Using Alembic.Document.from_json in a Phoenix controller

api_controller.ex

defmodule MyApp.ApiController do
  alias Alembic.Document
  alias Alembic.Source
  alias Plug.Conn
  
  @doc """
  Convert the `params` to a JSON API Document with `action` set as the `meta` `"action"`.  If there a parsing
  error, the error document is rendered as json to `conn` and the modified `conn` is returned.  If there is no parsing
  error then `{:ok, document}` is returned.
  """
  @spec document_from_json(Conn.t, map, action :: atom) :: {:ok, Document.t} | Conn.t
  def document_from_json(conn, params, action) do
    with {:error, document} <- Document.from_json(
                                 params,
                                 %Alembic.Error{
                                   meta: %{
                                     "action" => action,
                                     "sender" => :client
                                   },
                                   source: %Source{
                                     pointer: ""
                                   }
                                 }
                               )  do
      render_json(conn, document, :unprocessable_entity)
    end
  end