Active active journal support changes (#29421)

* Add missing serializers (and rename classes because metadata is a word)
* Add test instances for journal and snapshot support
* Method to add metadata to existing snapshotmetadata
* Better error message if replicated stream does not have metadata
* Snapshot store tck support for metadata
* Docs for tck coverage of AA metadata

akka-docs/src/main/paradox/typed/persistence-active-active.md

@@ -290,7 +290,9 @@ to fast forward the stream of events for the origin replica. (With additional po
 ## Journal Support
 
 For a journal plugin to support active active it needs to store and read metadata for each event if it is defined in the @apiref[PersistentRepr]
- `metadata` field. To attach the metadata after writing it, `PersistentRepr.withMetadata` is used.
+ `metadata` field. To attach the metadata after writing it, `PersistentRepr.withMetadata` is used. The @apidoc[JournalSpec] in the Persistence TCK provides 
+ a capability flag `supportsMetadata` to toggle verification that metadata is handled correctly.
  
 For a snapshot plugin to support active active it needs to store and read metadata for the snapshot if it is defined in the @apiref[akka.persistence.SnapshotMetadata] `metadata` field. 
-To attach the metadata when reading the snapshot the `akka.persistence.SnapshotMetadata.apply` factory overload taking a `metadata` parameter is used.
+To attach the metadata when reading the snapshot the `akka.persistence.SnapshotMetadata.apply` factory overload taking a `metadata` parameter is used.
+The @apidoc[SnapshotStoreSpec] in the Persistence TCK provides a capability flag `supportsMetadata` to toggle verification that metadata is handled correctly.

akka-persistence-tck/src/main/scala/akka/persistence/CapabilityFlags.scala

@@ -69,5 +69,11 @@ trait SnapshotStoreCapabilityFlags extends CapabilityFlags {
    * deserialize snapshots.
    */
   protected def supportsSerialization: CapabilityFlag
+
+  /**
+   * When `true` enables tests which check if the snapshot store properly stores and
+   * loads metadata (needed for Active Active) along with the snapshots
+   */
+  protected def supportsMetadata: CapabilityFlag
 }
 //#snapshot-store-flags

akka-persistence-tck/src/main/scala/akka/persistence/journal/JournalSpec.scala

@@ -323,7 +323,7 @@ abstract class JournalSpec(config: Config)
           AtomicWrite(
             PersistentRepr(
               payload = event,
-              sequenceNr = 1L,
+              sequenceNr = 6L,
               persistenceId = pid,
               sender = Actor.noSender,
               writerUuid = writerUuid).withMetadata(meta))
@@ -335,7 +335,7 @@ abstract class JournalSpec(config: Config)
         val WriterUuid = writerUuid
         probe.expectMsgPF() {
           case WriteMessageSuccess(
-              PersistentImpl(payload, 1L, Pid, _, _, Actor.noSender, WriterUuid, _, Some(`meta`)),
+              PersistentImpl(payload, 6L, Pid, _, _, Actor.noSender, WriterUuid, _, Some(`meta`)),
               _) =>
             payload should be(event)
         }

akka-persistence-tck/src/main/scala/akka/persistence/snapshot/SnapshotStoreSpec.scala

@@ -52,6 +52,7 @@ abstract class SnapshotStoreSpec(config: Config)
   private var metadata: Seq[SnapshotMetadata] = Nil
 
   override protected def supportsSerialization: CapabilityFlag = true
+  override protected def supportsMetadata: CapabilityFlag = false
 
   override protected def beforeEach(): Unit = {
     super.beforeEach()
@@ -199,5 +200,27 @@ abstract class SnapshotStoreSpec(config: Config)
         }
       }
     }
+    optional(flag = supportsMetadata) {
+      "store metadata" in {
+        // we do not have the actual ReplicatedSnapshot metadata on classpath, but since
+        // the plugin should defer to serialization defined by Akka, so in general the type
+        // should not really be important to the plugin
+        val fictionalMeta = "fictional metadata"
+        val metadata = SnapshotMetadata(pid, 100).withMetadata(fictionalMeta)
+        val snap = "snap"
+        snapshotStore.tell(SaveSnapshot(metadata, snap), senderProbe.ref)
+        senderProbe.expectMsgPF() { case SaveSnapshotSuccess(md) => md }
+
+        val Pid = pid
+        snapshotStore.tell(LoadSnapshot(pid, SnapshotSelectionCriteria.Latest, Long.MaxValue), senderProbe.ref)
+        senderProbe.expectMsgPF() {
+          case LoadSnapshotResult(
+              Some(SelectedSnapshot(meta @ SnapshotMetadata(Pid, 100, _), payload)),
+              Long.MaxValue) =>
+            payload should be(snap)
+            meta.metadata should ===(Some(fictionalMeta))
+        }
+      }
+    }
   }
 }

