Deserialize Protobuf list of objects

I started working on custom serializer since this: val protoSports = ProtoBuf.load(ProtoSports.serializer(), byteArrayRes) only works correctly on Android (iOS throws NotImplementedException due to lack of reflection).

ProtoSports has only one property: @SerialId(1) val sports: List<Sport>.

I’ve successfully deserialized ‘simpler’ objects with properties of type String, Long, etc. like this:

override fun deserialize(input: Decoder): Sport {
            val inp: CompositeDecoder = input.beginStructure(descriptor)
            var id: Long = 0
            lateinit var name: String
            loop@ while (true) {
                when (val i = inp.decodeElementIndex(descriptor)) {
                    CompositeDecoder.READ_DONE -> break@loop
                    0 -> id = inp.decodeLongElement(descriptor, i)
                    1 -> name = inp.decodeStringElement(descriptor, i)
                    else -> throw SerializationException("Unknown index $i")
                }
            }
            inp.endStructure(descriptor)
            return Sport(id, name)
        }

My question is, how can I deserialize list of objects e.g. Sport? I’ve tried like this, but it doesn’t work:

loop@ while (true) {
    when (val i = inp.decodeElementIndex(descriptor)) {
    0 -> {
        val sport = inp.decodeSerializableElement(descriptor, i, Sport.serializer())
        sports = sports.plus(sport)
    }
}

Thanks!

[sandwwraith]

I’ve finally figured this problem out, and it is not related to bytebuffer.

In the Native serialization plugin, there is no support for @SerialInfo annotations in the 1.3.11 versions, therefore protobuf ids were auto-assigned using property index: https://github.com/Kotlin/kotlinx.serialization/blob/master/runtime/native/src/main/kotlin/kotlinx/serialization/protobuf/ProtobufPlatform.kt#L22

Unfortunately, properties are enumerated from 0 and 0 is not a valid protobuf id, therefore externally produced bytes can’t be correctly parsed (fun fact, if bytes were produced by kotlinx.serialization itself, parser does not complain).

1.3.20 will have support for custom annotations on Native, and this problem is fixed in dev: https://github.com/Kotlin/kotlinx.serialization/commit/e62e23b559b4943d2b61a13b1ceaea939937ff4e

[sandwwraith]

This is also included in stable 0.10.0 release, which would be eventually compatible with all other libraries