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   * Copyright (c) 1994, 2013, 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
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   */
  
  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 {
  
      // Android-changed: made final
      private static final 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
       */
      // Android-changed: made final
      private static final 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     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     BufferedInputStream#mark(int)
       * @see     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     BufferedInputStream#mark(int)
       * @see     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        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 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     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        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     InputStream#mark(int)
       * @see     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()
          }
      }
  }
  