001/* InputStreamReader.java -- Reader than transforms bytes to chars
002   Copyright (C) 1998, 1999, 2001, 2003, 2004, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010 
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.io;
040
041import gnu.gcj.convert.*;
042import java.nio.charset.Charset;
043import java.nio.charset.CharsetDecoder;
044
045/**
046 * This class reads characters from a byte input stream.   The characters
047 * read are converted from bytes in the underlying stream by a 
048 * decoding layer.  The decoding layer transforms bytes to chars according
049 * to an encoding standard.  There are many available encodings to choose 
050 * from.  The desired encoding can either be specified by name, or if no
051 * encoding is selected, the system default encoding will be used.  The
052 * system default encoding name is determined from the system property
053 * <code>file.encoding</code>.  The only encodings that are guaranteed to 
054 * be availalbe are "8859_1" (the Latin-1 character set) and "UTF8".
055 * Unforunately, Java does not provide a mechanism for listing the
056 * ecodings that are supported in a given implementation.
057 * <p>
058 * Here is a list of standard encoding names that may be available:
059 * <p>
060 * <ul>
061 * <li>8859_1 (ISO-8859-1/Latin-1)</li>
062 * <li>8859_2 (ISO-8859-2/Latin-2)</li>
063 * <li>8859_3 (ISO-8859-3/Latin-3)</li>
064 * <li>8859_4 (ISO-8859-4/Latin-4)</li>
065 * <li>8859_5 (ISO-8859-5/Latin-5)</li>
066 * <li>8859_6 (ISO-8859-6/Latin-6)</li>
067 * <li>8859_7 (ISO-8859-7/Latin-7)</li>
068 * <li>8859_8 (ISO-8859-8/Latin-8)</li>
069 * <li>8859_9 (ISO-8859-9/Latin-9)</li>
070 * <li>ASCII (7-bit ASCII)</li>
071 * <li>UTF8 (UCS Transformation Format-8)</li>
072 * <li>More later</li>
073 * </ul>
074 * <p>
075 * It is recommended that applications do not use 
076 * <code>InputStreamReader</code>'s
077 * directly.  Rather, for efficiency purposes, an object of this class
078 * should be wrapped by a <code>BufferedReader</code>.
079 * <p>
080 * Due to a deficiency the Java class library design, there is no standard
081 * way for an application to install its own byte-character encoding.
082 *
083 * @see BufferedReader
084 * @see InputStream
085 *
086 * @author Aaron M. Renn (arenn@urbanophile.com)
087 * @author Per Bothner (bothner@cygnus.com)
088 * @date April 22, 1998.  
089 */
090public class InputStreamReader extends Reader
091{
092  BufferedInputStream in;
093
094  // Buffer of chars read from in and converted but not consumed.
095  char[] work;
096  // Next available character (in work buffer) to read.
097  int wpos;
098  // Last available character (in work buffer) to read.
099  int wcount;
100
101  /*
102   * This is the byte-character decoder class that does the reading and
103   * translation of bytes from the underlying stream.
104   */
105  BytesToUnicode converter;
106
107  /**
108   * This method initializes a new instance of <code>InputStreamReader</code>
109   * to read from the specified stream using the default encoding.
110   *
111   * @param in The <code>InputStream</code> to read from 
112   */
113  public InputStreamReader(InputStream in)
114  {
115    this(in, BytesToUnicode.getDefaultDecoder());
116  }
117
118  /**
119   * This method initializes a new instance of <code>InputStreamReader</code>
120   * to read from the specified stream using a caller supplied character
121   * encoding scheme.  Note that due to a deficiency in the Java language
122   * design, there is no way to determine which encodings are supported.
123   * 
124   * @param in The <code>InputStream</code> to read from
125   * @param encoding_name The name of the encoding scheme to use
126   *
127   * @exception UnsupportedEncodingException If the encoding scheme 
128   * requested is not available.
129   */
130  public InputStreamReader(InputStream in, String encoding_name)
131    throws UnsupportedEncodingException
132  {
133    this(in, BytesToUnicode.getDecoder(encoding_name));
134  }
135
136  /**
137   * Creates an InputStreamReader that uses a decoder of the given
138   * charset to decode the bytes in the InputStream into
139   * characters.
140   */
141  public InputStreamReader(InputStream in, Charset charset)
142  {
143    this(in, new BytesToCharsetAdaptor(charset));
144  }
145
146  /**
147   * Creates an InputStreamReader that uses the given charset decoder
148   * to decode the bytes in the InputStream into characters.
149   */
150  public InputStreamReader(InputStream in, CharsetDecoder decoder)
151  {
152    this(in, new BytesToCharsetAdaptor(decoder));
153  }
154
155  private InputStreamReader(InputStream in, BytesToUnicode decoder)
156  {
157    // FIXME: someone could pass in a BufferedInputStream whose buffer
158    // is smaller than the longest encoded character for this
159    // encoding.  We will probably go into an infinite loop in this
160    // case.  We probably ought to just have our own byte buffering
161    // here.
