/*
 * Copyright (c) 1994, 2016, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 */

package java.io;

import jdk.internal.misc.Unsafe;

/**
 * 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 1.0
 */
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;

 /**
 * 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</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 (!U.compareAndSetObject(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</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>.
 *
 * @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&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 (U.compareAndSetObject(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()
 }
 }
}