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 }