=cls #17908 Protobuf serializer for cluster sharding

akka-cluster-sharding/src/main/protobuf/ClusterShardingMessages.proto

@@ -0,0 +1,50 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+option java_package = "akka.cluster.sharding.protobuf.msg";
+option optimize_for = SPEED;
+
+message CoordinatorState {
+
+  message ShardEntry {
+    required string shardId = 1;
+    required string regionRef = 2;
+  }
+  
+  repeated ShardEntry shards = 1;
+  repeated string regions = 2;
+  repeated string regionProxies = 3;
+  repeated string unallocatedShards = 4; 
+}
+
+message ActorRefMessage {
+  required string ref = 1;
+}
+
+message ShardIdMessage {
+  required string shard = 1;
+}
+
+message ShardHomeAllocated {
+  required string shard = 1;
+  required string region = 2;
+}
+
+message ShardHome {
+  required string shard = 1;
+  required string region = 2;
+}
+
+message EntityState {
+  repeated string entities = 1;
+}
+
+message EntityStarted {
+  required string entityId = 1;
+}
+
+message EntityStopped {
+  required string entityId = 1;
+}
+

akka-cluster-sharding/src/main/resources/reference.conf

@@ -91,3 +91,17 @@ akka.cluster.sharding {
   use-dispatcher = ""
 }
 # //#sharding-ext-config
+
+
+# Protobuf serializer for Cluster Sharding messages
+akka.actor {
+  serializers {
+    akka-sharding = "akka.cluster.sharding.protobuf.ClusterShardingMessageSerializer"
+  }
+  serialization-bindings {
+    "akka.cluster.sharding.ClusterShardingSerializable" = akka-sharding
+  }
+  serialization-identifiers {
+    "akka.cluster.sharding.protobuf.ClusterShardingMessageSerializer" = 13
+  }
+}

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterShardingSerializable.scala

@@ -0,0 +1,9 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.cluster.sharding
+
+/**
+ * Marker trait for remote messages and persistent events/snapshots with special serializer.
+ */
+trait ClusterShardingSerializable extends Serializable

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/Shard.scala

@@ -36,7 +36,9 @@ private[akka] object Shard {
   /**
    * A case class which represents a state change for the Shard
    */
-  sealed trait StateChange { val entityId: EntityId }
+  sealed trait StateChange extends ClusterShardingSerializable {
+    val entityId: EntityId
+  }
 
   /**
    * `State` change for starting an entity in this `Shard`
@@ -55,8 +57,8 @@ private[akka] object Shard {
   /**
    * Persistent state of the Shard.
    */
-  @SerialVersionUID(1L) final case class State private (
-    entities: Set[EntityId] = Set.empty)
+  @SerialVersionUID(1L) final case class State private[akka] (
+    entities: Set[EntityId] = Set.empty) extends ClusterShardingSerializable
 
   /**
    * Factory method for the [[akka.actor.Props]] of the [[Shard]] actor.

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ShardCoordinator.scala

@@ -159,11 +159,11 @@ object ShardCoordinator {
     /**
      * Messages sent to the coordinator
      */
-    sealed trait CoordinatorCommand
+    sealed trait CoordinatorCommand extends ClusterShardingSerializable
     /**
      * Messages sent from the coordinator
      */
-    sealed trait CoordinatorMessage
+    sealed trait CoordinatorMessage extends ClusterShardingSerializable
     /**
      * `ShardRegion` registers to `ShardCoordinator`, until it receives [[RegisterAck]].
      */
@@ -218,24 +218,13 @@ object ShardCoordinator {
      */
     @SerialVersionUID(1L) final case class ShardStopped(shard: ShardId) extends CoordinatorCommand
 
