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	/*
	* Copyright (c) 1996, 2021, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.util.zip;

	import java.io.SequenceInputStream;
	import java.io.ByteArrayInputStream;
	import java.io.FilterInputStream;
	import java.io.InputStream;
	import java.io.IOException;
	import java.io.EOFException;

	/**
	* This class implements a stream filter for reading compressed data in
	* the GZIP file format.
	*
	* @see InflaterInputStream
	* @author David Connelly
	* @since 1.1
	*
	*/
	public class GZIPInputStream extends InflaterInputStream {
	/**
	* CRC-32 for uncompressed data.
	*/
	protected CRC32 crc = new CRC32();

	/**
	* Indicates end of input stream.
	*/
	protected boolean eos;

	private boolean closed = false;

	/**
	* Check to make sure that this stream has not been closed
	*/
	private void ensureOpen() throws IOException {
	if (closed) {
	throw new IOException("Stream closed");
	}
	}

	/**
	* Creates a new input stream with the specified buffer size.
	* @param in the input stream
	* @param size the input buffer size
	*
	* @throws ZipException if a GZIP format error has occurred or the
	* compression method used is unsupported
	* @throws IOException if an I/O error has occurred
	* @throws IllegalArgumentException if {@code size <= 0}
	*/
	public GZIPInputStream(InputStream in, int size) throws IOException {
	super(in, in != null ? new Inflater(true) : null, size);
	usesDefaultInflater = true;
	readHeader(in);
	}

	/**
	* Creates a new input stream with a default buffer size.
	* @param in the input stream
	*
	* @throws ZipException if a GZIP format error has occurred or the
	* compression method used is unsupported
	* @throws IOException if an I/O error has occurred
	*/
	public GZIPInputStream(InputStream in) throws IOException {
	this(in, 512);
	}

	/**
	* Reads uncompressed data into an array of bytes. If {@code len} is not
	* zero, the method will block until some input can be decompressed; otherwise,
	* no bytes are read and {@code 0} is returned.
	* @param buf the buffer into which the data is read
	* @param off the start offset in the destination array {@code b}
	* @param len the maximum number of bytes read
	* @return the actual number of bytes read, or -1 if the end of the
	* compressed input stream is reached
	*
	* @throws NullPointerException If {@code buf} is {@code null}.
	* @throws IndexOutOfBoundsException If {@code off} is negative,
	* {@code len} is negative, or {@code len} is greater than
	* {@code buf.length - off}
	* @throws ZipException if the compressed input data is corrupt.
	* @throws IOException if an I/O error has occurred.
	*
	*/
	public int read(byte[] buf, int off, int len) throws IOException {
	ensureOpen();
	if (eos) {
	return -1;
	}
	int n = super.read(buf, off, len);
	if (n == -1) {
	if (readTrailer())
	eos = true;
	else
	return this.read(buf, off, len);
	} else {
	crc.update(buf, off, n);
	}
	return n;
	}

	/**
	* Closes this input stream and releases any system resources associated
	* with the stream.
	* @throws IOException if an I/O error has occurred
	*/
	public void close() throws IOException {
	if (!closed) {
	super.close();
	eos = true;
	closed = true;
	}
	}

	/**
	* GZIP header magic number.
	*/
	public static final int GZIP_MAGIC = 0x8b1f;

	/*
	* File header flags.
	*/
	private static final int FTEXT = 1; // Extra text
	private static final int FHCRC = 2; // Header CRC
	private static final int FEXTRA = 4; // Extra field
	private static final int FNAME = 8; // File name
	private static final int FCOMMENT = 16; // File comment

	/*
	* Reads GZIP member header and returns the total byte number
	* of this member header.
	*/
	private int readHeader(InputStream this_in) throws IOException {
	CheckedInputStream in = new CheckedInputStream(this_in, crc);
	crc.reset();
	// Check header magic
	if (readUShort(in) != GZIP_MAGIC) {
	throw new ZipException("Not in GZIP format");
	}
	// Check compression method
	if (readUByte(in) != 8) {
	throw new ZipException("Unsupported compression method");
	}
	// Read flags
	int flg = readUByte(in);
	// Skip MTIME, XFL, and OS fields
	skipBytes(in, 6);
	int n = 2 + 2 + 6;
	// Skip optional extra field
	if ((flg & FEXTRA) == FEXTRA) {
	int m = readUShort(in);
	skipBytes(in, m);
	n += m + 2;
	}
	// Skip optional file name
	if ((flg & FNAME) == FNAME) {
	do {
	n++;
	} while (readUByte(in) != 0);
	}
	// Skip optional file comment
	if ((flg & FCOMMENT) == FCOMMENT) {
	do {
	n++;
	} while (readUByte(in) != 0);
	}
	// Check optional header CRC
	if ((flg & FHCRC) == FHCRC) {
	int v = (int)crc.getValue() & 0xffff;
	if (readUShort(in) != v) {
	throw new ZipException("Corrupt GZIP header");
	}
	n += 2;
	}
	crc.reset();
	return n;
	}

	/*
	* Reads GZIP member trailer and returns true if the eos
	* reached, false if there are more (concatenated gzip
	* data set)
	*/
	private boolean readTrailer() throws IOException {
	InputStream in = this.in;
	int n = inf.getRemaining();
	if (n > 0) {
	in = new SequenceInputStream(
	new ByteArrayInputStream(buf, len - n, n),
	new FilterInputStream(in) {
	public void close() throws IOException {}
	});
	}
	// Uses left-to-right evaluation order
	if ((readUInt(in) != crc.getValue()) \|\|
	// rfc1952; ISIZE is the input size modulo 2^32
	(readUInt(in) != (inf.getBytesWritten() & 0xffffffffL)))
	throw new ZipException("Corrupt GZIP trailer");

	// If there are more bytes available in "in" or
	// the leftover in the "inf" is > 26 bytes:
	// this.trailer(8) + next.header.min(10) + next.trailer(8)
	// try concatenated case
	if (this.in.available() > 0 \|\| n > 26) {
	int m = 8; // this.trailer
	try {
	m += readHeader(in); // next.header
	} catch (IOException ze) {
	return true; // ignore any malformed, do nothing
	}
	inf.reset();
	if (n > m)
	inf.setInput(buf, len - n + m, n - m);
	return false;
	}
	return true;
	}

	/*
	* Reads unsigned integer in Intel byte order.
	*/
	private long readUInt(InputStream in) throws IOException {
	long s = readUShort(in);
	return ((long)readUShort(in) << 16) \| s;
	}

	/*
	* Reads unsigned short in Intel byte order.
	*/
	private int readUShort(InputStream in) throws IOException {
	int b = readUByte(in);
	return (readUByte(in) << 8) \| b;
	}

	/*
	* Reads unsigned byte.
	*/
	private int readUByte(InputStream in) throws IOException {
	int b = in.read();
	if (b == -1) {
	throw new EOFException();
	}
	if (b < -1 \|\| b > 255) {
	// Report on this.in, not argument in; see read{Header, Trailer}.
	throw new IOException(this.in.getClass().getName()
	+ ".read() returned value out of range -1..255: " + b);
	}
	return b;
	}

	private byte[] tmpbuf = new byte[128];

	/*
	* Skips bytes of input data blocking until all bytes are skipped.
	* Does not assume that the input stream is capable of seeking.
	*/
	private void skipBytes(InputStream in, int n) throws IOException {
	while (n > 0) {
	int len = in.read(tmpbuf, 0, n < tmpbuf.length ? n : tmpbuf.length);
	if (len == -1) {
	throw new EOFException();
	}
	n -= len;
	}
	}
	}

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