Retrofit2 handling HTTP 204 (No Content response ) situation with RxJava's Observable concepts

Question

I have a web-service which return a list of users for a topic, if there is no any user for that topic it just returns HTTP code 204( No Content).

This is my retrofit2 call for that service (in Kotlin)

@GET("/user/{topic}")
fun getAllUserFor(@Path(value="topic",encoded=true) topic:String) :Observable<List<User>>

And my execution is :

fun getAllUsers(topic: String, onSuccess: Consumer<List<User>>, onFail:Consumer<Throwable>){

    val api = NetworkLayer.getUserApi()

    api.getAllUserFor(topic)
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeOn(Schedulers.io())
            .subscribe(onSuccess,onFail)

}

Works fine except when there is no users for the topic, because when there is no users server respond with code 204 which received as an exception.

I'm using ScalarsConverterFactory & GsonConverterFactory to parse the Json response with Retrofit2.

similar issue discussed here but their server responds only with http code without any content! In my case server will return a user list as a Json body when there is one or more users & response with 204 when there is no users, So I need to handle both cases along with other usual http errors.

Answer 1

Standard way is wrapping the response in a Result that comes with adapter-rxjava2 dependency.

        @GET("/user/{topic}")
        fun getAllUserFor(@Path(value="topic",encoded=true) topic:String) :Observable<Result<List<User>>>

this way errors too are delivered to your onNext and you can do something like this:

           api.getAllUserFor(topic)
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeOn(Schedulers.io())
            .subscribe{ result ->
               if(result.isError)
                   //Network Error
               result.response()?.also {
                   if(result.isSuccessful)
                       //Success
                   else{
                       //api error
                   }
            }
          }

much cleaner and more concise

check for status with

result.response?.code()

cheers!

Answer 2

You can achieve that by implementing an operator that will check whether the status code of the received response is 204:

class OnApiErrorOperator : ObservableOperator<OnApiErrorOperator.User, Response<OnApiErrorOperator.User>> {

    override fun apply(observer: Observer<in OnApiErrorOperator.User>): Observer<in Response<OnApiErrorOperator.User>> {
        return object : Observer<Response<OnApiErrorOperator.User>> {

            override fun onSubscribe(d: Disposable) {
                observer.onSubscribe(d)
            }

            override fun onNext(response: Response<OnApiErrorOperator.User>) {
                if (response.code() == 204) {
                    //return User object with empty list when response's status code is 204
                    observer.onNext(User(emptyList()))
                } else {
                    if (response.isSuccessful) {
                        observer.onNext(response.body()!!)
                    } else {
                        //don't forget to check for other statuses
                        observer.onError(OnApiServerErrorException(response.code()))
                    }
                }
            }

            override fun onError(e: Throwable) {
                observer.onError(e)
            }

            override fun onComplete() {
                observer.onComplete()
            }
        }
    }

    class User(
            @SerializedName("user_info")
            val userInfo: List<String>
    )

    class OnApiServerErrorException(val statusCode: Int) : Exception()
}

And then you can add operator lift in your observables chain to call it:

api.getAllUserFor(topic)
        .subscribeOn(Schedulers.io())
        .lift(OnApiErrorOperator())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(onSuccess, onFail)