content: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License
   */
  
  package com.android.server.backup.encryption.chunking;
  
  import com.android.server.backup.encryption.chunk.ChunkOrderingType;
  import com.android.server.backup.encryption.chunk.ChunksMetadataProto;
  import java.io.IOException;
  
  /**
   * Encodes an {@link EncryptedChunk} as bytes, prepending the length of the chunk.
   *
   * <p>This allows us to decode the backup file during restore without any extra information about
   * the boundaries of the chunks. The backup file should contain a chunk ordering in mode {@link
   * ChunksMetadataProto#INLINE_LENGTHS}.
   *
   * <p>We use this implementation during key value backup.
   */
  public class InlineLengthsEncryptedChunkEncoder implements EncryptedChunkEncoder {
      public static final int BYTES_LENGTH = Integer.SIZE / Byte.SIZE;
  
      private final LengthlessEncryptedChunkEncoder mLengthlessEncryptedChunkEncoder =
              new LengthlessEncryptedChunkEncoder();
  
      @Override
      public void writeChunkToWriter(BackupWriter writer, EncryptedChunk chunk) throws IOException {
          int length = mLengthlessEncryptedChunkEncoder.getEncodedLengthOfChunk(chunk);
          writer.writeBytes(toByteArray(length));
          mLengthlessEncryptedChunkEncoder.writeChunkToWriter(writer, chunk);
      }
  
      @Override
      public int getEncodedLengthOfChunk(EncryptedChunk chunk) {
          return BYTES_LENGTH + mLengthlessEncryptedChunkEncoder.getEncodedLengthOfChunk(chunk);
      }
  
      @Override
      @ChunkOrderingType
      public int getChunkOrderingType() {
          return ChunksMetadataProto.INLINE_LENGTHS;
      }
  
      /**
       * Returns a big-endian representation of {@code value} in a 4-element byte array; equivalent to
       * {@code ByteBuffer.allocate(4).putInt(value).array()}. For example, the input value {@code
       * 0x12131415} would yield the byte array {@code {0x12, 0x13, 0x14, 0x15}}.
       *
       * <p>Equivalent to guava's Ints.toByteArray.
       */
      static byte[] toByteArray(int value) {
          return new byte[] {
              (byte) (value >> 24), (byte) (value >> 16), (byte) (value >> 8), (byte) value
          };
      }
  }
  