/*
* @(#)UCDecoder.java 1.6 95/09/06 Chuck McManis
*
* Copyright (c) 1995 Sun Microsystems, Inc. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and without
* fee is hereby granted provided that this copyright notice
* appears in all copies. Please refer to the file "copyright.html"
* for further important copyright and licensing information.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*/
package sun.misc;
import java.io.OutputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
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:
* <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>
*
* @version 1.6, 06 Sep 1995
* @author Chuck McManis
* @see CharacterEncoder
* @see UCEncoder
*/
public class UCDecoder extends CharacterDecoder {
/** This class encodes two bytes per atom. */
int bytesPerAtom() {
return (2);
}
/** this class encodes 48 bytes per line */
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
'0','1','2','3','4','5','6','7', // 0
'8','9','A','B','C','D','E','F', // 1
'G','H','I','J','K','L','M','N', // 2
'O','P','Q','R','S','T','U','V', // 3
'W','X','Y','Z','a','b','c','d', // 4
'e','f','g','h','i','j','k','l', // 5
'm','n','o','p','q','r','s','t', // 6
'u','v','w','x','y','z','(',')' // 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.
*/
void decodeAtom(InputStream 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.
*/
void decodeBufferPrefix(InputStream 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.
*
* @exception CEFormatException out of sequence lines detected.
*/
int decodeLinePrefix(InputStream 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.
*
* @exception CEFormatException if CRC check fails.
*/
void decodeLineSuffix(InputStream 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.");
}
}
}