/*
 *  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.
 *
 */

/*
 * This package is based on the work done by Timothy Gerard Endres
 * (time@ice.com) to whom the Ant project is very grateful for his great code.
 */

package org.apache.commons.compress.archivers.tar;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.compress.archivers.ArchiveEntry;
import org.apache.commons.compress.archivers.ArchiveInputStream;
import org.apache.commons.compress.archivers.zip.ZipEncoding;
import org.apache.commons.compress.archivers.zip.ZipEncodingHelper;
import org.apache.commons.compress.utils.ArchiveUtils;
import org.apache.commons.compress.utils.BoundedInputStream;
import org.apache.commons.compress.utils.CharsetNames;
import org.apache.commons.compress.utils.IOUtils;

The TarInputStream reads a UNIX tar archive as an InputStream.
methods are provided to position at each successive entry in
the archive, and the read each entry as a normal input stream
using read().
@NotThreadSafe
/**
 * The TarInputStream reads a UNIX tar archive as an InputStream.
 * methods are provided to position at each successive entry in
 * the archive, and the read each entry as a normal input stream
 * using read().
 * @NotThreadSafe
 */
public class TarArchiveInputStream extends ArchiveInputStream {

    private static final int SMALL_BUFFER_SIZE = 256;

    private final byte[] smallBuf = new byte[SMALL_BUFFER_SIZE];

    
The size the TAR header /** The size the TAR header */
    private final int recordSize;

    
The size of a block /** The size of a block */
    private final int blockSize;

    
True if file has hit EOF /** True if file has hit EOF */
    private boolean hasHitEOF;

    
Size of the current entry /** Size of the current entry */
    private long entrySize;

    
How far into the entry the stream is at /** How far into the entry the stream is at */
    private long entryOffset;

    
An input stream to read from /** An input stream to read from */
    private final InputStream inputStream;

    
Input streams for reading sparse entries /** Input streams for reading sparse entries **/
    private List<InputStream> sparseInputStreams;

    
the index of current input stream being read when reading sparse entries /** the index of current input stream being read when reading sparse entries */
    private int currentSparseInputStreamIndex;

    
The meta-data about the current entry /** The meta-data about the current entry */
    private TarArchiveEntry currEntry;

    
The encoding of the file /** The encoding of the file */
    private final ZipEncoding zipEncoding;

    // the provided encoding (for unit tests)
    final String encoding;

    // the global PAX header
    private Map<String, String> globalPaxHeaders = new HashMap<>();

    // the global sparse headers, this is only used in PAX Format 0.X
    private final List<TarArchiveStructSparse> globalSparseHeaders = new ArrayList<>();

    private final boolean lenient;

    
Constructor for TarInputStream.
Params:
is – the input stream to use/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     */
    public TarArchiveInputStream(final InputStream is) {
        this(is, TarConstants.DEFAULT_BLKSIZE, TarConstants.DEFAULT_RCDSIZE);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
lenient – when set to true illegal values for group/userid, mode, device numbers and timestamp will be ignored and the fields set to TarArchiveEntry.UNKNOWN. When set to false such illegal fields cause an exception instead.
Since:
1.19/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param lenient when set to true illegal values for group/userid, mode, device numbers and timestamp will be
     * ignored and the fields set to {@link TarArchiveEntry#UNKNOWN}. When set to false such illegal fields cause an
     * exception instead.
     * @since 1.19
     */
    public TarArchiveInputStream(final InputStream is, boolean lenient) {
        this(is, TarConstants.DEFAULT_BLKSIZE, TarConstants.DEFAULT_RCDSIZE, null, lenient);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
encoding – name of the encoding to use for file names
Since:
1.4/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param encoding name of the encoding to use for file names
     * @since 1.4
     */
    public TarArchiveInputStream(final InputStream is, final String encoding) {
        this(is, TarConstants.DEFAULT_BLKSIZE, TarConstants.DEFAULT_RCDSIZE,
             encoding);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
blockSize – the block size to use/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param blockSize the block size to use
     */
    public TarArchiveInputStream(final InputStream is, final int blockSize) {
        this(is, blockSize, TarConstants.DEFAULT_RCDSIZE);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
blockSize – the block size to use
encoding – name of the encoding to use for file names
Since:
1.4/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param blockSize the block size to use
     * @param encoding name of the encoding to use for file names
     * @since 1.4
     */
    public TarArchiveInputStream(final InputStream is, final int blockSize,
                                 final String encoding) {
        this(is, blockSize, TarConstants.DEFAULT_RCDSIZE, encoding);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
blockSize – the block size to use
recordSize – the record size to use/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param blockSize the block size to use
     * @param recordSize the record size to use
     */
    public TarArchiveInputStream(final InputStream is, final int blockSize, final int recordSize) {
        this(is, blockSize, recordSize, null);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
blockSize – the block size to use
recordSize – the record size to use
encoding – name of the encoding to use for file names
Since:
1.4/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param blockSize the block size to use
     * @param recordSize the record size to use
     * @param encoding name of the encoding to use for file names
     * @since 1.4
     */
    public TarArchiveInputStream(final InputStream is, final int blockSize, final int recordSize,
                                 final String encoding) {
        this(is, blockSize, recordSize, encoding, false);
    }

