Append HTTP status to Poison encoded JSON before sending it out

Question

Is there a way to put HTTP status in a particular struct before it's encoded by Poison?

I guess the more general question would be can I access the conn at the level of my encoder's encode function? I am trying to build an API akin to what's specified here: http://jsonapi.org/examples/#error-objects

In my controller function, I have this, which transparently puts the HTTP status before the request is sent out the door. However, if some plug modifies the HTTP status down the pipeline whatever status I put during the create of ApiMessage also needs to be updated.

conn |> put_status(:forbidden) |> json(%ApiMessage{ status: 403, message: "Nope" })

This is the struct I want to encode:

defmodule MyApp.ApiMessage do
  @enforce_keys [:message]

  defstruct message: nil, success: false, status: 422
end

I want to use a custom encoder to put the HTTP status before the struct is encoded, something like this:

defimpl Poison.Encoder, for: [MyApp.ApiMessage] do
  def encode(t, _options) do
    # get conn here somehow and set the status to current
    # conn status
  end
end

Is this possible to do in Phoenix? I think I only need to figure out how to get the final conn in the encoder to get the status.