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	/*
	* Copyright (c) 1994, 2020, 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.io;

	import jdk.internal.misc.Unsafe;
	import jdk.internal.util.ArraysSupport;

	/**
	* A {@code BufferedInputStream} adds
	* functionality to another input stream-namely,
	* the ability to buffer the input and to
	* support the {@code mark} and {@code reset}
	* methods. When the {@code BufferedInputStream}
	* is created, an internal buffer array is
	* created. As bytes from the stream are read
	* or skipped, the internal buffer is refilled
	* as necessary from the contained input stream,
	* many bytes at a time. The {@code mark}
	* operation remembers a point in the input
	* stream and the {@code reset} operation
	* causes all the bytes read since the most
	* recent {@code mark} operation to be
	* reread before new bytes are taken from
	* the contained input stream.
	*
	* @author Arthur van Hoff
	* @since 1.0
	*/
	public class BufferedInputStream extends FilterInputStream {

	private static int DEFAULT_BUFFER_SIZE = 8192;

	/**
	* As this class is used early during bootstrap, it's motivated to use
	* Unsafe.compareAndSetObject instead of AtomicReferenceFieldUpdater
	* (or VarHandles) to reduce dependencies and improve startup time.
	*/
	private static final Unsafe U = Unsafe.getUnsafe();

	private static final long BUF_OFFSET
	= U.objectFieldOffset(BufferedInputStream.class, "buf");

	/**
	* The internal buffer array where the data is stored. When necessary,
	* it may be replaced by another array of
	* a different size.
	*/
	/*
	* We null this out with a CAS on close(), which is necessary since
	* closes can be asynchronous. We use nullness of buf[] as primary
	* indicator that this stream is closed. (The "in" field is also
	* nulled out on close.)
	*/
	protected volatile byte[] buf;

	/**
	* The index one greater than the index of the last valid byte in
	* the buffer.
	* This value is always
	* in the range {@code 0} through {@code buf.length};
	* elements {@code buf[0]} through {@code buf[count-1]}
	* contain buffered input data obtained
	* from the underlying input stream.
	*/
	protected int count;

	/**
	* The current position in the buffer. This is the index of the next
	* character to be read from the {@code buf} array.
	* <p>
	* This value is always in the range {@code 0}
	* through {@code count}. If it is less
	* than {@code count}, then {@code buf[pos]}
	* is the next byte to be supplied as input;
	* if it is equal to {@code count}, then
	* the next {@code read} or {@code skip}
	* operation will require more bytes to be
	* read from the contained input stream.
	*
	* @see java.io.BufferedInputStream#buf
	*/
	protected int pos;

	/**
	* The value of the {@code pos} field at the time the last
	* {@code mark} method was called.
	* <p>
	* This value is always
	* in the range {@code -1} through {@code pos}.
	* If there is no marked position in the input
	* stream, this field is {@code -1}. If
	* there is a marked position in the input
	* stream, then {@code buf[markpos]}
	* is the first byte to be supplied as input
	* after a {@code reset} operation. If
	* {@code markpos} is not {@code -1},
	* then all bytes from positions {@code buf[markpos]}
	* through {@code buf[pos-1]} must remain
	* in the buffer array (though they may be
	* moved to another place in the buffer array,
	* with suitable adjustments to the values
	* of {@code count}, {@code pos},
	* and {@code markpos}); they may not
	* be discarded unless and until the difference
	* between {@code pos} and {@code markpos}
	* exceeds {@code marklimit}.
	*
	* @see java.io.BufferedInputStream#mark(int)
	* @see java.io.BufferedInputStream#pos
	*/
	protected int markpos = -1;

	/**
	* The maximum read ahead allowed after a call to the
	* {@code mark} method before subsequent calls to the
	* {@code reset} method fail.
	* Whenever the difference between {@code pos}
	* and {@code markpos} exceeds {@code marklimit},
	* then the mark may be dropped by setting
	* {@code markpos} to {@code -1}.
	*
	* @see java.io.BufferedInputStream#mark(int)
	* @see java.io.BufferedInputStream#reset()
	*/
	protected int marklimit;

	/**
	* Check to make sure that underlying input stream has not been
	* nulled out due to close; if not return it;
	*/
	private InputStream getInIfOpen() throws IOException {
	InputStream input = in;
	if (input == null)
	throw new IOException("Stream closed");
	return input;
	}

	/**
	* Check to make sure that buffer has not been nulled out due to
	* close; if not return it;
	*/
	private byte[] getBufIfOpen() throws IOException {
	byte[] buffer = buf;
	if (buffer == null)
	throw new IOException("Stream closed");
	return buffer;
	}