    
Constructor for TarInputStream.
Params:
is – the input stream to use
blockSize – the block size to use
recordSize – the record size to use
encoding – name of the encoding to use for file names
lenient – when set to true illegal values for group/userid, mode, device numbers and timestamp will be ignored and the fields set to TarArchiveEntry.UNKNOWN. When set to false such illegal fields cause an exception instead.
Since:
1.19/**
     * Constructor for TarInputStream.
     * @param is the input stream to use
     * @param blockSize the block size to use
     * @param recordSize the record size to use
     * @param encoding name of the encoding to use for file names
     * @param lenient when set to true illegal values for group/userid, mode, device numbers and timestamp will be
     * ignored and the fields set to {@link TarArchiveEntry#UNKNOWN}. When set to false such illegal fields cause an
     * exception instead.
     * @since 1.19
     */
    public TarArchiveInputStream(final InputStream is, final int blockSize, final int recordSize,
                                 final String encoding, boolean lenient) {
        this.inputStream = is;
        this.hasHitEOF = false;
        this.encoding = encoding;
        this.zipEncoding = ZipEncodingHelper.getZipEncoding(encoding);
        this.recordSize = recordSize;
        this.blockSize = blockSize;
        this.lenient = lenient;
    }

    
Closes this stream. Calls the TarBuffer's close() method.
Throws:
IOException – on error/**
     * Closes this stream. Calls the TarBuffer's close() method.
     * @throws IOException on error
     */
    @Override
    public void close() throws IOException {
        // Close all the input streams in sparseInputStreams
        if(sparseInputStreams != null) {
            for (InputStream inputStream : sparseInputStreams) {
                inputStream.close();
            }
        }

        inputStream.close();
    }

    
Get the record size being used by this stream's buffer.
Returns:
The TarBuffer record size./**
     * Get the record size being used by this stream's buffer.
     *
     * @return The TarBuffer record size.
     */
    public int getRecordSize() {
        return recordSize;
    }

    
Get the available data that can be read from the current
entry in the archive. This does not indicate how much data
is left in the entire archive, only in the current entry.
This value is determined from the entry's size header field
and the amount of data already read from the current entry.
Integer.MAX_VALUE is returned in case more than Integer.MAX_VALUE
bytes are left in the current entry in the archive.
Throws:
IOException – for signature
Returns:
The number of available bytes for the current entry./**
     * Get the available data that can be read from the current
     * entry in the archive. This does not indicate how much data
     * is left in the entire archive, only in the current entry.
     * This value is determined from the entry's size header field
     * and the amount of data already read from the current entry.
     * Integer.MAX_VALUE is returned in case more than Integer.MAX_VALUE
     * bytes are left in the current entry in the archive.
     *
     * @return The number of available bytes for the current entry.
     * @throws IOException for signature
     */
    @Override
    public int available() throws IOException {
        if (isDirectory()) {
            return 0;
        }

        if (currEntry.getRealSize() - entryOffset > Integer.MAX_VALUE) {
            return Integer.MAX_VALUE;
        }
        return (int) (currEntry.getRealSize() - entryOffset);
    }


    
Skips over and discards n bytes of data from this input
stream. The skip method may, for a variety of reasons, end
up skipping over some smaller number of bytes, possibly 0.
This may result from any of a number of conditions; reaching end of file
or end of entry before n bytes have been skipped; are only
two possibilities. The actual number of bytes skipped is returned. If
n is negative, no bytes are skipped.
Params:
n – 
           the number of bytes to be skipped.
Throws:
IOException – 
               if some other I/O error occurs.
Returns:
the actual number of bytes skipped./**
     * Skips over and discards <code>n</code> bytes of data from this input
     * stream. The <code>skip</code> method may, for a variety of reasons, end
     * up skipping over some smaller number of bytes, possibly <code>0</code>.
     * This may result from any of a number of conditions; reaching end of file
     * or end of entry before <code>n</code> bytes have been skipped; are only
     * two possibilities. The actual number of bytes skipped is returned. If
     * <code>n</code> is negative, no bytes are skipped.
     *
     *
     * @param n
     *            the number of bytes to be skipped.
     * @return the actual number of bytes skipped.
     * @throws IOException
     *                if some other I/O error occurs.
     */
    @Override
    public long skip(final long n) throws IOException {
        if (n <= 0 || isDirectory()) {
            return 0;
        }

        final long available = currEntry.getRealSize() - entryOffset;
        final long skipped;
        if (!currEntry.isSparse()) {
            skipped = IOUtils.skip(inputStream, Math.min(n, available));
        } else {
            skipped = skipSparse(Math.min(n, available));
        }
        count(skipped);
        entryOffset += skipped;
        return skipped;
    }

    
Skip n bytes from current input stream, if the current input stream doesn't have enough data to skip,
jump to the next input stream and skip the rest bytes, keep doing this until total n bytes are skipped
or the input streams are all skipped
Params:
n – bytes of data to skip
Throws:
IOException – 
Returns:
actual bytes of data skipped/**
     * Skip n bytes from current input stream, if the current input stream doesn't have enough data to skip,
     * jump to the next input stream and skip the rest bytes, keep doing this until total n bytes are skipped
     * or the input streams are all skipped
     *
     * @param n bytes of data to skip
     * @return actual bytes of data skipped
     * @throws IOException
     */
    private long skipSparse(final long n) throws IOException {
        if (sparseInputStreams == null || sparseInputStreams.size() == 0) {
            return inputStream.skip(n);
        }

        long bytesSkipped = 0;

        while (bytesSkipped < n && currentSparseInputStreamIndex < sparseInputStreams.size()) {
            final InputStream  currentInputStream = sparseInputStreams.get(currentSparseInputStreamIndex);
            bytesSkipped += currentInputStream.skip(n - bytesSkipped);

            if (bytesSkipped < n) {
                currentSparseInputStreamIndex++;
            }
        }

        return bytesSkipped;
    }

    
Since we do not support marking just yet, we return false.
Returns:
False./**
     * Since we do not support marking just yet, we return false.
     *
     * @return False.
     */
    @Override
    public boolean markSupported() {
        return false;
    }

