!per #3652 Custom snapshot and persistent message serialization

- Protobuf serializer for Persistent message
- Configurable serializer for Persistent message's payload
- Configurable serializer for snapshots

akka-persistence/src/main/scala/akka/persistence/serialization/SnapshotSerializer.scala

@@ -0,0 +1,87 @@
+/**
+ * Copyright (C) 2012-2013 Eligotech BV.
+ */
+
+package akka.persistence.serialization
+
+import java.io._
+
+import akka.actor._
+import akka.serialization.{ Serializer, SerializationExtension }
+
+/**
+ * Wrapper for snapshot `data`. Snapshot `data` are the actual snapshot objects captured by
+ * a [[Processor]].
+ *
+ * @see [[SnapshotSerializer]]
+ */
+@SerialVersionUID(1L)
+case class Snapshot(data: Any)
+
+/**
+ * INTERNAL API.
+ */
+@SerialVersionUID(1L)
+private[serialization] case class SnapshotHeader(serializerId: Int, manifest: Option[String])
+
+/**
+ * [[Snapshot]] serializer.
+ */
+class SnapshotSerializer(system: ExtendedActorSystem) extends Serializer {
+  def identifier: Int = 8
+  def includeManifest: Boolean = false
+
+  /**
+   * Serializes a [[Snapshot]]. Delegates serialization of snapshot `data` to a matching
+   * `akka.serialization.Serializer`.
+   */
+  def toBinary(o: AnyRef): Array[Byte] = o match {
+    case Snapshot(data) ⇒ snapshotToBinary(data.asInstanceOf[AnyRef])
+    case _              ⇒ throw new IllegalArgumentException(s"Can't serialize object of type ${o.getClass}")
+  }
+
+  /**
+   * Deserializes a [[Snapshot]]. Delegates deserialization of snapshot `data` to a matching
+   * `akka.serialization.Serializer`.
+   */
+  def fromBinary(bytes: Array[Byte], manifest: Option[Class[_]]): AnyRef =
+    Snapshot(snapshotFromBinary(bytes))
+
+  private def snapshotToBinary(snapshot: AnyRef): Array[Byte] = {
+    val extension = SerializationExtension(system)
+
+    val snapshotSerializer = extension.findSerializerFor(snapshot)
+    val snapshotManifest = if (snapshotSerializer.includeManifest) Some(snapshot.getClass.getName) else None
+
+    val header = SnapshotHeader(snapshotSerializer.identifier, snapshotManifest)
+    val headerSerializer = extension.findSerializerFor(header)
+    val headerBytes = headerSerializer.toBinary(header)
+
+    val out = new ByteArrayOutputStream
+
+    writeInt(out, headerBytes.length)
+
+    out.write(headerBytes)
+    out.write(snapshotSerializer.toBinary(snapshot))
+    out.toByteArray
+  }
+
+  private def snapshotFromBinary(bytes: Array[Byte]): AnyRef = {
+    val extension = SerializationExtension(system)
+
+    val headerLength = readInt(new ByteArrayInputStream(bytes))
+    val headerBytes = bytes.slice(4, headerLength + 4)
+    val snapshotBytes = bytes.drop(headerLength + 4)
+
+    val header = extension.deserialize(headerBytes, classOf[SnapshotHeader]).get
+    val manifest = header.manifest.map(system.dynamicAccess.getClassFor[AnyRef](_).get)
+
+    extension.deserialize[AnyRef](snapshotBytes, header.serializerId, manifest).get
+  }
+
+  private def writeInt(outputStream: OutputStream, i: Int) =
+    0 to 24 by 8 foreach { shift ⇒ outputStream.write(i >> shift) }
+
+  private def readInt(inputStream: InputStream) =
+    (0 to 24 by 8).foldLeft(0) { (id, shift) ⇒ (id | (inputStream.read() >> shift)) }
+}