akka-persistence-typed/src/main/protobuf/ActiveActive.proto

@@ -48,3 +48,19 @@ message VersionVector {
   }
   repeated Entry entries = 1;
 }
+
+message ReplicatedEventMetadata {
+  required string originReplica = 1;
+  required int64 originSequenceNr = 2;
+  required VersionVector versionVector = 3;
+  required bool concurrent = 4;
+}
+
+message ReplicatedSnapshotMetadata {
+  message Seen {
+    required string replicaId = 1;
+    required int64 sequenceNr = 2;
+  }
+  required VersionVector version = 1;
+  repeated Seen seenPerReplica = 2;
+}

akka-persistence-typed/src/main/resources/reference.conf

@@ -1,15 +1,17 @@
 akka.actor {
 
-  serialization-identifiers."akka.persistence.typed.serialization.CrdtSerializer" = 40
+  serialization-identifiers."akka.persistence.typed.serialization.ActiveActiveSerializer" = 40
 
-  serializers.replicated-crdts = "akka.persistence.typed.serialization.CrdtSerializer"
+  serializers.active-active = "akka.persistence.typed.serialization.ActiveActiveSerializer"
 
   serialization-bindings {
-    "akka.persistence.typed.crdt.Counter" = replicated-crdts
+    "akka.persistence.typed.internal.VersionVector" = active-active
-    "akka.persistence.typed.crdt.Counter$Updated" = replicated-crdts
+    "akka.persistence.typed.crdt.Counter" = active-active
-    "akka.persistence.typed.internal.VersionVector" = replicated-crdts
+    "akka.persistence.typed.crdt.Counter$Updated" = active-active
-    "akka.persistence.typed.crdt.ORSet" = replicated-crdts
+    "akka.persistence.typed.crdt.ORSet" = active-active
-    "akka.persistence.typed.crdt.ORSet$DeltaOp" = replicated-crdts
+    "akka.persistence.typed.crdt.ORSet$DeltaOp" = active-active
+    "akka.persistence.typed.internal.ReplicatedEventMetadata" = active-active
+    "akka.persistence.typed.internal.ReplicatedSnapshotMetadata" = active-active
   }
 }
 

akka-persistence-typed/src/main/scala/akka/persistence/typed/internal/EventSourcedBehaviorImpl.scala

@@ -271,7 +271,16 @@ private[akka] final case class EventSourcedBehaviorImpl[Command, Event, State](
 
 }
 
-// FIXME serializer
+object ReplicatedEventMetadata {
+
+  /**
+   * For a journal supporting active active needing to add test coverage, use this instance as metadata and defer
+   * to the built in serializer for serialization format
+   */
+  @ApiMayChange
+  def instanceForJournalTest: Any = ReplicatedEventMetadata(ReplicaId("DC-A"), 1L, VersionVector.empty + "DC-A", true)
+}
+
 /**
  * @param originReplica Where the event originally was created
  * @param originSequenceNr The original sequenceNr in the origin DC
@@ -279,15 +288,28 @@ private[akka] final case class EventSourcedBehaviorImpl[Command, Event, State](
  *                at each location as they are received at different times
  */
 @InternalApi
-private[akka] final case class ReplicatedEventMetaData(
+private[akka] final case class ReplicatedEventMetadata(
     originReplica: ReplicaId,
     originSequenceNr: Long,
     version: VersionVector,
     concurrent: Boolean) // whether when the event handler was executed the event was concurrent
 
-// FIXME serializer
+object ReplicatedSnapshotMetadata {
+
+  /**
+   * For a snapshot store supporting active active needing to add test coverage, use this instance as metadata and defer
+   * to the built in serializer for serialization format
+   */
+  @ApiMayChange
+  def instanceForSnapshotStoreTest: Any =
+    ReplicatedSnapshotMetadata(
+      VersionVector.empty + "DC-B" + "DC-A",
+      Map(ReplicaId("DC-A") -> 1L, ReplicaId("DC-B") -> 1L))
+
+}
+
 @InternalApi
-private[akka] final case class ReplicatedSnapshotMetaData(version: VersionVector, seenPerReplica: Map[ReplicaId, Long])
+private[akka] final case class ReplicatedSnapshotMetadata(version: VersionVector, seenPerReplica: Map[ReplicaId, Long])
 
