1/*
2 * Copyright (c) 1996, 2006, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26package java.util.zip;
27
28import java.io.FilterInputStream;
29import java.io.InputStream;
30import java.io.IOException;
31
32/**
33 * An input stream that also maintains a checksum of the data being read.
34 * The checksum can then be used to verify the integrity of the input data.
35 *
36 * @see         Checksum
37 * @author      David Connelly
38 * @since 1.1
39 */
40public
41class CheckedInputStream extends FilterInputStream {
42    private Checksum cksum;
43
44    /**
45     * Creates an input stream using the specified Checksum.
46     * @param in the input stream
47     * @param cksum the Checksum
48     */
49    public CheckedInputStream(InputStream in, Checksum cksum) {
50        super(in);
51        this.cksum = cksum;
52    }
53
54    /**
55     * Reads a byte. Will block if no input is available.
56     * @return the byte read, or -1 if the end of the stream is reached.
57     * @exception IOException if an I/O error has occurred
58     */
59    public int read() throws IOException {
60        int b = in.read();
61        if (b != -1) {
62            cksum.update(b);
63        }
64        return b;
65    }
66
67    /**
68     * Reads into an array of bytes. If <code>len</code> is not zero, the method
69     * blocks until some input is available; otherwise, no
70     * bytes are read and <code>0</code> is returned.
71     * @param buf the buffer into which the data is read
72     * @param off the start offset in the destination array <code>b</code>
73     * @param len the maximum number of bytes read
74     * @return    the actual number of bytes read, or -1 if the end
75     *            of the stream is reached.
76     * @exception  NullPointerException If <code>buf</code> is <code>null</code>.
77     * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
78     * <code>len</code> is negative, or <code>len</code> is greater than
79     * <code>buf.length - off</code>
80     * @exception IOException if an I/O error has occurred
81     */
82    public int read(byte[] buf, int off, int len) throws IOException {
83        len = in.read(buf, off, len);
84        if (len != -1) {
85            cksum.update(buf, off, len);
86        }
87        return len;
88    }
89
90    /**
91     * Skips specified number of bytes of input.
92     * @param n the number of bytes to skip
93     * @return the actual number of bytes skipped
94     * @exception IOException if an I/O error has occurred
95     */
96    public long skip(long n) throws IOException {
97        byte[] buf = new byte[512];
98        long total = 0;
99        while (total < n) {
100            long len = n - total;
101            len = read(buf, 0, len < buf.length ? (int)len : buf.length);
102            if (len == -1) {
103                return total;
104            }
105            total += len;
106        }
107        return total;
108    }
109
110    /**
111     * Returns the Checksum for this input stream.
112     * @return the Checksum value
113     */
114    public Checksum getChecksum() {
115        return cksum;
116    }
117}
118