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/*
* Copyright 2009 Google Inc.
*
* 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.google.gwt.user.server;
/**
* A utility to decode and encode byte arrays as Strings, using only "safe"
* characters.
*/
public class Base64Utils {
/**
* An array mapping size but values to the characters that will be used to
* represent them. Note that this is not identical to the set of characters
* used by MIME-Base64.
*/
private static final char[] base64Chars = new char[] {
'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', '$', '_'};
/**
* An array mapping legal base 64 characters [a-zA-Z0-9$_] to their associated
* 6-bit values. The source indices will be given by 7-bit ASCII characters,
* thus the array size needs to be 128 (actually 123 would suffice for the
* given set of characters in use).
*/
private static final byte[] base64Values = new byte[128];
/**
* Initialize the base 64 encoder values.
*/
static {
// Invert the mapping (i -> base64Chars[i])
for (int i = 0; i < base64Chars.length; i++) {
base64Values[base64Chars[i]] = (byte) i;
}
}
/**
* Decode a base64 string into a byte array.
*
* @param data the encoded data.
* @return a byte array.
* @see #fromBase64(String)
*/
public static byte[] fromBase64(String data) {
if (data == null) {
return null;
}
int len = data.length();
assert (len % 4) == 0;
if (len == 0) {
return new byte[0];
}
char[] chars = new char[len];
data.getChars(0, len, chars, 0);
int olen = 3 * (len / 4);
if (chars[len - 2] == '=') {
--olen;
}
if (chars[len - 1] == '=') {
--olen;
}
byte[] bytes = new byte[olen];
int iidx = 0;
int oidx = 0;
while (iidx < len) {
int c0 = base64Values[chars[iidx++] & 0xff];
int c1 = base64Values[chars[iidx++] & 0xff];
int c2 = base64Values[chars[iidx++] & 0xff];
int c3 = base64Values[chars[iidx++] & 0xff];
int c24 = (c0 << 18) | (c1 << 12) | (c2 << 6) | c3;
bytes[oidx++] = (byte) (c24 >> 16);
if (oidx == olen) {
break;
}
bytes[oidx++] = (byte) (c24 >> 8);
if (oidx == olen) {
break;
}
bytes[oidx++] = (byte) c24;
}
return bytes;
}
/**
* Decode a base64 string into a long value.
*/
public static long longFromBase64(String value) {
int pos = 0;
long longVal = base64Values[value.charAt(pos++)];
int len = value.length();
while (pos < len) {
longVal <<= 6;
longVal |= base64Values[value.charAt(pos++)];
}
return longVal;
}
/**
* Converts a byte array into a base 64 encoded string. Null is encoded as
* null, and an empty array is encoded as an empty string. Otherwise, the byte
* data is read 3 bytes at a time, with bytes off the end of the array padded
* with zeros. Each 24-bit chunk is encoded as 4 characters from the sequence
* [A-Za-z0-9$_]. If one of the source positions consists entirely of padding
* zeros, an '=' character is used instead.
*
* @param data a byte array, which may be null or empty
* @return a String
*/
public static String toBase64(byte[] data) {
if (data == null) {
return null;
}
int len = data.length;
if (len == 0) {
return "";
}
int olen = 4 * ((len + 2) / 3);
char[] chars = new char[olen];
int iidx = 0;
int oidx = 0;
int charsLeft = len;
while (charsLeft > 0) {
int b0 = data[iidx++] & 0xff;
int b1 = (charsLeft > 1) ? data[iidx++] & 0xff : 0;
int b2 = (charsLeft > 2) ? data[iidx++] & 0xff : 0;
int b24 = (b0 << 16) | (b1 << 8) | b2;
int c0 = (b24 >> 18) & 0x3f;
int c1 = (b24 >> 12) & 0x3f;
int c2 = (b24 >> 6) & 0x3f;
int c3 = b24 & 0x3f;
chars[oidx++] = base64Chars[c0];
chars[oidx++] = base64Chars[c1];
chars[oidx++] = (charsLeft > 1) ? base64Chars[c2] : '=';
chars[oidx++] = (charsLeft > 2) ? base64Chars[c3] : '=';
charsLeft -= 3;
}
return new String(chars);
}
/**
* Return a string containing a base-64 encoded version of the given long
* value. Leading groups of all zero bits are omitted.
*/
public static String toBase64(long value) {
// Convert to ints early to avoid need for long ops
int low = (int) (value & 0xffffffff);
int high = (int) (value >> 32);
StringBuilder sb = new StringBuilder();
boolean haveNonZero = base64Append(sb, (high >> 28) & 0xf, false);
haveNonZero = base64Append(sb, (high >> 22) & 0x3f, haveNonZero);
haveNonZero = base64Append(sb, (high >> 16) & 0x3f, haveNonZero);
haveNonZero = base64Append(sb, (high >> 10) & 0x3f, haveNonZero);
haveNonZero = base64Append(sb, (high >> 4) & 0x3f, haveNonZero);
int v = ((high & 0xf) << 2) | ((low >> 30) & 0x3);
haveNonZero = base64Append(sb, v, haveNonZero);
haveNonZero = base64Append(sb, (low >> 24) & 0x3f, haveNonZero);
haveNonZero = base64Append(sb, (low >> 18) & 0x3f, haveNonZero);
haveNonZero = base64Append(sb, (low >> 12) & 0x3f, haveNonZero);
base64Append(sb, (low >> 6) & 0x3f, haveNonZero);
base64Append(sb, low & 0x3f, true);
return sb.toString();
}
private static boolean base64Append(StringBuilder sb, int digit,
boolean haveNonZero) {
if (digit > 0) {
haveNonZero = true;
}
if (haveNonZero) {
sb.append(base64Chars[digit]);
}
return haveNonZero;
}
}
