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 static final char[] HEX_LOWERCASE_ARRAY = "0123456789abcdef".toCharArray();
26    private static final char[] HEX_UPPERCASE_ARRAY = "0123456789ABCDEF".toCharArray();
27
28    private ByteStringUtils() {
29    /* hide constructor */
30    }
31
32    /**
33     * Returns the hex encoded string representation of bytes.
34     * @param bytes Byte array to encode.
35     * @return Hex encoded string representation of bytes.
36     */
37    public static String toHexString(byte[] bytes) {
38        if (bytes == null || bytes.length == 0 || bytes.length % 2 != 0) {
39            return null;
40        }
41
42        final int byteLength = bytes.length;
43        final int charCount = 2 * byteLength;
44        final char[] chars = new char[charCount];
45
46        for (int i = 0; i < byteLength; i++) {
47            final int byteHex = bytes[i] & 0xFF;
48            chars[i * 2] = HEX_UPPERCASE_ARRAY[byteHex >>> 4];
49            chars[i * 2 + 1] = HEX_UPPERCASE_ARRAY[byteHex & 0x0F];
50        }
51        return new String(chars);
52    }
53
54    /**
55     * Returns the decoded byte array representation of str.
56     * @param str Hex encoded string to decode.
57     * @return Decoded byte array representation of str.
58     */
59    public static byte[] fromHexToByteArray(String str) {
60        if (str == null || str.length() == 0 || str.length() % 2 != 0) {
61            return null;
62        }
63
64        final char[] chars = str.toCharArray();
65        final int charLength = chars.length;
66        final byte[] bytes = new byte[charLength / 2];
67
68        for (int i = 0; i < bytes.length; i++) {
69            bytes[i] =
70                    (byte) (((getIndex(chars[i * 2]) << 4) & 0xF0)
71                            | (getIndex(chars[i * 2 + 1]) & 0x0F));
72        }
73        return bytes;
74    }
75
76    private static int getIndex(char c) {
77        for (int i = 0; i < HEX_UPPERCASE_ARRAY.length; i++) {
78            if (HEX_UPPERCASE_ARRAY[i] == c || HEX_LOWERCASE_ARRAY[i] == c) {
79                return i;
80            }
81        }
82        return -1;
83    }
84}
85