Source for java.util.zip.CheckedInputStream

   1: /* CheckedInputStream.java - Compute checksum of data being read
   2:    Copyright (C) 1999, 2000, 2004  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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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: 
  39: package java.util.zip;
  40: 
  41: import java.io.FilterInputStream;
  42: import java.io.IOException;
  43: import java.io.InputStream;
  44: 
  45: /* Written using on-line Java Platform 1.2 API Specification
  46:  * and JCL book.
  47:  * Believed complete and correct.
  48:  */
  49: 
  50: /**
  51:  * InputStream that computes a checksum of the data being read using a
  52:  * supplied Checksum object.
  53:  *
  54:  * @see Checksum
  55:  *
  56:  * @author Tom Tromey
  57:  * @date May 17, 1999
  58:  */
  59: public class CheckedInputStream extends FilterInputStream
  60: {
  61:   /**
  62:    * Creates a new CheckInputStream on top of the supplied OutputStream
  63:    * using the supplied Checksum.
  64:    */
  65:   public CheckedInputStream (InputStream in, Checksum sum)
  66:   {
  67:     super (in);
  68:     this.sum = sum;
  69:   }
  70: 
  71:   /**
  72:    * Returns the Checksum object used. To get the data checksum computed so
  73:    * far call <code>getChecksum.getValue()</code>.
  74:    */
  75:   public Checksum getChecksum ()
  76:   {
  77:     return sum;
  78:   }
  79: 
  80:   /**
  81:    * Reads one byte, updates the checksum and returns the read byte
  82:    * (or -1 when the end of file was reached).
  83:    */
  84:   public int read () throws IOException
  85:   {
  86:     int x = in.read();
  87:     if (x != -1)
  88:       sum.update(x);
  89:     return x;
  90:   }
  91: 
  92:   /**
  93:    * Reads at most len bytes in the supplied buffer and updates the checksum
  94:    * with it. Returns the number of bytes actually read or -1 when the end
  95:    * of file was reached.
  96:    */
  97:   public int read (byte[] buf, int off, int len) throws IOException
  98:   {
  99:     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: }