Elixir marshal ISO 8583 message error with Erlang library

Question

I am new to elixir and I need to create ISO 8583 client with this language and Phoenix framework. I found an Erlang library for it from stackoverflow thread here , compiled successfully and followed the example in the repository here but got error when marshaling the message. Here is my Elixir code to marshal the message:

msg1 = :erl8583_message.new()
msg2 = :erl8583_message.set_mti("0800", msg1)
msg3 = :erl8583_message.set(3, "300000", msg2)
msg4 = :erl8583_message.set(24, "045", msg3)
msg5 = :erl8583_message.set(41, "11111111", msg4)
msg6 = :erl8583_message.set(42, "222222222222222", msg5)
msg7 = :erl8583_message.set(63, "This is a Test Message", msg6)
marshalled = :erl8583_marshaller_ascii.marshal(msg7)

That's just an elixir version from the example on the repo. This is the error I've got when running the app:

[error] #PID<0.438.0> running TestlangIsoClientWeb.Endpoint (cowboy_protocol) terminated
Server: 127.0.0.1:4001 (http)
Request: POST /api/process
** (exit) an exception was raised:
    ** (FunctionClauseError) no function clause matching in :erl8583_marshaller_ascii.marshal_data_element/2
        (erl8583) /home/muhammad/Workspace/testlang/testlang_iso_client/deps/erl8583/src/erl8583_marshaller_ascii.erl:168: :erl8583_marshaller_ascii.marshal_data_element({:n, :fixed, 4}, "0800")
        (erl8583) /home/muhammad/Workspace/testlang/testlang_iso_client/deps/erl8583/src/erl8583_marshaller.erl:108: :erl8583_marshaller.marshal/2
        (testlang_iso_client) lib/testlang_iso_client_web/controllers/my_controller.ex:61: TestlangIsoClientWeb.MyController.process/2
        (testlang_iso_client) lib/testlang_iso_client_web/controllers/my_controller.ex:1: TestlangIsoClientWeb.MyController.action/2
        (testlang_iso_client) lib/testlang_iso_client_web/controllers/my_controller.ex:1: TestlangIsoClientWeb.MyController.phoenix_controller_pipeline/2
        (testlang_iso_client) lib/testlang_iso_client_web/endpoint.ex:1: TestlangIsoClientWeb.Endpoint.instrument/4
        (phoenix) lib/phoenix/router.ex:278: Phoenix.Router.__call__/1
        (testlang_iso_client) lib/testlang_iso_client_web/endpoint.ex:1: TestlangIsoClientWeb.Endpoint.plug_builder_call/2
        (testlang_iso_client) lib/testlang_iso_client_web/endpoint.ex:1: TestlangIsoClientWeb.Endpoint.call/2
        (plug) lib/plug/adapters/cowboy/handler.ex:16: Plug.Adapters.Cowboy.Handler.upgrade/4
        (cowboy) /home/muhammad/Workspace/testlang/testlang_iso_client/deps/cowboy/src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

Is there something I missed to make it work? Any help would be very appreciated.

Updated

I have tried to changed the string parameter to charlist, but still got the same error. Here is the code snippet:

def test(conn, _params) do
  IO.puts("Test")
  msg1 = :erl8583_message.new()
  msg2 = :erl8583_message.set_mti('0800', msg1)
  msg3 = :erl8583_message.set(3, '300000', msg2)
  msg4 = :erl8583_message.set(24, '045', msg3)
  msg5 = :erl8583_message.set(41, '11111111', msg4)
  msg6 = :erl8583_message.set(42, '222222222222222', msg5)
  msg7 = :erl8583_message.set(63, 'This is a Test Message', msg6)
  marshalled = :erl8583_marshaller_ascii.marshal(msg7)
  json(conn, %{status: "ok"})
end

Here is the function erl8583_marshaller.erl:108 mentioned in the stacktrace:

marshal(Message, MarshalHandlers) ->
    OptionsRecord = parse_options(MarshalHandlers, #marshal_options{}),
    {Marshalled1, Message1} = init_marshalling(OptionsRecord, Message),
    MarshalledMti = encode_mti(OptionsRecord, Message1),  % --- Line 108
    Marshalled2 = <<Marshalled1/binary, MarshalledMti/binary>>,
    {MarshalledBitmap, Message2} = encode_bitmap(OptionsRecord, Message1),
    Marshalled3 = <<Marshalled2/binary, MarshalledBitmap/binary>>,
    MarshalledFields = encode_fields(OptionsRecord, Message2),
    Marshalled4 = <<Marshalled3/binary, MarshalledFields/binary>>,
    end_marshalling(OptionsRecord, Message2, Marshalled4).

And here is the function erl8583_marshaller_ascii.erl:168 mentioned in the stacktrace:

%%
%% Local Functions
%%
marshal_data_element({n, llvar, Length}, FieldValue) when length(FieldValue) =< Length ->
    erl8583_convert:integer_to_string(length(FieldValue), 2) ++ FieldValue;

I don't understand why the call to that function was failed to match with parameters {:n, :fixed, 4}, "0800" that was sent from my function. I have tried to change the double quotes to single quotes with no success. Is there any other suggestions what am I supposed to do?

Answer 1

there may be a bug in the code. you can reference this issue here

there is one elixir library out which is relatively new.

its called ale8583 .

documentation is still coming out on this one but looks very promising.

you can check it out.

Answer 2

Try passing charlists instead of strings:

msg1 = :erl8583_message.new()
msg2 = :erl8583_message.set_mti('0800', msg1)
msg3 = :erl8583_message.set(3, '300000', msg2)
msg4 = :erl8583_message.set(24, '045', msg3)
msg5 = :erl8583_message.set(41, '11111111', msg4)
msg6 = :erl8583_message.set(42, '222222222222222', msg5)
msg7 = :erl8583_message.set(63, 'This is a Test Message', msg6)
marshalled = :erl8583_marshaller_ascii.marshal(msg7)

There is potential for confusion here:

• What Erlang calls "strings" and puts in double quotes ( "foo" ), Elixir calls "charlists" and puts in single quotes ( 'foo' ).
• What Elixir calls "strings" and puts in double quotes ( "foo" ), Erlang calls "binaries" and puts in double quotes plus angle brackets ( <<"foo">> ).

It seems like the erl8583 library expects Erlang strings throughout.