json encoder error for List[String] parameter

[danielkirch]

Hello,

thanks for developing maru and maru_swagger.
I am currently trying to add a swagger documentation for my maru web service and I am struggling with the following error:

16:28:05.906 [error] #PID<0.488.0> running MaruSwaggerTest.Api (connection #PID<0.487.0>, stream id 1) terminated
Server: 0.0.0.0:3456 (http)
Request: GET /swagger
** (exit) an exception was raised:
    ** (Protocol.UndefinedError) protocol Jason.Encoder not implemented for {:list, "string"} of type Tuple, Jason.Encoder protocol must always be explicitly implemented. This protocol is implemented for the following type(s): Date, BitString, Jason.Fragment, Any, Map, NaiveDateTime, List, Integer, Time, DateTime, Decimal, Atom, Float
        (jason) lib/jason.ex:150: Jason.encode!/2
        (maru_swagger) lib/maru_swagger/plug.ex:12: MaruSwagger.Plug.call/2
        (maru_compile) lib/api.ex:1: anonymous fn/1 in MaruSwaggerTest.Api.call/2
        (plug_cowboy) lib/plug/cowboy/handler.ex:12: Plug.Cowboy.Handler.init/2
        (cowboy) deps/cowboy/src/cowboy_handler.erl:37: :cowboy_handler.execute/2
        (cowboy) deps/cowboy/src/cowboy_stream_h.erl:300: :cowboy_stream_h.execute/3
        (cowboy) deps/cowboy/src/cowboy_stream_h.erl:291: :cowboy_stream_h.request_process/3
        (stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3

Apparently, Swagger is trying to encode the tuple {:list, "string"} into a json and that does not work. My api file looks like this:

defmodule MaruSwaggerTest.Api do
  use MaruSwaggerTest.Server
  use MaruSwagger

  plug Plug.Logger

  swagger(
    at: "/swagger",
    pretty: true,
  
    swagger_inject: [
      host: "myapp",
      basePath: "/api",
      schemes:  [ "https" ],
      consumes: [ "application/json" ],
      produces: [ "application/json" ]
    ])

  params do
    optional :foo, type: List[String]
  end
  get "/" do
    IO.inspect(params[:foo])

    conn
    |> send_resp(200, "hello world")
    |> halt()
  end
end

The error occurs at runtime when I call the /swagger endpoint.
Is this a bug or am I missing something here?
What would be a possible workaround?

[danielkirch]

Hello again,

I think the issue is that List[String] is not supported as a parameter type for get requests as of now. I created a pull request where I try to address this issue.