1/*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package android.util;
18
19/**
20 * A utility class for common byte array to hex string operations and vise versa.
21 *
22 * @hide
23 */
24public final class ByteStringUtils {
25  private final static char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
26
27  private ByteStringUtils() {
28    /* hide constructor */
29  }
30
31  /**
32   * Returns the hex encoded string representation of bytes.
33   * @param bytes Byte array to encode.
34   * @return Hex encoded string representation of bytes.
35   */
36  public static String toHexString(byte[] bytes) {
37    if (bytes == null || bytes.length == 0 || bytes.length % 2 != 0) {
38      return null;
39    }
40
41    final int byteLength = bytes.length;
42    final int charCount = 2 * byteLength;
43    final char[] chars = new char[charCount];
44
45    for (int i = 0; i < byteLength; i++) {
46      final int byteHex = bytes[i] & 0xFF;
47      chars[i * 2] = HEX_ARRAY[byteHex >>> 4];
48      chars[i * 2 + 1] = HEX_ARRAY[byteHex & 0x0F];
49    }
50    return new String(chars);
51  }
52
53  /**
54   * Returns the decoded byte array representation of str.
55   * @param str Hex encoded string to decode.
56   * @return Decoded byte array representation of str.
57   */
58  public static byte[] fromHexToByteArray(String str) {
59    if (str == null || str.length() == 0 || str.length() % 2 != 0) {
60      return null;
61    }
62
63    final char[] chars = str.toCharArray();
64    final int charLength = chars.length;
65    final byte[] bytes = new byte[charLength / 2];
66
67    for (int i = 0; i < bytes.length; i++) {
68      bytes[i] =
69          (byte)(((getIndex(chars[i * 2]) << 4) & 0xF0) | (getIndex(chars[i * 2 + 1]) & 0x0F));
70    }
71    return bytes;
72  }
73
74  private static int getIndex(char c) {
75    for (int i = 0; i < HEX_ARRAY.length; i++) {
76      if (HEX_ARRAY[i] == c) {
77        return i;
78      }
79    }
80    return -1;
81  }
82}
83