	/**
	* Creates a {@code BufferedInputStream}
	* and saves its argument, the input stream
	* {@code in}, for later use. An internal
	* buffer array is created and stored in {@code buf}.
	*
	* @param in the underlying input stream.
	*/
	public BufferedInputStream(InputStream in) {
	this(in, DEFAULT_BUFFER_SIZE);
	}

	/**
	* Creates a {@code BufferedInputStream}
	* with the specified buffer size,
	* and saves its argument, the input stream
	* {@code in}, for later use. An internal
	* buffer array of length {@code size}
	* is created and stored in {@code buf}.
	*
	* @param in the underlying input stream.
	* @param size the buffer size.
	* @throws IllegalArgumentException if {@code size <= 0}.
	*/
	public BufferedInputStream(InputStream in, int size) {
	super(in);
	if (size <= 0) {
	throw new IllegalArgumentException("Buffer size <= 0");
	}
	buf = new byte[size];
	}

	/**
	* Fills the buffer with more data, taking into account
	* shuffling and other tricks for dealing with marks.
	* Assumes that it is being called by a synchronized method.
	* This method also assumes that all data has already been read in,
	* hence pos > count.
	*/
	private void fill() throws IOException {
	byte[] buffer = getBufIfOpen();
	if (markpos < 0)
	pos = 0; /* no mark: throw away the buffer */
	else if (pos >= buffer.length) { /* no room left in buffer */
	if (markpos > 0) { /* can throw away early part of the buffer */
	int sz = pos - markpos;
	System.arraycopy(buffer, markpos, buffer, 0, sz);
	pos = sz;
	markpos = 0;
	} else if (buffer.length >= marklimit) {
	markpos = -1; /* buffer got too big, invalidate mark */
	pos = 0; /* drop buffer contents */
	} else { /* grow buffer */
	int nsz = ArraysSupport.newLength(pos,
	1, /* minimum growth */
	pos /* preferred growth */);
	if (nsz > marklimit)
	nsz = marklimit;
	byte[] nbuf = new byte[nsz];
	System.arraycopy(buffer, 0, nbuf, 0, pos);
	if (!U.compareAndSetReference(this, BUF_OFFSET, buffer, nbuf)) {
	// Can't replace buf if there was an async close.
	// Note: This would need to be changed if fill()
	// is ever made accessible to multiple threads.
	// But for now, the only way CAS can fail is via close.
	// assert buf == null;
	throw new IOException("Stream closed");
	}
	buffer = nbuf;
	}
	}
	count = pos;
	int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
	if (n > 0)
	count = n + pos;
	}

	/**
	* See
	* the general contract of the {@code read}
	* method of {@code InputStream}.
	*
	* @return the next byte of data, or {@code -1} if the end of the
	* stream is reached.
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* or an I/O error occurs.
	* @see java.io.FilterInputStream#in
	*/
	public synchronized int read() throws IOException {
	if (pos >= count) {
	fill();
	if (pos >= count)
	return -1;
	}
	return getBufIfOpen()[pos++] & 0xff;
	}

	/**
	* Read characters into a portion of an array, reading from the underlying
	* stream at most once if necessary.
	*/
	private int read1(byte[] b, int off, int len) throws IOException {
	int avail = count - pos;
	if (avail <= 0) {
	/* If the requested length is at least as large as the buffer, and
	if there is no mark/reset activity, do not bother to copy the
	bytes into the local buffer. In this way buffered streams will
	cascade harmlessly. */
	if (len >= getBufIfOpen().length && markpos < 0) {
	return getInIfOpen().read(b, off, len);
	}
	fill();
	avail = count - pos;
	if (avail <= 0) return -1;
	}
	int cnt = (avail < len) ? avail : len;
	System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
	pos += cnt;
	return cnt;
	}

	/**
	* Reads bytes from this byte-input stream into the specified byte array,
	* starting at the given offset.
	*
	* <p> This method implements the general contract of the corresponding
	* {@link InputStream#read(byte[], int, int) read} method of
	* the {@link InputStream} class. As an additional
	* convenience, it attempts to read as many bytes as possible by repeatedly
	* invoking the {@code read} method of the underlying stream. This
	* iterated {@code read} continues until one of the following
	* conditions becomes true: <ul>
	*
	* <li> The specified number of bytes have been read,
	*
	* <li> The {@code read} method of the underlying stream returns
	* {@code -1}, indicating end-of-file, or
	*
	* <li> The {@code available} method of the underlying stream
	* returns zero, indicating that further input requests would block.
	*
	* </ul> If the first {@code read} on the underlying stream returns
	* {@code -1} to indicate end-of-file then this method returns
	* {@code -1}. Otherwise this method returns the number of bytes
	* actually read.
	*
	* <p> Subclasses of this class are encouraged, but not required, to
	* attempt to read as many bytes as possible in the same fashion.
	*
	* @param b destination buffer.
	* @param off offset at which to start storing bytes.
	* @param len maximum number of bytes to read.
	* @return the number of bytes read, or {@code -1} if the end of
	* the stream has been reached.
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* or an I/O error occurs.
	*/
	public synchronized int read(byte b[], int off, int len)
	throws IOException
	{
	getBufIfOpen(); // Check for closed stream
	if ((off \| len \| (off + len) \| (b.length - (off + len))) < 0) {
	throw new IndexOutOfBoundsException();
	} else if (len == 0) {
	return 0;
	}

