Elm Json Decode - do nothing, get original string back

Question

I'm using the-sett/elm-aws-core to get information from the AWS API, which unfortunately is very very inconsistent. Most of the endpoints return JSON and that works fine with that lib, which takes a JSON Decoder to make a request, but the EC2 endpoint returns XML (because why not).

The lib doesn't have any options not to decode JSON as far as I can tell, which does not work at all :

let ec2 region = Service.defineRegional "ec2" "2016-11-15" Service.QUERY Service.SignV4 (Service.setXmlNamespace "https://ec2.amazonaws.com/doc/2016-11-15/") region in
let params = [("Action", "DescribeImages"), ("Version", "2016-11-15"), ("Owner.1", "self")] in
Http.request "DescribeImages" GET "/" Http.emptyBody JSONDECODERHERE |> Http.addQuery params |> Http.send (ec2 region) creds |> Task.attempt msg

Failed : Problem with the given value:

"



As you can see in there you need to pass a JSON Decoder to Http.request, but that, of course, fails when receiving XML. Is there a way to build a "fake" JSON decoder that would actually do nothing and just pass on the raw string? I tried using Decode. string but that's still actually decoding it, which fails. If there is a way I could then run an XML decoder manually on it in my update function, which would be fine.

Thank you

user_7943564 · Answer

It's not possible to make a "fake" decoder that does what you want, because the problem isn't with the decoding. The problem is with the parsing, which is done before decoding. Parsing is the process of converting the string into a data structure typically called an Abstract Syntax Tree (AST), but since Elm compiles to JavaScript and JSON is also a subset of JavaScript the parse result of is really just a JavaScript object. Decoding is the process of turning that untyped data structure into a properly typed data structure.

It is therefore not possible to accomplish what you want with this API. Most likely you'll need to build the http request yourself and use elm/http directly.

Elm Json Decode - do nothing, get original string back

1 Answers