InputStreamReader.java

/* InputStreamReader.java -- Reader than transforms bytes to chars
   Copyright (C) 1998, 1999, 2001, 2003, 2004, 2005  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
the Free Software Foundation; either version 2, or (at your option)
any later version.
 
GNU Classpath 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 for more details.

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along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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
conditions of the GNU General Public License cover the whole
combination.

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
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
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package java.io;

import gnu.gcj.convert.*;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;

/**
 * This class reads characters from a byte input stream.   The characters
 * read are converted from bytes in the underlying stream by a 
 * decoding layer.  The decoding layer transforms bytes to chars according
 * to an encoding standard.  There are many available encodings to choose 
 * from.  The desired encoding can either be specified by name, or if no
 * encoding is selected, the system default encoding will be used.  The
 * system default encoding name is determined from the system property
 * <code>file.encoding</code>.  The only encodings that are guaranteed to 
 * be availalbe are "8859_1" (the Latin-1 character set) and "UTF8".
 * Unforunately, Java does not provide a mechanism for listing the
 * ecodings that are supported in a given implementation.
 * <p>
 * Here is a list of standard encoding names that may be available:
 * <p>
 * <ul>
 * <li>8859_1 (ISO-8859-1/Latin-1)</li>
 * <li>8859_2 (ISO-8859-2/Latin-2)</li>
 * <li>8859_3 (ISO-8859-3/Latin-3)</li>
 * <li>8859_4 (ISO-8859-4/Latin-4)</li>
 * <li>8859_5 (ISO-8859-5/Latin-5)</li>
 * <li>8859_6 (ISO-8859-6/Latin-6)</li>
 * <li>8859_7 (ISO-8859-7/Latin-7)</li>
 * <li>8859_8 (ISO-8859-8/Latin-8)</li>
 * <li>8859_9 (ISO-8859-9/Latin-9)</li>
 * <li>ASCII (7-bit ASCII)</li>
 * <li>UTF8 (UCS Transformation Format-8)</li>
 * <li>More later</li>
 * </ul>
 * <p>
 * It is recommended that applications do not use 
 * <code>InputStreamReader</code>'s
 * directly.  Rather, for efficiency purposes, an object of this class
 * should be wrapped by a <code>BufferedReader</code>.
 * <p>
 * Due to a deficiency the Java class library design, there is no standard
 * way for an application to install its own byte-character encoding.
 *
 * @see BufferedReader
 * @see InputStream
 *
 * @author Aaron M. Renn (arenn@urbanophile.com)
 * @author Per Bothner (bothner@cygnus.com)
 * @date April 22, 1998.  
 */
public class InputStreamReader extends Reader
{
  BufferedInputStream in;

  // Buffer of chars read from in and converted but not consumed.
  char[] work;
  // Next available character (in work buffer) to read.
  int wpos;
  // Last available character (in work buffer) to read.
  int wcount;

  /*
   * This is the byte-character decoder class that does the reading and
   * translation of bytes from the underlying stream.
   */
  BytesToUnicode converter;

  /**
   * This method initializes a new instance of <code>InputStreamReader</code>
   * to read from the specified stream using the default encoding.
   *
   * @param in The <code>InputStream</code> to read from 
   */
  public InputStreamReader(InputStream in)
  {
    this(in, BytesToUnicode.getDefaultDecoder());
  }

  /**
   * This method initializes a new instance of <code>InputStreamReader</code>
   * to read from the specified stream using a caller supplied character
   * encoding scheme.  Note that due to a deficiency in the Java language
   * design, there is no way to determine which encodings are supported.
   * 
   * @param in The <code>InputStream</code> to read from
   * @param encoding_name The name of the encoding scheme to use
   *
   * @exception UnsupportedEncodingException If the encoding scheme 
   * requested is not available.
   */
  public InputStreamReader(InputStream in, String encoding_name)
    throws UnsupportedEncodingException
  {
    this(in, BytesToUnicode.getDecoder(encoding_name));
  }

  /**
   * Creates an InputStreamReader that uses a decoder of the given
   * charset to decode the bytes in the InputStream into
   * characters.
   */
  public InputStreamReader(InputStream in, Charset charset)
  {
    this(in, new BytesToCharsetAdaptor(charset));
  }