 /**
  * An event replicated from a different replica.

akka-persistence-typed/src/main/scala/akka/persistence/typed/internal/ExternalInteractions.scala

@@ -29,7 +29,7 @@ private[akka] object JournalInteractions {
   final case class EventToPersist(
       adaptedEvent: EventOrTaggedOrReplicated,
       manifest: String,
-      metadata: Option[ReplicatedEventMetaData])
+      metadata: Option[ReplicatedEventMetadata])
 
 }
 
@@ -193,7 +193,7 @@ private[akka] trait SnapshotInteractions[C, E, S] {
     else {
       val meta = setup.activeActive match {
         case Some(_) =>
-          val m = ReplicatedSnapshotMetaData(state.version, state.seenPerReplica)
+          val m = ReplicatedSnapshotMetadata(state.version, state.seenPerReplica)
           Some(m)
         case None => None
       }

akka-persistence-typed/src/main/scala/akka/persistence/typed/internal/ReplayingEvents.scala

@@ -123,11 +123,11 @@ private[akka] final class ReplayingEvents[C, E, S](
               eventForErrorReporting = OptionVal.Some(event)
               state = state.copy(seqNr = repr.sequenceNr)
 
-              val aaMetaAndSelfReplica: Option[(ReplicatedEventMetaData, ReplicaId, ActiveActive)] =
+              val aaMetaAndSelfReplica: Option[(ReplicatedEventMetadata, ReplicaId, ActiveActive)] =
                 setup.activeActive match {
                   case Some(aa) =>
                     val meta = repr.metadata match {
-                      case Some(m) => m.asInstanceOf[ReplicatedEventMetaData]
+                      case Some(m) => m.asInstanceOf[ReplicatedEventMetadata]
                       case None =>
                         throw new IllegalStateException(
                           s"Active active enabled but existing event has no metadata. Migration isn't supported yet.")

akka-persistence-typed/src/main/scala/akka/persistence/typed/internal/ReplayingSnapshot.scala

@@ -152,7 +152,7 @@ private[akka] class ReplayingSnapshot[C, E, S](override val setup: BehaviorSetup
             state = setup.snapshotAdapter.fromJournal(snapshot)
             setup.context.log.debug("Loaded snapshot with metadata {}", metadata)
             metadata.metadata match {
-              case Some(rm: ReplicatedSnapshotMetaData) => (metadata.sequenceNr, rm.seenPerReplica, rm.version)
+              case Some(rm: ReplicatedSnapshotMetadata) => (metadata.sequenceNr, rm.seenPerReplica, rm.version)
               case _                                    => (metadata.sequenceNr, Map.empty.withDefaultValue(0L), VersionVector.empty)
             }
           case None => (0L, Map.empty.withDefaultValue(0L), VersionVector.empty)

akka-persistence-typed/src/main/scala/akka/persistence/typed/internal/Running.scala

