001/* ByteArrayInputStream.java -- Read an array as a stream
002   Copyright (C) 1998, 1999, 2001, 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 class permits an array of bytes to be read as an input stream.
043  *
044  * @author Warren Levy (warrenl@cygnus.com)
045  * @author Aaron M. Renn (arenn@urbanophile.com)
046  */ 
047public class ByteArrayInputStream extends InputStream
048{
049  /**
050   * The array that contains the data supplied during read operations
051   */
052  protected byte[] buf;
053
054  /**
055   * The array index of the next byte to be read from the buffer
056   * <code>buf</code>
057   */
058  protected int pos;
059
060  /**
061   * The currently marked position in the stream.  This defaults to 0, so a
062   * reset operation on the stream resets it to read from array index 0 in
063   * the buffer - even if the stream was initially created with an offset
064   * greater than 0
065   */
066  protected int mark;
067
068  /**
069   * This indicates the maximum number of bytes that can be read from this
070   * stream.  It is the array index of the position after the last valid
071   * byte in the buffer <code>buf</code>
072   */
073  protected int count;
074
075  /**
076   * Create a new ByteArrayInputStream that will read bytes from the passed
077   * in byte array.  This stream will read from the beginning to the end
078   * of the array.  It is identical to calling an overloaded constructor
079   * as <code>ByteArrayInputStream(buf, 0, buf.length)</code>.
080   * <p>
081   * Note that this array is not copied.  If its contents are changed 
082   * while this stream is being read, those changes will be reflected in the
083   * bytes supplied to the reader.  Please use caution in changing the 
084   * contents of the buffer while this stream is open.
085   *
086   * @param buffer The byte array buffer this stream will read from.
087   */
088  public ByteArrayInputStream(byte[] buffer)
089  {
090    this(buffer, 0, buffer.length);
091  }
092
093  /**
094   * Create a new ByteArrayInputStream that will read bytes from the
095   * passed in byte array.  This stream will read from position
096   * <code>offset</code> in the array for a length of
097   * <code>length</code> bytes past <code>offset</code>.  If the
098   * stream is reset to a position before <code>offset</code> then
099   * more than <code>length</code> bytes can be read from the stream.
100   * The <code>length</code> value should be viewed as the array index
101   * one greater than the last position in the buffer to read.
102   * <p>
103   * Note that this array is not copied.  If its contents are changed 
104   * while this stream is being read, those changes will be reflected in the
105   * bytes supplied to the reader.  Please use caution in changing the 
106   * contents of the buffer while this stream is open.
107   *
108   * @param buffer The byte array buffer this stream will read from.
109   * @param offset The index into the buffer to start reading bytes from
110   * @param length The number of bytes to read from the buffer
111   */
112  public ByteArrayInputStream(byte[] buffer, int offset, int length)
113  {
114    if (offset < 0  || length < 0 || offset > buffer.length)
115      throw new IllegalArgumentException();
116
117    buf = buffer;
118
119    count = offset + length;
120    if (count > buf.length)
121      count = buf.length;
122
123    pos = offset;
124    mark = pos;
125  }
126
127  /**
128   * This method returns the number of bytes available to be read from this
129   * stream.  The value returned will be equal to <code>count - pos</code>.
130   *
131   * @return The number of bytes that can be read from this stream
132   * before blocking, which is all of them 
133   */
134  public synchronized int available()
135  {
136    return count - pos;
137  }
138
139  /**
140   * This method sets the mark position in this stream to the current
141   * position.  Note that the <code>readlimit</code> parameter in this
142   * method does nothing as this stream is always capable of
143   * remembering all the bytes int it.
144   * <p>
145   * Note that in this class the mark position is set by default to
146   * position 0 in the stream.  This is in constrast to some other
147   * stream types where there is no default mark position.
148   *
149   * @param readLimit The number of bytes this stream must remember.
150   * This parameter is ignored.
151   */
152  public synchronized void mark(int readLimit)
153  {
154    // readLimit is ignored per Java Class Lib. book, p.220.
155    mark = pos;
156  }
157
158  /**
159   * This method overrides the <code>markSupported</code> method in
160   * <code>InputStream</code> in order to return <code>true</code> -
161   * indicating that this stream class supports mark/reset
162   * functionality.
163   *
164   * @return <code>true</code> to indicate that this class supports
165   * mark/reset.
166   */
167  public boolean markSupported()
168  {
169    return true;
170  }
171
172  /**
173   * This method reads one byte from the stream.  The <code>pos</code>
174   * counter is advanced to the next byte to be read.  The byte read is
175   * returned as an int in the range of 0-255.  If the stream position
176   * is already at the end of the buffer, no byte is read and a -1 is
177   * returned in order to indicate the end of the stream.
178   *
179   * @return The byte read, or -1 if end of stream
180   */
181  public synchronized int read()
182  {
183    if (pos < count)
184      return ((int) buf[pos++]) & 0xFF;
185    return -1;
186  }
187
188  /**
189   * This method reads bytes from the stream and stores them into a
190   * caller supplied buffer.  It starts storing the data at index
191   * <code>offset</code> into the buffer and attempts to read
192   * <code>len</code> bytes.  This method can return before reading
193   * the number of bytes requested if the end of the stream is
194   * encountered first.  The actual number of bytes read is returned.
195   * If no bytes can be read because the stream is already at the end
196   * of stream position, a -1 is returned.
197   * <p>
198   * This method does not block.
199   *
200   * @param buffer The array into which the bytes read should be stored.
201   * @param offset The offset into the array to start storing bytes
202   * @param length The requested number of bytes to read
203   *
204   * @return The actual number of bytes read, or -1 if end of stream.
205   */
206  public synchronized int read(byte[] buffer, int offset, int length)
207  {
208    if (pos >= count)
209      return -1;
210
211    int numBytes = Math.min(count - pos, length);
212    System.arraycopy(buf, pos, buffer, offset, numBytes);
213    pos += numBytes;
214    return numBytes;
215  }
216
217  /**
218   * This method sets the read position in the stream to the mark
219   * point by setting the <code>pos</code> variable equal to the
220   * <code>mark</code> variable.  Since a mark can be set anywhere in
221   * the array, the mark/reset methods int this class can be used to
222   * provide random search capabilities for this type of stream.
223   */
224  public synchronized void reset()
225  {
226    pos = mark;
227  }
228
229  /**
230   * This method attempts to skip the requested number of bytes in the
231   * input stream.  It does this by advancing the <code>pos</code>
232   * value by the specified number of bytes.  It this would exceed the
233   * length of the buffer, then only enough bytes are skipped to
234   * position the stream at the end of the buffer.  The actual number
235   * of bytes skipped is returned.
236   *
237   * @param num The requested number of bytes to skip
238   *
239   * @return The actual number of bytes skipped.
240   */
241  public synchronized long skip(long num)
242  {
243    // Even though the var numBytes is a long, in reality it can never
244    // be larger than an int since the result of subtracting 2 positive
245    // ints will always fit in an int.  Since we have to return a long
246    // anyway, numBytes might as well just be a long.
247    long numBytes = Math.min((long) (count - pos), num < 0 ? 0L : num);
248    pos += numBytes;
249    return numBytes;
250  }
251}