Calling exists? in the session store, without checking for stale sess…

…ions, 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 @@ def inspect
         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 @@ def extract_session_id(env)
         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 @@ def set_session(env, sid, session_data)
           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