hex(36)
    end
end

In this example, the subscribed and unsubscribed methods are not callable methods, as they were already declared in Base, but #appear and #away are. #generate_connection_token is also not callable, since it’s a private method. You’ll see that appear accepts a data parameter, which it then uses as part of its model call. #away does not, since it’s simply a trigger action.

Also note that in this example, current_user is available because it was marked as an identifying attribute on the connection. All such identifiers will automatically create a delegation method of the same name on the channel instance.

Rejecting subscription requests

A channel can reject a subscription request in the #subscribed callback by invoking the #reject method:

class ChatChannel < ApplicationCable::Channel
  def subscribed
    @room = Chat::Room[params[:room_number]]
    reject unless current_user.can_access?(@room)
  end
end

In this example, the subscription will be rejected if the current_user does not have access to the chat room. On the client-side, the Channel#rejected callback will get invoked when the server rejects the subscription request.

Constant Summary

`::ActiveSupport::Callbacks` - Included

CALLBACK_FILTER_TYPES

`::ActiveSupport::Rescuable` - Attributes & Methods

.rescue_handlers rw
#rescue_handlers rw
.rescue_handlers? ⇒ Boolean rw
#rescue_handlers? ⇒ Boolean rw

Class Method Summary

.action_methods

A list of method names that should be considered actions.
.new(connection, identifier, params = {}) ⇒ Base constructor
.clear_action_methods! private

action_methods are cached and there is sometimes need to refresh them.
.method_added(name) private

Refresh the cached action_methods when a new action_method is added.

`::ActiveSupport::DescendantsTracker` - self

descendants, subclasses, clear, disable_clear!, reject!

Instance Attribute Summary

#connection readonly
#identifier readonly
#logger readonly
#params readonly
#defer_subscription_confirmation? ⇒ Boolean readonly private
#subscription_confirmation_sent? ⇒ Boolean readonly private
#subscription_rejected? ⇒ Boolean readonly private

`Streams` - Included

#pubsub

`Callbacks` - Included

#__callbacks, #__callbacks?

Instance Method Summary

#perform_action(data)

Extract the action name from the passed data and process it via the channel.
#subscribe_to_channel

This method is called after subscription has been added to the connection and confirms or rejects the subscription.
#action_signature(action, data) private
#defer_subscription_confirmation! private
#delegate_connection_identifiers private
#dispatch_action(action, data) private
#ensure_confirmation_sent private
#extract_action(data) private
#parameter_filter private
#processable_action?(action) ⇒ Boolean private
#reject private
#reject_subscription private
#subscribed private

Called once a consumer has become a subscriber of the channel.
#transmit(data, via: nil) private

Transmit a hash of data to the subscriber.
#transmit_subscription_confirmation private
#transmit_subscription_rejection private
#unsubscribed private

Called once a consumer has cut its cable connection.
#unsubscribe_from_channel Internal use only

Called by the cable connection when it’s cut, so the channel has a chance to cleanup with callbacks.

`::ActiveSupport::Rescuable` - Included

#rescue_with_handler	Delegates to the class method, but uses the instance as the subject for rescue_from handlers (method calls, `instance_exec` blocks).
#handler_for_rescue	Internal handler lookup.

`Broadcasting` - Included

#broadcast_to, #broadcasting_for

`Naming` - Included

#channel_name

`Streams` - Included

#stop_all_streams	Unsubscribes all streams associated with this channel from the pubsub queue.
#stop_stream_for	Unsubscribes streams for the `model`.
#stop_stream_from	Unsubscribes streams from the named `broadcasting`.
#stream_for	Start streaming the pubsub queue for the `model` in this channel.
#stream_from	Start streaming from the named `broadcasting` pubsub queue.
#stream_or_reject_for	Calls stream_for with the given `model` if it’s present to start streaming, otherwise rejects the subscription.
#default_stream_handler	May be overridden to change the default stream handling behavior which decodes JSON and transmits to the client.
#identity_handler, #stream_decoder,
#stream_handler	May be overridden to add instrumentation, logging, specialized error handling, or other forms of handler decoration.
#stream_transmitter, #streams,
#worker_pool_stream_handler	Always wrap the outermost handler to invoke the user handler on the worker pool rather than blocking the event loop.

