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UCDecoder
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bytesPerAtom(): int
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bytesPerLine(): int
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map_array: byte[]
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sequence: int
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tmp: byte[]
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crc: CRC16
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decodeAtom(PushbackInputStream, OutputStream, int): void
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lineAndSeq: ByteArrayOutputStream
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decodeBufferPrefix(PushbackInputStream, OutputStream): void
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decodeLinePrefix(PushbackInputStream, OutputStream): int
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decodeLineSuffix(PushbackInputStream, OutputStream): void
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/*
* Copyright (c) 1995, 2000, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package sun.misc;
import java.io.OutputStream;
import java.io.ByteArrayOutputStream;
import java.io.PushbackInputStream;
import java.io.PrintStream;
import java.io.IOException;
This class implements a robust character decoder. The decoder will
converted encoded text into binary data.
The basic encoding unit is a 3 character atom. It encodes two bytes
of data. Bytes are encoded into a 64 character set, the characters
were chosen specifically because they appear in all codesets.
We don't care what their numerical equivalent is because
we use a character array to map them. This is like UUencoding
with the dependency on ASCII removed.
The three chars that make up an atom are encoded as follows:
00xxxyyy 00axxxxx 00byyyyy
00 = leading zeros, all values are 0 - 63
xxxyyy - Top 3 bits of X, Top 3 bits of Y
axxxxx - a = X parity bit, xxxxx lower 5 bits of X
byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y
The atoms are arranged into lines suitable for inclusion into an
email message or text file. The number of bytes that are encoded
per line is 48 which keeps the total line length under 80 chars)
Each line has the form(
*(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)
Where each (xxx) represents a three character atom.
(LLSS) - 8 bit length (high byte), and sequence number
modulo 256;
(DDDD) - Data byte atoms, if length is odd, last data
atom has (DD00) (high byte data, low byte 0)
(CRC) - 16 bit CRC for the line, includes length,
sequence, and all data bytes. If there is a
zero pad byte (odd length) it is _NOT_
included in the CRC.
If an error is encountered during decoding this class throws a
CEFormatException. The specific detail messages are:
"UCDecoder: High byte parity error."
"UCDecoder: Low byte parity error."
"UCDecoder: Out of sequence line."
"UCDecoder: CRC check failed."
Author: Chuck McManis See Also:
/**
* This class implements a robust character decoder. The decoder will
* converted encoded text into binary data.
*
* The basic encoding unit is a 3 character atom. It encodes two bytes
* of data. Bytes are encoded into a 64 character set, the characters
* were chosen specifically because they appear in all codesets.
* We don't care what their numerical equivalent is because
* we use a character array to map them. This is like UUencoding
* with the dependency on ASCII removed.
*
* The three chars that make up an atom are encoded as follows:
* <pre>
* 00xxxyyy 00axxxxx 00byyyyy
* 00 = leading zeros, all values are 0 - 63
* xxxyyy - Top 3 bits of X, Top 3 bits of Y
* axxxxx - a = X parity bit, xxxxx lower 5 bits of X
* byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y
* </pre>
*
* The atoms are arranged into lines suitable for inclusion into an
* email message or text file. The number of bytes that are encoded
* per line is 48 which keeps the total line length under 80 chars)
*
* Each line has the form(
* <pre>
* *(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)
* Where each (xxx) represents a three character atom.
* (LLSS) - 8 bit length (high byte), and sequence number
* modulo 256;
* (DDDD) - Data byte atoms, if length is odd, last data
* atom has (DD00) (high byte data, low byte 0)
* (CRC) - 16 bit CRC for the line, includes length,
* sequence, and all data bytes. If there is a
* zero pad byte (odd length) it is _NOT_
* included in the CRC.
* </pre>
*
* If an error is encountered during decoding this class throws a
* CEFormatException. The specific detail messages are:
*
* <pre>
* "UCDecoder: High byte parity error."
* "UCDecoder: Low byte parity error."
* "UCDecoder: Out of sequence line."
* "UCDecoder: CRC check failed."
* </pre>
*
* @author Chuck McManis
* @see CharacterEncoder
* @see UCEncoder
*/
public class UCDecoder extends CharacterDecoder {
This class encodes two bytes per atom. /** This class encodes two bytes per atom. */
protected int bytesPerAtom() {
return (2);
}
this class encodes 48 bytes per line /** this class encodes 48 bytes per line */
protected int bytesPerLine() {
return (48);
}
/* this is the UCE mapping of 0-63 to characters .. */
private final static byte map_array[] = {
// 0 1 2 3 4 5 6 7
(byte)'0',(byte)'1',(byte)'2',(byte)'3',(byte)'4',(byte)'5',(byte)'6',(byte)'7', // 0
(byte)'8',(byte)'9',(byte)'A',(byte)'B',(byte)'C',(byte)'D',(byte)'E',(byte)'F', // 1
(byte)'G',(byte)'H',(byte)'I',(byte)'J',(byte)'K',(byte)'L',(byte)'M',(byte)'N', // 2
(byte)'O',(byte)'P',(byte)'Q',(byte)'R',(byte)'S',(byte)'T',(byte)'U',(byte)'V', // 3
(byte)'W',(byte)'X',(byte)'Y',(byte)'Z',(byte)'a',(byte)'b',(byte)'c',(byte)'d', // 4
(byte)'e',(byte)'f',(byte)'g',(byte)'h',(byte)'i',(byte)'j',(byte)'k',(byte)'l', // 5
(byte)'m',(byte)'n',(byte)'o',(byte)'p',(byte)'q',(byte)'r',(byte)'s',(byte)'t', // 6
(byte)'u',(byte)'v',(byte)'w',(byte)'x',(byte)'y',(byte)'z',(byte)'(',(byte)')' // 7
};
private int sequence;
private byte tmp[] = new byte[2];
private CRC16 crc = new CRC16();
Decode one atom - reads the characters from the input stream, decodes
them, and checks for valid parity.
