/*******************************************************************************
* Copyright (c) 2005, 2006 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.erlide.util;
/**
* Base64 is a helper class for converting byte arrays to and from base 64
* encoded Strings.
*
*/
public final class Base64 {
private Base64() {
}
private static final byte EQUAL_SIGN = (byte) '=';
private static char[] digits = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y',
'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2',
'3', '4', '5', '6', '7', '8', '9', '+', '/' };
/**
* This method decodes the byte array in base 64 encoding into a char array
* Base 64 encoding has to be according to the specification given by the
* RFC 1521 (5.2).
*
* @param data
* the encoded byte array
* @return the decoded byte array
*/
public static byte[] decode(final byte[] data) {
if (data.length == 0) {
return data;
}
int lastRealDataIndex = data.length - 1;
while (data[lastRealDataIndex] == EQUAL_SIGN) {
lastRealDataIndex--;
}
// original data digit is 8 bits long, but base64 digit is 6 bits long
final int padBytes = data.length - 1 - lastRealDataIndex;
final int byteLength = data.length * 6 / 8 - padBytes;
final byte[] result = new byte[byteLength];
// Each 4 bytes of input (encoded) we end up with 3 bytes of output
int dataIndex = 0;
int resultIndex = 0;
int allBits = 0;
// how many result chunks we can process before getting to pad bytes
final int resultChunks = (lastRealDataIndex + 1) / 4;
for (int i = 0; i < resultChunks; i++) {
allBits = 0;
// Loop 4 times gathering input bits (4 * 6 = 24)
for (int j = 0; j < 4; j++) {
allBits = allBits << 6 | decodeDigit(data[dataIndex++]);
}
// Loop 3 times generating output bits (3 * 8 = 24)
for (int j = resultIndex + 2; j >= resultIndex; j--) {
result[j] = (byte) (allBits & 0xff); // Bottom 8 bits
allBits = allBits >>> 8;
}
resultIndex += 3; // processed 3 result bytes
}
// Now we do the extra bytes in case the original (non-encoded) data
// was not multiple of 3 bytes
if (padBytes == 1) {
// 1 pad byte means 3 (4-1) extra Base64 bytes of input, 18
// bits, of which only 16 are meaningful
// Or: 2 bytes of result data
allBits = 0;
// Loop 3 times gathering input bits
for (int j = 0; j < 3; j++) {
allBits = allBits << 6 | decodeDigit(data[dataIndex++]);
}
// NOTE - The code below ends up being equivalent to allBits =
// allBits>>>2
// But we code it in a non-optimized way for clarity
// The 4th, missing 6 bits are all 0
allBits = allBits << 6;
// The 3rd, missing 8 bits are all 0
allBits = allBits >>> 8;
// Loop 2 times generating output bits
for (int j = resultIndex + 1; j >= resultIndex; j--) {
result[j] = (byte) (allBits & 0xff); // Bottom 8
// bits
allBits = allBits >>> 8;
}
} else if (padBytes == 2) {
// 2 pad bytes mean 2 (4-2) extra Base64 bytes of input, 12 bits
// of data, of which only 8 are meaningful
// Or: 1 byte of result data
allBits = 0;
// Loop 2 times gathering input bits
for (int j = 0; j < 2; j++) {
allBits = allBits << 6 | decodeDigit(data[dataIndex++]);
}
// NOTE - The code below ends up being equivalent to allBits =
// allBits>>>4
// But we code it in a non-optimized way for clarity
// The 3rd and 4th, missing 6 bits are all 0
allBits = allBits << 6;
allBits = allBits << 6;
// The 3rd and 4th, missing 8 bits are all 0
allBits = allBits >>> 8;
allBits = allBits >>> 8;
result[resultIndex] = (byte) (allBits & 0xff); // Bottom
// 8
// bits
}
return result;
}
/**
* This method converts a Base 64 digit to its numeric value.
*
* @param data
* digit (character) to convert
* @return value for the digit
*/
static int decodeDigit(final byte data) {
final char charData = (char) data;
if (charData <= 'Z' && charData >= 'A') {
return charData - 'A';
}
if (charData <= 'z' && charData >= 'a') {
return charData - 'a' + 26;
}
if (charData <= '9' && charData >= '0') {
return charData - '0' + 52;
}
switch (charData) {
case '+':
return 62;
case '/':
return 63;
default:
throw new IllegalArgumentException("Invalid char to decode: " + data); //$NON-NLS-1$
}
}
/**
* This method encodes the byte array into a char array in base 64 according
* to the specification given by the RFC 1521 (5.2).
*
* @param data
* the encoded char array
* @return the byte array that needs to be encoded
*/
public static byte[] encode(final byte[] data) {
final int sourceChunks = data.length / 3;
final int len = (data.length + 2) / 3 * 4;
final byte[] result = new byte[len];
final int extraBytes = data.length - sourceChunks * 3;
// Each 4 bytes of input (encoded) we end up with 3 bytes of output
int dataIndex = 0;
int resultIndex = 0;
int allBits = 0;
for (int i = 0; i < sourceChunks; i++) {
allBits = 0;
// Loop 3 times gathering input bits (3 * 8 = 24)
for (int j = 0; j < 3; j++) {
allBits = allBits << 8 | data[dataIndex++] & 0xff;
}
// Loop 4 times generating output bits (4 * 6 = 24)
for (int j = resultIndex + 3; j >= resultIndex; j--) {
result[j] = (byte) digits[allBits & 0x3f]; // Bottom
// 6
// bits
allBits = allBits >>> 6;
}
resultIndex += 4; // processed 4 result bytes
}
// Now we do the extra bytes in case the original (non-encoded) data
// is not multiple of 4 bytes
if (extraBytes == 1) {
allBits = data[dataIndex++]; // actual byte
allBits = allBits << 8; // 8 bits of zeroes
allBits = allBits << 8; // 8 bits of zeroes
// Loop 4 times generating output bits (4 * 6 = 24)
for (int j = resultIndex + 3; j >= resultIndex; j--) {
result[j] = (byte) digits[allBits & 0x3f]; // Bottom
// 6
// bits
allBits = allBits >>> 6;
}
// 2 pad tags
result[result.length - 1] = (byte) '=';
result[result.length - 2] = (byte) '=';
} else if (extraBytes == 2) {
allBits = data[dataIndex++]; // actual byte
allBits = allBits << 8 | data[dataIndex++] & 0xff; // actual
// byte
allBits = allBits << 8; // 8 bits of zeroes
// Loop 4 times generating output bits (4 * 6 = 24)
for (int j = resultIndex + 3; j >= resultIndex; j--) {
result[j] = (byte) digits[allBits & 0x3f]; // Bottom
// 6
// bits
allBits = allBits >>> 6;
}
// 1 pad tag
result[result.length - 1] = (byte) '=';
}
return result;
}
}