1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.apache.commons.compress.archivers.tar;
20
21 import java.io.IOException;
22 import java.util.ArrayList;
23 import java.util.List;
24
25 /**
26 * This class represents a sparse entry in a Tar archive.
27 *
28 * <p>
29 * The C structure for a sparse entry is:
30 *
31 * <pre>
32 * struct posix_header {
33 * struct sparse sp[21]; // TarConstants.SPARSELEN_GNU_SPARSE - offset 0
34 * char isextended; // TarConstants.ISEXTENDEDLEN_GNU_SPARSE - offset 504
35 * };
36 * </pre>
37 *
38 * Whereas, "struct sparse" is:
39 *
40 * <pre>
41 * struct sparse {
42 * char offset[12]; // offset 0
43 * char numbytes[12]; // offset 12
44 * };
45 * </pre>
46 *
47 * <p>
48 * Each such struct describes a block of data that has actually been written to the archive. The offset describes where in the extracted file the data is
49 * supposed to start and the numbytes provides the length of the block. When extracting the entry the gaps between the sparse structs are equivalent to areas
50 * filled with zero bytes.
51 * </p>
52 */
53
54 public class TarArchiveSparseEntry implements TarConstants {
55 /** If an extension sparse header follows. */
56 private final boolean isExtended;
57
58 private final List<TarArchiveStructSparse> sparseHeaders;
59
60 /**
61 * Constructs an entry from an archive's header bytes. File is set to null.
62 *
63 * @param headerBuf The header bytes from a tar archive entry.
64 * @throws IOException on unknown format
65 */
66 public TarArchiveSparseEntry(final byte[] headerBuf) throws IOException {
67 int offset = 0;
68 sparseHeaders = new ArrayList<>(TarUtils.readSparseStructs(headerBuf, 0, SPARSE_HEADERS_IN_EXTENSION_HEADER));
69 offset += SPARSELEN_GNU_SPARSE;
70 isExtended = TarUtils.parseBoolean(headerBuf, offset);
71 }
72
73 /**
74 * Gets information about the configuration for the sparse entry.
75 *
76 * @since 1.20
77 * @return information about the configuration for the sparse entry.
78 */
79 public List<TarArchiveStructSparse> getSparseHeaders() {
80 return sparseHeaders;
81 }
82
83 public boolean isExtended() {
84 return isExtended;
85 }
86 }