    
Since we do not support marking just yet, we do nothing.
Params:
markLimit – The limit to mark./**
     * Since we do not support marking just yet, we do nothing.
     *
     * @param markLimit The limit to mark.
     */
    @Override
    public synchronized void mark(final int markLimit) {
    }

    
Since we do not support marking just yet, we do nothing.
/**
     * Since we do not support marking just yet, we do nothing.
     */
    @Override
    public synchronized void reset() {
    }

    
Get the next entry in this tar archive. This will skip
over any remaining data in the current entry, if there
is one, and place the input stream at the header of the
next entry, and read the header and instantiate a new
TarEntry from the header bytes and return that entry.
If there are no more entries in the archive, null will
be returned to indicate that the end of the archive has
been reached.
Throws:
IOException – on error
Returns:
The next TarEntry in the archive, or null./**
     * Get the next entry in this tar archive. This will skip
     * over any remaining data in the current entry, if there
     * is one, and place the input stream at the header of the
     * next entry, and read the header and instantiate a new
     * TarEntry from the header bytes and return that entry.
     * If there are no more entries in the archive, null will
     * be returned to indicate that the end of the archive has
     * been reached.
     *
     * @return The next TarEntry in the archive, or null.
     * @throws IOException on error
     */
    public TarArchiveEntry getNextTarEntry() throws IOException {
        if (isAtEOF()) {
            return null;
        }

        if (currEntry != null) {
            /* Skip will only go to the end of the current entry */
            IOUtils.skip(this, Long.MAX_VALUE);

            /* skip to the end of the last record */
            skipRecordPadding();
        }

        final byte[] headerBuf = getRecord();

        if (headerBuf == null) {
            /* hit EOF */
            currEntry = null;
            return null;
        }

        try {
            currEntry = new TarArchiveEntry(headerBuf, zipEncoding, lenient);
        } catch (final IllegalArgumentException e) {
            throw new IOException("Error detected parsing the header", e);
        }

        entryOffset = 0;
        entrySize = currEntry.getSize();

        if (currEntry.isGNULongLinkEntry()) {
            final byte[] longLinkData = getLongNameData();
            if (longLinkData == null) {
                // Bugzilla: 40334
                // Malformed tar file - long link entry name not followed by
                // entry
                return null;
            }
            currEntry.setLinkName(zipEncoding.decode(longLinkData));
        }

        if (currEntry.isGNULongNameEntry()) {
            final byte[] longNameData = getLongNameData();
            if (longNameData == null) {
                // Bugzilla: 40334
                // Malformed tar file - long entry name not followed by
                // entry
                return null;
            }
            currEntry.setName(zipEncoding.decode(longNameData));
        }

        if (currEntry.isGlobalPaxHeader()){ // Process Global Pax headers
            readGlobalPaxHeaders();
        }

        if (currEntry.isPaxHeader()){ // Process Pax headers
            paxHeaders();
        } else if (!globalPaxHeaders.isEmpty()) {
            applyPaxHeadersToCurrentEntry(globalPaxHeaders, globalSparseHeaders);
        }

        if (currEntry.isOldGNUSparse()){ // Process sparse files
            readOldGNUSparse();
        }

        // If the size of the next element in the archive has changed
        // due to a new size being reported in the posix header
        // information, we update entrySize here so that it contains
        // the correct value.
        entrySize = currEntry.getSize();

        return currEntry;
    }

    
The last record block should be written at the full size, so skip any
additional space used to fill a record after an entry
/**
     * The last record block should be written at the full size, so skip any
     * additional space used to fill a record after an entry
     */
    private void skipRecordPadding() throws IOException {
        if (!isDirectory() && this.entrySize > 0 && this.entrySize % this.recordSize != 0) {
            final long numRecords = (this.entrySize / this.recordSize) + 1;
            final long padding = (numRecords * this.recordSize) - this.entrySize;
            final long skipped = IOUtils.skip(inputStream, padding);
            count(skipped);
        }
    }

    
Get the next entry in this tar archive as longname data.
Throws:
IOException – on error
Returns:
The next entry in the archive as longname data, or null./**
     * Get the next entry in this tar archive as longname data.
     *
     * @return The next entry in the archive as longname data, or null.
     * @throws IOException on error
     */
    protected byte[] getLongNameData() throws IOException {
        // read in the name
        final ByteArrayOutputStream longName = new ByteArrayOutputStream();
        int length = 0;
        while ((length = read(smallBuf)) >= 0) {
            longName.write(smallBuf, 0, length);
        }
        getNextEntry();
        if (currEntry == null) {
            // Bugzilla: 40334
            // Malformed tar file - long entry name not followed by entry
            return null;
        }
        byte[] longNameData = longName.toByteArray();
        // remove trailing null terminator(s)
        length = longNameData.length;
        while (length > 0 && longNameData[length - 1] == 0) {
            --length;
        }
        if (length != longNameData.length) {
            final byte[] l = new byte[length];
            System.arraycopy(longNameData, 0, l, 0, length);
            longNameData = l;
        }
        return longNameData;
    }

