Issues with decoding rails 3.2 cookie - only string ivars are supported

[simonbowen]

I'm trying to use ExMarshal to decode the contents of a cookie set by rails. This is the ruby structure that is stored in the cookie in a marshal format.

{"session_id"=>"c0a56012635b795b0f6bd6a522fe3fae",
 "after_sign_up_redirect_to"=>"/",
 "after_sign_in_redirect_to"=>"/",
 "omniauth.is_abode"=>false,
 "warden.user.user.key"=>[[70989], "$2a$10$D4Msl4T4JHfkFOQHi0fKTe"],
 "warden.user.user.session"=>{"last_request_at"=>2017-02-22 20:44:16 UTC},
 "foo"=>"bar",
 "_csrf_token"=>"QUBPx+eyL2deFkAo3pA+xxMZmVso7hfLutVJlJoT8kg="}

The base64 of the Marshal object looks like..

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

I'm then decoding this on the Elixir end with

iex> {:ok, r} = Base.decode64("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")
iex> ExMarshal.decode(r)

However I get this error

** (ExMarshal.DecodeError) only string ivars are supported: <<58, 9, 84, 105, 109, 101, 13, 212, 70, 29, 192, 218, 152, 12, 177, 6, 58, 9, 122, 111, 110, 101, 73, 34, 8, 85, 84, 67, 6, 59, 0, 70, 73, 34, 8, 102, 111, 111, 6, 59, 0, 70, 73, 34, 8, 98, 97, 114, 6, 59, ...>>                                                                                       lib/ex_marshal/decoder.ex:109: ExMarshal.Decoder.decode_ivar/2
                         lib/ex_marshal/decoder.ex:248: ExMarshal.Decoder.decode_hash/4
                         lib/ex_marshal/decoder.ex:4: ExMarshal.Decoder.decode/1
                (stdlib) erl_eval.erl:670: :erl_eval.do_apply/6
                   (iex) lib/iex/evaluator.ex:182: IEx.Evaluator.handle_eval/6
                   (iex) lib/iex/evaluator.ex:175: IEx.Evaluator.do_eval/4
                   (iex) lib/iex/evaluator.ex:155: IEx.Evaluator.eval/4
                   (iex) lib/iex/evaluator.ex:61: IEx.Evaluator.loop/3
                   (iex) lib/iex/evaluator.ex:21: IEx.Evaluator.init/4
                   (iex) lib/iex.ex:471: IEx.pry/3
    (infabode_analytics) web/controllers/dashboard_controller.ex:9: InfabodeAnalytics.DashboardController.index/2
    (infabode_analytics) web/controllers/dashboard_controller.ex:1: InfabodeAnalytics.DashboardController.action/2
    (infabode_analytics) web/controllers/dashboard_controller.ex:1: InfabodeAnalytics.DashboardController.phoenix_controller_pipeline/2
    (infabode_analytics) lib/infabode_analytics/endpoint.ex:1: InfabodeAnalytics.Endpoint.instrument/4
    (infabode_analytics) lib/phoenix/router.ex:261: InfabodeAnalytics.Router.dispatch/2
    (infabode_analytics) web/router.ex:1: InfabodeAnalytics.Router.do_call/2
    (infabode_analytics) lib/infabode_analytics/endpoint.ex:1: InfabodeAnalytics.Endpoint.phoenix_pipeline/1
    (infabode_analytics) lib/plug/debugger.ex:123: InfabodeAnalytics.Endpoint."call (overridable 3)"/2

I'm at a bit of loss since I've been manually creating objects in the ruby console encoding them with marshal and then base64 encoding it. Copying the base64 string across to the Elixir console, base64 decoding and decoding with ExMarshal and it works.

Is there something in my cookie structure that is causing ExMarshal to throw this error?

[simonbowen]

Duh, it's because my marshal serialization has a date type in, I didn't fully read the docs and see that this isn't supported by ExMarshal.