	int n = 0;
	for (;;) {
	int nread = read1(b, off + n, len - n);
	if (nread <= 0)
	return (n == 0) ? nread : n;
	n += nread;
	if (n >= len)
	return n;
	// if not closed but no bytes available, return
	InputStream input = in;
	if (input != null && input.available() <= 0)
	return n;
	}
	}

	/**
	* See the general contract of the {@code skip}
	* method of {@code InputStream}.
	*
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* {@code in.skip(n)} throws an IOException,
	* or an I/O error occurs.
	*/
	public synchronized long skip(long n) throws IOException {
	getBufIfOpen(); // Check for closed stream
	if (n <= 0) {
	return 0;
	}
	long avail = count - pos;

	if (avail <= 0) {
	// If no mark position set then don't keep in buffer
	if (markpos <0)
	return getInIfOpen().skip(n);

	// Fill in buffer to save bytes for reset
	fill();
	avail = count - pos;
	if (avail <= 0)
	return 0;
	}

	long skipped = (avail < n) ? avail : n;
	pos += skipped;
	return skipped;
	}

	/**
	* Returns an estimate of the number of bytes that can be read (or
	* skipped over) from this input stream without blocking by the next
	* invocation of a method for this input stream. The next invocation might be
	* the same thread or another thread. A single read or skip of this
	* many bytes will not block, but may read or skip fewer bytes.
	* <p>
	* This method returns the sum of the number of bytes remaining to be read in
	* the buffer ({@code count - pos}) and the result of calling the
	* {@link java.io.FilterInputStream#in in}{@code .available()}.
	*
	* @return an estimate of the number of bytes that can be read (or skipped
	* over) from this input stream without blocking.
	* @throws IOException if this input stream has been closed by
	* invoking its {@link #close()} method,
	* or an I/O error occurs.
	*/
	public synchronized int available() throws IOException {
	int n = count - pos;
	int avail = getInIfOpen().available();
	return n > (Integer.MAX_VALUE - avail)
	? Integer.MAX_VALUE
	: n + avail;
	}

	/**
	* See the general contract of the {@code mark}
	* method of {@code InputStream}.
	*
	* @param readlimit the maximum limit of bytes that can be read before
	* the mark position becomes invalid.
	* @see java.io.BufferedInputStream#reset()
	*/
	public synchronized void mark(int readlimit) {
	marklimit = readlimit;
	markpos = pos;
	}

	/**
	* See the general contract of the {@code reset}
	* method of {@code InputStream}.
	* <p>
	* If {@code markpos} is {@code -1}
	* (no mark has been set or the mark has been
	* invalidated), an {@code IOException}
	* is thrown. Otherwise, {@code pos} is
	* set equal to {@code markpos}.
	*
	* @throws IOException if this stream has not been marked or,
	* if the mark has been invalidated, or the stream
	* has been closed by invoking its {@link #close()}
	* method, or an I/O error occurs.
	* @see java.io.BufferedInputStream#mark(int)
	*/
	public synchronized void reset() throws IOException {
	getBufIfOpen(); // Cause exception if closed
	if (markpos < 0)
	throw new IOException("Resetting to invalid mark");
	pos = markpos;
	}

	/**
	* Tests if this input stream supports the {@code mark}
	* and {@code reset} methods. The {@code markSupported}
	* method of {@code BufferedInputStream} returns
	* {@code true}.
	*
	* @return a {@code boolean} indicating if this stream type supports
	* the {@code mark} and {@code reset} methods.
	* @see java.io.InputStream#mark(int)
	* @see java.io.InputStream#reset()
	*/
	public boolean markSupported() {
	return true;
	}

	/**
	* Closes this input stream and releases any system resources
	* associated with the stream.
	* Once the stream has been closed, further read(), available(), reset(),
	* or skip() invocations will throw an IOException.
	* Closing a previously closed stream has no effect.
	*
	* @throws IOException if an I/O error occurs.
	*/
	public void close() throws IOException {
	byte[] buffer;
	while ( (buffer = buf) != null) {
	if (U.compareAndSetReference(this, BUF_OFFSET, buffer, null)) {
	InputStream input = in;
	in = null;
	if (input != null)
	input.close();
	return;
	}
	// Else retry in case a new buf was CASed in fill()
	}
	}
	}

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