UCDecoder

Class Overview

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."
 

Summary

Public Constructors
	UCDecoder()

Protected Methods
int	bytesPerAtom() This class encodes two bytes per atom.
int	bytesPerLine() this class encodes 48 bytes per line
void	decodeAtom(PushbackInputStream inStream, OutputStream outStream, int l) Decode one atom - reads the characters from the input stream, decodes them, and checks for valid parity.
void	decodeBufferPrefix(PushbackInputStream inStream, OutputStream outStream) decodeBufferPrefix initializes the sequence number to zero.
int	decodeLinePrefix(PushbackInputStream inStream, OutputStream outStream) decodeLinePrefix reads the sequence number and the number of encoded bytes from the line.
void	decodeLineSuffix(PushbackInputStream inStream, OutputStream outStream) this method reads the CRC that is at the end of every line and verifies that it matches the computed CRC.

[Expand] Inherited Methods
From class sun.misc.CharacterDecoder abstract int bytesPerAtom() Return the number of bytes per atom of decoding abstract int bytesPerLine() Return the maximum number of bytes that can be encoded per line void decodeAtom(PushbackInputStream aStream, OutputStream bStream, int l) This method does an actual decode. void decodeBuffer(InputStream aStream, OutputStream bStream) Decode the text from the InputStream and write the decoded octets to the OutputStream. byte[] decodeBuffer(InputStream in) Decode the contents of the inputstream into a buffer. byte[] decodeBuffer(String inputString) Alternate decode interface that takes a String containing the encoded buffer and returns a byte array containing the data. void decodeBufferPrefix(PushbackInputStream aStream, OutputStream bStream) decode the beginning of the buffer, by default this is a NOP. void decodeBufferSuffix(PushbackInputStream aStream, OutputStream bStream) decode the buffer suffix, again by default it is a NOP. ByteBuffer decodeBufferToByteBuffer(InputStream in) Decode the contents of the inputStream into a ByteBuffer. ByteBuffer decodeBufferToByteBuffer(String inputString) Decode the contents of the String into a ByteBuffer. int decodeLinePrefix(PushbackInputStream aStream, OutputStream bStream) This method should return, if it knows, the number of bytes that will be decoded. void decodeLineSuffix(PushbackInputStream aStream, OutputStream bStream) This method post processes the line, if there are error detection or correction codes in a line, they are generally processed by this method. int readFully(InputStream in, byte[] buffer, int offset, int len) This method works around the bizarre semantics of BufferedInputStream's read method.
From class java.lang.Object Object clone() Creates and returns a copy of this object. boolean equals(Object obj) Indicates whether some other object is "equal to" this one. void finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. final Class<?> getClass() Returns the runtime class of this Object. int hashCode() Returns a hash code value for the object. final void notify() Wakes up a single thread that is waiting on this object's monitor. final void notifyAll() Wakes up all threads that are waiting on this object's monitor. String toString() Returns a string representation of the object. final void wait() Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object. final void wait(long timeout, int nanos) Causes the current thread to wait until another thread invokes the notify() method or the notifyAll() method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed. final void wait(long timeout) Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed.