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    1   /*
    2    * Copyright (c) 1995, 2004, 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   
   26   package sun.misc;
   27   
   28   import java.io.OutputStream;
   29   import java.io.ByteArrayOutputStream;
   30   import java.io.InputStream;
   31   import java.io.PushbackInputStream;
   32   import java.io.ByteArrayInputStream;
   33   import java.io.IOException;
   34   import java.nio.ByteBuffer;
   35   
   36   /**
   37    * This class defines the decoding half of character encoders.
   38    * A character decoder is an algorithim for transforming 8 bit
   39    * binary data that has been encoded into text by a character
   40    * encoder, back into original binary form.
   41    *
   42    * The character encoders, in general, have been structured
   43    * around a central theme that binary data can be encoded into
   44    * text that has the form:
   45    *
   46    * <pre>
   47    *      [Buffer Prefix]
   48    *      [Line Prefix][encoded data atoms][Line Suffix]
   49    *      [Buffer Suffix]
   50    * </pre>
   51    *
   52    * Of course in the simplest encoding schemes, the buffer has no
   53    * distinct prefix of suffix, however all have some fixed relationship
   54    * between the text in an 'atom' and the binary data itself.
   55    *
   56    * In the CharacterEncoder and CharacterDecoder classes, one complete
   57    * chunk of data is referred to as a <i>buffer</i>. Encoded buffers
   58    * are all text, and decoded buffers (sometimes just referred to as
   59    * buffers) are binary octets.
   60    *
   61    * To create a custom decoder, you must, at a minimum,  overide three
   62    * abstract methods in this class.
   63    * <DL>
   64    * <DD>bytesPerAtom which tells the decoder how many bytes to
   65    * expect from decodeAtom
   66    * <DD>decodeAtom which decodes the bytes sent to it as text.
   67    * <DD>bytesPerLine which tells the encoder the maximum number of
   68    * bytes per line.
   69    * </DL>
   70    *
   71    * In general, the character decoders return error in the form of a
   72    * CEFormatException. The syntax of the detail string is
   73    * <pre>
   74    *      DecoderClassName: Error message.
   75    * </pre>
   76    *
   77    * Several useful decoders have already been written and are
   78    * referenced in the See Also list below.
   79    *
   80    * @author      Chuck McManis
   81    * @see         CEFormatException
   82    * @see         CharacterEncoder
   83    * @see         UCDecoder
   84    * @see         UUDecoder
   85    * @see         BASE64Decoder
   86    */
   87   
   88   public abstract class CharacterDecoder {
   89   
   90       /** Return the number of bytes per atom of decoding */
   91       abstract protected int bytesPerAtom();
   92   
   93       /** Return the maximum number of bytes that can be encoded per line */
   94       abstract protected int bytesPerLine();
   95   
   96       /** decode the beginning of the buffer, by default this is a NOP. */
   97       protected void decodeBufferPrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
   98   
   99       /** decode the buffer suffix, again by default it is a NOP. */
  100       protected void decodeBufferSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
  101   
  102       /**
  103        * This method should return, if it knows, the number of bytes
  104        * that will be decoded. Many formats such as uuencoding provide
  105        * this information. By default we return the maximum bytes that
  106        * could have been encoded on the line.
  107        */
  108       protected int decodeLinePrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException {
  109           return (bytesPerLine());
  110       }
  111   
  112       /**
  113        * This method post processes the line, if there are error detection
  114        * or correction codes in a line, they are generally processed by
  115        * this method. The simplest version of this method looks for the
  116        * (newline) character.
  117        */
  118       protected void decodeLineSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
  119   
  120       /**
  121        * This method does an actual decode. It takes the decoded bytes and
  122        * writes them to the OutputStream. The integer <i>l</i> tells the
  123        * method how many bytes are required. This is always <= bytesPerAtom().
  124        */
  125       protected void decodeAtom(PushbackInputStream aStream, OutputStream bStream, int l) throws IOException {
  126           throw new CEStreamExhausted();
  127       }
  128   
  129       /**
  130        * This method works around the bizarre semantics of BufferedInputStream's
  131        * read method.
  132        */
  133       protected int readFully(InputStream in, byte buffer[], int offset, int len)
  134           throws java.io.IOException {
  135           for (int i = 0; i < len; i++) {
  136               int q = in.read();
  137               if (q == -1)
  138                   return ((i == 0) ? -1 : i);
  139               buffer[i+offset] = (byte)q;
  140           }
  141           return len;
  142       }
  143   
  144       /**
  145        * Decode the text from the InputStream and write the decoded
  146        * octets to the OutputStream. This method runs until the stream
  147        * is exhausted.
  148        * @exception CEFormatException An error has occured while decoding
  149        * @exception CEStreamExhausted The input stream is unexpectedly out of data
  150        */
  151       public void decodeBuffer(InputStream aStream, OutputStream bStream) throws IOException {
  152           int     i;
  153           int     totalBytes = 0;
  154   
  155           PushbackInputStream ps = new PushbackInputStream (aStream);
  156           decodeBufferPrefix(ps, bStream);
  157           while (true) {
  158               int length;
  159   
  160               try {
  161                   length = decodeLinePrefix(ps, bStream);
  162                   for (i = 0; (i+bytesPerAtom()) < length; i += bytesPerAtom()) {
  163                       decodeAtom(ps, bStream, bytesPerAtom());
  164                       totalBytes += bytesPerAtom();
  165                   }
  166                   if ((i + bytesPerAtom()) == length) {
  167                       decodeAtom(ps, bStream, bytesPerAtom());
  168                       totalBytes += bytesPerAtom();
  169                   } else {
  170                       decodeAtom(ps, bStream, length - i);
  171                       totalBytes += (length - i);
  172                   }
  173                   decodeLineSuffix(ps, bStream);
  174               } catch (CEStreamExhausted e) {
  175                   break;
  176               }
  177           }
  178           decodeBufferSuffix(ps, bStream);
  179       }
  180   
  181       /**
  182        * Alternate decode interface that takes a String containing the encoded
  183        * buffer and returns a byte array containing the data.
  184        * @exception CEFormatException An error has occured while decoding
  185        */
  186       public byte decodeBuffer(String inputString)[] throws IOException {
  187           byte    inputBuffer[] = new byte[inputString.length()];
  188           ByteArrayInputStream inStream;
  189           ByteArrayOutputStream outStream;
  190   
  191           inputString.getBytes(0, inputString.length(), inputBuffer, 0);
  192           inStream = new ByteArrayInputStream(inputBuffer);
  193           outStream = new ByteArrayOutputStream();
  194           decodeBuffer(inStream, outStream);
  195           return (outStream.toByteArray());
  196       }
  197   
  198       /**
  199        * Decode the contents of the inputstream into a buffer.
  200        */
  201       public byte decodeBuffer(InputStream in)[] throws IOException {
  202           ByteArrayOutputStream outStream = new ByteArrayOutputStream();
  203           decodeBuffer(in, outStream);
  204           return (outStream.toByteArray());
  205       }
  206   
  207       /**
  208        * Decode the contents of the String into a ByteBuffer.
  209        */
  210       public ByteBuffer decodeBufferToByteBuffer(String inputString)
  211           throws IOException {
  212           return ByteBuffer.wrap(decodeBuffer(inputString));
  213       }
  214   
  215       /**
  216        * Decode the contents of the inputStream into a ByteBuffer.
  217        */
  218       public ByteBuffer decodeBufferToByteBuffer(InputStream in)
  219           throws IOException {
  220           return ByteBuffer.wrap(decodeBuffer(in));
  221       }
  222   }

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