/**
* Decode one atom - reads the characters from the input stream, decodes
* them, and checks for valid parity.
*/
protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int l) throws IOException {
int i, p1, p2, np1, np2;
byte a = -1, b = -1, c = -1;
byte high_byte, low_byte;
byte tmp[] = new byte[3];
i = inStream.read(tmp);
if (i != 3) {
throw new CEStreamExhausted();
}
for (i = 0; (i < 64) && ((a == -1) || (b == -1) || (c == -1)); i++) {
if (tmp[0] == map_array[i]) {
a = (byte) i;
}
if (tmp[1] == map_array[i]) {
b = (byte) i;
}
if (tmp[2] == map_array[i]) {
c = (byte) i;
}
}
high_byte = (byte) (((a & 0x38) << 2) + (b & 0x1f));
low_byte = (byte) (((a & 0x7) << 5) + (c & 0x1f));
p1 = 0;
p2 = 0;
for (i = 1; i < 256; i = i * 2) {
if ((high_byte & i) != 0)
p1++;
if ((low_byte & i) != 0)
p2++;
}
np1 = (b & 32) / 32;
np2 = (c & 32) / 32;
if ((p1 & 1) != np1) {
throw new CEFormatException("UCDecoder: High byte parity error.");
}
if ((p2 & 1) != np2) {
throw new CEFormatException("UCDecoder: Low byte parity error.");
}
outStream.write(high_byte);
crc.update(high_byte);
if (l == 2) {
outStream.write(low_byte);
crc.update(low_byte);
}
}
private ByteArrayOutputStream lineAndSeq = new ByteArrayOutputStream(2);
decodeBufferPrefix initializes the sequence number to zero.
/**
* decodeBufferPrefix initializes the sequence number to zero.
*/
protected void decodeBufferPrefix(PushbackInputStream inStream, OutputStream outStream) {
sequence = 0;
}
decodeLinePrefix reads the sequence number and the number of
encoded bytes from the line. If the sequence number is not the
previous sequence number + 1 then an exception is thrown.
UCE lines are line terminator immune, they all start with *
so the other thing this method does is scan for the next line
by looking for the * character.
Throws: - CEFormatException – out of sequence lines detected.
/**
* decodeLinePrefix reads the sequence number and the number of
* encoded bytes from the line. If the sequence number is not the
* previous sequence number + 1 then an exception is thrown.
* UCE lines are line terminator immune, they all start with *
* so the other thing this method does is scan for the next line
* by looking for the * character.
*
* @exception CEFormatException out of sequence lines detected.
*/
protected int decodeLinePrefix(PushbackInputStream inStream, OutputStream outStream) throws IOException {
int i;
int nLen, nSeq;
byte xtmp[];
int c;
crc.value = 0;
while (true) {
c = inStream.read(tmp, 0, 1);
if (c == -1) {
throw new CEStreamExhausted();
}
if (tmp[0] == '*') {
break;
}
}
lineAndSeq.reset();
decodeAtom(inStream, lineAndSeq, 2);
xtmp = lineAndSeq.toByteArray();
nLen = xtmp[0] & 0xff;
nSeq = xtmp[1] & 0xff;
if (nSeq != sequence) {
throw new CEFormatException("UCDecoder: Out of sequence line.");
}
sequence = (sequence + 1) & 0xff;
return (nLen);
}
this method reads the CRC that is at the end of every line and
verifies that it matches the computed CRC.
Throws: - CEFormatException – if CRC check fails.
/**
* this method reads the CRC that is at the end of every line and
* verifies that it matches the computed CRC.
*
* @exception CEFormatException if CRC check fails.
*/
protected void decodeLineSuffix(PushbackInputStream inStream, OutputStream outStream) throws IOException {
int i;
int lineCRC = crc.value;
int readCRC;
byte tmp[];
lineAndSeq.reset();
decodeAtom(inStream, lineAndSeq, 2);
tmp = lineAndSeq.toByteArray();
readCRC = ((tmp[0] << 8) & 0xFF00) + (tmp[1] & 0xff);
if (readCRC != lineCRC) {
throw new CEFormatException("UCDecoder: CRC check failed.");
}
}
}