-    /**
-     * Result of `allocateShard` is piped to self with this message.
-     */
-    @SerialVersionUID(1L) final case class AllocateShardResult(
-      shard: ShardId, shardRegion: Option[ActorRef], getShardHomeSender: ActorRef) extends CoordinatorCommand
-
-    /**
-     * Result of `rebalance` is piped to self with this message.
-     */
-    @SerialVersionUID(1L) final case class RebalanceResult(shards: Set[ShardId]) extends CoordinatorCommand
-
     /**
      * `ShardRegion` requests full handoff to be able to shutdown gracefully.
      */
     @SerialVersionUID(1L) final case class GracefulShutdownReq(shardRegion: ActorRef) extends CoordinatorCommand
 
     // DomainEvents for the persistent state of the event sourced ShardCoordinator
-    sealed trait DomainEvent
+    sealed trait DomainEvent extends ClusterShardingSerializable
     @SerialVersionUID(1L) final case class ShardRegionRegistered(region: ActorRef) extends DomainEvent
     @SerialVersionUID(1L) final case class ShardRegionProxyRegistered(regionProxy: ActorRef) extends DomainEvent
     @SerialVersionUID(1L) final case class ShardRegionTerminated(region: ActorRef) extends DomainEvent
@@ -250,13 +239,13 @@ object ShardCoordinator {
     /**
      * Persistent state of the event sourced ShardCoordinator.
      */
-    @SerialVersionUID(1L) final case class State private (
+    @SerialVersionUID(1L) final case class State private[akka] (
       // region for each shard
       shards: Map[ShardId, ActorRef] = Map.empty,
       // shards for each region
       regions: Map[ActorRef, Vector[ShardId]] = Map.empty,
       regionProxies: Set[ActorRef] = Set.empty,
-      unallocatedShards: Set[ShardId] = Set.empty) {
+      unallocatedShards: Set[ShardId] = Set.empty) extends ClusterShardingSerializable {
 
       def updated(event: DomainEvent): State = event match {
         case ShardRegionRegistered(region) ⇒
@@ -309,6 +298,17 @@ object ShardCoordinator {
 
   private final case class DelayedShardRegionTerminated(region: ActorRef)
 
+  /**
+   * Result of `allocateShard` is piped to self with this message.
+   */
+  private final case class AllocateShardResult(
+    shard: ShardId, shardRegion: Option[ActorRef], getShardHomeSender: ActorRef)
+
+  /**
+   * Result of `rebalance` is piped to self with this message.
+   */
+  private final case class RebalanceResult(shards: Set[ShardId])
+
   /**
    * INTERNAL API. Rebalancing process is performed by this actor.
    * It sends `BeginHandOff` to all `ShardRegion` actors followed by

akka-cluster-sharding/src/main/scala/akka/cluster/sharding/protobuf/ClusterShardingMessageSerializer.scala

