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
045public class TarArchiveSparseEntry implements TarConstants {
046    /** If an extension sparse header follows. */
047    private final boolean isExtended;
048
049    private List<TarArchiveStructSparse> sparseHeaders;
050
051    /**
052     * Construct an entry from an archive's header bytes. File is set
053     * to null.
054     *
055     * @param headerBuf The header bytes from a tar archive entry.
056     * @throws IOException on unknown format
057     */
058    public TarArchiveSparseEntry(final byte[] headerBuf) throws IOException {
059        int offset = 0;
060        sparseHeaders = new ArrayList<>();
061        for(int i = 0; i < SPARSE_HEADERS_IN_EXTENSION_HEADER;i++) {
062            TarArchiveStructSparse sparseHeader = TarUtils.parseSparse(headerBuf,
063                    offset + i * (SPARSE_OFFSET_LEN + SPARSE_NUMBYTES_LEN));
064
065            // some sparse headers are empty, we need to skip these sparse headers
066            if(sparseHeader.getOffset() > 0 || sparseHeader.getNumbytes() > 0) {
067                sparseHeaders.add(sparseHeader);
068            }
069        }
070
071        offset += SPARSELEN_GNU_SPARSE;
072        isExtended = TarUtils.parseBoolean(headerBuf, offset);
073    }
074
075    public boolean isExtended() {
076        return isExtended;
077    }
078
079    /**
080     * Obtains information about the configuration for the sparse entry.
081     * @since 1.20
082     * @return information about the configuration for the sparse entry.
083     */
084    public List<TarArchiveStructSparse> getSparseHeaders() {
085        return sparseHeaders;
086    }
087}