    
Get the next record in this tar archive. This will skip
over any remaining data in the current entry, if there
is one, and place the input stream at the header of the
next entry.
If there are no more entries in the archive, null will be returned to indicate that the end of the archive has been reached. At the same time the hasHitEOF marker will be set to true.
Throws:
IOException – on error
Returns:
The next header in the archive, or null./**
     * Get the next record in this tar archive. This will skip
     * over any remaining data in the current entry, if there
     * is one, and place the input stream at the header of the
     * next entry.
     *
     * <p>If there are no more entries in the archive, null will be
     * returned to indicate that the end of the archive has been
     * reached.  At the same time the {@code hasHitEOF} marker will be
     * set to true.</p>
     *
     * @return The next header in the archive, or null.
     * @throws IOException on error
     */
    private byte[] getRecord() throws IOException {
        byte[] headerBuf = readRecord();
        setAtEOF(isEOFRecord(headerBuf));
        if (isAtEOF() && headerBuf != null) {
            tryToConsumeSecondEOFRecord();
            consumeRemainderOfLastBlock();
            headerBuf = null;
        }
        return headerBuf;
    }

    
Determine if an archive record indicate End of Archive. End of
archive is indicated by a record that consists entirely of null bytes.
Params:
record – The record data to check.
Returns:
true if the record data is an End of Archive/**
     * Determine if an archive record indicate End of Archive. End of
     * archive is indicated by a record that consists entirely of null bytes.
     *
     * @param record The record data to check.
     * @return true if the record data is an End of Archive
     */
    protected boolean isEOFRecord(final byte[] record) {
        return record == null || ArchiveUtils.isArrayZero(record, recordSize);
    }

    
Read a record from the input stream and return the data.
Throws:
IOException – on error
Returns:
The record data or null if EOF has been hit./**
     * Read a record from the input stream and return the data.
     *
     * @return The record data or null if EOF has been hit.
     * @throws IOException on error
     */
    protected byte[] readRecord() throws IOException {

        final byte[] record = new byte[recordSize];

        final int readNow = IOUtils.readFully(inputStream, record);
        count(readNow);
        if (readNow != recordSize) {
            return null;
        }

        return record;
    }

    private void readGlobalPaxHeaders() throws IOException {
        globalPaxHeaders = parsePaxHeaders(this, globalSparseHeaders);
        getNextEntry(); // Get the actual file entry
    }

    
For PAX Format 0.0, the sparse headers(GNU.sparse.offset and GNU.sparse.numbytes)
may appear multi times, and they look like:
GNU.sparse.size=size
GNU.sparse.numblocks=numblocks
repeat numblocks times
  GNU.sparse.offset=offset
  GNU.sparse.numbytes=numbytes
end repeat
For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map
GNU.sparse.map
   Map of non-null data chunks. It is a string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
For PAX Format 1.X:
The sparse map itself is stored in the file data block, preceding the actual file data.
It consists of a series of decimal numbers delimited by newlines. The map is padded with nulls to the nearest block boundary.
The first number gives the number of entries in the map. Following are map entries, each one consisting of two numbers
giving the offset and size of the data block it describes.
Throws:
IOException – /**
     * For PAX Format 0.0, the sparse headers(GNU.sparse.offset and GNU.sparse.numbytes)
     * may appear multi times, and they look like:
     *
     * GNU.sparse.size=size
     * GNU.sparse.numblocks=numblocks
     * repeat numblocks times
     *   GNU.sparse.offset=offset
     *   GNU.sparse.numbytes=numbytes
     * end repeat
     *
     *
     * For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map
     *
     * GNU.sparse.map
     *    Map of non-null data chunks. It is a string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
     *
     *
     * For PAX Format 1.X:
     * The sparse map itself is stored in the file data block, preceding the actual file data.
     * It consists of a series of decimal numbers delimited by newlines. The map is padded with nulls to the nearest block boundary.
     * The first number gives the number of entries in the map. Following are map entries, each one consisting of two numbers
     * giving the offset and size of the data block it describes.
     * @throws IOException
     */
    private void paxHeaders() throws IOException{
        List<TarArchiveStructSparse> sparseHeaders = new ArrayList<>();
        final Map<String, String> headers = parsePaxHeaders(this, sparseHeaders);

        // for 0.1 PAX Headers
        if (headers.containsKey("GNU.sparse.map")) {
            sparseHeaders = parsePAX01SparseHeaders(headers.get("GNU.sparse.map"));
        }
        getNextEntry(); // Get the actual file entry
        applyPaxHeadersToCurrentEntry(headers, sparseHeaders);

        // for 1.0 PAX Format, the sparse map is stored in the file data block
        if (currEntry.isPaxGNU1XSparse()) {
            sparseHeaders = parsePAX1XSparseHeaders();
            currEntry.setSparseHeaders(sparseHeaders);
        }

        // sparse headers are all done reading, we need to build
        // sparse input streams using these sparse headers
        buildSparseInputStreams();
    }

