Add a disconnect callback

lib/action_cable/channel/base.rb

@@ -5,9 +5,11 @@ class Base
       include Callbacks
       include Redis
 
-      on_subscribe :start_periodic_timers
+      on_subscribe   :start_periodic_timers
       on_unsubscribe :stop_periodic_timers
 
+      on_unsubscribe :disconnect
+
       attr_reader :params
 
       class_attribute :channel_name
@@ -54,6 +56,10 @@ def connect
           # Override in subclasses
         end
 
+        def disconnect
+          # Override in subclasses
+        end
+
         def broadcast(data)
           @connection.broadcast({ identifier: @channel_identifier, message: data }.to_json)
         end