/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
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 *
 *
 *
 *
 *
 *
 *
 */

package goodjava.io;

import java.io.InputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

/**
 * A <code>BufferedInputStream</code> adds
 * functionality to another input stream-namely,
 * the ability to buffer the input and to
 * support the <code>mark</code> and <code>reset</code>
 * methods. When  the <code>BufferedInputStream</code>
 * 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</code>
 * operation  remembers a point in the input
 * stream and the <code>reset</code> operation
 * causes all the  bytes read since the most
 * recent <code>mark</code> operation to be
 * reread before new bytes are  taken from
 * the contained input stream.
 *
 * @author  Arthur van Hoff
 * @since   JDK1.0
 */
public class BufferedInputStream extends FilterInputStream {

	private static int DEFAULT_BUFFER_SIZE = 8192;

	/**
	 * The maximum size of array to allocate.
	 * Some VMs reserve some header words in an array.
	 * Attempts to allocate larger arrays may result in
	 * OutOfMemoryError: Requested array size exceeds VM limit
	 */
	private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;

	/**
	 * The internal buffer array where the data is stored. When necessary,
	 * it may be replaced by another array of
	 * a different size.
	 */
	protected volatile byte buf[];

	/**
	 * Atomic updater to provide compareAndSet for buf. This is
	 * necessary because 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.)
	 */
	private static final
		AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
		AtomicReferenceFieldUpdater.newUpdater
		(BufferedInputStream.class,  byte[].class, "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</code> through <code>buf.length</code>;
	 * elements <code>buf[0]</code>  through <code>buf[count-1]
	 * </code>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</code> array.
	 * <p>
	 * This value is always in the range <code>0</code>
	 * through <code>count</code>. If it is less
	 * than <code>count</code>, then  <code>buf[pos]</code>
	 * is the next byte to be supplied as input;
	 * if it is equal to <code>count</code>, then
	 * the  next <code>read</code> or <code>skip</code>
	 * 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</code> field at the time the last
	 * <code>mark</code> method was called.
	 * <p>
	 * This value is always
	 * in the range <code>-1</code> through <code>pos</code>.
	 * If there is no marked position in  the input
	 * stream, this field is <code>-1</code>. If
	 * there is a marked position in the input
	 * stream,  then <code>buf[markpos]</code>
	 * is the first byte to be supplied as input
	 * after a <code>reset</code> operation. If
	 * <code>markpos</code> is not <code>-1</code>,
	 * then all bytes from positions <code>buf[markpos]</code>
	 * through  <code>buf[pos-1]</code> 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>,  <code>pos</code>,
	 * and <code>markpos</code>); they may not
	 * be discarded unless and until the difference
	 * between <code>pos</code> and <code>markpos</code>
	 * exceeds <code>marklimit</code>.
	 *
	 * @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</code> method before subsequent calls to the
	 * <code>reset</code> method fail.
	 * Whenever the difference between <code>pos</code>
	 * and <code>markpos</code> exceeds <code>marklimit</code>,
	 * then the  mark may be dropped by setting
	 * <code>markpos</code> to <code>-1</code>.
	 *
	 * @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</code>
	 * and saves its  argument, the input stream
	 * <code>in</code>, for later use. An internal
	 * buffer array is created and  stored in <code>buf</code>.
	 *
	 * @param   in   the underlying input stream.
	 */
	public BufferedInputStream(InputStream in) {
		this(in, DEFAULT_BUFFER_SIZE);
	}

	/**
	 * Creates a <code>BufferedInputStream</code>
	 * with the specified buffer size,
	 * and saves its  argument, the input stream
	 * <code>in</code>, for later use.  An internal
	 * buffer array of length  <code>size</code>
	 * is created and stored in <code>buf</code>.
	 *
	 * @param   in     the underlying input stream.
	 * @param   size   the buffer size.
	 * @exception 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 if (buffer.length >= MAX_BUFFER_SIZE) {
				throw new OutOfMemoryError("Required array size too large");
			} else {            /* grow buffer */
				int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
						pos * 2 : MAX_BUFFER_SIZE;
				if (nsz > marklimit)
					nsz = marklimit;
				byte nbuf[] = new byte[nsz];
				System.arraycopy(buffer, 0, nbuf, 0, pos);
				if (!bufUpdater.compareAndSet(this, 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</code>
	 * method of <code>InputStream</code>.
	 *
	 * @return     the next byte of data, or <code>-1</code> if the end of the
	 *             stream is reached.
	 * @exception  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
	 * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
	 * the <code>{@link InputStream}</code> class.  As an additional
	 * convenience, it attempts to read as many bytes as possible by repeatedly
	 * invoking the <code>read</code> method of the underlying stream.  This
	 * iterated <code>read</code> continues until one of the following
	 * conditions becomes true: <ul>
	 *
	 *   <li> The specified number of bytes have been read,
	 *
	 *   <li> The <code>read</code> method of the underlying stream returns
	 *   <code>-1</code>, indicating end-of-file, or
	 *
	 *   <li> The <code>available</code> method of the underlying stream
	 *   returns zero, indicating that further input requests would block.
	 *
	 * </ul> If the first <code>read</code> on the underlying stream returns
	 * <code>-1</code> to indicate end-of-file then this method returns
	 * <code>-1</code>.  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</code> if the end of
	 *             the stream has been reached.
	 * @exception  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</code>
	 * method of <code>InputStream</code>.
	 *
	 * @exception  IOException  if the stream does not support seek,
	 *                          or if this input stream has been closed by
	 *                          invoking its {@link #close()} method, 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&nbsp;- pos</code>) and the result of calling the
	 * {@link java.io.FilterInputStream#in in}.available().
	 *
	 * @return     an estimate of the number of bytes that can be read (or skipped
	 *             over) from this input stream without blocking.
	 * @exception  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</code>
	 * method of <code>InputStream</code>.
	 *
	 * @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</code>
	 * method of <code>InputStream</code>.
	 * <p>
	 * If <code>markpos</code> is <code>-1</code>
	 * (no mark has been set or the mark has been
	 * invalidated), an <code>IOException</code>
	 * is thrown. Otherwise, <code>pos</code> is
	 * set equal to <code>markpos</code>.
	 *
	 * @exception  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</code>
	 * and <code>reset</code> methods. The <code>markSupported</code>
	 * method of <code>BufferedInputStream</code> returns
	 * <code>true</code>.
	 *
	 * @return  a <code>boolean</code> indicating if this stream type supports
	 *          the <code>mark</code> and <code>reset</code> 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.
	 *
	 * @exception  IOException  if an I/O error occurs.
	 */
	public void close() throws IOException {
		byte[] buffer;
		while ( (buffer = buf) != null) {
			if (bufUpdater.compareAndSet(this, buffer, null)) {
				InputStream input = in;
				in = null;
				if (input != null)
					input.close();
				return;
			}
			// Else retry in case a new buf was CASed in fill()
		}
	}
}