001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.commons.compress.archivers.tar;
020
021import java.io.IOException;
022import java.util.ArrayList;
023import java.util.List;
024
025/**
026 * This class represents a sparse entry in a Tar archive.
027 *
028 * <p>
029 * The C structure for a sparse entry is:
030 * <pre>
031 * struct posix_header {
032 * struct sparse sp[21]; // TarConstants.SPARSELEN_GNU_SPARSE     - offset 0
033 * char isextended;      // TarConstants.ISEXTENDEDLEN_GNU_SPARSE - offset 504
034 * };
035 * </pre>
036 * Whereas, "struct sparse" is:
037 * <pre>
038 * struct sparse {
039 * char offset[12];   // offset 0
040 * char numbytes[12]; // offset 12
041 * };
042 * </pre>
043 *
044 * <p>Each such struct describes a block of data that has actually been written to the archive. The offset describes
045 * where in the extracted file the data is supposed to start and the numbytes provides the length of the block. When
046 * extracting the entry the gaps between the sparse structs are equivalent to areas filled with zero bytes.</p>
047 */
048
049public class TarArchiveSparseEntry implements TarConstants {
050    /** If an extension sparse header follows. */
051    private final boolean isExtended;
052
053    private final List<TarArchiveStructSparse> sparseHeaders;
054
055    /**
056     * Construct an entry from an archive's header bytes. File is set
057     * to null.
058     *
059     * @param headerBuf The header bytes from a tar archive entry.
060     * @throws IOException on unknown format
061     */
062    public TarArchiveSparseEntry(final byte[] headerBuf) throws IOException {
063        int offset = 0;
064        sparseHeaders = new ArrayList<>(TarUtils.readSparseStructs(headerBuf, 0, SPARSE_HEADERS_IN_EXTENSION_HEADER));
065        offset += SPARSELEN_GNU_SPARSE;
066        isExtended = TarUtils.parseBoolean(headerBuf, offset);
067    }
068
069    /**
070     * Obtains information about the configuration for the sparse entry.
071     * @since 1.20
072     * @return information about the configuration for the sparse entry.
073     */
074    public List<TarArchiveStructSparse> getSparseHeaders() {
075        return sparseHeaders;
076    }
077
078    public boolean isExtended() {
079        return isExtended;
080    }
081}