Main.kt

        service.loadDataWithoutAnyParsingAtAll()
                .flatMapObservable { responseBody ->
                    Observable.create<DataItem> { emitter ->
                        JsonReader(responseBody.charStream())
                                .use { reader ->
                                    while (reader.hasNext()) {
                                        if (reader.peek() == JsonToken.BEGIN_OBJECT) {
                                            reader.beginObject()
                                            if (reader.nextName() == "data") {
                                                reader.beginArray()
                                                while (reader.hasNext() && reader.peek() != JsonToken.END_ARRAY) {
                                                    emitter.onNext(Gson().fromJson<DataItem>(reader, DataItem::class.java))
                                                }
                                            }
                                        }
                                    }
                                    emitter.onComplete()
                                }
                    }
                }
                .count()
                .subscribe({ result ->
                    println("Size is: $result")
                }, { error -> error.printStackTrace() })