libjava/java/util/zip/CheckedInputStream.java

   1 /* CheckedInputStream.java - Compute checksum of data being read
   2    Copyright (C) 1999, 2000 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.util.zip;
  39
  40 import java.io.FilterInputStream;
  41 import java.io.InputStream;
  42 import java.io.IOException;
  43
  44 /* Written using on-line Java Platform 1.2 API Specification
  45  * and JCL book.
  46  * Believed complete and correct.
  47  */
  48
  49 /**
  50  * InputStream that computes a checksum of the data being read using a
  51  * supplied Checksum object.
  52  *
  53  * @see Checksum
  54  *
  55  * @author Tom Tromey
  56  * @date May 17, 1999
  57  */
  58 public class CheckedInputStream extends FilterInputStream
  59 {
  60   /**
  61    * Creates a new CheckInputStream on top of the supplied OutputStream
  62    * using the supplied Checksum.
  63    */
  64   public CheckedInputStream (InputStream in, Checksum sum)
  65   {
  66     super (in);
  67     this.sum = sum;
  68   }
  69
  70   /**
  71    * Returns the Checksum object used. To get the data checksum computed so
  72    * far call <code>getChecksum.getValue()</code>.
  73    */
  74   public Checksum getChecksum ()
  75   {
  76     return sum;
  77   }
  78
  79   /**
  80    * Reads one byte, updates the checksum and returns the read byte
  81    * (or -1 when the end of file was reached).
  82    */
  83   public int read () throws IOException
  84   {
  85     int x = in.read();
  86     if (x != -1)
  87       sum.update(x);
  88     return x;
  89   }
  90
  91   /**
  92    * Reads at most len bytes in the supplied buffer and updates the checksum
  93    * with it. Returns the number of bytes actually read or -1 when the end
  94    * of file was reached.
  95    */
  96   public int read (byte[] buf, int off, int len) throws IOException
  97   {
  98     int r = in.read(buf, off, len);
  99     if (r != -1)
 100       sum.update(buf, off, r);
 101     return r;
 102   }
 103
 104   /**
 105    * Skips n bytes by reading them in a temporary buffer and updating the
 106    * the checksum with that buffer. Returns the actual number of bytes skiped
 107    * which can be less then requested when the end of file is reached.
 108    */
 109   public long skip (long n) throws IOException
 110   {
 111     if (n == 0)
 112       return 0;
 113
 114     int min = (int) Math.min(n, 1024);
 115     byte[] buf = new byte[min];
 116
 117     long s = 0;
 118     while (n > 0)
 119       {
 120         int r = in.read(buf, 0, min);
 121         if (r == -1)
 122           break;
 123         n -= r;
 124         s += r;
 125         min = (int) Math.min(n, 1024);
 126         sum.update(buf, 0, r);
 127       }
 128
 129     return s;
 130   }
 131
 132   /** The checksum object. */
 133   private Checksum sum;
 134 }