@@ -0,0 +1,276 @@
+/**
+ * Copyright (C) 2009-2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.cluster.sharding.protobuf
+
+import java.io.{ ByteArrayInputStream, ByteArrayOutputStream }
+import java.util.zip.GZIPInputStream
+import java.util.zip.GZIPOutputStream
+
+import scala.annotation.tailrec
+import scala.collection.JavaConverters._
+import scala.collection.breakOut
+
+import akka.actor.ActorRef
+import akka.actor.ExtendedActorSystem
+import akka.cluster.sharding.Shard
+import akka.cluster.sharding.ShardCoordinator
+import akka.cluster.sharding.protobuf.msg.{ ClusterShardingMessages => sm }
+import akka.serialization.BaseSerializer
+import akka.serialization.Serialization
+import akka.serialization.SerializationExtension
+import akka.serialization.SerializerWithStringManifest
+import com.google.protobuf.MessageLite
+
+/**
+ * INTERNAL API: Protobuf serializer of ClusterSharding messages.
+ */
+private[akka] class ClusterShardingMessageSerializer(val system: ExtendedActorSystem)
+  extends SerializerWithStringManifest with BaseSerializer {
+  import ShardCoordinator.Internal._
+  import Shard.{ State ⇒ EntityState, EntityStarted, EntityStopped }
+
+  private lazy val serialization = SerializationExtension(system)
+
+  private final val BufferSize = 1024 * 4
+
+  private val CoordinatorStateManifest = "AA"
+  private val ShardRegionRegisteredManifest = "AB"
+  private val ShardRegionProxyRegisteredManifest = "AC"
+  private val ShardRegionTerminatedManifest = "AD"
+  private val ShardRegionProxyTerminatedManifest = "AE"
+  private val ShardHomeAllocatedManifest = "AF"
+  private val ShardHomeDeallocatedManifest = "AG"
+
+  private val RegisterManifest = "BA"
+  private val RegisterProxyManifest = "BB"
+  private val RegisterAckManifest = "BC"
+  private val GetShardHomeManifest = "BD"
+  private val ShardHomeManifest = "BE"
+  private val HostShardManifest = "BF"
+  private val ShardStartedManifest = "BG"
+  private val BeginHandOffManifest = "BH"
+  private val BeginHandOffAckManifest = "BI"
+  private val HandOffManifest = "BJ"
+  private val ShardStoppedManifest = "BK"
+  private val GracefulShutdownReqManifest = "BL"
+
+  private val EntityStateManifest = "CA"
+  private val EntityStartedManifest = "CB"
+  private val EntityStoppedManifest = "CD"
+
+  private val fromBinaryMap = collection.immutable.HashMap[String, Array[Byte] ⇒ AnyRef](
+    EntityStateManifest -> entityStateFromBinary,
+    EntityStartedManifest -> entityStartedFromBinary,
+    EntityStoppedManifest -> entityStoppedFromBinary,
+
+    CoordinatorStateManifest -> coordinatorStateFromBinary,
+    ShardRegionRegisteredManifest -> { bytes ⇒ ShardRegionRegistered(actorRefMessageFromBinary(bytes)) },
+    ShardRegionProxyRegisteredManifest -> { bytes ⇒ ShardRegionProxyRegistered(actorRefMessageFromBinary(bytes)) },
+    ShardRegionTerminatedManifest -> { bytes ⇒ ShardRegionTerminated(actorRefMessageFromBinary(bytes)) },
+    ShardRegionProxyTerminatedManifest -> { bytes ⇒ ShardRegionProxyTerminated(actorRefMessageFromBinary(bytes)) },
+    ShardHomeAllocatedManifest -> shardHomeAllocatedFromBinary,
+    ShardHomeDeallocatedManifest -> { bytes ⇒ ShardHomeDeallocated(shardIdMessageFromBinary(bytes)) },
+
+    RegisterManifest -> { bytes ⇒ Register(actorRefMessageFromBinary(bytes)) },
+    RegisterProxyManifest -> { bytes ⇒ RegisterProxy(actorRefMessageFromBinary(bytes)) },
+    RegisterAckManifest -> { bytes ⇒ RegisterAck(actorRefMessageFromBinary(bytes)) },
+    GetShardHomeManifest -> { bytes ⇒ GetShardHome(shardIdMessageFromBinary(bytes)) },
+    ShardHomeManifest -> shardHomeFromBinary,
+    HostShardManifest -> { bytes ⇒ HostShard(shardIdMessageFromBinary(bytes)) },
+    ShardStartedManifest -> { bytes ⇒ ShardStarted(shardIdMessageFromBinary(bytes)) },
+    BeginHandOffManifest -> { bytes ⇒ BeginHandOff(shardIdMessageFromBinary(bytes)) },
+    BeginHandOffAckManifest -> { bytes ⇒ BeginHandOffAck(shardIdMessageFromBinary(bytes)) },
+    HandOffManifest -> { bytes ⇒ HandOff(shardIdMessageFromBinary(bytes)) },
+    ShardStoppedManifest -> { bytes ⇒ ShardStopped(shardIdMessageFromBinary(bytes)) },
+    GracefulShutdownReqManifest -> { bytes ⇒ GracefulShutdownReq(actorRefMessageFromBinary(bytes)) })
+
+  override def manifest(obj: AnyRef): String = obj match {
+    case _: EntityState                ⇒ EntityStateManifest
