So the conversion to a sealed error hierarchy is solved for me.

What I want to do though, is also to emit a side effect when

IOException

is received.

And I don't want to do it in the existing

CallAdapter

(because I get it from the library and I don't want to fork it). I want to add another adapter just for this case (or something like this). I guess your library cannot really support me in emitting this side effect, right?

My question is "How do I create a

CallAdapter

which just passes the request completely unchanged and only emits a side effect under some condition?"

I.e. so that the UI is notified from a central point (and not specifically at the API call site) that an

IOException

has occurred. Currently we have in every Presenter/ViewModel the check for this:

apiService.getSomeData().fold(
    ifLeft = { if(it is IOError) showConnectionLost() },
    ifRight = { /* success case */ }
)

(left/right are error/success cases in Arrow Either type). And it's very repetitive to check every time if the error is

IOError

.

The example you linked is already in the Adapter I'm using.

It works.

Yes, I tried creating another adapter but I cannot get it to work 😞

Probably I'm doing something wrong because Moshi tries to parse the result of the second adapter...

I will link the code I'm trying to write here tomorrow (it's already night here in Germany).

Basically I want this other adapter to just pass the call through unchanged, only emitting the side effect when the result is of specific type. But it returns a

Call<T>

and then Moshi tries to parse it.

You're returning the full type instead of unwrapping the body type

Are you returning delegate.responseType() from your response type function?

I unwrapped the body type by means of

getParameterUpperBound(0, returnType)

. I still get the error for not having a converter, although now for the unwrapped type:

java.lang.IllegalArgumentException: Unable to create converter for arrow.core.Either<? extends arrow.retrofit.adapter.either.networkhandling.CallError, de.myapp.gatewayapi.data.remote.air.model.ControlDeviceList>

I suspect the problem is that I now have registered two call adapter factories:

Retrofit.Builder()
                .baseUrl(baseUrl)
                .client(client)
                .addCallAdapterFactory(IOExceptionCallAdapterFactory())
                .addCallAdapterFactory(EitherCallAdapterFactory())
                .addConverterFactory(MoshiConverterFactory.create(moshiForKotlin))
                .build()
                .create(AirConnectorApi::class.java)

The first one,

IOExceptionCallAdapterFactory

, creates the pass-through adapter, which should not modify the call in any way but only look if there was an

IOException

and emit a side effect for the UI. The second one,

EitherCallAdapterFactory

, creates the actual adapter which type-safely wraps success results in

Either.Right

and failures or exceptions in

Either.Left

. That means that I want to skip the converter created by

MoshiConverterFactory

after the first adapter and only call it after both of the adapters have run. Only then can the response body actually be deserialized. Is it possible to configure Retrofit to only call the converter after all adapters have run?

Yes, when I reverse the adapters the app doesn't crash.

But the

println

which I put into `onResponse()`/`onFailure()` inside of

IOExceptionCall.enqueque()

(

IOExceptionCall

is returned by the pass-through adapter) doesn't register in logs... Looks like the second adapter is not being called at all.