/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.commons.fileupload.util.mime;
import java.io.IOException;
import java.io.OutputStream;
Since: 1.3
/**
* @since 1.3
*/
final class Base64Decoder {
Decoding table value for invalid bytes.
/**
* Decoding table value for invalid bytes.
*/
private static final int INVALID_BYTE = -1; // must be outside range 0-63
Decoding table value for padding bytes, so can detect PAD afer conversion.
/**
* Decoding table value for padding bytes, so can detect PAD afer conversion.
*/
private static final int PAD_BYTE = -2; // must be outside range 0-63
Mask to treat byte as unsigned integer.
/**
* Mask to treat byte as unsigned integer.
*/
private static final int MASK_BYTE_UNSIGNED = 0xFF;
Number of bytes per encoded chunk - 4 6bit bytes produce 3 8bit bytes on output.
/**
* Number of bytes per encoded chunk - 4 6bit bytes produce 3 8bit bytes on output.
*/
private static final int INPUT_BYTES_PER_CHUNK = 4;
Set up the encoding table.
/**
* Set up the encoding table.
*/
private static final byte[] ENCODING_TABLE = {
(byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G',
(byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N',
(byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
(byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
(byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g',
(byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n',
(byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u',
(byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z',
(byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6',
(byte) '7', (byte) '8', (byte) '9',
(byte) '+', (byte) '/'
};
The padding byte.
/**
* The padding byte.
*/
private static final byte PADDING = (byte) '=';
Set up the decoding table; this is indexed by a byte converted to an unsigned int,
so must be at least as large as the number of different byte values,
positive and negative and zero.
/**
* Set up the decoding table; this is indexed by a byte converted to an unsigned int,
* so must be at least as large as the number of different byte values,
* positive and negative and zero.
*/
private static final byte[] DECODING_TABLE = new byte[Byte.MAX_VALUE - Byte.MIN_VALUE + 1];
static {
// Initialise as all invalid characters
for (int i = 0; i < DECODING_TABLE.length; i++) {
DECODING_TABLE[i] = INVALID_BYTE;
}
// set up valid characters
for (int i = 0; i < ENCODING_TABLE.length; i++) {
DECODING_TABLE[ENCODING_TABLE[i]] = (byte) i;
}
// Allow pad byte to be easily detected after conversion
DECODING_TABLE[PADDING] = PAD_BYTE;
}
Hidden constructor, this class must not be instantiated.
/**
* Hidden constructor, this class must not be instantiated.
*/
private Base64Decoder() {
// do nothing
}
Decode the base 64 encoded byte data writing it to the given output stream,
whitespace characters will be ignored.
Params: - data – the buffer containing the Base64-encoded data
- out – the output stream to hold the decoded bytes
Throws: - IOException – thrown when the padding is incorrect or the input is truncated.
Returns: the number of bytes produced.
/**
* Decode the base 64 encoded byte data writing it to the given output stream,
* whitespace characters will be ignored.
*
* @param data the buffer containing the Base64-encoded data
* @param out the output stream to hold the decoded bytes
*
* @return the number of bytes produced.
* @throws IOException thrown when the padding is incorrect or the input is truncated.
*/
public static int decode(byte[] data, OutputStream out) throws IOException {
int outLen = 0;
byte [] cache = new byte[INPUT_BYTES_PER_CHUNK];
int cachedBytes = 0;
for (byte b : data) {
final byte d = DECODING_TABLE[MASK_BYTE_UNSIGNED & b];
if (d == INVALID_BYTE) {
continue; // Ignore invalid bytes
}
cache[cachedBytes++] = d;
if (cachedBytes == INPUT_BYTES_PER_CHUNK) {
// CHECKSTYLE IGNORE MagicNumber FOR NEXT 4 LINES
final byte b1 = cache[0];
final byte b2 = cache[1];
final byte b3 = cache[2];
final byte b4 = cache[3];
if (b1 == PAD_BYTE || b2 == PAD_BYTE) {
throw new IOException("Invalid Base64 input: incorrect padding, first two bytes cannot be padding");
}
// Convert 4 6-bit bytes to 3 8-bit bytes
// CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
out.write((b1 << 2) | (b2 >> 4)); // 6 bits of b1 plus 2 bits of b2
outLen++;
if (b3 != PAD_BYTE) {
// CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
out.write((b2 << 4) | (b3 >> 2)); // 4 bits of b2 plus 4 bits of b3
outLen++;
if (b4 != PAD_BYTE) {
// CHECKSTYLE IGNORE MagicNumber FOR NEXT 1 LINE
out.write((b3 << 6) | b4); // 2 bits of b3 plus 6 bits of b4
outLen++;
}
} else if (b4 != PAD_BYTE) { // if byte 3 is pad, byte 4 must be pad too
throw new // line wrap to avoid 120 char limit
IOException("Invalid Base64 input: incorrect padding, 4th byte must be padding if 3rd byte is");
}
cachedBytes = 0;
}
}
// Check for anything left over
if (cachedBytes != 0) {
throw new IOException("Invalid Base64 input: truncated");
}
return outLen;
}
}