Using Erlang library with Elixir

Question

I'm having a small issue trying to use a Erlang library within an Elixir project. The library in question is the erl8583 for ISO-8583 message packing and unpacking.

I found a github repository for erl8583, and adjusted my mix.exs to the following:

defmodule Iso.Mixfile do
  use Mix.Project

  def project do
    [app: :iso,
     version: "0.0.1",
     elixir: "~> 1.0",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     deps: deps]
  end

  def application do
    [applications: [:logger]]
  end

  defp deps do
    [{:erl8583, github: "mgwidmann/erl8583"}]
  end
end

When I run mix deps.get and mix deps.compile, it runs smoothly.

Then, I try to start a IEx session with iex -S mix, and get the following error:

Unchecked dependencies for environment dev:
* erl8583 (git://github.com/mgwidmann/erl8583.git)
  could not find an app file at _build/dev/lib/erl8583/ebin/erl8583.app. This may happen if the dependency was not yet compiled, or you specified the wrong application name in your deps, or the dependency indeed has no            app file (then you can pass app: false as option)
** (Mix) Can't continue due to errors on dependencies

It says it could not find an app file at _build/dev/lib/erl8583/ebin/erl8583.app. As I understand, mix should have just grabbed that file from deps/erl8583/src and included there (that file exists, I checked).

I tried to manually copy the file from deps to _build but no success. What am I doing wrong?

Answer 1

The erl8583 application's source .app file is misnamed. A .app file normally lives in the ebin directory for an Erlang application; if it's a source file used to generate a .app file, it should be named .app.src instead. If you rename it, it will work, as my shell session below shows:

$ mix deps.get
* Getting erl8583 (https://github.com/mgwidmann/erl8583.git)
Cloning into '/private/tmp/m/deps/erl8583'...
remote: Counting objects: 3468, done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 3468 (delta 1), reused 0 (delta 0), pack-reused 3464
Receiving objects: 100% (3468/3468), 1002.71 KiB | 618.00 KiB/s, done.
Resolving deltas: 100% (2640/2640), done.
Checking connectivity... done.
$ mv ./deps/erl8583/src/erl8583.app ./deps/erl8583/src/erl8583.app.src
$ mix deps.compile
==> erl8583 (compile)
Compiled src/erl8583_message_helpers.erl
Compiled src/erl8583_message.erl
Compiled src/erl8583_marshaller_xml.erl
Compiled src/erl8583_marshaller_ebcdic.erl
Compiled src/erl8583_marshaller_json.erl
Compiled src/erl8583_marshaller_binary.erl
Compiled src/erl8583_marshaller_ascii.erl
Compiled src/erl8583_fields_2003.erl
Compiled src/erl8583_fields_1993.erl
Compiled src/erl8583_fields.erl
Compiled src/erl8583_marshaller.erl
src/erl8583_convert.erl:133: Warning: variable 'AsciiHex' is unused
src/erl8583_convert.erl:136: Warning: variable 'IntValue' is unused
Compiled src/erl8583_convert.erl
$ iex -S mix
Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:10] [hipe] [kernel-poll:false]

Generated iso app
Interactive Elixir (1.1.0-rc.0) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)>