@@ -144,7 +144,16 @@ private[akka] object Running {
               .eventsByPersistenceId(pid.id, seqNr + 1, Long.MaxValue)
               // from each replica, only get the events that originated there, this prevents most of the event filtering
               // the downside is that events can't be received via other replicas in the event of an uneven network partition
-              .filter(_.eventMetadata.get.asInstanceOf[ReplicatedEventMetaData].originReplica == replicaId)
+              .filter(event =>
+                event.eventMetadata match {
+                  case Some(replicatedMeta: ReplicatedEventMetadata) => replicatedMeta.originReplica == replicaId
+                  case _ =>
+                    throw new IllegalArgumentException(
+                      s"Replication stream from replica ${replicaId} for ${setup.persistenceId} contains event " +
+                      s"(sequence nr ${event.sequenceNr}) without replication metadata. " +
+                      s"Is the persistence id used by a regular event sourced actor there or the journal for that replica (${queryPluginId}) " +
+                      "used that does not support active active?")
+                })
               .viaMat(new FastForwardingFilter)(Keep.right)
               .mapMaterializedValue(streamControl => controlRef.set(streamControl))
           }
@@ -152,7 +161,7 @@ private[akka] object Running {
           .via(ActorFlow
             .ask[EventEnvelope, ReplicatedEventEnvelope[E], ReplicatedEventAck.type](ref) { (eventEnvelope, replyTo) =>
               // Need to handle this not being available migration from non-active-active is supported
-              val meta = eventEnvelope.eventMetadata.get.asInstanceOf[ReplicatedEventMetaData]
+              val meta = eventEnvelope.eventMetadata.get.asInstanceOf[ReplicatedEventMetadata]
               val re =
                 ReplicatedEvent[E](
                   eventEnvelope.event.asInstanceOf[E],
@@ -412,7 +421,7 @@ private[akka] object Running {
         event.event,
         "",
         OptionVal.Some(
-          ReplicatedEventMetaData(event.originReplica, event.originSequenceNr, updatedVersion, isConcurrent)))
+          ReplicatedEventMetadata(event.originReplica, event.originSequenceNr, updatedVersion, isConcurrent)))
       val shouldSnapshotAfterPersist = setup.shouldSnapshot(newState2.state, event.event, newState2.seqNr)
       // FIXME validate this is the correct sequence nr from that replica https://github.com/akka/akka/issues/29259
       val updatedSeen = newState2.seenPerReplica.updated(event.originReplica, event.originSequenceNr)
@@ -457,7 +466,7 @@ private[akka] object Running {
             eventToPersist,
             eventAdapterManifest,
             OptionVal.Some(
-              ReplicatedEventMetaData(aa.replicaId, _currentSequenceNumber, updatedVersion, concurrent = false)))
+              ReplicatedEventMetadata(aa.replicaId, _currentSequenceNumber, updatedVersion, concurrent = false)))
             .copy(version = updatedVersion)
 
           if (setup.log.isTraceEnabled())
@@ -485,10 +494,10 @@ private[akka] object Running {
         // also, ensure that there is an event handler for each single event
         _currentSequenceNumber = state.seqNr
 
-        val metadataTemplate: Option[ReplicatedEventMetaData] = setup.activeActive match {
+        val metadataTemplate: Option[ReplicatedEventMetadata] = setup.activeActive match {
           case Some(aa) =>
             aa.setContext(recoveryRunning = false, aa.replicaId, concurrent = false) // local events are never concurrent
-            Some(ReplicatedEventMetaData(aa.replicaId, 0L, state.version, concurrent = false)) // we replace it with actual seqnr later
+            Some(ReplicatedEventMetadata(aa.replicaId, 0L, state.version, concurrent = false)) // we replace it with actual seqnr later
           case None => None
         }
 

akka-persistence-typed/src/main/scala/akka/persistence/typed/serialization/ActiveActiveSerializer.scala

@@ -10,7 +10,10 @@ import java.{ lang => jl }
 
 import akka.actor.ExtendedActorSystem
 import akka.annotation.InternalApi
+import akka.persistence.typed.ReplicaId
 import akka.persistence.typed.crdt.{ Counter, ORSet }
+import akka.persistence.typed.internal.ReplicatedEventMetadata
+import akka.persistence.typed.internal.ReplicatedSnapshotMetadata
 import akka.persistence.typed.internal.VersionVector
 import akka.protobufv3.internal.ByteString
 import akka.remote.ContainerFormats.Payload
@@ -21,7 +24,7 @@ import scala.annotation.tailrec
 import scala.collection.JavaConverters._
 import scala.collection.immutable.TreeMap
 
-object CrdtSerializer {
+object ActiveActiveSerializer {
   object Comparator extends Comparator[Payload] {
     override def compare(a: Payload, b: Payload): Int = {
       val aByteString = a.getEnclosedMessage
@@ -50,7 +53,7 @@ object CrdtSerializer {
 /**
  * INTERNAL API
  */
-@InternalApi private[akka] final class CrdtSerializer(val system: ExtendedActorSystem)
+@InternalApi private[akka] final class ActiveActiveSerializer(val system: ExtendedActorSystem)
     extends SerializerWithStringManifest
     with BaseSerializer {
 
@@ -67,6 +70,9 @@ object CrdtSerializer {
 
   private val VersionVectorManifest = "DA"
 
