Make sure the subscription confirmaion is only sent out once

lib/action_cable/channel/base.rb

@@ -180,6 +180,10 @@ module ActionCable
           @defer_subscription_confirmation
         end
 
+        def subscription_confirmation_sent?
+          @subscription_confirmation_sent
+        end
+
       private
         def delegate_connection_identifiers
           connection.identifiers.each do |identifier|
@@ -231,8 +235,12 @@ module ActionCable
         end
 
         def transmit_subscription_confirmation
-          logger.info "#{self.class.name} is transmitting the subscription confirmation"
-          connection.transmit ActiveSupport::JSON.encode(identifier: @identifier, type: SUBSCRIPTION_CONFIRMATION_INTERNAL_MESSAGE)
+          unless subscription_confirmation_sent?
+            logger.info "#{self.class.name} is transmitting the subscription confirmation"
+            connection.transmit ActiveSupport::JSON.encode(identifier: @identifier, type: SUBSCRIPTION_CONFIRMATION_INTERNAL_MESSAGE)
+
+            @subscription_confirmation_sent = true
+          end
         end
 
     end

test/channel/stream_test.rb

@@ -10,6 +10,11 @@ class ActionCable::Channel::StreamTest < ActionCable::TestCase
         stream_from "test_room_#{@room.id}"
       end
     end
+
+    def send_confirmation
+      transmit_subscription_confirmation
+    end
+
   end
 
   test "streaming start and stop" do
@@ -53,4 +58,23 @@ class ActionCable::Channel::StreamTest < ActionCable::TestCase
     end
   end
 
+  test "stream_from subscription confirmation should only be sent out once" do
+    EM.run do
+      connection = TestConnection.new
+      connection.stubs(:pubsub).returns EM::Hiredis.connect.pubsub
+
+      channel = ChatChannel.new connection, "test_channel"
+      channel.send_confirmation
+      channel.send_confirmation
+
+      EM.run_deferred_callbacks
+
+      expected = ActiveSupport::JSON.encode "identifier" => "test_channel", "type" => "confirm_subscription"
+      assert_equal expected, connection.last_transmission, "Did not receive subscription confirmation within 0.1s"
+
+      assert_equal 1, connection.transmissions.size
+      EM.stop
+    end
+  end
+
 end