1 /*
2 * Copyright (C) 2017, Google Inc.
3 * and other copyright owners as documented in the project's IP log.
4 *
5 * This program and the accompanying materials are made available
6 * under the terms of the Eclipse Distribution License v1.0 which
7 * accompanies this distribution, is reproduced below, and is
8 * available at http://www.eclipse.org/org/documents/edl-v10.php
9 *
10 * All rights reserved.
11 *
12 * Redistribution and use in source and binary forms, with or
13 * without modification, are permitted provided that the following
14 * conditions are met:
15 *
16 * - Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 *
19 * - Redistributions in binary form must reproduce the above
20 * copyright notice, this list of conditions and the following
21 * disclaimer in the documentation and/or other materials provided
22 * with the distribution.
23 *
24 * - Neither the name of the Eclipse Foundation, Inc. nor the
25 * names of its contributors may be used to endorse or promote
26 * products derived from this software without specific prior
27 * written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
30 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
31 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
32 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
34 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
35 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
36 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
37 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
38 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
41 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
42 */
43
44 package org.eclipse.jgit.internal.storage.io;
45
46 import java.io.FileInputStream;
47 import java.io.IOException;
48 import java.nio.ByteBuffer;
49 import java.nio.channels.FileChannel;
50
51 /**
52 * Provides content blocks of file.
53 * <p>
54 * {@code BlockSource} implementations must decide if they will be thread-safe,
55 * or not.
56 */
57 public abstract class BlockSource implements AutoCloseable {
58 /**
59 * Wrap a byte array as a {@code BlockSource}.
60 *
61 * @param content
62 * input file.
63 * @return block source to read from {@code content}.
64 */
65 public static BlockSource from(byte[] content) {
66 return new BlockSource() {
67 @Override
68 public ByteBuffer read(long pos, int cnt) {
69 ByteBuffer buf = ByteBuffer.allocate(cnt);
70 if (pos < content.length) {
71 int p = (int) pos;
72 int n = Math.min(cnt, content.length - p);
73 buf.put(content, p, n);
74 }
75 return buf;
76 }
77
78 @Override
79 public long size() {
80 return content.length;
81 }
82
83 @Override
84 public void close() {
85 // Do nothing.
86 }
87 };
88 }
89
90 /**
91 * Read from a {@code FileInputStream}.
92 * <p>
93 * The returned {@code BlockSource} is not thread-safe, as it must seek the
94 * file channel to read a block.
95 *
96 * @param in
97 * the file. The {@code BlockSource} will close {@code in}.
98 * @return wrapper for {@code in}.
99 */
100 public static BlockSource from(FileInputStream in) {
101 return from(in.getChannel());
102 }
103
104 /**
105 * Read from a {@code FileChannel}.
106 * <p>
107 * The returned {@code BlockSource} is not thread-safe, as it must seek the
108 * file channel to read a block.
109 *
110 * @param ch
111 * the file. The {@code BlockSource} will close {@code ch}.
112 * @return wrapper for {@code ch}.
113 */
114 public static BlockSource from(FileChannel ch) {
115 return new BlockSource() {
116 @Override
117 public ByteBuffer read(long pos, int blockSize) throws IOException {
118 ByteBuffer b = ByteBuffer.allocate(blockSize);
119 ch.position(pos);
120 int n;
121 do {
122 n = ch.read(b);
123 } while (n > 0 && b.position() < blockSize);
124 return b;
125 }
126
127 @Override
128 public long size() throws IOException {
129 return ch.size();
130 }
131
132 @Override
133 public void close() {
134 try {
135 ch.close();
136 } catch (IOException e) {
137 // Ignore close failures of read-only files.
138 }
139 }
140 };
141 }
142
143 /**
144 * Read a block from the file.
145 * <p>
146 * To reduce copying, the returned ByteBuffer should have an accessible
147 * array and {@code arrayOffset() == 0}. The caller will discard the
148 * ByteBuffer and directly use the backing array.
149 *
150 * @param position
151 * position of the block in the file, specified in bytes from the
152 * beginning of the file.
153 * @param blockSize
154 * size to read.
155 * @return buffer containing the block content.
156 * @throws java.io.IOException
157 * if block cannot be read.
158 */
159 public abstract ByteBuffer read(long position, int blockSize)
160 throws IOException;
161
162 /**
163 * Determine the size of the file.
164 *
165 * @return total number of bytes in the file.
166 * @throws java.io.IOException
167 * if size cannot be obtained.
168 */
169 public abstract long size() throws IOException;
170
171 /**
172 * Advise the {@code BlockSource} a sequential scan is starting.
173 *
174 * @param startPos
175 * starting position.
176 * @param endPos
177 * ending position.
178 */
179 public void adviseSequentialRead(long startPos, long endPos) {
180 // Do nothing by default.
181 }
182
183 /** {@inheritDoc} */
184 @Override
185 public abstract void close();
186 }