001    /* CheckedInputStream.java - Compute checksum of data being read
002       Copyright (C) 1999, 2000, 2004  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.util.zip;
040    
041    import java.io.FilterInputStream;
042    import java.io.IOException;
043    import 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     */
059    public 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    }