Fix unsubscribed server side behavior

Before this commit, the `unsubscribed` callbacks in Action Cable server
side channels were never called. This is because when a WebSocket
"goodbye" message was sent from the client, the Action Cable server
didn't properly clean up after the now closed WebSocket. This means that
memory could possibly skyrocket with this behavior, since part of this
commit is to properly remove closed subscriptions from the global
subscriptions hash. Say you have 10,000 users currently connected, and
then all 10,000 disconnect -- before this patch, Action Cable would
still hold onto information (and Ruby objects!) for all of these now
dead connections.

actioncable/lib/action_cable/connection/client_socket.rb

@@ -132,12 +132,9 @@ module ActionCable
           @ready_state = CLOSING
           @close_params = [reason, code]
 
-          if @stream
-            @stream.shutdown
-          else
+          @stream.shutdown if @stream
           finalize_close
         end
-        end
 
         def finalize_close
           return if @ready_state == CLOSED

actioncable/lib/action_cable/connection/subscriptions.rb

@@ -54,7 +54,7 @@ module ActionCable
       end
 
       def unsubscribe_from_all
-        subscriptions.each { |id, channel| channel.unsubscribe_from_channel }
+        subscriptions.each { |id, channel| remove_subscription(channel) }
       end
 
       protected

actioncable/test/client/echo_channel.rb

@@ -3,6 +3,10 @@ class EchoChannel < ActionCable::Channel::Base
     stream_from "global"
   end
 
+  def unsubscribed
+    'Goodbye from EchoChannel!'
+  end
+
   def ding(data)
     transmit(dong: data['message'])
   end

actioncable/test/client_test.rb

@@ -198,4 +198,25 @@ class ClientTest < ActionCable::TestCase
       c.close # disappear before read
     end
   end
+
+  def test_unsubscribe_client
+    with_puma_server do |port|
+      app = ActionCable.server
+      identifier = JSON.dump(channel: 'EchoChannel')
+
+      c = faye_client(port)
+      c.send_message command: 'subscribe', identifier: identifier
+      assert_equal({"identifier"=>"{\"channel\":\"EchoChannel\"}", "type"=>"confirm_subscription"}, c.read_message)
+      assert_equal(1, app.connections.count)
+      assert(app.remote_connections.where(identifier: identifier))
+
+      channel = app.connections.first.subscriptions.send(:subscriptions).first[1]
+      channel.expects(:unsubscribed)
+      c.close
+      sleep 0.1 # Data takes a moment to process
+
+      # All data is removed: No more connection or subscription information!
+      assert_equal(0, app.connections.count)
+    end
+  end
 end