    
For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map
GNU.sparse.map
   Map of non-null data chunks. It is a string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
Params:
sparseMap – the sparse map string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
Throws:
IOException – 
Returns:
sparse headers parsed from sparse map/**
     * For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map
     * GNU.sparse.map
     *    Map of non-null data chunks. It is a string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
     *
     * @param sparseMap the sparse map string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
     * @return sparse headers parsed from sparse map
     * @throws IOException
     */
    private List<TarArchiveStructSparse> parsePAX01SparseHeaders(String sparseMap) throws IOException {
        List<TarArchiveStructSparse> sparseHeaders = new ArrayList<>();
        String[] sparseHeaderStrings = sparseMap.split(",");

        for (int i = 0; i < sparseHeaderStrings.length;i += 2) {
            long sparseOffset = Long.parseLong(sparseHeaderStrings[i]);
            long sparseNumbytes = Long.parseLong(sparseHeaderStrings[i + 1]);
            sparseHeaders.add(new TarArchiveStructSparse(sparseOffset, sparseNumbytes));
        }

        return sparseHeaders;
    }

    
For PAX Format 1.X:
The sparse map itself is stored in the file data block, preceding the actual file data.
It consists of a series of decimal numbers delimited by newlines. The map is padded with nulls to the nearest block boundary.
The first number gives the number of entries in the map. Following are map entries, each one consisting of two numbers
giving the offset and size of the data block it describes.
Throws:
IOException – 
Returns:
sparse headers/**
     * For PAX Format 1.X:
     * The sparse map itself is stored in the file data block, preceding the actual file data.
     * It consists of a series of decimal numbers delimited by newlines. The map is padded with nulls to the nearest block boundary.
     * The first number gives the number of entries in the map. Following are map entries, each one consisting of two numbers
     * giving the offset and size of the data block it describes.
     * @return sparse headers
     * @throws IOException
     */
    private List<TarArchiveStructSparse> parsePAX1XSparseHeaders() throws IOException {
        // for 1.X PAX Headers
        List<TarArchiveStructSparse> sparseHeaders = new ArrayList<>();
        long bytesRead = 0;

        long[] readResult = readLineOfNumberForPax1X(inputStream);
        long sparseHeadersCount = readResult[0];
        bytesRead += readResult[1];
        while (sparseHeadersCount-- > 0) {
            readResult = readLineOfNumberForPax1X(inputStream);
            long sparseOffset = readResult[0];
            bytesRead += readResult[1];

            readResult = readLineOfNumberForPax1X(inputStream);
            long sparseNumbytes = readResult[0];
            bytesRead += readResult[1];
            sparseHeaders.add(new TarArchiveStructSparse(sparseOffset, sparseNumbytes));
        }

        // skip the rest of this record data
        long bytesToSkip = recordSize - bytesRead % recordSize;
        IOUtils.skip(inputStream, bytesToSkip);
        return sparseHeaders;
    }

    
For 1.X PAX Format, the sparse headers are stored in the file data block, preceding the actual file data.
It consists of a series of decimal numbers delimited by newlines.
Params:
inputStream – the input stream of the tar file
Throws:
IOException – 
Returns:
the decimal number delimited by '\n', and the bytes read from input stream/**
     * For 1.X PAX Format, the sparse headers are stored in the file data block, preceding the actual file data.
     * It consists of a series of decimal numbers delimited by newlines.
     *
     * @param inputStream the input stream of the tar file
     * @return the decimal number delimited by '\n', and the bytes read from input stream
     * @throws IOException
     */
    private long[] readLineOfNumberForPax1X(InputStream inputStream) throws IOException {
        int number;
        long result = 0;
        long bytesRead = 0;

        while((number = inputStream.read()) != '\n') {
            bytesRead += 1;
            if(number == -1) {
                throw new IOException("Unexpected EOF when reading parse information of 1.X PAX format");
            }
            result = result * 10 + (number - '0');
        }
        bytesRead += 1;

        return new long[] {result, bytesRead};
    }

    
For PAX Format 0.0, the sparse headers(GNU.sparse.offset and GNU.sparse.numbytes)
may appear multi times, and they look like:
GNU.sparse.size=size
GNU.sparse.numblocks=numblocks
repeat numblocks times
  GNU.sparse.offset=offset
  GNU.sparse.numbytes=numbytes
end repeat
For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map
GNU.sparse.map
   Map of non-null data chunks. It is a string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
Params:
inputstream – inputstream to read keys and values
sparseHeaders – used in PAX Format 0.0 & 0.1, as it may appear multi times,
                     the sparse headers need to be stored in an array, not a map
Throws:
IOException – 
Returns:
map of PAX headers values found inside of the current (local or global) PAX headers tar entry./**
     * For PAX Format 0.0, the sparse headers(GNU.sparse.offset and GNU.sparse.numbytes)
     * may appear multi times, and they look like:
     *
     * GNU.sparse.size=size
     * GNU.sparse.numblocks=numblocks
     * repeat numblocks times
     *   GNU.sparse.offset=offset
     *   GNU.sparse.numbytes=numbytes
     * end repeat
     *
     * For PAX Format 0.1, the sparse headers are stored in a single variable : GNU.sparse.map
     *
     * GNU.sparse.map
     *    Map of non-null data chunks. It is a string consisting of comma-separated values "offset,size[,offset-1,size-1...]"
     *
     * @param inputstream inputstream to read keys and values
     * @param sparseHeaders used in PAX Format 0.0 &amp; 0.1, as it may appear multi times,
     *                      the sparse headers need to be stored in an array, not a map
     * @return map of PAX headers values found inside of the current (local or global) PAX headers tar entry.
     * @throws IOException
     */
    Map<String, String> parsePaxHeaders(final InputStream inputStream, List<TarArchiveStructSparse> sparseHeaders)
        throws IOException {
        final Map<String, String> headers = new HashMap<>(globalPaxHeaders);
        Long offset = null;
        // Format is "length keyword=value\n";
        while(true) { // get length
            int ch;
            int len = 0;
            int read = 0;
            while((ch = inputStream.read()) != -1) {
                read++;
                if (ch == '\n') { // blank line in header
                    break;
                } else if (ch == ' '){ // End of length string
                    // Get keyword
                    final ByteArrayOutputStream coll = new ByteArrayOutputStream();
                    while((ch = inputStream.read()) != -1) {
                        read++;
                        if (ch == '='){ // end of keyword
                            final String keyword = coll.toString(CharsetNames.UTF_8);
                            // Get rest of entry
                            final int restLen = len - read;
                            if (restLen == 1) { // only NL
                                headers.remove(keyword);
                            } else {
                                final byte[] rest = new byte[restLen];
                                final int got = IOUtils.readFully(inputStream, rest);
                                if (got != restLen) {
                                    throw new IOException("Failed to read "
                                                          + "Paxheader. Expected "
                                                          + restLen
                                                          + " bytes, read "
                                                          + got);
                                }
                                // Drop trailing NL
                                final String value = new String(rest, 0,
                                                          restLen - 1, CharsetNames.UTF_8);
                                headers.put(keyword, value);

