provide retrofit2.Response on retrofit2.Callback.onFailure (if error happened on "processing the response")

[cakcaraka]

What kind of issue is this?

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In my project, currently I'm using MoshiConverterFactory which returns JsonDataException when the payload returned from server is invalid (This one is expected), which triggers onFailure on retrofit2.Callback.onFailure (as stated in the docs https://github.com/square/retrofit/blob/master/retrofit/src/main/java/retrofit2/Callback.java#L43, this is an unexpected exception during 'processing the response')

Right now, I want to build some logging capability which logs an event every time JsonDataException happens, And i need to log some extra information that is returned from the response's header [returned by server, need to log these for cross-reference checking between logs]).

Reference that I have checked:

1. https://github.com/square/retrofit/blob/master/retrofit/src/main/java/retrofit2/OkHttpCall.java#L156, it doesn't propagate the rawResponse to callFailure
2. https://github.com/square/retrofit/blob/master/retrofit/src/main/java/retrofit2/OkHttpCall.java#L243, it only sends the rawBody instead of rawResponse so logging it inside a custom converter isn't possible as well.

Is it sensible to request a retrofit.Response instance on retrofit2.Callback.onFailure? Or is there any way I can achieve this?

[JakeWharton]

Unfortunately the callback can be invoked before a response is received if the transport fails sending the request or it fails while reading the response so it wasn't designed in a way where the response was available. Additionally, the response isn't given to the converter so there isn't a good way to provide such functionality through a converter wrapper.

I don't have a good way to do this off the top of my head.

[cakcaraka]

One workaround I can think of is to create a CallAdapter that expects Map<String, Any> instead of the actual ResponseModel, and then do the moshi conversion manually on the retrofit2.Callback.onResponse (do try..catch here).

I think this might work but the cons is it does double de-serialization (rawResponse -> Map<String, Any> -> ResponseModel), but I'm not sure the perf impact of doing this.

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Or is there a way for the CallAdapter to receive the RawResponse directly so no need to convert into an temporary Map<String,Any>?

[cakcaraka]

Okay..
Looks like I was able to do it by making changing CallAdapter<ResponseModel, T> to CallAdapter<ResponseBody,T>, and then convert it to ReponseModel manually on retrofit.Callback.onResponse by using moshi.adapter<ResponseModel>(returnType).fromJson(response.body.source()). (try catch here and log if it returns JsonDataException)..So far it works but I haven't done any benchmarks yet.

Do you think I'm heading into the right direction on achieving what I'm intended to? 🤔