001    /* InputStreamReader.java -- Reader than transforms bytes to chars
002       Copyright (C) 1998, 1999, 2001, 2003, 2004, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.io;
040    
041    import gnu.gcj.convert.*;
042    import java.nio.charset.Charset;
043    import 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     */
090    public 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    }