Scalapb: Akka ProtobufSerializer does not play nicely with nested generated classes

[zhangandyx]

Relates to #27

When using a nested message, Java reflection fails to see the parseFrom method but has no trouble with toByteArray.

[zhangandyx]

Reproduction steps

Created a nested message

message OuterMessage {
    message InnerMessage {
        string hiField = 1;
    }
    string helloField = 1;
   ...
}

Try to send just the inner message in a remote actor setting, i.e. through the PubSubMediator to a remote actor

mediator ! Publish(InnerMessage("hello"))

Using these settings:

actor {
    provider = "akka.cluster.ClusterActorRefProvider"
    serializers {
      proto = "akka.remote.serialization.ProtobufSerializer"
    }

    serialization-bindings {
      "com.trueaccord.scalapb.GeneratedMessage" = proto
    }
  }

The serializer throws an NoSuchMethodException from not being able to find the parseFrom method. This is coming from this line -> akka.remote.serialization.ProtobufSerializer.scalaLL69:

                if (method eq null) clazz.getDeclaredMethod("parseFrom", ProtobufSerializer.ARRAY_OF_BYTE_ARRAY: _*)

[eiennohito]

@nadavsr will decide, but I think that compatibility with akka's default protobuf serializer is out of scope of ScalaPB. Its messages even does not implement protobuf's message interface.

[zhangandyx]

Gotcha. Yes, from what I can tell, the issue is on the akka protobuf side. The nested class that is generated by ScalaPB looks consistent.

[thesamet]

The culprit is that from some reason the scala compiler does not generate static methods for methods defined in a companion object of a nested class (but does so for companion objects of top level classes). This is why parseFrom isn't found.

I wrote a quick implementation Akka serializer that works with ScalaPB. Can you give it a try?

https://gist.github.com/thesamet/5d0349b40d3dc92859a1a2eafba448d5

[zhangandyx]

Thanks for sending, very helpful!