+  private val ReplicatedEventMetadataManifest = "RE"
+  private val ReplicatedSnapshotMetadataManifest = "RS"
+
   def manifest(o: AnyRef) = o match {
     case _: ORSet[_]                  => ORSetManifest
     case _: ORSet.AddDeltaOp[_]       => ORSetAddManifest
@@ -78,11 +84,19 @@ object CrdtSerializer {
     case _: Counter.Updated => CrdtCounterUpdatedManifest
 
     case _: VersionVector => VersionVectorManifest
+
+    case _: ReplicatedEventMetadata    => ReplicatedEventMetadataManifest
+    case _: ReplicatedSnapshotMetadata => ReplicatedSnapshotMetadataManifest
     case _ =>
       throw new IllegalArgumentException(s"Can't serialize object of type ${o.getClass} in [${getClass.getName}]")
   }
 
   def toBinary(o: AnyRef) = o match {
+    case m: ReplicatedEventMetadata    => replicatedEventMetadataToProtoByteArray(m)
+    case m: ReplicatedSnapshotMetadata => replicatedSnapshotMetadataToByteArray(m)
+
+    case m: VersionVector => versionVectorToProto(m).toByteArray
+
     case m: ORSet[_]                  => orsetToProto(m).toByteArray
     case m: ORSet.AddDeltaOp[_]       => orsetToProto(m.underlying).toByteArray
     case m: ORSet.RemoveDeltaOp[_]    => orsetToProto(m.underlying).toByteArray
@@ -91,12 +105,18 @@ object CrdtSerializer {
 
     case m: Counter         => counterToProtoByteArray(m)
     case m: Counter.Updated => counterUpdatedToProtoBufByteArray(m)
-    case m: VersionVector   => versionVectorToProto(m).toByteArray
+
     case _ =>
       throw new IllegalArgumentException(s"Can't serialize object of type ${o.getClass}")
   }
 
   def fromBinary(bytes: Array[Byte], manifest: String) = manifest match {
+
+    case ReplicatedEventMetadataManifest    => replicatedEventMetadataFromBinary(bytes)
+    case ReplicatedSnapshotMetadataManifest => replicatedSnapshotMetadataFromBinary(bytes)
+
+    case VersionVectorManifest => versionVectorFromBinary(bytes)
+
     case ORSetManifest           => orsetFromBinary(bytes)
     case ORSetAddManifest        => orsetAddFromBinary(bytes)
     case ORSetRemoveManifest     => orsetRemoveFromBinary(bytes)
@@ -106,29 +126,29 @@ object CrdtSerializer {
     case CrdtCounterManifest        => counterFromBinary(bytes)
     case CrdtCounterUpdatedManifest => counterUpdatedFromBinary(bytes)
 
-    case VersionVectorManifest => versionVectorFromBinary(bytes)
     case _ =>
       throw new NotSerializableException(
         s"Unimplemented deserialization of message with manifest [$manifest] in [${getClass.getName}]")
   }
 
   def counterFromBinary(bytes: Array[Byte]): Counter =
-    Counter(BigInt(Crdts.Counter.parseFrom(bytes).getValue.toByteArray))
+    Counter(BigInt(ActiveActive.Counter.parseFrom(bytes).getValue.toByteArray))
 
   def counterUpdatedFromBinary(bytes: Array[Byte]): Counter.Updated =
-    Counter.Updated(BigInt(Crdts.CounterUpdate.parseFrom(bytes).getDelta.toByteArray))
+    Counter.Updated(BigInt(ActiveActive.CounterUpdate.parseFrom(bytes).getDelta.toByteArray))
 
   def counterToProtoByteArray(counter: Counter): Array[Byte] =
-    Crdts.Counter.newBuilder().setValue(ByteString.copyFrom(counter.value.toByteArray)).build().toByteArray
+    ActiveActive.Counter.newBuilder().setValue(ByteString.copyFrom(counter.value.toByteArray)).build().toByteArray
 
   def counterUpdatedToProtoBufByteArray(updated: Counter.Updated): Array[Byte] =
-    Crdts.CounterUpdate.newBuilder().setDelta(ByteString.copyFrom(updated.delta.toByteArray)).build().toByteArray
+    ActiveActive.CounterUpdate.newBuilder().setDelta(ByteString.copyFrom(updated.delta.toByteArray)).build().toByteArray
 
-  def orsetToProto(orset: ORSet[_]): Crdts.ORSet =
+  def orsetToProto(orset: ORSet[_]): ActiveActive.ORSet =
     orsetToProtoImpl(orset.asInstanceOf[ORSet[Any]])
 