                                // for 0.0 PAX Headers
                                if (keyword.equals("GNU.sparse.offset")) {
                                    if (offset != null) {
                                        // previous GNU.sparse.offset header but but no numBytes
                                        sparseHeaders.add(new TarArchiveStructSparse(offset, 0));
                                    }
                                    offset = Long.valueOf(value);
                                }

                                // for 0.0 PAX Headers
                                if (keyword.equals("GNU.sparse.numbytes")) {
                                    if (offset == null) {
                                        throw new IOException("Failed to read Paxheader." +
                                                "GNU.sparse.offset is expected before GNU.sparse.numbytes shows up.");
                                    }
                                    sparseHeaders.add(new TarArchiveStructSparse(offset, Long.parseLong(value)));
                                    offset = null;
                                }
                            }
                            break;
                        }
                        coll.write((byte) ch);
                    }
                    break; // Processed single header
                }
                len *= 10;
                len += ch - '0';
            }
            if (ch == -1){ // EOF
                break;
            }
        }
        if (offset != null) {
            // offset but no numBytes
            sparseHeaders.add(new TarArchiveStructSparse(offset, 0));
        }
        return headers;
    }

    private void applyPaxHeadersToCurrentEntry(final Map<String, String> headers, final List<TarArchiveStructSparse> sparseHeaders) {
        currEntry.updateEntryFromPaxHeaders(headers);
        currEntry.setSparseHeaders(sparseHeaders);
    }

    
Adds the sparse chunks from the current entry to the sparse chunks,
including any additional sparse entries following the current entry.
Throws:
IOException – on error/**
     * Adds the sparse chunks from the current entry to the sparse chunks,
     * including any additional sparse entries following the current entry.
     *
     * @throws IOException on error
     */
    private void readOldGNUSparse() throws IOException {
        if (currEntry.isExtended()) {
            TarArchiveSparseEntry entry;
            do {
                final byte[] headerBuf = getRecord();
                if (headerBuf == null) {
                    currEntry = null;
                    break;
                }
                entry = new TarArchiveSparseEntry(headerBuf);
                currEntry.getSparseHeaders().addAll(entry.getSparseHeaders());
            } while (entry.isExtended());
        }

        // sparse headers are all done reading, we need to build
        // sparse input streams using these sparse headers
        buildSparseInputStreams();
    }

    private boolean isDirectory() {
        return currEntry != null && currEntry.isDirectory();
    }

    
Returns the next Archive Entry in this Stream.
Throws:
IOException – if the next entry could not be read
Returns:
the next entry, or null if there are no more entries/**
     * Returns the next Archive Entry in this Stream.
     *
     * @return the next entry,
     *         or {@code null} if there are no more entries
     * @throws IOException if the next entry could not be read
     */
    @Override
    public ArchiveEntry getNextEntry() throws IOException {
        return getNextTarEntry();
    }

    
Tries to read the next record rewinding the stream if it is not a EOF record.
This is meant to protect against cases where a tar
implementation has written only one EOF record when two are
expected.  Actually this won't help since a non-conforming
implementation likely won't fill full blocks consisting of - by
default - ten records either so we probably have already read
beyond the archive anyway.
/**
     * Tries to read the next record rewinding the stream if it is not a EOF record.
     *
     * <p>This is meant to protect against cases where a tar
     * implementation has written only one EOF record when two are
     * expected.  Actually this won't help since a non-conforming
     * implementation likely won't fill full blocks consisting of - by
     * default - ten records either so we probably have already read
     * beyond the archive anyway.</p>
     */
    private void tryToConsumeSecondEOFRecord() throws IOException {
        boolean shouldReset = true;
        final boolean marked = inputStream.markSupported();
        if (marked) {
            inputStream.mark(recordSize);
        }
        try {
            shouldReset = !isEOFRecord(readRecord());
        } finally {
            if (shouldReset && marked) {
                pushedBackBytes(recordSize);
            	inputStream.reset();
            }
        }
    }

