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    1   /*
    2    * Copyright (c) 1995, 2000, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   package sun.misc;
   26   
   27   import java.io.OutputStream;
   28   import java.io.ByteArrayOutputStream;
   29   import java.io.PushbackInputStream;
   30   import java.io.PrintStream;
   31   import java.io.IOException;
   32   
   33   /**
   34    * This class implements a robust character decoder. The decoder will
   35    * converted encoded text into binary data.
   36    *
   37    * The basic encoding unit is a 3 character atom. It encodes two bytes
   38    * of data. Bytes are encoded into a 64 character set, the characters
   39    * were chosen specifically because they appear in all codesets.
   40    * We don't care what their numerical equivalent is because
   41    * we use a character array to map them. This is like UUencoding
   42    * with the dependency on ASCII removed.
   43    *
   44    * The three chars that make up an atom are encoded as follows:
   45    * <pre>
   46    *      00xxxyyy 00axxxxx 00byyyyy
   47    *      00 = leading zeros, all values are 0 - 63
   48    *      xxxyyy - Top 3 bits of X, Top 3 bits of Y
   49    *      axxxxx - a = X parity bit, xxxxx lower 5 bits of X
   50    *      byyyyy - b = Y parity bit, yyyyy lower 5 bits of Y
   51    * </pre>
   52    *
   53    * The atoms are arranged into lines suitable for inclusion into an
   54    * email message or text file. The number of bytes that are encoded
   55    * per line is 48 which keeps the total line length  under 80 chars)
   56    *
   57    * Each line has the form(
   58    * <pre>
   59    *  *(LLSS)(DDDD)(DDDD)(DDDD)...(CRC)
   60    *  Where each (xxx) represents a three character atom.
   61    *  (LLSS) - 8 bit length (high byte), and sequence number
   62    *           modulo 256;
   63    *  (DDDD) - Data byte atoms, if length is odd, last data
   64    *           atom has (DD00) (high byte data, low byte 0)
   65    *  (CRC)  - 16 bit CRC for the line, includes length,
   66    *           sequence, and all data bytes. If there is a
   67    *           zero pad byte (odd length) it is _NOT_
   68    *           included in the CRC.
   69    * </pre>
   70    *
   71    * If an error is encountered during decoding this class throws a
   72    * CEFormatException. The specific detail messages are:
   73    *
   74    * <pre>
   75    *    "UCDecoder: High byte parity error."
   76    *    "UCDecoder: Low byte parity error."
   77    *    "UCDecoder: Out of sequence line."
   78    *    "UCDecoder: CRC check failed."
   79    * </pre>
   80    *
   81    * @author      Chuck McManis
   82    * @see         CharacterEncoder
   83    * @see         UCEncoder
   84    */
   85   public class UCDecoder extends CharacterDecoder {
   86   
   87       /** This class encodes two bytes per atom. */
   88       protected int bytesPerAtom() {
   89           return (2);
   90       }
   91   
   92       /** this class encodes 48 bytes per line */
   93       protected int bytesPerLine() {
   94           return (48);
   95       }
   96   
   97       /* this is the UCE mapping of 0-63 to characters .. */
   98       private final static byte map_array[] = {
   99           //     0         1         2         3         4         5         6         7
  100           (byte)'0',(byte)'1',(byte)'2',(byte)'3',(byte)'4',(byte)'5',(byte)'6',(byte)'7', // 0
  101           (byte)'8',(byte)'9',(byte)'A',(byte)'B',(byte)'C',(byte)'D',(byte)'E',(byte)'F', // 1
  102           (byte)'G',(byte)'H',(byte)'I',(byte)'J',(byte)'K',(byte)'L',(byte)'M',(byte)'N', // 2
  103           (byte)'O',(byte)'P',(byte)'Q',(byte)'R',(byte)'S',(byte)'T',(byte)'U',(byte)'V', // 3
  104           (byte)'W',(byte)'X',(byte)'Y',(byte)'Z',(byte)'a',(byte)'b',(byte)'c',(byte)'d', // 4
  105           (byte)'e',(byte)'f',(byte)'g',(byte)'h',(byte)'i',(byte)'j',(byte)'k',(byte)'l', // 5
  106           (byte)'m',(byte)'n',(byte)'o',(byte)'p',(byte)'q',(byte)'r',(byte)'s',(byte)'t', // 6
  107           (byte)'u',(byte)'v',(byte)'w',(byte)'x',(byte)'y',(byte)'z',(byte)'(',(byte)')'  // 7
  108       };
  109   
  110       private int sequence;
  111       private byte tmp[] = new byte[2];
  112       private CRC16 crc = new CRC16();
  113   
  114       /**
  115        * Decode one atom - reads the characters from the input stream, decodes
  116        * them, and checks for valid parity.