-  private def orsetToProtoImpl(orset: ORSet[Any]): Crdts.ORSet = {
+  private def orsetToProtoImpl(orset: ORSet[Any]): ActiveActive.ORSet = {
-    val b = Crdts.ORSet.newBuilder().setOriginDc(orset.originReplica).setVvector(versionVectorToProto(orset.vvector))
+    val b =
+      ActiveActive.ORSet.newBuilder().setOriginDc(orset.originReplica).setVvector(versionVectorToProto(orset.vvector))
     // using java collections and sorting for performance (avoid conversions)
     val stringElements = new ArrayList[String]
     val intElements = new ArrayList[Integer]
@@ -174,7 +194,7 @@ object CrdtSerializer {
       addDots(longElements)
     }
     if (!otherElements.isEmpty) {
-      Collections.sort(otherElements, CrdtSerializer.Comparator)
+      Collections.sort(otherElements, ActiveActiveSerializer.Comparator)
       b.addAllOtherElements(otherElements)
       addDots(otherElements)
     }
@@ -182,31 +202,55 @@ object CrdtSerializer {
     b.build()
   }
 
+  def replicatedEventMetadataToProtoByteArray(rem: ReplicatedEventMetadata): Array[Byte] = {
+    ActiveActive.ReplicatedEventMetadata
+      .newBuilder()
+      .setOriginSequenceNr(rem.originSequenceNr)
+      .setConcurrent(rem.concurrent)
+      .setOriginReplica(rem.originReplica.id)
+      .setVersionVector(versionVectorToProto(rem.version))
+      .build()
+      .toByteArray
+  }
+
+  def replicatedSnapshotMetadataToByteArray(rsm: ReplicatedSnapshotMetadata): Array[Byte] = {
+    ActiveActive.ReplicatedSnapshotMetadata
+      .newBuilder()
+      .setVersion(versionVectorToProto(rsm.version))
+      .addAllSeenPerReplica(rsm.seenPerReplica.map(seenToProto).asJava)
+      .build()
+      .toByteArray
+  }
+
+  def seenToProto(t: (ReplicaId, Long)): ActiveActive.ReplicatedSnapshotMetadata.Seen = {
+    ActiveActive.ReplicatedSnapshotMetadata.Seen.newBuilder().setReplicaId(t._1.id).setSequenceNr(t._2).build()
+  }
+
   def orsetFromBinary(bytes: Array[Byte]): ORSet[Any] =
-    orsetFromProto(Crdts.ORSet.parseFrom(bytes))
+    orsetFromProto(ActiveActive.ORSet.parseFrom(bytes))
 
   private def orsetAddFromBinary(bytes: Array[Byte]): ORSet.AddDeltaOp[Any] =
-    new ORSet.AddDeltaOp(orsetFromProto(Crdts.ORSet.parseFrom(bytes)))
+    new ORSet.AddDeltaOp(orsetFromProto(ActiveActive.ORSet.parseFrom(bytes)))
 
   private def orsetRemoveFromBinary(bytes: Array[Byte]): ORSet.RemoveDeltaOp[Any] =
-    new ORSet.RemoveDeltaOp(orsetFromProto(Crdts.ORSet.parseFrom(bytes)))
+    new ORSet.RemoveDeltaOp(orsetFromProto(ActiveActive.ORSet.parseFrom(bytes)))
 
   private def orsetFullFromBinary(bytes: Array[Byte]): ORSet.FullStateDeltaOp[Any] =
-    new ORSet.FullStateDeltaOp(orsetFromProto(Crdts.ORSet.parseFrom(bytes)))
+    new ORSet.FullStateDeltaOp(orsetFromProto(ActiveActive.ORSet.parseFrom(bytes)))
 
-  private def orsetDeltaGroupToProto(deltaGroup: ORSet.DeltaGroup[_]): Crdts.ORSetDeltaGroup = {
+  private def orsetDeltaGroupToProto(deltaGroup: ORSet.DeltaGroup[_]): ActiveActive.ORSetDeltaGroup = {
-    def createEntry(opType: Crdts.ORSetDeltaOp, u: ORSet[_]) = {
+    def createEntry(opType: ActiveActive.ORSetDeltaOp, u: ORSet[_]) = {
-      Crdts.ORSetDeltaGroup.Entry.newBuilder().setOperation(opType).setUnderlying(orsetToProto(u))
+      ActiveActive.ORSetDeltaGroup.Entry.newBuilder().setOperation(opType).setUnderlying(orsetToProto(u))
     }
 
-    val b = Crdts.ORSetDeltaGroup.newBuilder()
+    val b = ActiveActive.ORSetDeltaGroup.newBuilder()
     deltaGroup.ops.foreach {
       case ORSet.AddDeltaOp(u) =>
-        b.addEntries(createEntry(Crdts.ORSetDeltaOp.Add, u))
+        b.addEntries(createEntry(ActiveActive.ORSetDeltaOp.Add, u))
       case ORSet.RemoveDeltaOp(u) =>
-        b.addEntries(createEntry(Crdts.ORSetDeltaOp.Remove, u))
+        b.addEntries(createEntry(ActiveActive.ORSetDeltaOp.Remove, u))
       case ORSet.FullStateDeltaOp(u) =>
-        b.addEntries(createEntry(Crdts.ORSetDeltaOp.Full, u))
+        b.addEntries(createEntry(ActiveActive.ORSetDeltaOp.Full, u))
       case ORSet.DeltaGroup(_) =>
         throw new IllegalArgumentException("ORSet.DeltaGroup should not be nested")
     }
@@ -214,14 +258,14 @@ object CrdtSerializer {
   }
 
   private def orsetDeltaGroupFromBinary(bytes: Array[Byte]): ORSet.DeltaGroup[Any] = {
-    val deltaGroup = Crdts.ORSetDeltaGroup.parseFrom(bytes)
+    val deltaGroup = ActiveActive.ORSetDeltaGroup.parseFrom(bytes)
     val ops: Vector[ORSet.DeltaOp] =
       deltaGroup.getEntriesList.asScala.map { entry =>
-        if (entry.getOperation == Crdts.ORSetDeltaOp.Add)
+        if (entry.getOperation == ActiveActive.ORSetDeltaOp.Add)
           ORSet.AddDeltaOp(orsetFromProto(entry.getUnderlying))
-        else if (entry.getOperation == Crdts.ORSetDeltaOp.Remove)
+        else if (entry.getOperation == ActiveActive.ORSetDeltaOp.Remove)
           ORSet.RemoveDeltaOp(orsetFromProto(entry.getUnderlying))
-        else if (entry.getOperation == Crdts.ORSetDeltaOp.Full)
+        else if (entry.getOperation == ActiveActive.ORSetDeltaOp.Full)
           ORSet.FullStateDeltaOp(orsetFromProto(entry.getUnderlying))
         else
           throw new NotSerializableException(s"Unknow ORSet delta operation ${entry.getOperation}")
@@ -229,7 +273,7 @@ object CrdtSerializer {
     ORSet.DeltaGroup(ops)
   }
 
-  def orsetFromProto(orset: Crdts.ORSet): ORSet[Any] = {
+  def orsetFromProto(orset: ActiveActive.ORSet): ORSet[Any] = {
     val elements: Iterator[Any] =
       (orset.getStringElementsList.iterator.asScala ++
       orset.getIntElementsList.iterator.asScala ++
@@ -242,18 +286,18 @@ object CrdtSerializer {
     new ORSet(orset.getOriginDc, elementsMap, vvector = versionVectorFromProto(orset.getVvector))
   }
 
-  def versionVectorToProto(versionVector: VersionVector): Crdts.VersionVector = {
+  def versionVectorToProto(versionVector: VersionVector): ActiveActive.VersionVector = {
-    val b = Crdts.VersionVector.newBuilder()
+    val b = ActiveActive.VersionVector.newBuilder()
     versionVector.versionsIterator.foreach {
-      case (key, value) => b.addEntries(Crdts.VersionVector.Entry.newBuilder().setKey(key).setVersion(value))
+      case (key, value) => b.addEntries(ActiveActive.VersionVector.Entry.newBuilder().setKey(key).setVersion(value))
     }
     b.build()
   }
 
   def versionVectorFromBinary(bytes: Array[Byte]): VersionVector =
-    versionVectorFromProto(Crdts.VersionVector.parseFrom(bytes))
+    versionVectorFromProto(ActiveActive.VersionVector.parseFrom(bytes))
 
-  def versionVectorFromProto(versionVector: Crdts.VersionVector): VersionVector = {
+  def versionVectorFromProto(versionVector: ActiveActive.VersionVector): VersionVector = {
     val entries = versionVector.getEntriesList
     if (entries.isEmpty)
       VersionVector.empty
@@ -266,4 +310,20 @@ object CrdtSerializer {
     }
   }
 
