How to check size of session in rails?

Question

I would expect session.size, session.length or session.count to work, but they all return "undefined method". Why, isn't session a hash?

That was curiosity. The actual question: is there a way to check the size of session in KB? Currently my sessions are stored in cookies and it has a 4 KB limit, and when it exceeds, it simply stops putting new data in there. It would be nice to know when in happens, to reset the session or remove old data.

Answer 1

Following is how rails get the session size:

Firstly, get the session data, see (gems/rack/lib/rack/session/abstract/id.rb:352 commit_session)

data = session.to_hash.delete_if { |k,v| v.nil? }

Then it will encrypt the data, see (gems/actionpack/lib/action_dispatch/middleware/cookies.rb:640):

data = @encryptor.encrypt_and_sign(serialize(name, data))

Lastly, get the bytes:

data.bytesize

You can directly get the session data but it's hard to encrypt it manually. I usually add a log at the gem code to check the data:

options[:value] = @encryptor.encrypt_and_sign(serialize(name, options[:value]))

puts options[:value].bytesize

raise CookieOverflow if options[:value].bytesize > MAX_COOKIE_SIZE