  117        */
  118       protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int l) throws IOException {
  119           int i, p1, p2, np1, np2;
  120           byte a = -1, b = -1, c = -1;
  121           byte high_byte, low_byte;
  122           byte tmp[] = new byte[3];
  123   
  124           i = inStream.read(tmp);
  125           if (i != 3) {
  126                   throw new CEStreamExhausted();
  127           }
  128           for (i = 0; (i < 64) && ((a == -1) || (b == -1) || (c == -1)); i++) {
  129               if (tmp[0] == map_array[i]) {
  130                   a = (byte) i;
  131               }
  132               if (tmp[1] == map_array[i]) {
  133                   b = (byte) i;
  134               }
  135               if (tmp[2] == map_array[i]) {
  136                   c = (byte) i;
  137               }
  138           }
  139           high_byte = (byte) (((a & 0x38) << 2) + (b & 0x1f));
  140           low_byte = (byte) (((a & 0x7) << 5) + (c & 0x1f));
  141           p1 = 0;
  142           p2 = 0;
  143           for (i = 1; i < 256; i = i * 2) {
  144               if ((high_byte & i) != 0)
  145                   p1++;
  146               if ((low_byte & i) != 0)
  147                   p2++;
  148           }
  149           np1 = (b & 32) / 32;
  150           np2 = (c & 32) / 32;
  151           if ((p1 & 1) != np1) {
  152               throw new CEFormatException("UCDecoder: High byte parity error.");
  153           }
  154           if ((p2 & 1) != np2) {
  155               throw new CEFormatException("UCDecoder: Low byte parity error.");
  156           }
  157           outStream.write(high_byte);
  158           crc.update(high_byte);
  159           if (l == 2) {
  160               outStream.write(low_byte);
  161               crc.update(low_byte);
  162           }
  163       }
  164   
  165       private ByteArrayOutputStream lineAndSeq = new ByteArrayOutputStream(2);
  166   
  167       /**
  168        * decodeBufferPrefix initializes the sequence number to zero.
  169        */
  170       protected void decodeBufferPrefix(PushbackInputStream inStream, OutputStream outStream) {
  171           sequence = 0;
  172       }
  173   
  174       /**
  175        * decodeLinePrefix reads the sequence number and the number of
  176        * encoded bytes from the line. If the sequence number is not the
  177        * previous sequence number + 1 then an exception is thrown.
  178        * UCE lines are line terminator immune, they all start with *
  179        * so the other thing this method does is scan for the next line
  180        * by looking for the * character.
  181        *
  182        * @exception CEFormatException out of sequence lines detected.
  183        */
  184       protected int decodeLinePrefix(PushbackInputStream inStream, OutputStream outStream)  throws IOException {
  185           int     i;
  186           int     nLen, nSeq;
  187           byte    xtmp[];
  188           int     c;
  189   
  190           crc.value = 0;
  191           while (true) {
  192               c = inStream.read(tmp, 0, 1);
  193               if (c == -1) {
  194                   throw new CEStreamExhausted();
  195               }
  196               if (tmp[0] == '*') {
  197                   break;
  198               }
  199           }
  200           lineAndSeq.reset();
  201           decodeAtom(inStream, lineAndSeq, 2);
  202           xtmp = lineAndSeq.toByteArray();
  203           nLen = xtmp[0] & 0xff;
  204           nSeq = xtmp[1] & 0xff;
  205           if (nSeq != sequence) {
  206               throw new CEFormatException("UCDecoder: Out of sequence line.");
  207           }
  208           sequence = (sequence + 1) & 0xff;
  209           return (nLen);
  210       }
  211   
  212   
  213       /**
  214        * this method reads the CRC that is at the end of every line and
  215        * verifies that it matches the computed CRC.
  216        *
  217        * @exception CEFormatException if CRC check fails.
  218        */
  219       protected void decodeLineSuffix(PushbackInputStream inStream, OutputStream outStream) throws IOException {
  220           int i;
  221           int lineCRC = crc.value;
  222           int readCRC;
  223           byte tmp[];
  224   
  225           lineAndSeq.reset();
  226           decodeAtom(inStream, lineAndSeq, 2);
  227           tmp = lineAndSeq.toByteArray();
  228           readCRC = ((tmp[0] << 8) & 0xFF00) + (tmp[1] & 0xff);
  229           if (readCRC != lineCRC) {
  230               throw new CEFormatException("UCDecoder: CRC check failed.");
  231           }
  232       }
  233   }

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