+    case _: EntityStarted              ⇒ EntityStartedManifest
+    case _: EntityStopped              ⇒ EntityStoppedManifest
+
+    case _: State                      ⇒ CoordinatorStateManifest
+    case _: ShardRegionRegistered      ⇒ ShardRegionRegisteredManifest
+    case _: ShardRegionProxyRegistered ⇒ ShardRegionProxyRegisteredManifest
+    case _: ShardRegionTerminated      ⇒ ShardRegionTerminatedManifest
+    case _: ShardRegionProxyTerminated ⇒ ShardRegionProxyTerminatedManifest
+    case _: ShardHomeAllocated         ⇒ ShardHomeAllocatedManifest
+    case _: ShardHomeDeallocated       ⇒ ShardHomeDeallocatedManifest
+
+    case _: Register                   ⇒ RegisterManifest
+    case _: RegisterProxy              ⇒ RegisterProxyManifest
+    case _: RegisterAck                ⇒ RegisterAckManifest
+    case _: GetShardHome               ⇒ GetShardHomeManifest
+    case _: ShardHome                  ⇒ ShardHomeManifest
+    case _: HostShard                  ⇒ HostShardManifest
+    case _: ShardStarted               ⇒ ShardStartedManifest
+    case _: BeginHandOff               ⇒ BeginHandOffManifest
+    case _: BeginHandOffAck            ⇒ BeginHandOffAckManifest
+    case _: HandOff                    ⇒ HandOffManifest
+    case _: ShardStopped               ⇒ ShardStoppedManifest
+    case _: GracefulShutdownReq        ⇒ GracefulShutdownReqManifest
+    case _ ⇒
+      throw new IllegalArgumentException(s"Can't serialize object of type ${obj.getClass} in [${getClass.getName}]")
+  }
+
+  override def toBinary(obj: AnyRef): Array[Byte] = obj match {
+    case m: State                        ⇒ compress(coordinatorStateToProto(m))
+    case ShardRegionRegistered(ref)      ⇒ actorRefMessageToProto(ref).toByteArray
+    case ShardRegionProxyRegistered(ref) ⇒ actorRefMessageToProto(ref).toByteArray
+    case ShardRegionTerminated(ref)      ⇒ actorRefMessageToProto(ref).toByteArray
+    case ShardRegionProxyTerminated(ref) ⇒ actorRefMessageToProto(ref).toByteArray
+    case m: ShardHomeAllocated           ⇒ shardHomeAllocatedToProto(m).toByteArray
+    case ShardHomeDeallocated(shardId)   ⇒ shardIdMessageToProto(shardId).toByteArray
+
+    case Register(ref)                   ⇒ actorRefMessageToProto(ref).toByteArray
+    case RegisterProxy(ref)              ⇒ actorRefMessageToProto(ref).toByteArray
+    case RegisterAck(ref)                ⇒ actorRefMessageToProto(ref).toByteArray
+    case GetShardHome(shardId)           ⇒ shardIdMessageToProto(shardId).toByteArray
+    case m: ShardHome                    ⇒ shardHomeToProto(m).toByteArray
+    case HostShard(shardId)              ⇒ shardIdMessageToProto(shardId).toByteArray
+    case ShardStarted(shardId)           ⇒ shardIdMessageToProto(shardId).toByteArray
+    case BeginHandOff(shardId)           ⇒ shardIdMessageToProto(shardId).toByteArray
+    case BeginHandOffAck(shardId)        ⇒ shardIdMessageToProto(shardId).toByteArray
+    case HandOff(shardId)                ⇒ shardIdMessageToProto(shardId).toByteArray
+    case ShardStopped(shardId)           ⇒ shardIdMessageToProto(shardId).toByteArray
+    case GracefulShutdownReq(ref) ⇒
+      actorRefMessageToProto(ref).toByteArray
+
+    case m: EntityState   ⇒ entityStateToProto(m).toByteArray
+    case m: EntityStarted ⇒ entityStartedToProto(m).toByteArray
+    case m: EntityStopped ⇒ entityStoppedToProto(m).toByteArray
+    case _ ⇒
+      throw new IllegalArgumentException(s"Can't serialize object of type ${obj.getClass} in [${getClass.getName}]")
+  }
+
+  override def fromBinary(bytes: Array[Byte], manifest: String): AnyRef =
+    fromBinaryMap.get(manifest) match {
+      case Some(f) ⇒ f(bytes)
+      case None ⇒ throw new IllegalArgumentException(
+        s"Unimplemented deserialization of message with manifest [$manifest] in [${getClass.getName}]")
+    }
+
+  private def coordinatorStateToProto(state: State): sm.CoordinatorState = {
+    val regions = state.regions.map {
+      case (regionRef, _) ⇒ Serialization.serializedActorPath(regionRef)
+    }.toVector.asJava
+
+    val builder = sm.CoordinatorState.newBuilder()
+
+    state.shards.foreach {
+      case (shardId, regionRef) ⇒
+        val b = sm.CoordinatorState.ShardEntry.newBuilder()
+          .setShardId(shardId)
+          .setRegionRef(Serialization.serializedActorPath(regionRef))
+        builder.addShards(b)
+    }
