Base32.java

/* (PD) 2001 The Bitzi Corporation
 * Please see http://bitzi.com/publicdomain for more info.
 *
 * As modified by Patrick Woodworth:
 *
 * Copyright 2011 Patrick Woodworth
 *
 * 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 org.emergent.android.weave.client;

/**
 * Base32 - encodes and decodes RFC3548 Base32 (see
 * http://www.faqs.org/rfcs/rfc3548.html )
 * 
 * @author Robert Kaye
 * @author Gordon Mohr
 */
public class Base32 {
	private static final String base32Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
	private static final int[] base32Lookup = { 0xFF, 0xFF, 0x1A, 0x1B, 0x1C,
			0x1D, 0x1E, 0x1F, // '0', '1', '2', '3', '4', '5', '6', '7'
			0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // '8', '9', ':',
															// ';', '<', '=',
															// '>', '?'
			0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, // '@', 'A', 'B',
															// 'C', 'D', 'E',
															// 'F', 'G'
			0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, // 'H', 'I', 'J',
															// 'K', 'L', 'M',
															// 'N', 'O'
			0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, // 'P', 'Q', 'R',
															// 'S', 'T', 'U',
															// 'V', 'W'
			0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, // 'X', 'Y', 'Z',
															// '[', '\', ']',
															// '^', '_'
			0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, // '`', 'a', 'b',
															// 'c', 'd', 'e',
															// 'f', 'g'
			0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, // 'h', 'i', 'j',
															// 'k', 'l', 'm',
															// 'n', 'o'
			0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, // 'p', 'q', 'r',
															// 's', 't', 'u',
															// 'v', 'w'
			0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF // 'x', 'y', 'z',
															// '{', '|', '}',
															// '~', 'DEL'
	};

	/**
	 * Decodes the given Base32 String to a raw byte array.
	 * 
	 * @param base32
	 * @return Decoded <code>base32</code> String as a raw byte array.
	 */
	static public byte[] decode(final String base32) {
		int i, index, lookup, offset, digit;
		byte[] bytes = new byte[base32.length() * 5 / 8];

		for (i = 0, index = 0, offset = 0; i < base32.length(); i++) {
			lookup = base32.charAt(i) - '0';

			/* Skip chars outside the lookup table */
			if (lookup < 0 || lookup >= base32Lookup.length) {
				continue;
			}

			digit = base32Lookup[lookup];

			/* If this digit is not in the table, ignore it */
			if (digit == 0xFF) {
				continue;
			}

			if (index <= 3) {
				index = (index + 5) % 8;
				if (index == 0) {
					bytes[offset] |= digit;
					offset++;
					if (offset >= bytes.length)
						break;
				} else {
					bytes[offset] |= digit << (8 - index);
				}
			} else {
				index = (index + 5) % 8;
				bytes[offset] |= (digit >>> index);
				offset++;

				if (offset >= bytes.length) {
					break;
				}
				bytes[offset] |= digit << (8 - index);
			}
		}
		return bytes;
	}

	public static byte[] decodeModified(String data) {
		return decode(data.replace('8', 'L').replace('9', 'O'));
	}

	public static byte[] encode(byte[] data) {
		return WeaveUtil.toAsciiBytes(encodeOriginal(data).toLowerCase());
	}

	/**
	 * Encodes byte array to Base32 String.
	 * 
	 * @param bytes
	 *            Bytes to encode.
	 * @return Encoded byte array <code>bytes</code> as a String.
	 * 
	 */
	static public String encodeOriginal(final byte[] bytes) {
		int i = 0, index = 0, digit = 0;
		int currByte, nextByte;
		StringBuffer base32 = new StringBuffer((bytes.length + 7) * 8 / 5);

		while (i < bytes.length) {
			currByte = (bytes[i] >= 0) ? bytes[i] : (bytes[i] + 256); // unsign

			/* Is the current digit going to span a byte boundary? */
			if (index > 3) {
				if ((i + 1) < bytes.length) {
					nextByte = (bytes[i + 1] >= 0) ? bytes[i + 1]
							: (bytes[i + 1] + 256);
				} else {
					nextByte = 0;
				}

				digit = currByte & (0xFF >> index);
				index = (index + 5) % 8;
				digit <<= index;
				digit |= nextByte >> (8 - index);
				i++;
			} else {
				digit = (currByte >> (8 - (index + 5))) & 0x1F;
				index = (index + 5) % 8;
				if (index == 0)
					i++;
			}
			base32.append(base32Chars.charAt(digit));
		}

		return base32.toString();
	}

	/**
	 * For testing, take a command-line argument in Base32, decode, print in
	 * hex, encode, print
	 * 
	 * @param args
	 */
	static public void main(String[] args) {
		if (args.length == 0) {
			System.out.println("Supply a Base32-encoded argument.");
			return;
		}
		System.out.println(" Original: " + args[0]);
		byte[] decoded = Base32.decode(args[0]);
		System.out.print("      Hex: ");
		for (int i = 0; i < decoded.length; i++) {
			int b = decoded[i];
			if (b < 0) {
				b += 256;
			}
			System.out.print((Integer.toHexString(b + 256)).substring(1));
		}
		System.out.println();
		System.out.println("Reencoded: " + Base32.encode(decoded));
	}
}