module ActionCable module Channel # 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. # # 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 Action Controllers, channels do not follow a REST constraint form for its actions. It's an 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, subscribed/unsubscribed are not callable methods, as they were already declared in ActionCable::Channel::Base, but #appear/away # are. #generate_connection_token is also not callable as its 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, 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. class Base include Callbacks include PeriodicTimers include Streams include Naming include Broadcasting on_subscribe :subscribed on_unsubscribe :unsubscribed attr_reader :params, :connection delegate :logger, to: :connection class << self # 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. 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 protected # 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 def clear_action_methods! @action_methods = nil end # Refresh the cached action_methods when a new action_method is added. def method_added(name) super clear_action_methods! end end def initialize(connection, identifier, params = {}) @connection = connection @identifier = identifier @params = params delegate_connection_identifiers subscribe_to_channel end # 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). def perform_action(data) action = extract_action(data) if processable_action?(action) dispatch_action(action, data) else logger.error "Unable to process #{action_signature(action, data)}" end end # Called by the cable connection when its cut so the channel has a chance to cleanup with callbacks. # This method is not intended to be called directly by the user. Instead, overwrite the #unsubscribed callback. def unsubscribe_from_channel run_unsubscribe_callbacks logger.info "#{self.class.name} unsubscribed" end protected # Called once a consumer has become a subscriber of the channel. Usually the place to setup any streams # you want this channel to be sending to the subscriber. def subscribed # Override in subclasses end # Called once a consumer has cut its cable connection. Can be used for cleaning up connections or marking # people as offline or the like. def unsubscribed # Override in subclasses end # 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. def transmit(data, via: nil) logger.info "#{self.class.name} transmitting #{data.inspect}".tap { |m| m << " (via #{via})" if via } connection.transmit({ identifier: @identifier, message: data }.to_json) end private def delegate_connection_identifiers connection.identifiers.each do |identifier| define_singleton_method(identifier) do connection.send(identifier) end end end def subscribe_to_channel logger.info "#{self.class.name} subscribing" run_subscribe_callbacks end def extract_action(data) (data['action'].presence || :receive).to_sym end def processable_action?(action) self.class.action_methods.include?(action.to_s) end def dispatch_action(action, data) logger.info action_signature(action, data) if method(action).arity == 1 public_send action, data else public_send action end end def action_signature(action, data) "#{self.class.name}##{action}".tap do |signature| if (arguments = data.except('action')).any? signature << "(#{arguments.inspect})" end end end def run_subscribe_callbacks self.class.on_subscribe_callbacks.each { |callback| send(callback) } end def run_unsubscribe_callbacks self.class.on_unsubscribe_callbacks.each { |callback| send(callback) } end end end end