/* ==================================================================== * Copyright (c) 2006 J.T. Beetstra * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated documentation files (the * "Software"), to deal in the Software without restriction, including * without limitation the rights to use, copy, modify, merge, publish, * distribute, sublicense, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to * the following conditions: * * The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. * ==================================================================== */ package com.beetstra.jutf7; import java.util.Arrays; /** *

* Represent a base 64 mapping. The 64 characters used in the encoding can be * specified, since modified-UTF-7 uses other characters than UTF-7 (',' instead * of '/'). *

*

* The exact type of the arguments and result values is adapted to the needs of * the encoder and decoder, as opposed to following a strict interpretation of * base 64. *

*

* Base 64, as specified in RFC 2045, is an encoding used to encode bytes as * characters. In (modified-)UTF-7 however, it is used to encode characters as * bytes, using some intermediate steps: *

*
    *
  1. Encode all characters as a 16-bit (UTF-16) integer value
  2. *
  3. Write this as stream of bytes (most-significant first)
  4. *
  5. Encode these bytes using (modified) base 64 encoding
  6. *
  7. Write the thus formed stream of characters as a stream of bytes, using * ASCII encoding
  8. *
* * @author Jaap Beetstra */ class Base64Util { private static final int ALPHABET_LENGTH = 64; private final char[] alphabet; private final int[] inverseAlphabet; /** * Initializes the class with the specified encoding/decoding alphabet. * * @param alphabet * @throws IllegalArgumentException if alphabet is not 64 characters long or * contains characters which are not 7-bit ASCII */ Base64Util(final String alphabet) { this.alphabet = alphabet.toCharArray(); if (alphabet.length() != ALPHABET_LENGTH) throw new IllegalArgumentException("alphabet has incorrect length (should be 64, not " + alphabet.length() + ")"); inverseAlphabet = new int[128]; Arrays.fill(inverseAlphabet, -1); for (int i = 0; i < this.alphabet.length; i++) { final char ch = this.alphabet[i]; if (ch >= 128) throw new IllegalArgumentException("invalid character in alphabet: " + ch); inverseAlphabet[ch] = i; } } /** * Returns the integer value of the six bits represented by the specified * character. * * @param ch The character, as a ASCII encoded byte * @return The six bits, as an integer value, or -1 if the byte is not in * the alphabet */ int getSextet(final byte ch) { if (ch >= 128) return -1; return inverseAlphabet[ch]; } /** * Tells whether the alphabet contains the specified character. * * @param ch The character * @return true if the alphabet contains ch, false otherwise */ boolean contains(final char ch) { if (ch >= 128) return false; return inverseAlphabet[ch] >= 0; } /** * Encodes the six bit group as a character. * * @param sextet The six bit group to be encoded * @return The ASCII value of the character */ byte getChar(final int sextet) { return (byte)alphabet[sextet]; } }