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ActionCableを読み解く(cable server 編)

Last updated at Posted at 2015-12-25

Introduction

Socket.ioもびっくりのスーパー抽象化がなされたActionCableについて,実装を覗いて理解を深めましょう.

なお,Rails 5-beta1を参考にしていきます.

ActionCable.server

Rails.application.routes.draw do
  mount ActionCable.server => '/cable'
end

ActionCable.serverの実装.ActionCable::Server::Baseのインスタンスを返しているだけ.

# https://github.com/rails/rails/blob/v5.0.0.beta1/actioncable/lib/action_cable.rb#L42-L44
module ActionCable
  module_function def server
    @server ||= ActionCable::Server::Base.new
  end
end

ActionCable::Server

ActionCable::Server::Base#call(env)を実装しているので,mountable engineとして動作する.

# https://github.com/rails/rails/blob/v5.0.0.beta1/actioncable/lib/action_cable/server/base.rb#L25-L28
class ActionCable::Server::Base
  def call(env)
    setup_heartbeat_timer
    config.connection_class.new(self, env).process
  end
end

setup_heartbeat_timerActionCable::Server::Connection moduleに定義されている.EventMachineで処理をスケジューリングしている.connectionsの各要素のbeatメソッドを叩いているようだ.ここは後で見ていくことにする.

# https://github.com/rails/rails/blob/v5.0.0.beta1/actioncable/lib/action_cable/server/connections.rb#L24-L30
module ActionCable::Server::Connection
  def setup_heartbeat_timer
    EM.next_tick do
      @heartbeat_timer ||= EventMachine.add_periodic_timer(BEAT_INTERVAL) do
        EM.next_tick { connections.map(&:beat) }
      end
    end
  end
end

ActionCable::Server::Base#initializeに戻る.2行目には次のようなコードがある.config.connection_classのインスタンスを作ってからprocessを呼んでいるらしい.

config.connection_class.new(self, env).process

configcattr_accessorで宣言されている.ActionCable::Server::Configurationのインスタンスらしい.

# https://github.com/rails/rails/blob/v5.0.0.beta1/actioncable/lib/action_cable/server/base.rb#L16
cattr_accessor(:config, instance_accessor: true) { ActionCable::Server::Configuration.new }

ActionCable::Server::Configurationを見てみると,connection_classのなかみはApplicationCable::Connectionであることがわかる.

# https://github.com/rails/rails/blob/v5.0.0.beta1/actioncable/lib/action_cable/server/configuration.rb#L15
class ActionCable::Server::Configuration
  attr_accessor :connection_class

  def initialize
    @connection_class  = ApplicationCable::Connection
  end
end

ActionCable::Connection

ActionCable::Connection::Base#processではWebSocketの各種イベントのコールバックを登録している.ちゃんと接続できたらMountable Engineのcallメソッドが要求する返り値を返す.

# https://github.com/rails/rails/blob/master/actioncable/lib/action_cable/connection/base.rb#L71-L83
class ActionCable::Connection::Base
  def initialize
    @websocket = ActionCable::Connection::WebSocket.new(env)
  end

  def process
    logger.info started_request_message

    if websocket.possible? && allow_request_origin?
      websocket.on(:open)    { |event| send_async :on_open   }
      websocket.on(:message) { |event| on_message event.data }
      websocket.on(:close)   { |event| send_async :on_close  }

      respond_to_successful_request
    else
      respond_to_invalid_request
    end
  end
end

ActionCable::Connection::WebSocketFaye::WebSocketのラッパになっており,主要なメソッド(?)は大抵delegateされる.

# https://github.com/rails/rails/blob/v5.0.0.beta1/actioncable/lib/action_cable/connection/web_socket.rb#L7-L11
class ActionCable::Connection::WebSocket
  delegate :rack_response, :close, :on, to: :websocket

  def initialize(env)
    @websocket = Faye::WebSocket.websocket?(env) ? Faye::WebSocket.new(env) : nil
   end
end

メッセージ受信時の流れ

めんどくさくなってきたのでざっくり(そのうちちゃんと書きます:bow:

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