Use HTTPoison to initialize a module attribute

Question

I am trying to do initialize a module attribute like this

  response = HTTPoison.get! url
  {:ok, response} = Poison.decode(response.body)
  @attr response

I have done it before with a file, something like this:

  @external_resource file = Path.join([__DIR__, "file.txt"])
  Module.register_attribute __MODULE__, :attr, accumulate: true

  for line <- File.stream!(file, [], :line) do
    @attr line
    ...

Is not possible to do the same with HTTPoison and fetching the response of an API? I am receiving this error:

== Compilation error in file lib/module.ex ==
** (ArgumentError) argument error
    (stdlib) :ets.lookup_element(:hackney_config, :mod_metrics, 2)
    /project/deps/hackney/src/hackney_metrics.erl:27: :hackney_metrics.get_engine/0
    /project/deps/hackney/src/hackney_connect.erl:69: :hackney_connect.create_connection/5
    /project/deps/hackney/src/hackney_connect.erl:37: :hackney_connect.connect/5
    /project/deps/hackney/src/hackney.erl:316: :hackney.request/5
    lib/httpoison/base.ex:630: HTTPoison.Base.request/9
    lib/httpoison.ex:66: HTTPoison.request!/5
    lib/module.ex:4: (module)

Try putting `HTTPoison.start()` above `response =`. – Dogbert Jun 19 '18 at 15:02 — Dogbert, Jun 19 '18 at 15:02

score 5 · Accepted Answer · answered Jun 19 '18 at 15:28

5

The dependent applications are not started automatically at compile time. You need to explicitly start HTTPoison before using it:

HTTPoison.start()
response = HTTPoison.get! url
{:ok, response} = Poison.decode(response.body)
@attr response

answered Jun 19 '18 at 15:28

Dogbert

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Could HTTPoison.start() be added on the mix.exs file instead in the module? – lapinkoira Jun 20 '18 at 14:58
I mean, I added it to applications: [:httpoison] and tried also with extra_applications but didnt work, is to avoid having to explicitly call it on the module – lapinkoira Jun 21 '18 at 07:41
I don't think there is. I see you posted a new question about that. Let's see if someone else can give a definitive answer. – Dogbert Jun 21 '18 at 13:27
1

I am afraid is not possible, from elixir forum: "Applications listed in extra_applications are still started at start up time, not at compile-time. If you need to use HTTPoison at compile-time, you need to start it at compile time manually." – lapinkoira Jun 21 '18 at 13:41

Use HTTPoison to initialize a module attribute

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