impl/src/main/java/org/apache/myfaces/util/lang/Hex.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.myfaces.util.lang;

// minimal version of org.apache.commons.codec.binary.Hex to avoid commons-codec or JAXB DatatypeConverter dependency.
public class Hex
{
    /**
     * Used to build output as Hex
     */
    private static final char[] DIGITS_LOWER
            = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};

    /**
     * Used to build output as Hex
     */
    private static final char[] DIGITS_UPPER
            = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};

    /**
     * Converts a String representing hexadecimal values into an array of bytes of those same values. The
     * returned array will be half the length of the passed String, as it takes two characters to represent any given
     * byte. An exception is thrown if the passed String has an odd number of elements.
     *
     * @param data
     * A String containing hexadecimal digits
     *
     * @return A byte array containing binary data decoded from the supplied char array.
     *
     * @throws IllegalArgumentException
     * Thrown if an odd number or illegal of characters is supplied
     * @since 1.11
     */
    public static byte[] decodeHex(final String data) throws IllegalArgumentException
    {
        return decodeHex(data.toCharArray());
    }

    /**
     * Converts an array of characters representing hexadecimal values into an array of bytes of those same values. The
     * returned array will be half the length of the passed array, as it takes two characters to represent any given
     * byte. An exception is thrown if the passed char array has an odd number of elements.
     *
     * @param data
     * An array of characters containing hexadecimal digits
     *
     * @return A byte array containing binary data decoded from the supplied char array.
     *
     * @throws IllegalArgumentException
     * Thrown if an odd number or illegal of characters is supplied
     */
    public static byte[] decodeHex(final char[] data) throws IllegalArgumentException
    {
        final int len = data.length;

        if ((len & 0x01) != 0)
        {
            throw new IllegalArgumentException("Odd number of characters.");
        }

        final byte[] out = new byte[len >> 1];

        // two characters form the hex value.
        for (int i = 0, j = 0; j < len; i++)
        {
            int f = toDigit(data[j], j) << 4;
            j++;
            f = f | toDigit(data[j], j);
            j++;
            out[i] = (byte) (f & 0xFF);
        }

        return out;
    }

    /**
     * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
     * The returned array will be double the length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data
     * a byte[] to convert to Hex characters
     *
     * @return A char[] containing lower-case hexadecimal characters
     */
    public static char[] encodeHex(final byte[] data)
    {
        return encodeHex(data, true);
    }

    /**
     * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
     * The returned array will be double the length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data
     * a byte[] to convert to Hex characters
     * @param toLowerCase
     * <code>true</code> converts to lowercase, <code>false</code> to uppercase
     *
     * @return A char[] containing hexadecimal characters in the selected case
     *
     * @since 1.4
     */
    public static char[] encodeHex(final byte[] data, final boolean toLowerCase)
    {
        return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
    }

    /**
     * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
     * The returned array will be double the length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data
     * a byte[] to convert to Hex characters
     * @param toDigits
     * the output alphabet (must contain at least 16 chars)
     *
     * @return A char[] containing the appropriate characters from the alphabet
     * For best results, this should be either upper- or lower-case hex.
     *
     * @since 1.4
     */
    protected static char[] encodeHex(final byte[] data, final char[] toDigits)
    {
        final int l = data.length;
        final char[] out = new char[l << 1];
        // two characters form the hex value.
        for (int i = 0, j = 0; i < l; i++)
        {
            out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
            out[j++] = toDigits[0x0F & data[i]];
        }
        return out;
    }

    /**
     * Converts a hexadecimal character to an integer.
     *
     * @param ch
     * A character to convert to an integer digit
     * @param index
     * The index of the character in the source
     *
     * @return An integer
     *
     * @throws IllegalArgumentException
     * Thrown if ch is an illegal hex character
     */
    protected static int toDigit(final char ch, final int index) throws IllegalArgumentException
    {
        final int digit = Character.digit(ch, 16);
        if (digit == -1)
        {
            throw new IllegalArgumentException("Illegal hexadecimal character " + ch + " at index " + index);
        }
        return digit;
    }
}