Event objects can't be properly serialized using Rails :json serializer

[jhilden]

Background: Rails.application.config.action_dispatch.cookies_serializer is set to :json (or :hybrid)

Problem: A rack tracker event object (such as Rack::Tracker::GoogleAnalytics::Send) wich was stored in the session and retrieved again, will be deserialized as a string like "#<Rack::Tracker::GoogleAnalytics::Send type=\"event\", category=\"...\", action=\"...\">"" instead of a proper object.

This results in an exception like NoMethodError: undefined method 'write' for #<String:0x00000007ae8bf0>

I'm not sure what the event objects need to implement in order to serialize well to JSON. Maybe include http://api.rubyonrails.org/classes/ActiveModel/Serializers/JSON.html ?

[jhilden]

As far as I can tell, the JSON serializer in rails 4.1+ simply cannot be used for serializing objects but only for primitves such as hashes, arrays, strings, etc.

So I guess the only possible solution would be to store the events using a hash representation in the session and then reinitialize the original event objects from those hashes.

[jhilden]

Fix was merged into master.

[jhilden]

This issue has been resolved by PR #16 but when this change is deployed there can be exceptions with old session data that still contains serialized objects instead of the new hashes.

NoMethodError: undefined method `except' for #<Rack::Tracker::GoogleAnalytics::Send category=...>

/ruby/2.1.0/bundler/gems/rack-tracker-2f0c5b612141/lib/rack/tracker/handler.rb:16 in "block in events"

How should we react to that? Just put a warning in the changelog? Build some migration code?

[jhilden]

This only happens if a users last request before the deployment was a redirect that stored the rack-tracker event in the session (as a serialized object) and the next request is after the deployment and excepts a serialized hash. All further requests are not affected. In our case it produced 2 exceptions after the deployment.

[kangguru]

¯_(ツ)_/¯

maybe advise users to change the session secret, so everything is invalidated

[jhilden]

wouldn't that be pretty drastic to invalidate thousands of sessions just to prevent 2 exceptions?