  /**
   * Creates an InputStreamReader that uses the given charset decoder
   * to decode the bytes in the InputStream into characters.
   */
  public InputStreamReader(InputStream in, CharsetDecoder decoder)
  {
    this(in, new BytesToCharsetAdaptor(decoder));
  }

  private InputStreamReader(InputStream in, BytesToUnicode decoder)
  {
    // FIXME: someone could pass in a BufferedInputStream whose buffer
    // is smaller than the longest encoded character for this
    // encoding.  We will probably go into an infinite loop in this
    // case.  We probably ought to just have our own byte buffering
    // here.
    this.in = in instanceof BufferedInputStream
              ? (BufferedInputStream) in
              : new BufferedInputStream(in);
    /* Don't need to call super(in) here as long as the lock gets set. */
    this.lock = in;
    converter = decoder;
    converter.setInput(this.in.buf, 0, 0);
  }

  /**
   * This method closes this stream, as well as the underlying 
   * <code>InputStream</code>.
   *
   * @exception IOException If an error occurs
   */
  public void close() throws IOException
  {
    synchronized (lock)
      {
	if (in != null)
	  in.close();
	in = null;
	work = null;
	wpos = wcount = 0;
      }
  }

  /**
   * This method returns the name of the encoding that is currently in use
   * by this object.  If the stream has been closed, this method is allowed
   * to return <code>null</code>.
   *
   * @return The current encoding name
   */
  public String getEncoding()
  {
    return in != null ? converter.getName() : null;
  }

  /**
   * This method checks to see if the stream is read to be read.  It
   * will return <code>true</code> if is, or <code>false</code> if it is not.
   * If the stream is not ready to be read, it could (although is not required
   * to) block on the next read attempt.
   *
   * @return <code>true</code> if the stream is ready to be read, 
   * <code>false</code> otherwise
   *
   * @exception IOException If an error occurs
   */
  public boolean ready() throws IOException
  {
    synchronized (lock)
      {
	if (in == null)
	  throw new IOException("Stream closed");

	if (wpos < wcount)
	  return true;

	// According to the spec, an InputStreamReader is ready if its
	// input buffer is not empty (above), or if bytes are
	// available on the underlying byte stream.
	return in.available () > 0;
      }
  }

  /**
   * This method reads up to <code>length</code> characters from the stream into
   * the specified array starting at index <code>offset</code> into the
   * array.
   *
   * @param buf The character array to recieve the data read
   * @param offset The offset into the array to start storing characters
   * @param length The requested number of characters to read.
   *
   * @return The actual number of characters read, or -1 if end of stream.
   *
   * @exception IOException If an error occurs
   */
  public int read (char[] buf, int offset, int length) throws IOException
  {
    synchronized (lock)
      {
	if (in == null)
	  throw new IOException("Stream closed");

	if (length == 0)
	  return 0;

	int wavail = wcount - wpos;
	if (wavail <= 0)
	  {
	    // Nothing waiting, so refill their buffer.
	    return refill(buf, offset, length);
	  }

	if (length > wavail)
	  length = wavail;
	System.arraycopy(work, wpos, buf, offset, length);
	wpos += length;
	return length;
      }
  }

  /**
   * This method reads a single character of data from the stream.
   *
   * @return The char read, as an int, or -1 if end of stream.
   *
   * @exception IOException If an error occurs
   */
  public int read() throws IOException
  {
    synchronized (lock)
      {
	if (in == null)
	  throw new IOException("Stream closed");

	int wavail = wcount - wpos;
	if (wavail <= 0)
	  {
	    // Nothing waiting, so refill our internal buffer.
	    wpos = wcount = 0;
	    if (work == null)
	       work = new char[100];
	    int count = refill(work, 0, work.length);
	    if (count == -1)
	      return -1;
	    wcount += count;
	  }

	return work[wpos++];
      }
  }

  // Read more bytes and convert them into the specified buffer.
  // Returns the number of converted characters or -1 on EOF.
  private int refill(char[] buf, int offset, int length) throws IOException
  {
    for (;;)
      {
	// We have knowledge of the internals of BufferedInputStream
	// here.  Eww.
	// BufferedInputStream.refill() can only be called when
	// `pos>=count'.
	boolean r = in.pos < in.count || in.refill ();
	if (! r)
	  return -1;
	converter.setInput(in.buf, in.pos, in.count);
	int count = converter.read(buf, offset, length);

	// We might have bytes but not have made any progress.  In
	// this case we try to refill.  If refilling fails, we assume
	// we have a malformed character at the end of the stream.
	if (count == 0 && converter.inpos == in.pos)
	  {
	    in.mark(in.count);
	    if (! in.refill ())
	      throw new CharConversionException ();
	    in.reset();
	  }
	else
	  {
	    in.skip(converter.inpos - in.pos);
	    if (count > 0)
	      return count;
	  }
      }
  }
}