`PeriodicTimers` - Included

#active_periodic_timers, #start_periodic_timer, #start_periodic_timers, #stop_periodic_timers

`::ActiveSupport::Callbacks` - Included

#run_callbacks	Runs the callbacks for the given event.
#halted_callback_hook	A hook invoked every time a before callback is halted.

Constructor Details

.new(connection, identifier, params = {}) ⇒ `Base`

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 156


def initialize(connection, identifier, params = {})
  @connection = connection
  @identifier = identifier
  @params     = params

  # When a channel is streaming via pubsub, we want to delay the confirmation
  # transmission until pubsub subscription is confirmed.
  #
  # The counter starts at 1 because it's awaiting a call to #subscribe_to_channel
  @defer_subscription_confirmation_counter = Concurrent::AtomicFixnum.new(1)

  @reject_subscription = nil
  @subscription_confirmation_sent = nil

  delegate_connection_identifiers
end

Class Attribute Details

.periodic_timers (rw)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/periodic_timers.rb', line 11


class_attribute :periodic_timers, instance_reader: false, default: []

.periodic_timers? ⇒ `Boolean` (rw)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/periodic_timers.rb', line 11


class_attribute :periodic_timers, instance_reader: false, default: []

.rescue_handlers (rw)

[ GitHub ]

# File 'activesupport/lib/active_support/rescuable.rb', line 15


class_attribute :rescue_handlers, default: []

.rescue_handlers? ⇒ `Boolean` (rw)

[ GitHub ]

# File 'activesupport/lib/active_support/rescuable.rb', line 15


class_attribute :rescue_handlers, default: []

Class Method Details

.action_methods

A list of method names that should be considered actions. This includes all public instance methods on a channel, less any internal methods (defined on Base), adding back in any methods that are internal, but still exist on the class itself.

#### Returns

Set - A set of all methods that should be considered actions.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 129


def action_methods
  @action_methods ||= begin
    # All public instance methods of this class, including ancestors
    methods = (public_instance_methods(true) -
      # Except for public instance methods of Base and its ancestors
      ActionCable::Channel::Base.public_instance_methods(true) +
      # Be sure to include shadowed public instance methods of this class
      public_instance_methods(false)).uniq.map(&:to_s)
    methods.to_set
  end
end

.clear_action_methods! (private)

action_methods are cached and there is sometimes need to refresh them. .clear_action_methods! allows you to do that, so next time you run action_methods, they will be recalculated.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 145


def clear_action_methods! # :doc:
  @action_methods = nil
end

.method_added(name) (private)

Refresh the cached action_methods when a new action_method is added.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 150


def method_added(name) # :doc:
  super
  clear_action_methods!
end

Instance Attribute Details

#connection (readonly)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 118


attr_reader :params, :connection, :identifier

#defer_subscription_confirmation? ⇒ `Boolean` (readonly, private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 249


def defer_subscription_confirmation? # :doc:
  @defer_subscription_confirmation_counter.value > 0
end

#identifier (readonly)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 118


attr_reader :params, :connection, :identifier

#logger (readonly)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 119


delegate :logger, to: :connection

#params (readonly)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 118


attr_reader :params, :connection, :identifier

#rescue_handlers (rw)

[ GitHub ]

# File 'activesupport/lib/active_support/rescuable.rb', line 15


class_attribute :rescue_handlers, default: []

#rescue_handlers? ⇒ `Boolean` (rw)

[ GitHub ]

# File 'activesupport/lib/active_support/rescuable.rb', line 15


class_attribute :rescue_handlers, default: []

#subscription_confirmation_sent? ⇒ `Boolean` (readonly, private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 253


def subscription_confirmation_sent? # :doc:
  @subscription_confirmation_sent
end

#subscription_rejected? ⇒ `Boolean` (readonly, private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 261


def subscription_rejected? # :doc:
  @reject_subscription
end

Instance Method Details

#action_signature(action, data) (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 293


def action_signature(action, data)
  (+"#{self.class.name}##{action}").tap do |signature|
    arguments = data.except("action")

    if arguments.any?
      arguments = parameter_filter.filter(arguments)
      signature << "(#{arguments.inspect})"
    end
  end
end

#defer_subscription_confirmation! (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 245


def defer_subscription_confirmation! # :doc:
  @defer_subscription_confirmation_counter.increment
end

#delegate_connection_identifiers (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 265


def delegate_connection_identifiers
  connection.identifiers.each do |identifier|
    define_singleton_method(identifier) do
      connection.send(identifier)
    end
  end
end

#dispatch_action(action, data) (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 281


def dispatch_action(action, data)
  logger.debug action_signature(action, data)

  if method(action).arity == 1
    public_send action, data
  else
    public_send action
  end
rescue Exception => exception
  rescue_with_handler(exception) || raise
end

#ensure_confirmation_sent (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 239


def ensure_confirmation_sent # :doc:
  return if subscription_rejected?
  @defer_subscription_confirmation_counter.decrement
  transmit_subscription_confirmation unless defer_subscription_confirmation?
end

#extract_action(data) (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 273


def extract_action(data)
  (data["action"].presence || :receive).to_sym
end

#parameter_filter (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 304


def parameter_filter
  @parameter_filter ||= ActiveSupport::ParameterFilter.new(connection.config.filter_parameters)
end

#perform_action(data)

Extract the action name from the passed data and process it via the channel. The process will ensure that the action requested is a public method on the channel declared by the user (so not one of the callbacks like #subscribed).

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 176


def perform_action(data)
  action = extract_action(data)

  if processable_action?(action)
    payload = { channel_class: self.class.name, action: action, data: data }
    ActiveSupport::Notifications.instrument("perform_action.action_cable", payload) do
      dispatch_action(action, data)
    end
  else
    logger.error "Unable to process #{action_signature(action, data)}"
  end
end

#processable_action?(action) ⇒ `Boolean` (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 277


def processable_action?(action)
  self.class.action_methods.include?(action.to_s) unless subscription_rejected?
end

#reject (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 257


def reject # :doc:
  @reject_subscription = true
end

#reject_subscription (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 319


def reject_subscription
  connection.subscriptions.remove_subscription self
  transmit_subscription_rejection
end

#subscribe_to_channel

This method is called after subscription has been added to the connection and confirms or rejects the subscription.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 191


def subscribe_to_channel
  run_callbacks :subscribe do
    subscribed
  end

  reject_subscription if subscription_rejected?
  ensure_confirmation_sent
end

#subscribed (private)

Called once a consumer has become a subscriber of the channel. Usually the place to set up any streams you want this channel to be sending to the subscriber.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 213


def subscribed # :doc:
  # Override in subclasses
end

#transmit(data, via: nil) (private)

Transmit a hash of data to the subscriber. The hash will automatically be wrapped in a JSON envelope with the proper channel identifier marked as the recipient.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 226


def transmit(data, via: nil) # :doc:
  logger.debug do
    status = "#{self.class.name} transmitting #{data.inspect.truncate(300)}"
    status += " (via #{via})" if via
    status
  end

  payload = { channel_class: self.class.name, data: data, via: via }
  ActiveSupport::Notifications.instrument("transmit.action_cable", payload) do
    connection.transmit identifier: @identifier, message: data
  end
end

#transmit_subscription_confirmation (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 308


def transmit_subscription_confirmation
  unless subscription_confirmation_sent?
    logger.debug "#{self.class.name} is transmitting the subscription confirmation"

    ActiveSupport::Notifications.instrument("transmit_subscription_confirmation.action_cable", channel_class: self.class.name) do
      connection.transmit identifier: @identifier, type: ActionCable::INTERNAL[:message_types][:confirmation]
      @subscription_confirmation_sent = true
    end
  end
end

#transmit_subscription_rejection (private)

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 324


def transmit_subscription_rejection
  logger.debug "#{self.class.name} is transmitting the subscription rejection"

  ActiveSupport::Notifications.instrument("transmit_subscription_rejection.action_cable", channel_class: self.class.name) do
    connection.transmit identifier: @identifier, type: ActionCable::INTERNAL[:message_types][:rejection]
  end
end

#unsubscribe_from_channel

This method is for internal use only.

