Merge pull request #26547 from palkan/fix/actioncable-confirmation-race-condition

Avoid race condition on subscription confirmation

actioncable/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Prevent race where the client could receive and act upon a
+    subscription confirmation before the channel's `subscribed` method
+    completed.
+
+    Fixes #25381.
+
+    *Vladimir Dementyev*
+
 *   Buffer writes to websocket connections, to avoid blocking threads
     that could be doing more useful things.
 

actioncable/lib/action_cable/channel/base.rb

@@ -144,13 +144,14 @@ module ActionCable
 
         # When a channel is streaming via pubsub, we want to delay the confirmation
         # transmission until pubsub subscription is confirmed.
-        @defer_subscription_confirmation = false
+        #
+        # 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
-        subscribe_to_channel
       end
 
       # Extract the action name from the passed data and process it via the channel. The process will ensure
@@ -169,6 +170,17 @@ module ActionCable
         end
       end
 
+      # This method is called after subscription has been added to the connection
+      # and confirms or rejects the subscription.
+      def subscribe_to_channel
+        run_callbacks :subscribe do
+          subscribed
+        end
+
+        reject_subscription if subscription_rejected?
+        ensure_confirmation_sent
+      end
+
       # 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, overwrite the #unsubscribed callback.
       def unsubscribe_from_channel # :nodoc:
@@ -201,12 +213,18 @@ module ActionCable
           end
         end
 
+        def ensure_confirmation_sent
+          return if subscription_rejected?
+          @defer_subscription_confirmation_counter.decrement
+          transmit_subscription_confirmation unless defer_subscription_confirmation?
+        end
+
         def defer_subscription_confirmation!
-          @defer_subscription_confirmation = true
+          @defer_subscription_confirmation_counter.increment
         end
 
         def defer_subscription_confirmation?
-          @defer_subscription_confirmation
+          @defer_subscription_confirmation_counter.value > 0
         end
 
         def subscription_confirmation_sent?
@@ -230,18 +248,6 @@ module ActionCable
           end
         end
 
-        def subscribe_to_channel
-          run_callbacks :subscribe do
-            subscribed
-          end
-
-          if subscription_rejected?
-            reject_subscription
-          else
-            transmit_subscription_confirmation unless defer_subscription_confirmation?
-          end
-        end
-
         def extract_action(data)
           (data["action"].presence || :receive).to_sym
         end

actioncable/lib/action_cable/channel/streams.rb

@@ -84,7 +84,7 @@ module ActionCable
 
         connection.server.event_loop.post do
           pubsub.subscribe(broadcasting, handler, lambda do
-            transmit_subscription_confirmation
+            ensure_confirmation_sent
             logger.info "#{self.class.name} is streaming from #{broadcasting}"
           end)
         end

actioncable/lib/action_cable/connection/subscriptions.rb

@@ -26,10 +26,14 @@ module ActionCable
         id_key = data["identifier"]
         id_options = ActiveSupport::JSON.decode(id_key).with_indifferent_access
 
+        return if subscriptions.key?(id_key)
+
         subscription_klass = id_options[:channel].safe_constantize
 
         if subscription_klass && ActionCable::Channel::Base >= subscription_klass
-          subscriptions[id_key] ||= subscription_klass.new(connection, id_key, id_options)
+          subscription = subscription_klass.new(connection, id_key, id_options)
+          subscriptions[id_key] = subscription
+          subscription.subscribe_to_channel
         else
           logger.error "Subscription class not found: #{id_options[:channel].inspect}"
         end

actioncable/test/channel/base_test.rb

@@ -77,11 +77,13 @@ class ActionCable::Channel::BaseTest < ActiveSupport::TestCase
     @channel = ChatChannel.new @connection, "{id: 1}", id: 1
   end
 
-  test "should subscribe to a channel on initialize" do
+  test "should subscribe to a channel" do
+    @channel.subscribe_to_channel
     assert_equal 1, @channel.room.id
   end
 
   test "on subscribe callbacks" do
+    @channel.subscribe_to_channel
     assert @channel.subscribed
   end
 
@@ -90,6 +92,8 @@ class ActionCable::Channel::BaseTest < ActiveSupport::TestCase
   end
 
   test "unsubscribing from a channel" do
+    @channel.subscribe_to_channel
+
     assert @channel.room
     assert @channel.subscribed?
 
@@ -150,8 +154,13 @@ class ActionCable::Channel::BaseTest < ActiveSupport::TestCase
     assert_equal expected, @connection.last_transmission
   end
 
-  test "subscription confirmation" do
+  test "do not send subscription confirmation on initialize" do
+    assert_nil @connection.last_transmission
+  end
+
+  test "subscription confirmation on subscribe_to_channel" do
     expected = { "identifier" => "{id: 1}", "type" => "confirm_subscription" }
+    @channel.subscribe_to_channel
     assert_equal expected, @connection.last_transmission
   end
 
@@ -208,6 +217,8 @@ class ActionCable::Channel::BaseTest < ActiveSupport::TestCase
 
   test "notification for transmit_subscription_confirmation" do
     begin
+      @channel.subscribe_to_channel
+
       events = []
       ActiveSupport::Notifications.subscribe "transmit_subscription_confirmation.action_cable" do |*args|
         events << ActiveSupport::Notifications::Event.new(*args)

actioncable/test/channel/periodic_timers_test.rb

@@ -62,6 +62,7 @@ class ActionCable::Channel::PeriodicTimersTest < ActiveSupport::TestCase
     @connection.server.event_loop.expects(:timer).times(3).returns(stub(shutdown: nil))
     channel = ChatChannel.new @connection, "{id: 1}", id: 1
 
