1package android.content.pm;
2
3import java.io.FilterInputStream;
4import java.io.IOException;
5import java.io.InputStream;
6import java.util.Arrays;
7
8/**
9 * A class that limits the amount of data that is read from an InputStream. When
10 * the specified length is reached, the stream returns an EOF even if the
11 * underlying stream still has more data.
12 *
13 * @hide
14 */
15public class LimitedLengthInputStream extends FilterInputStream {
16    /**
17     * The end of the stream where we don't want to allow more data to be read.
18     */
19    private final long mEnd;
20
21    /**
22     * Current offset in the stream.
23     */
24    private long mOffset;
25
26    /**
27     * @param in underlying stream to wrap
28     * @param offset offset into stream where data starts
29     * @param length length of data at offset
30     * @throws IOException if an error occurred with the underlying stream
31     */
32    public LimitedLengthInputStream(InputStream in, long offset, long length) throws IOException {
33        super(in);
34
35        if (in == null) {
36            throw new IOException("in == null");
37        }
38
39        if (offset < 0) {
40            throw new IOException("offset < 0");
41        }
42
43        if (length < 0) {
44            throw new IOException("length < 0");
45        }
46
47        if (length > Long.MAX_VALUE - offset) {
48            throw new IOException("offset + length > Long.MAX_VALUE");
49        }
50
51        mEnd = offset + length;
52
53        skip(offset);
54        mOffset = offset;
55    }
56
57    @Override
58    public synchronized int read() throws IOException {
59        if (mOffset >= mEnd) {
60            return -1;
61        }
62
63        mOffset++;
64        return super.read();
65    }
66
67    @Override
68    public int read(byte[] buffer, int offset, int byteCount) throws IOException {
69        if (mOffset >= mEnd) {
70            return -1;
71        }
72
73        final int arrayLength = buffer.length;
74        Arrays.checkOffsetAndCount(arrayLength, offset, byteCount);
75
76        if (mOffset > Long.MAX_VALUE - byteCount) {
77            throw new IOException("offset out of bounds: " + mOffset + " + " + byteCount);
78        }
79
80        if (mOffset + byteCount > mEnd) {
81            byteCount = (int) (mEnd - mOffset);
82        }
83
84        final int numRead = super.read(buffer, offset, byteCount);
85        mOffset += numRead;
86
87        return numRead;
88    }
89
90    @Override
91    public int read(byte[] buffer) throws IOException {
92        return read(buffer, 0, buffer.length);
93    }
94}
95