/*

 * Copyright (c) 1994, 2019, 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

 */

    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

     * <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} 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&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.

     * @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()

        }

    }

}