001/* CheckedInputStream.java - Compute checksum of data being read
002   Copyright (C) 1999, 2000, 2004  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.util.zip;
040
041import java.io.FilterInputStream;
042import java.io.IOException;
043import java.io.InputStream;
044
045/* Written using on-line Java Platform 1.2 API Specification
046 * and JCL book.
047 * Believed complete and correct.
048 */
049
050/**
051 * InputStream that computes a checksum of the data being read using a
052 * supplied Checksum object.
053 *
054 * @see Checksum
055 *
056 * @author Tom Tromey
057 * @date May 17, 1999
058 */
059public class CheckedInputStream extends FilterInputStream
060{
061  /**
062   * Creates a new CheckInputStream on top of the supplied OutputStream
063   * using the supplied Checksum.
064   */
065  public CheckedInputStream (InputStream in, Checksum sum)
066  {
067    super (in);
068    this.sum = sum;
069  }
070
071  /**
072   * Returns the Checksum object used. To get the data checksum computed so
073   * far call <code>getChecksum.getValue()</code>.
074   */
075  public Checksum getChecksum ()
076  {
077    return sum;
078  }
079
080  /**
081   * Reads one byte, updates the checksum and returns the read byte
082   * (or -1 when the end of file was reached).
083   */
084  public int read () throws IOException
085  {
086    int x = in.read();
087    if (x != -1)
088      sum.update(x);
089    return x;
090  }
091
092  /**
093   * Reads at most len bytes in the supplied buffer and updates the checksum
094   * with it. Returns the number of bytes actually read or -1 when the end
095   * of file was reached.
096   */
097  public int read (byte[] buf, int off, int len) throws IOException
098  {
099    int r = in.read(buf, off, len);
100    if (r != -1)
101      sum.update(buf, off, r);
102    return r;
103  }
104
105  /**
106   * Skips n bytes by reading them in a temporary buffer and updating the
107   * the checksum with that buffer. Returns the actual number of bytes skiped
108   * which can be less then requested when the end of file is reached.
109   */
110  public long skip (long n) throws IOException
111  {
112    if (n == 0)
113      return 0;
114
115    int min = (int) Math.min(n, 1024);
116    byte[] buf = new byte[min];
117
118    long s = 0;
119    while (n > 0)
120      {
121        int r = in.read(buf, 0, min);
122        if (r == -1)
123          break;
124        n -= r;
125        s += r;
126        min = (int) Math.min(n, 1024);
127        sum.update(buf, 0, r);
128      }
129
130    return s;
131  }
132
133  /** The checksum object. */
134  private Checksum sum;
135}