1/*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements.  See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License.  You may obtain a copy of the License at
8 *
9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18package java.util.zip;
19
20import java.io.IOException;
21import java.io.OutputStream;
22
23/**
24 * The {@code CheckedOutputStream} class is used to maintain a running checksum
25 * of all data written to a stream. The purpose of this checksum is to establish
26 * data integrity, by publishing the checksum to other parties wanting to read
27 * the non corrupted data.
28 */
29public class CheckedOutputStream extends java.io.FilterOutputStream {
30
31    private final Checksum check;
32
33    /**
34     * Constructs a new {@code CheckedOutputStream} on {@code OutputStream}
35     * {@code os}. The checksum is calculated using the algorithm implemented
36     * by {@code csum}.
37     *
38     * @param os
39     *            the output stream to calculate checksum for.
40     * @param cs
41     *            an entity implementing the checksum algorithm.
42     */
43    public CheckedOutputStream(OutputStream os, Checksum cs) {
44        super(os);
45        check = cs;
46    }
47
48    /**
49     * Returns the checksum calculated on the stream read so far.
50     *
51     * @return the updated checksum.
52     */
53    public Checksum getChecksum() {
54        return check;
55    }
56
57    /**
58     * Writes the specified byte to the underlying stream. The checksum is
59     * updated with {@code val}.
60     *
61     * @param val
62     *            the data value to written to the output stream.
63     * @throws IOException
64     *             if an IO error has occurred.
65     */
66    @Override
67    public void write(int val) throws IOException {
68        out.write(val);
69        check.update(val);
70    }
71
72    /**
73     * Writes n bytes of data from {@code buf} starting at offset {@code off} to
74     * the underlying stream. The checksum is updated with the bytes written.
75     *
76     * @param buf
77     *            data written to the output stream.
78     * @param off
79     *            the offset to start reading the data from {@code buf} written
80     *            to the output stream.
81     * @param nbytes
82     *            number of bytes to write to the output stream.
83     * @throws IOException
84     *             if an IO error has occurred.
85     */
86    @Override
87    public void write(byte[] buf, int off, int nbytes) throws IOException {
88        out.write(buf, off, nbytes);
89        check.update(buf, off, nbytes);
90    }
91}
92