    
Reads bytes from the current tar archive entry.
This method is aware of the boundaries of the current
entry in the archive and will deal with them as if they
were this stream's start and EOF.
Params:
buf – The buffer into which to place bytes read.
offset – The offset at which to place bytes read.
numToRead – The number of bytes to read.
Throws:
IOException – on error
Returns:
The number of bytes read, or -1 at EOF./**
     * Reads bytes from the current tar archive entry.
     *
     * This method is aware of the boundaries of the current
     * entry in the archive and will deal with them as if they
     * were this stream's start and EOF.
     *
     * @param buf The buffer into which to place bytes read.
     * @param offset The offset at which to place bytes read.
     * @param numToRead The number of bytes to read.
     * @return The number of bytes read, or -1 at EOF.
     * @throws IOException on error
     */
    @Override
    public int read(final byte[] buf, final int offset, int numToRead) throws IOException {
        if (numToRead == 0) {
            return 0;
        }
    	int totalRead = 0;

        if (isAtEOF() || isDirectory()) {
            return -1;
        }

        if (currEntry == null) {
            throw new IllegalStateException("No current tar entry");
        }

        if (!currEntry.isSparse()) {
            if (entryOffset >= entrySize) {
                return -1;
            }
        } else {
            // for sparse entries, there are actually currEntry.getRealSize() bytes to read
            if (entryOffset >= currEntry.getRealSize()) {
                return -1;
            }
        }

        numToRead = Math.min(numToRead, available());

        if (currEntry.isSparse()) {
            // for sparse entries, we need to read them in another way
            totalRead = readSparse(buf, offset, numToRead);
        } else {
            totalRead = inputStream.read(buf, offset, numToRead);
        }

        if (totalRead == -1) {
            if (numToRead > 0) {
                throw new IOException("Truncated TAR archive");
            }
            setAtEOF(true);
        } else {
            count(totalRead);
            entryOffset += totalRead;
        }

        return totalRead;
    }

    
For sparse tar entries, there are many "holes"(consisting of all 0) in the file. Only the non-zero data is
stored in tar files, and they are stored separately. The structure of non-zero data is introduced by the
sparse headers using the offset, where a block of non-zero data starts, and numbytes, the length of the
non-zero data block.
When reading sparse entries, the actual data is read out with "holes" and non-zero data combined together
according to the sparse headers.
Params:
buf – The buffer into which to place bytes read.
offset – The offset at which to place bytes read.
numToRead – The number of bytes to read.
Throws:
IOException – on error
Returns:
The number of bytes read, or -1 at EOF./**
     * For sparse tar entries, there are many "holes"(consisting of all 0) in the file. Only the non-zero data is
     * stored in tar files, and they are stored separately. The structure of non-zero data is introduced by the
     * sparse headers using the offset, where a block of non-zero data starts, and numbytes, the length of the
     * non-zero data block.
     * When reading sparse entries, the actual data is read out with "holes" and non-zero data combined together
     * according to the sparse headers.
     *
     * @param buf The buffer into which to place bytes read.
     * @param offset The offset at which to place bytes read.
     * @param numToRead The number of bytes to read.
     * @return The number of bytes read, or -1 at EOF.
     * @throws IOException on error
     */
    private int readSparse(final byte[] buf, final int offset, int numToRead) throws IOException {
        // if there are no actual input streams, just read from the original input stream
        if (sparseInputStreams == null || sparseInputStreams.size() == 0) {
            return inputStream.read(buf, offset, numToRead);
        }

        if(currentSparseInputStreamIndex >= sparseInputStreams.size()) {
            return -1;
        }

        InputStream currentInputStream = sparseInputStreams.get(currentSparseInputStreamIndex);
        int readLen = currentInputStream.read(buf, offset, numToRead);

        // if the current input stream is the last input stream,
        // just return the number of bytes read from current input stream
        if (currentSparseInputStreamIndex == sparseInputStreams.size() - 1) {
            return readLen;
        }

        // if EOF of current input stream is meet, open a new input stream and recursively call read
        if (readLen == -1) {
            currentSparseInputStreamIndex++;
            return readSparse(buf, offset, numToRead);
        }

        // if the rest data of current input stream is not long enough, open a new input stream
        // and recursively call read
        if (readLen < numToRead) {
            currentSparseInputStreamIndex++;
            int readLenOfNext = readSparse(buf, offset + readLen, numToRead - readLen);
            if (readLenOfNext == -1) {
                return readLen;
            }

            return readLen + readLenOfNext;
        }

        // if the rest data of current input stream is enough(which means readLen == len), just return readLen
        return readLen;
    }

    
Whether this class is able to read the given entry.
May return false if the current entry is a sparse file.
/**
     * Whether this class is able to read the given entry.
     *
     * <p>May return false if the current entry is a sparse file.</p>
     */
    @Override
    public boolean canReadEntryData(final ArchiveEntry ae) {
        if (ae instanceof TarArchiveEntry) {
            final TarArchiveEntry te = (TarArchiveEntry) ae;
            return !te.isSparse();
        }
        return false;
    }

    
Get the current TAR Archive Entry that this input stream is processing
Returns:
The current Archive Entry/**
     * Get the current TAR Archive Entry that this input stream is processing
     *
     * @return The current Archive Entry
     */
    public TarArchiveEntry getCurrentEntry() {
        return currEntry;
    }

    protected final void setCurrentEntry(final TarArchiveEntry e) {
        currEntry = e;
    }

    protected final boolean isAtEOF() {
        return hasHitEOF;
    }

    protected final void setAtEOF(final boolean b) {
        hasHitEOF = b;
    }

    
This method is invoked once the end of the archive is hit, it
tries to consume the remaining bytes under the assumption that
the tool creating this archive has padded the last block.
/**
     * This method is invoked once the end of the archive is hit, it
     * tries to consume the remaining bytes under the assumption that
     * the tool creating this archive has padded the last block.
     */
    private void consumeRemainderOfLastBlock() throws IOException {
        final long bytesReadOfLastBlock = getBytesRead() % blockSize;
        if (bytesReadOfLastBlock > 0) {
            final long skipped = IOUtils.skip(inputStream, blockSize - bytesReadOfLastBlock);
            count(skipped);
        }
    }

