001/* InputStream.java -- Base class for input
002   Copyright (C) 1998, 1999, 2001, 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
041/**
042  * This abstract class forms the base of the hierarchy of classes that read
043  * input as a stream of bytes.  It provides a common set of methods for
044  * reading bytes from streams.  Subclasses implement and extend these
045  * methods to read bytes from a particular input source such as a file
046  * or network connection.
047  *
048  * @author Aaron M. Renn (arenn@urbanophile.com)
049  * @author Warren Levy (warrenl@cygnus.com)
050  */
051public abstract class InputStream implements Closeable
052{
053  /**
054   * Default, no-arg, public constructor
055   */
056  public InputStream()
057  {
058  }
059
060  /**
061   * This method returns the number of bytes that can be read from this
062   * stream before a read can block.  A return of 0 indicates that blocking
063   * might (or might not) occur on the very next read attempt.
064   * <p>
065   * This method always returns 0 in this class
066   *
067   * @return The number of bytes that can be read before blocking could occur
068   *
069   * @exception IOException If an error occurs
070   */
071  public int available() throws IOException
072  {
073    return 0;
074  }
075
076  /**
077   * This method closes the stream.  Any futher attempts to read from the
078   * stream may generate an <code>IOException</code>
079   * <p>
080   * This method does nothing in this class, but subclasses may override
081   * this method in order to provide additional functionality.
082   *
083   * @exception IOException If an error occurs, which can only happen
084   * in a subclass
085   */
086  public void close() throws IOException
087  {
088    // Do nothing
089  }
090
091  /**
092   * This method marks a position in the input to which the stream can
093   * be "reset" by calling the <code>reset()</code> method.  The
094   * parameter @code{readlimit} is the number of bytes that can be read
095   * from the stream after setting the mark before the mark becomes
096   * invalid.  For example, if <code>mark()</code> is called with a
097   * read limit of 10, then when 11 bytes of data are read from the
098   * stream before the <code>reset()</code> method is called, then the
099   * mark is invalid and the stream object instance is not required to
100   * remember the mark.
101   * <p>
102   * This method does nothing in this class, but subclasses may override it
103   * to provide mark/reset functionality.
104   *
105   * @param readLimit The number of bytes that can be read before the
106   *                  mark becomes invalid
107   */
108  public void mark(int readLimit)
109  {
110    // Do nothing
111  }
112
113  /**
114   * This method returns a boolean that indicates whether the mark/reset
115   * methods are supported in this class.  Those methods can be used to
116   * remember a specific point in the stream and reset the stream to that
117   * point.
118   * <p>
119   * This method always returns <code>false</code> in this class, but
120   * subclasses can override this method to return <code>true</code>
121   * if they support mark/reset functionality.
122   *
123   * @return <code>true</code> if mark/reset functionality is
124   * supported, <code>false</code> otherwise
125   */
126  public boolean markSupported()
127  {
128    return false;
129  }
130
131  /**
132   * This method reads an unsigned byte from the input stream and returns it
133   * as an int in the range of 0-255.  This method also will return -1 if
134   * the end of the stream has been reached.
135   * <p>
136   * This method will block until the byte can be read.
137   *
138   * @return The byte read or -1 if end of stream
139   *
140   * @exception IOException If an error occurs
141   */
142  public abstract int read() throws IOException;
143
144  /**
145   * This method reads bytes from a stream and stores them into a caller
146   * supplied buffer.  This method attempts to completely fill the buffer,
147   * but can return before doing so.  The actual number of bytes read is
148   * returned as an int.  A -1 is returned to indicate the end of the stream.
149   * <p>
150   * This method will block until some data can be read.
151   * <p>
152   * This method operates by calling an overloaded read method like so:
153   * <code>read(b, 0, b.length)</code>
154   *
155   * @param b The buffer into which the bytes read will be stored.
156   *
157   * @return The number of bytes read or -1 if end of stream.
158   *
159   * @exception IOException If an error occurs.
160   */
161  public int read(byte[] b) throws IOException
162  {
163    return read(b, 0, b.length);
164  }
165
166  /**
167   * This method read bytes from a stream and stores them into a
168   * caller supplied buffer.  It starts storing the data at index
169   * <code>off</code> into the buffer and attempts to read
170   * <code>len</code> bytes.  This method can return before reading the
171   * number of bytes requested.  The actual number of bytes read is
172   * returned as an int.  A -1 is returned to indicate the end of the
173   * stream.
174   *  <p>
175   * This method will block until some data can be read.
176   * <p>
177   * This method operates by calling the single byte <code>read()</code> method
178   * in a loop until the desired number of bytes are read.  The read loop
179   * stops short if the end of the stream is encountered or if an IOException
180   * is encountered on any read operation except the first.  If the first
181   * attempt to read a bytes fails, the IOException is allowed to propagate
182   * upward.  And subsequent IOException is caught and treated identically
183   * to an end of stream condition.  Subclasses can (and should if possible)
184   * override this method to provide a more efficient implementation.
185   *
186   * @param b The array into which the bytes read should be stored
187   * @param off The offset into the array to start storing bytes
188   * @param len The requested number of bytes to read
189   *
190   * @return The actual number of bytes read, or -1 if end of stream.
191   *
192   * @exception IOException If an error occurs.
193   */
194  public int read(byte[] b, int off, int len) throws IOException
195  {
196    if (off < 0 || len < 0 || b.length - off < len)
197      throw new IndexOutOfBoundsException();
198
199    int i, ch;
200
201    for (i = 0; i < len; ++i)
202      try
203        {
204          if ((ch = read()) < 0)
205            return i == 0 ? -1 : i;             // EOF
206          b[off + i] = (byte) ch;
207        }
208      catch (IOException ex)
209        {
210          // Only reading the first byte should cause an IOException.
211          if (i == 0)
212            throw ex;
213          return i;
214        }
215
216    return i;
217  }
218
219  /**
220   * This method resets a stream to the point where the
221   * <code>mark()</code> method was called.  Any bytes that were read
222   * after the mark point was set will be re-read during subsequent
223   * reads.
224   * <p>
225   * This method always throws an IOException in this class, but subclasses
226   * can override this method if they provide mark/reset functionality.
227   *
228   * @exception IOException Always thrown for this class
229   */
230  public void reset() throws IOException
231  {
232    throw new IOException("mark/reset not supported");
233  }
234
235  /**
236   * This method skips the specified number of bytes in the stream.  It
237   * returns the actual number of bytes skipped, which may be less than the
238   * requested amount.
239   * <p>
240   * This method reads and discards bytes into a byte array until the
241   * specified number of bytes were skipped or until either the end of stream
242   * is reached or a read attempt returns a short count.  Subclasses can
243   * override this metho to provide a more efficient implementation where
244   * one exists.
245   *
246   * @param n The requested number of bytes to skip
247   *
248   * @return The actual number of bytes skipped.
249   *
250   * @exception IOException If an error occurs
251   */
252  public long skip(long n) throws IOException
253  {
254    // Throw away n bytes by reading them into a temp byte[].
255    // Limit the temp array to 2Kb so we don't grab too much memory.
256    final int buflen = n > 2048 ? 2048 : (int) n;
257    byte[] tmpbuf = new byte[buflen];
258    final long origN = n;
259
260    while (n > 0L)
261      {
262        int numread = read(tmpbuf, 0, n > buflen ? buflen : (int) n);
263        if (numread <= 0)
264          break;
265        n -= numread;
266      }
267
268    return origN - n;
269  }
270}