1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
|
// Copyright 2015 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.android.ziputils;
import com.google.common.base.Preconditions;
import java.nio.ByteBuffer;
/**
* Helper class for finding byte patterns in a byte buffer, scanning forwards or backwards.
* This is used to located the "end of central directory" marker, and in other instances
* where zip file elements must be located by scanning for known signatures.
* For instance, when it's necessary to scan for zip entries, without
* relying on the central directory to provide the exact location, or when scanning for
* data descriptor at the end of an entry of unknown size.
*/
public class ScanUtil {
/**
* Finds the next previous position of a given byte sequence in a given byte buffer,
* starting from the buffer's current position (excluded).
*
* @param target byte sequence to search for.
* @param buffer byte buffer in which to search.
* @return position of the last location of the target sequence, at a position
* strictly smaller than the current position, or -1 if not found.
* @throws IllegalArgumentException if either {@code target} or {@code buffer} is {@code null}.
*/
static int scanBackwardsTo(byte[] target, ByteBuffer buffer) {
Preconditions.checkNotNull(target);
Preconditions.checkNotNull(buffer);
if (target.length == 0) {
return buffer.position() - 1;
}
int pos = buffer.position() - target.length;
if (pos < 0) {
return -1;
}
scan:
while (true) {
while (pos >= 0 && buffer.get(pos) != target[0]) {
pos--;
}
if (pos < 0) {
return -1;
}
for (int i = 1; i < target.length; i++) {
if (buffer.get(pos + i) != target[i]) {
pos--;
continue scan;
}
}
return pos;
}
}
/**
* Finds the next position of a given byte sequence in a given byte buffer, starting from the
* buffer's current position (included).
*
* @param target byte sequence to search for.
* @param buffer byte buffer in which to search.
* @return position of the first location of the target sequence, or -1 if not found.
* @throws IllegalArgumentException if either {@code target} or {@code buffer} is {@code null}.
*/
static int scanTo(byte[] target, ByteBuffer buffer) {
Preconditions.checkNotNull(target);
Preconditions.checkNotNull(buffer);
if (!buffer.hasRemaining()) {
return -1;
}
int pos = buffer.position();
if (target.length == 0) {
return pos;
}
scan:
while (true) {
while (pos <= buffer.limit() - target.length && buffer.get(pos) != target[0]) {
pos++;
}
if (pos > buffer.limit() - target.length + 1) {
return -1;
}
for (int i = 1; i < target.length; i++) {
if (buffer.get(pos + i) != target[i]) {
pos++;
continue scan;
}
}
return pos;
}
}
}
|