162    this.in = in instanceof BufferedInputStream
163              ? (BufferedInputStream) in
164              : new BufferedInputStream(in);
165    /* Don't need to call super(in) here as long as the lock gets set. */
166    this.lock = in;
167    converter = decoder;
168    converter.setInput(this.in.buf, 0, 0);
169  }
170
171  /**
172   * This method closes this stream, as well as the underlying 
173   * <code>InputStream</code>.
174   *
175   * @exception IOException If an error occurs
176   */
177  public void close() throws IOException
178  {
179    synchronized (lock)
180      {
181        if (in != null)
182          in.close();
183        in = null;
184        work = null;
185        wpos = wcount = 0;
186      }
187  }
188
189  /**
190   * This method returns the name of the encoding that is currently in use
191   * by this object.  If the stream has been closed, this method is allowed
192   * to return <code>null</code>.
193   *
194   * @return The current encoding name
195   */
196  public String getEncoding()
197  {
198    return in != null ? converter.getName() : null;
199  }
200
201  /**
202   * This method checks to see if the stream is read to be read.  It
203   * will return <code>true</code> if is, or <code>false</code> if it is not.
204   * If the stream is not ready to be read, it could (although is not required
205   * to) block on the next read attempt.
206   *
207   * @return <code>true</code> if the stream is ready to be read, 
208   * <code>false</code> otherwise
209   *
210   * @exception IOException If an error occurs
211   */
212  public boolean ready() throws IOException
213  {
214    synchronized (lock)
215      {
216        if (in == null)
217          throw new IOException("Stream closed");
218
219        if (wpos < wcount)
220          return true;
221
222        // According to the spec, an InputStreamReader is ready if its
223        // input buffer is not empty (above), or if bytes are
224        // available on the underlying byte stream.
225        return in.available () > 0;
226      }
227  }
228
229  /**
230   * This method reads up to <code>length</code> characters from the stream into
231   * the specified array starting at index <code>offset</code> into the
232   * array.
233   *
234   * @param buf The character array to recieve the data read
235   * @param offset The offset into the array to start storing characters
236   * @param length The requested number of characters to read.
237   *
238   * @return The actual number of characters read, or -1 if end of stream.
239   *
240   * @exception IOException If an error occurs
241   */
242  public int read (char[] buf, int offset, int length) throws IOException
243  {
244    synchronized (lock)
245      {
246        if (in == null)
247          throw new IOException("Stream closed");
248
249        if (length == 0)
250          return 0;
251
252        int wavail = wcount - wpos;
253        if (wavail <= 0)
254          {
255            // Nothing waiting, so refill their buffer.
256            return refill(buf, offset, length);
257          }
258
259        if (length > wavail)
260          length = wavail;
261        System.arraycopy(work, wpos, buf, offset, length);
262        wpos += length;
263        return length;
264      }
265  }
266
267  /**
268   * This method reads a single character of data from the stream.
269   *
270   * @return The char read, as an int, or -1 if end of stream.
271   *
272   * @exception IOException If an error occurs
273   */
274  public int read() throws IOException
275  {
276    synchronized (lock)
277      {
278        if (in == null)
279          throw new IOException("Stream closed");
280
281        int wavail = wcount - wpos;
282        if (wavail <= 0)
283          {
284            // Nothing waiting, so refill our internal buffer.
285            wpos = wcount = 0;
286            if (work == null)
287               work = new char[100];
288            int count = refill(work, 0, work.length);
289            if (count == -1)
290              return -1;
291            wcount += count;
292          }
293
294        return work[wpos++];
295      }
296  }
297
298  // Read more bytes and convert them into the specified buffer.
299  // Returns the number of converted characters or -1 on EOF.
300  private int refill(char[] buf, int offset, int length) throws IOException
301  {
302    for (;;)
303      {
304        // We have knowledge of the internals of BufferedInputStream
305        // here.  Eww.
306        // BufferedInputStream.refill() can only be called when
307        // `pos>=count'.
308        boolean r = in.pos < in.count || in.refill ();
309        if (! r)
310          return -1;
311        converter.setInput(in.buf, in.pos, in.count);
312        int count = converter.read(buf, offset, length);
313
314        // We might have bytes but not have made any progress.  In
315        // this case we try to refill.  If refilling fails, we assume
316        // we have a malformed character at the end of the stream.
317        if (count == 0 && converter.inpos == in.pos)
318          {
319            in.mark(in.count);
320            if (! in.refill ())
321              throw new CharConversionException ();
322            in.reset();
323          }
324        else
325          {
326            in.skip(converter.inpos - in.pos);
327            if (count > 0)
328              return count;
329          }
330      }
331  }
332}