/*
* Copyright 2013-2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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.amazonaws.util;
import static com.amazonaws.util.CodecUtils.sanityCheckLastPos;
/**
* A Base 64 codec implementation.
*
* @author Hanson Char
*/
class Base64Codec implements Codec {
private static final int OFFSET_OF_a = 'a' - 26;
private static final int OFFSET_OF_0 = '0' - 52;
private static final int OFFSET_OF_PLUS = '+' - 62;
private static final int OFFSET_OF_SLASH = '/' - 63;
private static final int MASK_2BITS = (1 << 2) - 1;
private static final int MASK_4BITS = (1 << 4) - 1;
private static final int MASK_6BITS = (1 << 6) - 1;
// Alphabet as defined at http://www.ietf.org/rfc/rfc4648.txt
private static final byte PAD = '=';
private static class LazyHolder {
private static final byte[] DECODED = decodeTable();
private static byte[] decodeTable() {
final byte[] dest = new byte['z'+1];
for (int i=0; i <= 'z'; i++)
{
if (i >= 'A' && i <= 'Z')
dest[i] = (byte)(i - 'A');
else if (i >= '0' && i <= '9')
dest[i] = (byte)(i - OFFSET_OF_0);
else if (i == '+')
dest[i] = (byte)(i - OFFSET_OF_PLUS);
else if (i == '/')
dest[i] = (byte)(i - OFFSET_OF_SLASH);
else if (i >= 'a' && i <= 'z')
dest[i] = (byte)(i - OFFSET_OF_a);
else
dest[i] = -1;
}
return dest;
}
}
private final byte[] alphabets;
Base64Codec() {
this.alphabets = CodecUtils.toBytesDirect("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/");
}
protected Base64Codec(byte[] alphabets) {
this.alphabets = alphabets;
}
@Override
public byte[] encode(byte[] src) {
final int num3bytes = src.length / 3;
final int remainder = src.length % 3;
if (remainder == 0)
{
byte[] dest = new byte[num3bytes * 4];
for (int s=0,d=0; s < src.length; s+=3, d+=4)
encode3bytes(src, s, dest, d);
return dest;
}
byte[] dest = new byte[(num3bytes+1) * 4];
int s=0, d=0;
for (; s < src.length-remainder; s+=3, d+=4)
encode3bytes(src, s, dest, d);
switch(remainder) {
case 1:
encode1byte(src, s, dest, d);
break;
case 2:
encode2bytes(src, s, dest, d);
break;
default:
throw new IllegalStateException();
}
return dest;
}
void encode3bytes(byte[] src, int s, byte[] dest, int d) {
// operator precedence in descending order: >>> or <<, &, |
byte p;
dest[d++] = (byte)alphabets[(p=src[s++]) >>> 2 & MASK_6BITS]; // 6
dest[d++] = (byte)alphabets[(p & MASK_2BITS) << 4 | (p=src[s++]) >>> 4 & MASK_4BITS]; // 2 4
dest[d++] = (byte)alphabets[(p & MASK_4BITS) << 2 | (p=src[s]) >>> 6 & MASK_2BITS]; // 4 2
dest[d] = (byte)alphabets[p & MASK_6BITS]; // 6
return;
}
void encode2bytes(byte[] src, int s, byte[] dest, int d) {
// operator precedence in descending order: >>> or <<, &, |
byte p;
dest[d++] = (byte)alphabets[(p=src[s++]) >>> 2 & MASK_6BITS]; // 6
dest[d++] = (byte)alphabets[(p & MASK_2BITS) << 4 | (p=src[s]) >>> 4 & MASK_4BITS]; // 2 4
dest[d++] = (byte)alphabets[(p & MASK_4BITS) << 2]; // 4
dest[d] = PAD;
return;
}
void encode1byte(byte[] src, int s, byte[] dest, int d) {
// operator precedence in descending order: >>> or <<, &, |
byte p;
dest[d++] = (byte)alphabets[(p=src[s]) >>> 2 & MASK_6BITS]; // 6
dest[d++] = (byte)alphabets[(p & MASK_2BITS) << 4]; // 2
dest[d++] = PAD;
dest[d] = PAD;
return;
}
void decode4bytes(byte[] src, int s, byte[] dest, int d) {
int p=0;
// operator precedence in descending order: >>> or <<, &, |
dest[d++] = (byte)
(
pos(src[s++]) << 2
| (p=pos(src[s++])) >>> 4 & MASK_2BITS
)
; // 6 2
dest[d++] = (byte)
(
(p & MASK_4BITS) << 4
| (p=pos(src[s++])) >>> 2 & MASK_4BITS
)
; // 4 4
dest[d] = (byte)
(
(p & MASK_2BITS) << 6
| pos(src[s])
)
; // 2 6
return;
}
/**
* @param n the number of final quantum in bytes to decode into. Ranges from 1 to 3, inclusive.
*/
void decode1to3bytes(int n, byte[] src, int s, byte[] dest, int d) {
int p=0;
// operator precedence in descending order: >>> or <<, &, |
dest[d++] = (byte)
(
pos(src[s++]) << 2
| (p=pos(src[s++])) >>> 4 & MASK_2BITS
)
; // 6 2
if (n == 1) {
sanityCheckLastPos(p, MASK_4BITS);
return;
}
dest[d++] = (byte)
(
(p & MASK_4BITS) << 4
| (p=pos(src[s++])) >>> 2 & MASK_4BITS
)
; // 4 4
if (n == 2) {
sanityCheckLastPos(p, MASK_2BITS);
return;
}
dest[d] = (byte)
(
(p & MASK_2BITS) << 6
| pos(src[s])
)
; // 2 6
return;
}
@Override
public byte[] decode(byte[] src, final int length)
{
if (length % 4 != 0)
throw new IllegalArgumentException
("Input is expected to be encoded in multiple of 4 bytes but found: " + length);
int pads=0;
int last = length-1;
// max possible padding in b64 encoding is 2
for (; pads < 2 && last > -1; last--, pads++) {
if (src[last] != PAD)
break;
}
final int fq; // final quantum in unit of bytes
switch(pads) {
case 0:
fq=3;
break; // final quantum of encoding input is an integral multiple of 24 bits
case 1:
fq=2;
break; // final quantum of encoding input is exactly 16 bits
case 2:
fq=1;
break; // final quantum of encoding input is exactly 8 bits
default:
throw new Error("Impossible");
}
final byte[] dest = new byte[length / 4 * 3 - (3-fq)];
int s=0, d=0;
// % has a higher precedence than - than <
for (; d < dest.length - fq%3; s+=4,d+=3)
decode4bytes(src, s, dest, d);
if (fq < 3)
decode1to3bytes(fq, src, s, dest, d);
return dest;
}
protected int pos(byte in) {
int pos = LazyHolder.DECODED[in];
if (pos > -1)
return pos;
throw new IllegalArgumentException("Invalid base 64 character: \'" + (char)in + "\'");
}
}