| /* |
| * Copyright (C) 2012 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.apksig.internal.util; |
| |
| import java.nio.ByteBuffer; |
| |
| /** |
| * Hexadecimal encoding where each byte is represented by two hexadecimal digits. |
| */ |
| public class HexEncoding { |
| |
| /** Hidden constructor to prevent instantiation. */ |
| private HexEncoding() {} |
| |
| private static final char[] HEX_DIGITS = "0123456789abcdef".toCharArray(); |
| |
| /** |
| * Encodes the provided data as a hexadecimal string. |
| */ |
| public static String encode(byte[] data) { |
| return encode(data, 0, data.length); |
| } |
| |
| /** |
| * Encodes the provided data as a hexadecimal string. |
| */ |
| public static String encode(byte[] data, int offset, int len) { |
| StringBuilder result = new StringBuilder(len * 2); |
| for (int i = 0; i < len; i++) { |
| byte b = data[offset + i]; |
| result.append(HEX_DIGITS[(b >>> 4) & 0x0f]); |
| result.append(HEX_DIGITS[b & 0x0f]); |
| } |
| return result.toString(); |
| } |
| |
| /** |
| * Encodes the provided data as a hexadecimal string. |
| */ |
| public static String encode(ByteBuffer buf) { |
| return encode(buf.array(), buf.arrayOffset() + buf.position(), buf.remaining()); |
| } |
| |
| /** |
| * Decodes the provided hexadecimal string into an array of bytes. |
| */ |
| public static byte[] decode(String encoded) { |
| // IMPLEMENTATION NOTE: Special care is taken to permit odd number of hexadecimal digits. |
| int resultLengthBytes = (encoded.length() + 1) / 2; |
| byte[] result = new byte[resultLengthBytes]; |
| int resultOffset = 0; |
| int encodedCharOffset = 0; |
| if ((encoded.length() % 2) != 0) { |
| // Odd number of digits -- the first digit is the lower 4 bits of the first result byte. |
| result[resultOffset++] = |
| (byte) getHexadecimalDigitValue(encoded.charAt(encodedCharOffset)); |
| encodedCharOffset++; |
| } |
| for (int len = encoded.length(); encodedCharOffset < len; encodedCharOffset += 2) { |
| result[resultOffset++] = (byte) |
| ((getHexadecimalDigitValue(encoded.charAt(encodedCharOffset)) << 4) |
| | getHexadecimalDigitValue(encoded.charAt(encodedCharOffset + 1))); |
| } |
| return result; |
| } |
| |
| private static int getHexadecimalDigitValue(char c) { |
| if ((c >= 'a') && (c <= 'f')) { |
| return (c - 'a') + 0x0a; |
| } else if ((c >= 'A') && (c <= 'F')) { |
| return (c - 'A') + 0x0a; |
| } else if ((c >= '0') && (c <= '9')) { |
| return c - '0'; |
| } else { |
| throw new IllegalArgumentException( |
| "Invalid hexadecimal digit at position : '" |
| + c + "' (0x" + Integer.toHexString(c) + ")"); |
| } |
| } |
| } |