CharsetDecoder.java

/* CharsetDecoder.java -- 
   Copyright (C) 2002 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package java.nio.charset;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;

/**
 * @author Jesse Rosenstock
 * @since 1.4
 */
public abstract class CharsetDecoder
{
  private static final int STATE_RESET   = 0;
  private static final int STATE_CODING  = 1;
  private static final int STATE_END     = 2;
  private static final int STATE_FLUSHED = 3;

  private static final String DEFAULT_REPLACEMENT = "\uFFFD";

  private final Charset charset;
  private final float averageCharsPerByte;
  private final float maxCharsPerByte;
  private String replacement;

  private int state = STATE_RESET;

  private CodingErrorAction malformedInputAction
    = CodingErrorAction.REPORT;
  private CodingErrorAction unmappableCharacterAction
    = CodingErrorAction.REPORT;

  private CharsetDecoder (Charset cs, float averageCharsPerByte,
                          float maxCharsPerByte, String replacement)
  {
    if (averageCharsPerByte <= 0.0f)
      throw new IllegalArgumentException ("Non-positive averageCharsPerByte");
    if (maxCharsPerByte <= 0.0f)
      throw new IllegalArgumentException ("Non-positive maxCharsPerByte");

    this.charset = cs;
    this.averageCharsPerByte
      = averageCharsPerByte;
    this.maxCharsPerByte
      = maxCharsPerByte;
    this.replacement = replacement;
    implReplaceWith (replacement);
  }

  protected CharsetDecoder (Charset cs, float averageCharsPerByte,
                            float maxCharsPerByte)
  {
    this (cs, averageCharsPerByte, maxCharsPerByte, DEFAULT_REPLACEMENT);
  }

  public final float averageCharsPerByte ()
  {
    return averageCharsPerByte;
  }

  public final Charset charset ()
  {
    return charset;
  }

  public final CharBuffer decode (ByteBuffer in)
    throws CharacterCodingException
  {
    // XXX: Sun's Javadoc seems to contradict itself saying an
    // IllegalStateException is thrown "if a decoding operation is already
    // in progress" and also that "it resets this Decoder".
    // Should we check to see that the state is reset, or should we
    // call reset()?
    if (state != STATE_RESET)
      throw new IllegalStateException ();

    // REVIEW: Using max instead of average may allocate a very large
    // buffer.  Maybe we should do something more efficient?
    int remaining = in.remaining ();
    int n = (int) (remaining * maxCharsPerByte ());
    CharBuffer out = CharBuffer.allocate (n);

    if (remaining == 0)
      {
        state = STATE_FLUSHED;
        return out;
      }

    CoderResult cr = decode (in, out, true);
    if (cr.isError ())
      cr.throwException ();

    cr = flush (out);
    if (cr.isError ())
      cr.throwException ();

    reset();
    out.flip ();

    // Unfortunately, resizing the actual charbuffer array is required.
    char[] resized = new char[out.remaining()];
    out.get(resized);
    return CharBuffer.wrap(resized);
  }

  public final CoderResult decode (ByteBuffer in, CharBuffer out,
                                   boolean endOfInput)
  {
    int newState = endOfInput ? STATE_END : STATE_CODING;
    // XXX: Need to check for "previous step was an invocation [not] of
    // this method with a value of true for the endOfInput parameter but
    // a return value indicating an incomplete decoding operation"
    // XXX: We will not check the previous return value, just
    // that the previous call passed true for endOfInput
    if (state != STATE_RESET && state != STATE_CODING
        && !(endOfInput && state == STATE_END))
      throw new IllegalStateException ();
    state = newState;

    for (;;)
      {
        CoderResult cr;
        try
          {
            cr = decodeLoop (in, out);
          }
        catch (RuntimeException e)
	  {
            throw new CoderMalfunctionError (e);
          }

        if (cr.isOverflow ())
          return cr;

        if (cr.isUnderflow ())
          {
            if (endOfInput && in.hasRemaining ())
              cr = CoderResult.malformedForLength (in.remaining ());
            else
              return cr;
          }

        CodingErrorAction action = cr.isMalformed ()
                                     ? malformedInputAction
                                     : unmappableCharacterAction;

        if (action == CodingErrorAction.REPORT)
          return cr;

        if (action == CodingErrorAction.REPLACE)
          {
            if (out.remaining () < replacement.length ())
              return CoderResult.OVERFLOW;
            out.put (replacement);
          }

        in.position (in.position () + cr.length ());
      }
  }

  protected abstract CoderResult decodeLoop (ByteBuffer in, CharBuffer out);

  public Charset detectedCharset ()
  {
    throw new UnsupportedOperationException ();
  }
    
  public final CoderResult flush (CharBuffer out)
  {
    // It seems weird that you can flush after reset, but Sun's javadoc
    // says an IllegalStateException is thrown "If the previous step of the
    // current decoding operation was an invocation neither of the reset
    // method nor ... of the three-argument decode method with a value of
    // true for the endOfInput parameter."
    // Further note that flush() only requires that there not be
    // an IllegalStateException if the previous step was a call to
    // decode with true as the last argument.  It does not require
    // that the call succeeded.  decode() does require that it succeeded.
    // XXX: test this to see if reality matches javadoc
    if (state != STATE_RESET && state != STATE_END)
      throw new IllegalStateException ();

    state = STATE_FLUSHED;
    return implFlush (out);
  }

  protected CoderResult implFlush (CharBuffer out)
  {
    return CoderResult.UNDERFLOW;
  }

  public final CharsetDecoder onMalformedInput (CodingErrorAction newAction)
  {
    if (newAction == null)
      throw new IllegalArgumentException ("Null action");

    malformedInputAction = newAction;
    implOnMalformedInput (newAction);
    return this;
  }

  protected void implOnMalformedInput (CodingErrorAction newAction)
  {
    // default implementation does nothing
  }

  protected void implOnUnmappableCharacter (CodingErrorAction newAction)
  {
    // default implementation does nothing
  }

  protected void implReplaceWith (String newReplacement)
  {
    // default implementation does nothing
  }

  protected void implReset ()
  {
    // default implementation does nothing
  }

  public boolean isAutoDetecting ()
  {
    return false;
  }

  public boolean isCharsetDetected ()
  {
    throw new UnsupportedOperationException ();
  }

  public CodingErrorAction malformedInputAction ()
  {
    return malformedInputAction;
  }

  public final float maxCharsPerByte ()
  {
    return maxCharsPerByte;
  }

  public final CharsetDecoder onUnmappableCharacter
    (CodingErrorAction newAction)
  {
    if (newAction == null)
      throw new IllegalArgumentException ("Null action");

    unmappableCharacterAction = newAction;
    implOnUnmappableCharacter (newAction);
    return this;
  }

  public final String replacement ()
  {
    return replacement;
  }

  public final CharsetDecoder replaceWith (String newReplacement)
  {
    if (newReplacement == null)
      throw new IllegalArgumentException ("Null replacement");
    if (newReplacement.length () == 0)
      throw new IllegalArgumentException ("Empty replacement");
    // XXX: what about maxCharsPerByte?

    this.replacement = newReplacement;
    implReplaceWith (newReplacement);
    return this;
  }

  public final CharsetDecoder reset ()
  {
    state = STATE_RESET;
    implReset ();
    return this;
  }

  public CodingErrorAction unmappableCharacterAction ()
  {
    return unmappableCharacterAction;
  }
}