+    state.regions.foreach {
+      case (regionRef, _) ⇒ builder.addRegions(Serialization.serializedActorPath(regionRef))
+    }
+    state.regionProxies.foreach { ref ⇒ builder.addRegionProxies(Serialization.serializedActorPath(ref)) }
+    state.unallocatedShards.foreach { builder.addUnallocatedShards }
+
+    builder.build()
+  }
+
+  private def coordinatorStateFromBinary(bytes: Array[Byte]): State =
+    coordinatorStateFromProto(sm.CoordinatorState.parseFrom(decompress(bytes)))
+
+  private def coordinatorStateFromProto(state: sm.CoordinatorState): State = {
+    val shards: Map[String, ActorRef] =
+      state.getShardsList.asScala.toVector.map { entry ⇒
+        entry.getShardId -> resolveActorRef(entry.getRegionRef)
+      }(breakOut)
+
+    val regionsZero: Map[ActorRef, Vector[String]] =
+      state.getRegionsList.asScala.toVector.map(resolveActorRef(_) -> Vector.empty[String])(breakOut)
+    val regions: Map[ActorRef, Vector[String]] =
+      shards.foldLeft(regionsZero) { case (acc, (shardId, regionRef)) ⇒ acc.updated(regionRef, acc(regionRef) :+ shardId) }
+
+    val proxies: Set[ActorRef] = state.getRegionProxiesList.asScala.map { resolveActorRef }(breakOut)
+    val unallocatedShards: Set[String] = state.getUnallocatedShardsList.asScala.toSet
+
+    State(shards, regions, proxies, unallocatedShards)
+  }
+
+  private def actorRefMessageToProto(ref: ActorRef): sm.ActorRefMessage =
+    sm.ActorRefMessage.newBuilder().setRef(Serialization.serializedActorPath(ref)).build()
+
+  private def actorRefMessageFromBinary(bytes: Array[Byte]): ActorRef =
+    resolveActorRef(sm.ActorRefMessage.parseFrom(bytes).getRef)
+
+  private def shardIdMessageToProto(shardId: String): sm.ShardIdMessage =
+    sm.ShardIdMessage.newBuilder().setShard(shardId).build()
+
+  private def shardIdMessageFromBinary(bytes: Array[Byte]): String =
+    sm.ShardIdMessage.parseFrom(bytes).getShard
+
+  private def shardHomeAllocatedToProto(evt: ShardHomeAllocated): sm.ShardHomeAllocated =
+    sm.ShardHomeAllocated.newBuilder().setShard(evt.shard)
+      .setRegion(Serialization.serializedActorPath(evt.region)).build()
+
+  private def shardHomeAllocatedFromBinary(bytes: Array[Byte]): ShardHomeAllocated = {
+    val m = sm.ShardHomeAllocated.parseFrom(bytes)
+    ShardHomeAllocated(m.getShard, resolveActorRef(m.getRegion))
+  }
+
+  private def shardHomeToProto(m: ShardHome): sm.ShardHome =
+    sm.ShardHome.newBuilder().setShard(m.shard)
+      .setRegion(Serialization.serializedActorPath(m.ref)).build()
+
+  private def shardHomeFromBinary(bytes: Array[Byte]): ShardHome = {
+    val m = sm.ShardHome.parseFrom(bytes)
+    ShardHome(m.getShard, resolveActorRef(m.getRegion))
+  }
+
+  private def entityStateToProto(m: EntityState): sm.EntityState = {
+    val b = sm.EntityState.newBuilder()
+    m.entities.foreach(b.addEntities)
+    b.build()
+  }
+
+  private def entityStateFromBinary(bytes: Array[Byte]): EntityState =
+    EntityState(sm.EntityState.parseFrom(bytes).getEntitiesList.asScala.toSet)
+
+  private def entityStartedToProto(evt: EntityStarted): sm.EntityStarted =
+    sm.EntityStarted.newBuilder().setEntityId(evt.entityId).build()
+
+  private def entityStartedFromBinary(bytes: Array[Byte]): EntityStarted =
+    EntityStarted(sm.EntityStarted.parseFrom(bytes).getEntityId)
+
+  private def entityStoppedToProto(evt: EntityStopped): sm.EntityStopped =
+    sm.EntityStopped.newBuilder().setEntityId(evt.entityId).build()
+
+  private def entityStoppedFromBinary(bytes: Array[Byte]): EntityStopped =
+    EntityStopped(sm.EntityStopped.parseFrom(bytes).getEntityId)
+
+  private def resolveActorRef(path: String): ActorRef = {
+    system.provider.resolveActorRef(path)
+  }
+
+  private def compress(msg: MessageLite): Array[Byte] = {
+    val bos = new ByteArrayOutputStream(BufferSize)
+    val zip = new GZIPOutputStream(bos)
+    msg.writeTo(zip)
+    zip.close()
+    bos.toByteArray
+  }
+
+  private def decompress(bytes: Array[Byte]): Array[Byte] = {
+    val in = new GZIPInputStream(new ByteArrayInputStream(bytes))
+    val out = new ByteArrayOutputStream()
+    val buffer = new Array[Byte](BufferSize)
+
+    @tailrec def readChunk(): Unit = in.read(buffer) match {
+      case -1 ⇒ ()
+      case n ⇒
+        out.write(buffer, 0, n)
+        readChunk()
+    }
+
+    readChunk()
+    out.toByteArray
+  }
+
+}

