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Apache Commons Compress defines an API for working with compression and archive formats. These include bzip2, gzip, pack200, LZMA, XZ, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4, Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.commons.compress.archivers.tar;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * This class represents a sparse entry in a Tar archive.
 *
 * 
 * The C structure for a sparse entry is:
 *
 * 
 * struct posix_header {
 * struct sparse sp[21]; // TarConstants.SPARSELEN_GNU_SPARSE     - offset 0
 * char isextended;      // TarConstants.ISEXTENDEDLEN_GNU_SPARSE - offset 504
 * };
 * 
 *
 * Whereas, "struct sparse" is:
 *
 *  * struct sparse {
 * char offset[12];   // offset 0
 * char numbytes[12]; // offset 12
 * };
 * 
 *
 * 
 * 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
 * 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
 * filled with zero bytes.
 * 
 */

public class TarArchiveSparseEntry implements TarConstants {
    /** If an extension sparse header follows. */
    private final boolean isExtended;

    private final List sparseHeaders;

    /**
     * Constructs an entry from an archive's header bytes. File is set to null.
     *
     * @param headerBuf The header bytes from a tar archive entry.
     * @throws IOException on unknown format
     */
    public TarArchiveSparseEntry(final byte[] headerBuf) throws IOException {
        int offset = 0;
        sparseHeaders = new ArrayList<>(TarUtils.readSparseStructs(headerBuf, 0, SPARSE_HEADERS_IN_EXTENSION_HEADER));
        offset += SPARSELEN_GNU_SPARSE;
        isExtended = TarUtils.parseBoolean(headerBuf, offset);
    }

    /**
     * Obtains information about the configuration for the sparse entry.
     *
     * @since 1.20
     * @return information about the configuration for the sparse entry.
     */
    public List getSparseHeaders() {
        return sparseHeaders;
    }

    public boolean isExtended() {
        return isExtended;
    }
}