1 /*
2 * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
3 * Copyright (C) 2006-2008, Shawn O. Pearce <spearce@spearce.org> and others
4 *
5 * This program and the accompanying materials are made available under the
6 * terms of the Eclipse Distribution License v. 1.0 which is available at
7 * https://www.eclipse.org/org/documents/edl-v10.php.
8 *
9 * SPDX-License-Identifier: BSD-3-Clause
10 */
11
12 package org.eclipse.jgit.internal.storage.file;
13
14 import java.io.IOException;
15 import java.util.zip.DataFormatException;
16 import java.util.zip.Inflater;
17
18 import org.eclipse.jgit.internal.storage.pack.PackOutputStream;
19
20 /**
21 * A window of data currently stored within a cache.
22 * <p>
23 * All bytes in the window can be assumed to be "immediately available", that is
24 * they are very likely already in memory, unless the operating system's memory
25 * is very low and has paged part of this process out to disk. Therefore copying
26 * bytes from a window is very inexpensive.
27 * </p>
28 */
29 abstract class ByteWindow {
30 protected final PackFile pack;
31
32 protected final long start;
33
34 protected final long end;
35
36 /**
37 * Constructor for ByteWindow.
38 *
39 * @param p
40 * a {@link org.eclipse.jgit.internal.storage.file.PackFile}.
41 * @param s
42 * where the byte window starts in the pack file
43 * @param n
44 * size of the byte window
45 */
46 protected ByteWindow(PackFile p, long s, int n) {
47 pack = p;
48 start = s;
49 end = start + n;
50 }
51
52 final int size() {
53 return (int) (end - start);
54 }
55
56 final boolean contains(PackFile neededFile, long neededPos) {
57 return pack == neededFile && start <= neededPos && neededPos < end;
58 }
59
60 /**
61 * Copy bytes from the window to a caller supplied buffer.
62 *
63 * @param pos
64 * offset within the file to start copying from.
65 * @param dstbuf
66 * destination buffer to copy into.
67 * @param dstoff
68 * offset within <code>dstbuf</code> to start copying into.
69 * @param cnt
70 * number of bytes to copy. This value may exceed the number of
71 * bytes remaining in the window starting at offset
72 * <code>pos</code>.
73 * @return number of bytes actually copied; this may be less than
74 * <code>cnt</code> if <code>cnt</code> exceeded the number of
75 * bytes available.
76 */
77 final int copy(long pos, byte[] dstbuf, int dstoff, int cnt) {
78 return copy((int) (pos - start), dstbuf, dstoff, cnt);
79 }
80
81 /**
82 * Copy bytes from the window to a caller supplied buffer.
83 *
84 * @param pos
85 * offset within the window to start copying from.
86 * @param dstbuf
87 * destination buffer to copy into.
88 * @param dstoff
89 * offset within <code>dstbuf</code> to start copying into.
90 * @param cnt
91 * number of bytes to copy. This value may exceed the number of
92 * bytes remaining in the window starting at offset
93 * <code>pos</code>.
94 * @return number of bytes actually copied; this may be less than
95 * <code>cnt</code> if <code>cnt</code> exceeded the number of
96 * bytes available.
97 */
98 protected abstract int copy(int pos, byte[] dstbuf, int dstoff, int cnt);
99
100 abstract void write(PackOutputStream out, long pos, int cnt)
101 throws IOException;
102
103 final int setInput(long pos, Inflater inf) throws DataFormatException {
104 return setInput((int) (pos - start), inf);
105 }
106
107 /**
108 * Set the input
109 *
110 * @param pos
111 * position
112 * @param inf
113 * an {@link java.util.zip.Inflater} object.
114 * @return size of the byte window
115 * @throws java.util.zip.DataFormatException
116 * if any.
117 */
118 protected abstract int setInput(int pos, Inflater inf)
119 throws DataFormatException;
120 }