akka-cluster-sharding/src/test/scala/akka/cluster/sharding/protobuf/ClusterShardingMessageSerializerSpec.scala

@@ -0,0 +1,73 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.cluster.sharding.protobuf
+
+import akka.actor.{ ExtendedActorSystem, Address }
+import akka.testkit.AkkaSpec
+import akka.actor.Props
+import akka.cluster.sharding.ShardCoordinator
+import akka.cluster.sharding.Shard
+
+class ClusterShardingMessageSerializerSpec extends AkkaSpec {
+  import ShardCoordinator.Internal._
+
+  val serializer = new ClusterShardingMessageSerializer(system.asInstanceOf[ExtendedActorSystem])
+
+  val region1 = system.actorOf(Props.empty, "region1")
+  val region2 = system.actorOf(Props.empty, "region2")
+  val region3 = system.actorOf(Props.empty, "region3")
+  val regionProxy1 = system.actorOf(Props.empty, "regionProxy1")
+  val regionProxy2 = system.actorOf(Props.empty, "regionProxy2")
+
+  def checkSerialization(obj: AnyRef): Unit = {
+    val blob = serializer.toBinary(obj)
+    val ref = serializer.fromBinary(blob, serializer.manifest(obj))
+    ref should ===(obj)
+  }
+
+  "ClusterShardingMessageSerializer" must {
+
+    "be able to serializable ShardCoordinator snapshot State" in {
+      val state = State(
+        shards = Map("a" -> region1, "b" -> region2, "c" -> region2),
+        regions = Map(region1 -> Vector("a"), region2 -> Vector("b", "c"), region3 -> Vector.empty[String]),
+        regionProxies = Set(regionProxy1, regionProxy2),
+        unallocatedShards = Set("d"))
+      checkSerialization(state)
+    }
+
+    "be able to serializable ShardCoordinator domain events" in {
+      checkSerialization(ShardRegionRegistered(region1))
+      checkSerialization(ShardRegionProxyRegistered(regionProxy1))
+      checkSerialization(ShardRegionTerminated(region1))
+      checkSerialization(ShardRegionProxyTerminated(regionProxy1))
+      checkSerialization(ShardHomeAllocated("a", region1))
+      checkSerialization(ShardHomeDeallocated("a"))
+    }
+
+    "be able to serializable ShardCoordinator remote messages" in {
+      checkSerialization(Register(region1))
+      checkSerialization(RegisterProxy(regionProxy1))
+      checkSerialization(RegisterAck(region1))
+      checkSerialization(GetShardHome("a"))
+      checkSerialization(ShardHome("a", region1))
+      checkSerialization(HostShard("a"))
+      checkSerialization(ShardStarted("a"))
+      checkSerialization(BeginHandOff("a"))
+      checkSerialization(BeginHandOffAck("a"))
+      checkSerialization(HandOff("a"))
+      checkSerialization(ShardStopped("a"))
+      checkSerialization(GracefulShutdownReq(region1))
+    }
+
+    "be able to serializable PersistentShard snapshot state" in {
+      checkSerialization(Shard.State(Set("e1", "e2", "e3")))
+    }
+
+    "be able to serializable PersistentShard domain events" in {
+      checkSerialization(Shard.EntityStarted("e1"))
+      checkSerialization(Shard.EntityStopped("e1"))
+    }
+  }
+}

