[elm] add function to allow more fine grained error handling

[7omb]

This is a backwards compatible change. It adds the additional function sendWithCustomExpect to the provided helper functions in Api.elm to make requests.

It can be used to implement a more fine grained error handling as described here. Before it was e.g. not possible to access the response body if the server responded with an error like 404.

@eriktim

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[eriktim]

Thanks for your PR @7omb. Please see the note.

[eriktim]

Not sure I'm following why this takes a decoder to message function. Can you give me a basic example of what you would to with it?

[7omb]

The decoders in the signature are the ones provided by the Requests from Api/Request/Default.elm. To use sendWithCustomExpect one has to provide the logic to interpret the response body given the decoders.

My goal was make it possible to use a custom error type (the current send and sendWithCustomError both expect a Http.Error). A shortened example for String that e.g. accesses the body of a Http.BadStatus_ could e.g. look like this:

customSend : (Result String a -> msg) -> Api.Request a -> Cmd msg
customSend toMsg req =
    Api.sendWithCustomExpect (Http.expectStringResponse toMsg << decodeResponse) req


decodeResponse : Json.Decode.Decoder a -> Http.Response String -> Result String a
decodeResponse decoder response =
    case response of
        ...
        Http.BadStatus_ _ body ->
            Err body

        ...

Where decodeResponse goes from:

Json.Decode.Decoder a -> (Http.Response String -> Result String a)

and expectStringResponse toMsg from:

(Response String -> Result String a) -> Expect msg

[eriktim]

Ah yes, that makes sense to support. Thanks for clarifying!

[eriktim]

@wing328 is the failed build to be expected?

[wing328]

@eriktim thanks for reviewing the change. The circleci build failure can be ignore.

when you've time, can you please PM me via Slack? thanks

https://join.slack.com/t/openapi-generator/shared_invite/zt-12jxxd7p2-XUeQM~4pzsU9x~eGLQqX2g

[eriktim]

Thanks, @7omb!

[7omb]

Thank you for talking the time to review the PR @eriktim