/*

  * Copyright (c) 1994, 2010, 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 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 defaultBufferSize = 8192;

     /**

      * 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, defaultBufferSize);

     }

     /**

      * 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 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 = pos * 2;

                 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()

         }

     }

 }