[SPARK-25827][CORE] Avoid converting incoming encrypted blocks to byte buffers

## What changes were proposed in this pull request?

Avoid converting encrypted bocks to regular ByteBuffers, to ensure they can be sent over the network for replication & remote reads even when > 2GB.

Also updates some TODOs with links to a SPARK-25905 for improving the
handling here.

## How was this patch tested?

Tested on a cluster with encrypted data > 2GB (after SPARK-25904 was
applied as well).

Closes apache#22917 from squito/real_SPARK-25827.

Authored-by: Imran Rashid <[email protected]>
Signed-off-by: Marcelo Vanzin <[email protected]>

Author: squito

core/src/main/scala/org/apache/spark/network/BlockTransferService.scala

@@ -27,7 +27,7 @@ import scala.reflect.ClassTag
 import org.apache.spark.internal.Logging
 import org.apache.spark.network.buffer.{FileSegmentManagedBuffer, ManagedBuffer, NioManagedBuffer}
 import org.apache.spark.network.shuffle.{BlockFetchingListener, DownloadFileManager, ShuffleClient}
-import org.apache.spark.storage.{BlockId, StorageLevel}
+import org.apache.spark.storage.{BlockId, EncryptedManagedBuffer, StorageLevel}
 import org.apache.spark.util.ThreadUtils
 
 private[spark]
@@ -104,6 +104,8 @@ abstract class BlockTransferService extends ShuffleClient with Closeable with Lo
           data match {
             case f: FileSegmentManagedBuffer =>
               result.success(f)
+            case e: EncryptedManagedBuffer =>
+              result.success(e)
             case _ =>
               val ret = ByteBuffer.allocate(data.size.toInt)
               ret.put(data.nioByteBuffer())

core/src/main/scala/org/apache/spark/storage/BlockManager.scala

@@ -721,7 +721,7 @@ private[spark] class BlockManager(
    * Get block from remote block managers as serialized bytes.
    */
   def getRemoteBytes(blockId: BlockId): Option[ChunkedByteBuffer] = {
-    // TODO if we change this method to return the ManagedBuffer, then getRemoteValues
+    // TODO SPARK-25905 if we change this method to return the ManagedBuffer, then getRemoteValues
     // could just use the inputStream on the temp file, rather than reading the file into memory.
     // Until then, replication can cause the process to use too much memory and get killed
     // even though we've read the data to disk.

core/src/main/scala/org/apache/spark/storage/DiskStore.scala

@@ -201,7 +201,7 @@ private class DiskBlockData(
   private def open() = new FileInputStream(file).getChannel
 }
 
-private class EncryptedBlockData(
+private[spark] class EncryptedBlockData(
     file: File,
     blockSize: Long,
     conf: SparkConf,
@@ -263,7 +263,8 @@ private class EncryptedBlockData(
   }
 }
 
-private class EncryptedManagedBuffer(val blockData: EncryptedBlockData) extends ManagedBuffer {
+private[spark] class EncryptedManagedBuffer(
+    val blockData: EncryptedBlockData) extends ManagedBuffer {
 
   // This is the size of the decrypted data
   override def size(): Long = blockData.size

core/src/main/scala/org/apache/spark/util/io/ChunkedByteBuffer.scala

@@ -29,7 +29,7 @@ import org.apache.spark.SparkEnv
 import org.apache.spark.internal.config
 import org.apache.spark.network.buffer.{FileSegmentManagedBuffer, ManagedBuffer}
 import org.apache.spark.network.util.{ByteArrayWritableChannel, LimitedInputStream}
-import org.apache.spark.storage.StorageUtils
+import org.apache.spark.storage.{EncryptedManagedBuffer, StorageUtils}
 import org.apache.spark.unsafe.array.ByteArrayMethods
 import org.apache.spark.util.Utils
 
@@ -173,11 +173,13 @@ private[spark] class ChunkedByteBuffer(var chunks: Array[ByteBuffer]) {
 private[spark] object ChunkedByteBuffer {
 
 
-  // TODO eliminate this method if we switch BlockManager to getting InputStreams
+  // TODO SPARK-25905 eliminate this method if we switch BlockManager to getting InputStreams
   def fromManagedBuffer(data: ManagedBuffer): ChunkedByteBuffer = {
     data match {
       case f: FileSegmentManagedBuffer =>
         fromFile(f.getFile, f.getOffset, f.getLength)
+      case e: EncryptedManagedBuffer =>
+        e.blockData.toChunkedByteBuffer(ByteBuffer.allocate _)
       case other =>
         new ChunkedByteBuffer(other.nioByteBuffer())
     }