/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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.
*/
/**
* This class defines the decoding half of character encoders.
* A character decoder is an algorithim for transforming 8 bit
* binary data that has been encoded into text by a character
* encoder, back into original binary form.
*
* The character encoders, in general, have been structured
* around a central theme that binary data can be encoded into
* text that has the form:
*
* <pre>
* [Buffer Prefix]
* [Line Prefix][encoded data atoms][Line Suffix]
* [Buffer Suffix]
* </pre>
*
* Of course in the simplest encoding schemes, the buffer has no
* distinct prefix of suffix, however all have some fixed relationship
* between the text in an 'atom' and the binary data itself.
*
* In the CharacterEncoder and CharacterDecoder classes, one complete
* chunk of data is referred to as a <i>buffer</i>. Encoded buffers
* are all text, and decoded buffers (sometimes just referred to as
* buffers) are binary octets.
*
* To create a custom decoder, you must, at a minimum, overide three
* abstract methods in this class.
* <DL>
* <DD>bytesPerAtom which tells the decoder how many bytes to
* expect from decodeAtom
* <DD>decodeAtom which decodes the bytes sent to it as text.
* <DD>bytesPerLine which tells the encoder the maximum number of
* bytes per line.
* </DL>
*
* In general, the character decoders return error in the form of a
* CEFormatException. The syntax of the detail string is
* <pre>
* DecoderClassName: Error message.
* </pre>
*
* Several useful decoders have already been written and are
* referenced in the See Also list below.
*
* @author Chuck McManis
* @see CEFormatException
* @see CharacterEncoder
* @see UCDecoder
* @see UUDecoder
* @see BASE64Decoder
*/
public abstract class CharacterDecoder {
/** Return the number of bytes per atom of decoding */
abstract protected int bytesPerAtom();
/** Return the maximum number of bytes that can be encoded per line */
abstract protected int bytesPerLine();
/** decode the beginning of the buffer, by default this is a NOP. */
protected void decodeBufferPrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
/** decode the buffer suffix, again by default it is a NOP. */
protected void decodeBufferSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
/**
* This method should return, if it knows, the number of bytes
* that will be decoded. Many formats such as uuencoding provide
* this information. By default we return the maximum bytes that
* could have been encoded on the line.
*/
protected int decodeLinePrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException {
return (bytesPerLine());
}
/**
* This method post processes the line, if there are error detection
* or correction codes in a line, they are generally processed by
* this method. The simplest version of this method looks for the
* (newline) character.
*/
protected void decodeLineSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
/**
* This method does an actual decode. It takes the decoded bytes and
* writes them to the OutputStream. The integer <i>l</i> tells the
* method how many bytes are required. This is always <= bytesPerAtom().
*/
protected void decodeAtom(PushbackInputStream aStream, OutputStream bStream, int l) throws IOException {
throw new CEStreamExhausted();
}
/**
* This method works around the bizarre semantics of BufferedInputStream's
* read method.
*/
for (int i = 0; i < len; i++) {
if (q == -1)
return ((i == 0) ? -1 : i);
}
return len;
}
/**
* Decode the text from the InputStream and write the decoded
* octets to the OutputStream. This method runs until the stream
* is exhausted.
* @exception CEFormatException An error has occured while decoding
* @exception CEStreamExhausted The input stream is unexpectedly out of data
*/
int i;
int totalBytes = 0;
while (true) {
int length;
try {
totalBytes += bytesPerAtom();
}
if ((i + bytesPerAtom()) == length) {
totalBytes += bytesPerAtom();
} else {
totalBytes += (length - i);
}
} catch (CEStreamExhausted e) {
break;
}
}
}
/**
* Alternate decode interface that takes a String containing the encoded
* buffer and returns a byte array containing the data.
* @exception CEFormatException An error has occured while decoding
*/
outStream = new ByteArrayOutputStream();
return (outStream.toByteArray());
}
/**
* Decode the contents of the inputstream into a buffer.
*/
return (outStream.toByteArray());
}
/**
* Decode the contents of the String into a ByteBuffer.
*/
throws IOException {
}
/**
* Decode the contents of the inputStream into a ByteBuffer.
*/
throws IOException {
}
}