+    channel.subscribe_to_channel
     channel.unsubscribe_from_channel
     assert_equal [], channel.send(:active_periodic_timers)
   end

actioncable/test/channel/rejection_test.rb

@@ -20,6 +20,7 @@ class ActionCable::Channel::RejectionTest < ActiveSupport::TestCase
   test "subscription rejection" do
     @connection.expects(:subscriptions).returns mock().tap { |m| m.expects(:remove_subscription).with instance_of(SecretChannel) }
     @channel = SecretChannel.new @connection, "{id: 1}", id: 1
+    @channel.subscribe_to_channel
 
     expected = { "identifier" => "{id: 1}", "type" => "reject_subscription" }
     assert_equal expected, @connection.last_transmission
@@ -28,6 +29,7 @@ class ActionCable::Channel::RejectionTest < ActiveSupport::TestCase
   test "does not execute action if subscription is rejected" do
     @connection.expects(:subscriptions).returns mock().tap { |m| m.expects(:remove_subscription).with instance_of(SecretChannel) }
     @channel = SecretChannel.new @connection, "{id: 1}", id: 1
+    @channel.subscribe_to_channel
 
     expected = { "identifier" => "{id: 1}", "type" => "reject_subscription" }
     assert_equal expected, @connection.last_transmission

actioncable/test/channel/stream_test.rb

@@ -53,6 +53,7 @@ module ActionCable::StreamTests
         connection = TestConnection.new
         connection.expects(:pubsub).returns mock().tap { |m| m.expects(:subscribe).with("test_room_1", kind_of(Proc), kind_of(Proc)).returns stub_everything(:pubsub) }
         channel = ChatChannel.new connection, "{id: 1}", id: 1
+        channel.subscribe_to_channel
 
         connection.expects(:pubsub).returns mock().tap { |m| m.expects(:unsubscribe) }
         channel.unsubscribe_from_channel
@@ -64,6 +65,7 @@ module ActionCable::StreamTests
         connection = TestConnection.new
         connection.expects(:pubsub).returns mock().tap { |m| m.expects(:subscribe).with("channel", kind_of(Proc), kind_of(Proc)).returns stub_everything(:pubsub) }
         channel = SymbolChannel.new connection, ""
+        channel.subscribe_to_channel
 
         connection.expects(:pubsub).returns mock().tap { |m| m.expects(:unsubscribe) }
         channel.unsubscribe_from_channel
@@ -76,6 +78,7 @@ module ActionCable::StreamTests
         connection.expects(:pubsub).returns mock().tap { |m| m.expects(:subscribe).with("action_cable:stream_tests:chat:Room#1-Campfire", kind_of(Proc), kind_of(Proc)).returns stub_everything(:pubsub) }
 
         channel = ChatChannel.new connection, ""
+        channel.subscribe_to_channel
         channel.stream_for Room.new(1)
       end
     end
@@ -84,7 +87,9 @@ module ActionCable::StreamTests
       run_in_eventmachine do
         connection = TestConnection.new
 
-        ChatChannel.new connection, "{id: 1}", id: 1
+        channel = ChatChannel.new connection, "{id: 1}", id: 1
+        channel.subscribe_to_channel
+
         assert_nil connection.last_transmission
 
         wait_for_async
@@ -114,7 +119,7 @@ module ActionCable::StreamTests
     end
   end
 
-  require "action_cable/subscription_adapter/inline"
+  require "action_cable/subscription_adapter/async"
 
   class UserCallbackChannel < ActionCable::Channel::Base
     def subscribed
@@ -124,9 +129,16 @@ module ActionCable::StreamTests
     end
   end
 
-  class StreamEncodingTest < ActionCable::TestCase
+  class MultiChatChannel < ActionCable::Channel::Base
+    def subscribed
+      stream_from "main_room"
+      stream_from "test_all_rooms"
+    end
+  end
+
+  class StreamFromTest < ActionCable::TestCase
     setup do
-      @server = TestServer.new(subscription_adapter: ActionCable::SubscriptionAdapter::Inline)
+      @server = TestServer.new(subscription_adapter: ActionCable::SubscriptionAdapter::Async)
       @server.config.allowed_request_origins = %w( http://rubyonrails.com )
     end
 
@@ -153,6 +165,17 @@ module ActionCable::StreamTests
       end
     end
 
+    test "subscription confirmation should only be sent out once with muptiple stream_from" do
+      run_in_eventmachine do
+        connection = open_connection
+        expected = { "identifier" => { "channel" => MultiChatChannel.name }.to_json, "type" => "confirm_subscription" }
+        connection.websocket.expects(:transmit).with(expected.to_json)
+        receive(connection, command: "subscribe", channel: MultiChatChannel.name, identifiers: {})
+
+        wait_for_async
+      end
+    end
+
     private
       def subscribe_to(connection, identifiers:)
         receive connection, command: "subscribe", identifiers: identifiers

actioncable/test/test_helper.rb

@@ -66,8 +66,12 @@ class ActionCable::TestCase < ActiveSupport::TestCase
   end
 
   def wait_for_executor(executor)
+    # do not wait forever, wait 2s
+    timeout = 2
     until executor.completed_task_count == executor.scheduled_task_count
       sleep 0.1
+      timeout -= 0.1
+      raise "Executor could not complete all tasks in 2 seconds" unless timeout > 0
     end
   end
 end