akka-cluster-tools/src/main/scala/akka/cluster/pubsub/protobuf/DistributedPubSubMessageSerializer.scala

@@ -30,9 +30,9 @@ import scala.collection.immutable.TreeMap
 import akka.serialization.SerializerWithStringManifest
 
 /**
- * Protobuf serializer of DistributedPubSubMediator messages.
+ * INTERNAL API: Protobuf serializer of DistributedPubSubMediator messages.
  */
-class DistributedPubSubMessageSerializer(val system: ExtendedActorSystem)
+private[akka] class DistributedPubSubMessageSerializer(val system: ExtendedActorSystem)
   extends SerializerWithStringManifest with BaseSerializer {
 
   private lazy val serialization = SerializationExtension(system)
@@ -79,7 +79,7 @@ class DistributedPubSubMessageSerializer(val system: ExtendedActorSystem)
         s"Unimplemented deserialization of message with manifest [$manifest] in [${getClass.getName}]")
     }
 
-  def compress(msg: MessageLite): Array[Byte] = {
+  private def compress(msg: MessageLite): Array[Byte] = {
     val bos = new ByteArrayOutputStream(BufferSize)
     val zip = new GZIPOutputStream(bos)
     msg.writeTo(zip)
@@ -87,7 +87,7 @@ class DistributedPubSubMessageSerializer(val system: ExtendedActorSystem)
     bos.toByteArray
   }
 
-  def decompress(bytes: Array[Byte]): Array[Byte] = {
+  private def decompress(bytes: Array[Byte]): Array[Byte] = {
     val in = new GZIPInputStream(new ByteArrayInputStream(bytes))
     val out = new ByteArrayOutputStream()
     val buffer = new Array[Byte](BufferSize)