Called by the cable connection when it’s cut, so the channel has a chance to cleanup with callbacks. This method is not intended to be called directly by the user. Instead, override the #unsubscribed callback.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 203


def unsubscribe_from_channel # :nodoc:
  run_callbacks :unsubscribe do
    unsubscribed
  end
end

#unsubscribed (private)

Called once a consumer has cut its cable connection. Can be used for cleaning up connections or marking users as offline or the like.

[ GitHub ]

# File 'actioncable/lib/action_cable/channel/base.rb', line 219


def unsubscribed # :doc:
  # Override in subclasses
end

Class: ActionCable::Channel::Base

Overview

Action processing

Rejecting subscription requests

Constant Summary

::ActiveSupport::Callbacks - Included

PeriodicTimers - Attributes & Methods

::ActiveSupport::Rescuable - Attributes & Methods

Class Method Summary

::ActiveSupport::DescendantsTracker - self

Instance Attribute Summary

Streams - Included

Callbacks - Included

Instance Method Summary

::ActiveSupport::Rescuable - Included

Broadcasting - Included

Naming - Included

Streams - Included

PeriodicTimers - Included

::ActiveSupport::Callbacks - Included

Constructor Details

.new(connection, identifier, params = {}) ⇒ Base

Class Attribute Details

.periodic_timers (rw)

.periodic_timers? ⇒ Boolean (rw)

.rescue_handlers (rw)

.rescue_handlers? ⇒ Boolean (rw)

Class Method Details

.action_methods

.clear_action_methods! (private)

.method_added(name) (private)

Instance Attribute Details

#connection (readonly)

#defer_subscription_confirmation? ⇒ Boolean (readonly, private)

#identifier (readonly)

#logger (readonly)

#params (readonly)

#rescue_handlers (rw)

#rescue_handlers? ⇒ Boolean (rw)

#subscription_confirmation_sent? ⇒ Boolean (readonly, private)

#subscription_rejected? ⇒ Boolean (readonly, private)

Instance Method Details

#action_signature(action, data) (private)

#defer_subscription_confirmation! (private)

#delegate_connection_identifiers (private)

#dispatch_action(action, data) (private)

#ensure_confirmation_sent (private)

#extract_action(data) (private)

#parameter_filter (private)

#perform_action(data)

#processable_action?(action) ⇒ Boolean (private)

#reject (private)

#reject_subscription (private)

#subscribe_to_channel

#subscribed (private)

#transmit(data, via: nil) (private)

#transmit_subscription_confirmation (private)

#transmit_subscription_rejection (private)

#unsubscribe_from_channel

#unsubscribed (private)

`::ActiveSupport::Callbacks` - Included

`PeriodicTimers` - Attributes & Methods

`::ActiveSupport::Rescuable` - Attributes & Methods

`::ActiveSupport::DescendantsTracker` - self

`Streams` - Included

`Callbacks` - Included

`::ActiveSupport::Rescuable` - Included

`Broadcasting` - Included

`Naming` - Included

`Streams` - Included

`PeriodicTimers` - Included

`::ActiveSupport::Callbacks` - Included

.new(connection, identifier, params = {}) ⇒ `Base`

.periodic_timers? ⇒ `Boolean` (rw)

.rescue_handlers? ⇒ `Boolean` (rw)

#defer_subscription_confirmation? ⇒ `Boolean` (readonly, private)

#rescue_handlers? ⇒ `Boolean` (rw)

#subscription_confirmation_sent? ⇒ `Boolean` (readonly, private)

#subscription_rejected? ⇒ `Boolean` (readonly, private)

#processable_action?(action) ⇒ `Boolean` (private)