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.chunk;
  
  import com.android.internal.util.Preconditions;
  import java.util.Arrays;
  import java.util.Base64;
  
  /**
   * Represents the SHA-256 hash of the plaintext of a chunk, which is frequently used as a key.
   *
   * <p>This class is {@link Comparable} and implements {@link #equals(Object)} and {@link
   * #hashCode()}.
   */
  public class ChunkHash implements Comparable<ChunkHash> {
      /** The length of the hash in bytes. The hash is a SHA-256, so this is 256 bits. */
      public static final int HASH_LENGTH_BYTES = 256 / 8;
  
      private static final int UNSIGNED_MASK = 0xFF;
  
      private final byte[] mHash;
  
      /** Constructs a new instance which wraps the given SHA-256 hash bytes. */
      public ChunkHash(byte[] hash) {
          Preconditions.checkArgument(hash.length == HASH_LENGTH_BYTES, "Hash must have 256 bits");
          mHash = hash;
      }
  
      public byte[] getHash() {
          return mHash;
      }
  
      @Override
      public boolean equals(Object o) {
          if (this == o) {
              return true;
          }
          if (!(o instanceof ChunkHash)) {
              return false;
          }
  
          ChunkHash chunkHash = (ChunkHash) o;
          return Arrays.equals(mHash, chunkHash.mHash);
      }
  
      @Override
      public int hashCode() {
          return Arrays.hashCode(mHash);
      }
  
      @Override
      public int compareTo(ChunkHash other) {
          return lexicographicalCompareUnsignedBytes(getHash(), other.getHash());
      }
  
      @Override
      public String toString() {
          return Base64.getEncoder().encodeToString(mHash);
      }
  
      private static int lexicographicalCompareUnsignedBytes(byte[] left, byte[] right) {
          int minLength = Math.min(left.length, right.length);
          for (int i = 0; i < minLength; i++) {
              int result = toInt(left[i]) - toInt(right[i]);
              if (result != 0) {
                  return result;
              }
          }
          return left.length - right.length;
      }
  
      private static int toInt(byte value) {
          return value & UNSIGNED_MASK;
      }
  }
  