Calling exists? in the session store, without checking for stale sessions, was causing the cookie store to panic because we need to unpack the whole session to get its key. This commit fixes this issue and also caches exists calls for performance improvements.

actionpack/lib/action_dispatch/middleware/session/abstract_store.rb

@@ -88,7 +88,10 @@ module ActionDispatch
         end
 
         def exists?
-          @by.send(:exists?, @env)
+          return @exists if instance_variable_defined?(:@exists)
+          stale_session_check! do
+            @exists = @by.send(:exists?, @env)
+          end
         end
 
         def loaded?

actionpack/lib/action_dispatch/middleware/session/cookie_store.rb

@@ -62,11 +62,12 @@ module ActionDispatch
         end
 
         def unpacked_cookie_data(env)
-          request = ActionDispatch::Request.new(env)
-          if data = request.cookie_jar.signed[@key]
-            data.stringify_keys!
-          else
-            {}
+          env["action_dispatch.request.unsigned_session_cookie"] ||= begin
+            request = ActionDispatch::Request.new(env)
+            if data = request.cookie_jar.signed[@key]
+              data.stringify_keys!
+            end
+            data || {}
           end
         end
 
@@ -78,10 +79,6 @@ module ActionDispatch
           persistent_session_id!(session_data, sid)
         end
 
-        def exists?(env)
-          ActionDispatch::Request.new(env).cookie_jar.key?(@key)
-        end
-
         def destroy(env)
           # session data is stored on client; nothing to do here
         end