    
Checks if the signature matches what is expected for a tar file.
Params:
signature – 
           the bytes to check
length – 
           the number of bytes to check
Returns:
true, if this stream is a tar archive stream, false otherwise/**
     * Checks if the signature matches what is expected for a tar file.
     *
     * @param signature
     *            the bytes to check
     * @param length
     *            the number of bytes to check
     * @return true, if this stream is a tar archive stream, false otherwise
     */
    public static boolean matches(final byte[] signature, final int length) {
        if (length < TarConstants.VERSION_OFFSET+TarConstants.VERSIONLEN) {
            return false;
        }

        if (ArchiveUtils.matchAsciiBuffer(TarConstants.MAGIC_POSIX,
                signature, TarConstants.MAGIC_OFFSET, TarConstants.MAGICLEN)
            &&
            ArchiveUtils.matchAsciiBuffer(TarConstants.VERSION_POSIX,
                signature, TarConstants.VERSION_OFFSET, TarConstants.VERSIONLEN)
                ){
            return true;
        }
        if (ArchiveUtils.matchAsciiBuffer(TarConstants.MAGIC_GNU,
                signature, TarConstants.MAGIC_OFFSET, TarConstants.MAGICLEN)
            &&
            (
             ArchiveUtils.matchAsciiBuffer(TarConstants.VERSION_GNU_SPACE,
                signature, TarConstants.VERSION_OFFSET, TarConstants.VERSIONLEN)
            ||
            ArchiveUtils.matchAsciiBuffer(TarConstants.VERSION_GNU_ZERO,
                signature, TarConstants.VERSION_OFFSET, TarConstants.VERSIONLEN)
            )
                ){
            return true;
        }
        // COMPRESS-107 - recognise Ant tar files
        return ArchiveUtils.matchAsciiBuffer(TarConstants.MAGIC_ANT,
                signature, TarConstants.MAGIC_OFFSET, TarConstants.MAGICLEN)
                &&
                ArchiveUtils.matchAsciiBuffer(TarConstants.VERSION_ANT,
                        signature, TarConstants.VERSION_OFFSET, TarConstants.VERSIONLEN);
    }

    
Build the input streams consisting of all-zero input streams and non-zero input streams.
When reading from the non-zero input streams, the data is actually read from the original input stream.
The size of each input stream is introduced by the sparse headers.
NOTE : Some all-zero input streams and non-zero input streams have the size of 0. We DO NOT store the
       0 size input streams because they are meaningless.
/**
     * Build the input streams consisting of all-zero input streams and non-zero input streams.
     * When reading from the non-zero input streams, the data is actually read from the original input stream.
     * The size of each input stream is introduced by the sparse headers.
     *
     * NOTE : Some all-zero input streams and non-zero input streams have the size of 0. We DO NOT store the
     *        0 size input streams because they are meaningless.
     */
    private void buildSparseInputStreams() throws IOException {
        currentSparseInputStreamIndex = -1;
        sparseInputStreams = new ArrayList<>();

        final List<TarArchiveStructSparse> sparseHeaders = currEntry.getSparseHeaders();
        // sort the sparse headers in case they are written in wrong order
        if (sparseHeaders != null && sparseHeaders.size() > 1) {
            final Comparator<TarArchiveStructSparse> sparseHeaderComparator = new Comparator<TarArchiveStructSparse>() {
                @Override
                public int compare(final TarArchiveStructSparse p, final TarArchiveStructSparse q) {
                    Long pOffset = p.getOffset();
                    Long qOffset = q.getOffset();
                    return pOffset.compareTo(qOffset);
                }
            };
            Collections.sort(sparseHeaders, sparseHeaderComparator);
        }

        if (sparseHeaders != null) {
            // Stream doesn't need to be closed at all as it doesn't use any resources
            final InputStream zeroInputStream = new TarArchiveSparseZeroInputStream(); //NOSONAR
            long offset = 0;
            for (TarArchiveStructSparse sparseHeader : sparseHeaders) {
                if (sparseHeader.getOffset() == 0 && sparseHeader.getNumbytes() == 0) {
                    break;
                }

                if ((sparseHeader.getOffset() - offset) < 0) {
                    throw new IOException("Corrupted struct sparse detected");
                }

                // only store the input streams with non-zero size
                if ((sparseHeader.getOffset() - offset) > 0) {
                    sparseInputStreams.add(new BoundedInputStream(zeroInputStream, sparseHeader.getOffset() - offset));
                }

                // only store the input streams with non-zero size
                if (sparseHeader.getNumbytes() > 0) {
                    sparseInputStreams.add(new BoundedInputStream(inputStream, sparseHeader.getNumbytes()));
                }

                offset = sparseHeader.getOffset() + sparseHeader.getNumbytes();
            }
        }

        if (sparseInputStreams.size() > 0) {
            currentSparseInputStreamIndex = 0;
        }
    }

    
This is an inputstream that always return 0,
this is used when reading the "holes" of a sparse file
/**
     * This is an inputstream that always return 0,
     * this is used when reading the "holes" of a sparse file
     */
    private static class TarArchiveSparseZeroInputStream extends InputStream {
        
Just return 0
Throws:
IOException – 
Returns:
/**
         * Just return 0
         * @return
         * @throws IOException
         */
        @Override
        public int read() throws IOException {
            return 0;
        }

        
these's nothing need to do when skipping
Params:
n – bytes to skip
Returns:
bytes actually skipped/**
         * these's nothing need to do when skipping
         *
         * @param n bytes to skip
         * @return bytes actually skipped
         */
        @Override
        public long skip(final long n) {
            return n;
        }
    }
}