+  def replicatedEventMetadataFromBinary(bytes: Array[Byte]): ReplicatedEventMetadata = {
+    val parsed = ActiveActive.ReplicatedEventMetadata.parseFrom(bytes)
+    ReplicatedEventMetadata(
+      ReplicaId(parsed.getOriginReplica),
+      parsed.getOriginSequenceNr,
+      versionVectorFromProto(parsed.getVersionVector),
+      parsed.getConcurrent)
+  }
+
+  def replicatedSnapshotMetadataFromBinary(bytes: Array[Byte]): ReplicatedSnapshotMetadata = {
+    val parsed = ActiveActive.ReplicatedSnapshotMetadata.parseFrom(bytes)
+    ReplicatedSnapshotMetadata(
+      versionVectorFromProto(parsed.getVersion),
+      parsed.getSeenPerReplicaList.asScala.map(seen => ReplicaId(seen.getReplicaId) -> seen.getSequenceNr).toMap)
+  }
+
 }

akka-persistence-typed/src/test/scala/akka/persistence/typed/ActiveActiveSerializationSpec.scala

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package akka.persistence.typed
+
+import akka.actor.testkit.typed.scaladsl.LogCapturing
+import akka.actor.testkit.typed.scaladsl.ScalaTestWithActorTestKit
+import akka.persistence.typed.crdt.Counter
+import akka.persistence.typed.crdt.ORSet
+import akka.persistence.typed.internal.ReplicatedEventMetadata
+import akka.persistence.typed.internal.ReplicatedSnapshotMetadata
+import akka.persistence.typed.internal.VersionVector
+import org.scalatest.wordspec.AnyWordSpecLike
+
+class ActiveActiveSerializationSpec
+    extends ScalaTestWithActorTestKit(ClusterSingletonPersistenceSpec.config)
+    with AnyWordSpecLike
+    with LogCapturing {
+
+  "The ActiveActive components that needs to be serializable" must {
+
+    "be serializable" in {
+      serializationTestKit.verifySerialization(
+        ReplicatedEventMetadata(ReplicaId("DC-A"), 2L, VersionVector.empty.increment("DC-B"), true))
+
+      serializationTestKit.verifySerialization(
+        ReplicatedSnapshotMetadata(
+          VersionVector.empty.increment("DC-B"),
+          Map(ReplicaId("DC-A") -> 1L, ReplicaId("DC-B") -> 2L)))
+
+      serializationTestKit.verifySerialization(Counter(BigInt(24)))
+      serializationTestKit.verifySerialization(Counter.Updated(BigInt(1)))
+      serializationTestKit.verifySerialization(ORSet(ReplicaId("DC-A")))
+      serializationTestKit.verifySerialization(ORSet.AddDeltaOp(ORSet(ReplicaId("DC-A"))))
+      // FIXME DeltaGroup?
+    }
+  }
+
+}

akka-persistence/src/main/scala/akka/persistence/SnapshotProtocol.scala

@@ -30,6 +30,9 @@ final class SnapshotMetadata(
     this(persistenceId, sequenceNr, 0L, meta)
   }
 
+  def withMetadata(metadata: Any): SnapshotMetadata =
+    new SnapshotMetadata(persistenceId, sequenceNr, timestamp, Some(metadata))
+
   // for bincompat, used to be a case class
   def copy(
       persistenceId: String = this.persistenceId,

project/OSGi.scala

@@ -65,15 +65,14 @@ object OSGi {
   val protobuf = exports(Seq("akka.protobuf.*"))
 
   val protobufV3 = osgiSettings ++ Seq(
-    OsgiKeys.importPackage := Seq(
+      OsgiKeys.importPackage := Seq(
-      "!sun.misc",
+          "!sun.misc",
-      scalaJava8CompatImport(),
+          scalaJava8CompatImport(),
-      scalaVersion(scalaImport).value,
+          scalaVersion(scalaImport).value,
-      configImport(),
+          configImport(),
-      "*"),
+          "*"),
-    OsgiKeys.exportPackage := Seq("akka.protobufv3.internal.*"),
+      OsgiKeys.exportPackage := Seq("akka.protobufv3.internal.*"),
-    OsgiKeys.privatePackage := Seq("google.protobuf.*")
+      OsgiKeys.privatePackage := Seq("google.protobuf.*"))
-  )
 
   val jackson = exports(Seq("akka.serialization.jackson.*"))