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    1   /*
    2    * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.io;
   27   import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
   28   
   29   /**
   30    * A <code>BufferedInputStream</code> adds
   31    * functionality to another input stream-namely,
   32    * the ability to buffer the input and to
   33    * support the <code>mark</code> and <code>reset</code>
   34    * methods. When  the <code>BufferedInputStream</code>
   35    * is created, an internal buffer array is
   36    * created. As bytes  from the stream are read
   37    * or skipped, the internal buffer is refilled
   38    * as necessary  from the contained input stream,
   39    * many bytes at a time. The <code>mark</code>
   40    * operation  remembers a point in the input
   41    * stream and the <code>reset</code> operation
   42    * causes all the  bytes read since the most
   43    * recent <code>mark</code> operation to be
   44    * reread before new bytes are  taken from
   45    * the contained input stream.
   46    *
   47    * @author  Arthur van Hoff
   48    * @since   JDK1.0
   49    */
   50   public
   51   class BufferedInputStream extends FilterInputStream {
   52   
   53       private static int defaultBufferSize = 8192;
   54   
   55       /**
   56        * The internal buffer array where the data is stored. When necessary,
   57        * it may be replaced by another array of
   58        * a different size.
   59        */
   60       protected volatile byte buf[];
   61   
   62       /**
   63        * Atomic updater to provide compareAndSet for buf. This is
   64        * necessary because closes can be asynchronous. We use nullness
   65        * of buf[] as primary indicator that this stream is closed. (The
   66        * "in" field is also nulled out on close.)
   67        */
   68       private static final
   69           AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
   70           AtomicReferenceFieldUpdater.newUpdater
   71           (BufferedInputStream.class,  byte[].class, "buf");
   72   
   73       /**
   74        * The index one greater than the index of the last valid byte in
   75        * the buffer.
   76        * This value is always
   77        * in the range <code>0</code> through <code>buf.length</code>;
   78        * elements <code>buf[0]</code>  through <code>buf[count-1]
   79        * </code>contain buffered input data obtained
   80        * from the underlying  input stream.
   81        */
   82       protected int count;
   83   
   84       /**
   85        * The current position in the buffer. This is the index of the next
   86        * character to be read from the <code>buf</code> array.
   87        * <p>
   88        * This value is always in the range <code>0</code>
   89        * through <code>count</code>. If it is less
   90        * than <code>count</code>, then  <code>buf[pos]</code>
   91        * is the next byte to be supplied as input;
   92        * if it is equal to <code>count</code>, then
   93        * the  next <code>read</code> or <code>skip</code>
   94        * operation will require more bytes to be
   95        * read from the contained  input stream.
   96        *
   97        * @see     java.io.BufferedInputStream#buf
   98        */
   99       protected int pos;
  100   
  101       /**
  102        * The value of the <code>pos</code> field at the time the last
  103        * <code>mark</code> method was called.
  104        * <p>
  105        * This value is always
  106        * in the range <code>-1</code> through <code>pos</code>.
  107        * If there is no marked position in  the input
  108        * stream, this field is <code>-1</code>. If
  109        * there is a marked position in the input
  110        * stream,  then <code>buf[markpos]</code>
  111        * is the first byte to be supplied as input
  112        * after a <code>reset</code> operation. If
  113        * <code>markpos</code> is not <code>-1</code>,
  114        * then all bytes from positions <code>buf[markpos]</code>
  115        * through  <code>buf[pos-1]</code> must remain
  116        * in the buffer array (though they may be
  117        * moved to  another place in the buffer array,
  118        * with suitable adjustments to the values
  119        * of <code>count</code>,  <code>pos</code>,
  120        * and <code>markpos</code>); they may not
  121        * be discarded unless and until the difference
  122        * between <code>pos</code> and <code>markpos</code>
  123        * exceeds <code>marklimit</code>.
  124        *
  125        * @see     java.io.BufferedInputStream#mark(int)
  126        * @see     java.io.BufferedInputStream#pos
  127        */
  128       protected int markpos = -1;
  129   
  130       /**
  131        * The maximum read ahead allowed after a call to the
  132        * <code>mark</code> method before subsequent calls to the
  133        * <code>reset</code> method fail.
  134        * Whenever the difference between <code>pos</code>
  135        * and <code>markpos</code> exceeds <code>marklimit</code>,
  136        * then the  mark may be dropped by setting
  137        * <code>markpos</code> to <code>-1</code>.
  138        *
  139        * @see     java.io.BufferedInputStream#mark(int)
  140        * @see     java.io.BufferedInputStream#reset()
  141        */
  142       protected int marklimit;
  143   
  144       /**
  145        * Check to make sure that underlying input stream has not been
  146        * nulled out due to close; if not return it;
  147        */
  148       private InputStream getInIfOpen() throws IOException {
  149           InputStream input = in;
  150           if (input == null)
  151               throw new IOException("Stream closed");
  152           return input;
  153       }
  154   
  155       /**
  156        * Check to make sure that buffer has not been nulled out due to
  157        * close; if not return it;
  158        */
  159       private byte[] getBufIfOpen() throws IOException {
  160           byte[] buffer = buf;
  161           if (buffer == null)
  162               throw new IOException("Stream closed");
  163           return buffer;
  164       }
  165   
  166       /**
  167        * Creates a <code>BufferedInputStream</code>
  168        * and saves its  argument, the input stream
  169        * <code>in</code>, for later use. An internal
  170        * buffer array is created and  stored in <code>buf</code>.
  171        *
  172        * @param   in   the underlying input stream.
  173        */
  174       public BufferedInputStream(InputStream in) {
  175           this(in, defaultBufferSize);
  176       }
  177   
  178       /**
  179        * Creates a <code>BufferedInputStream</code>
  180        * with the specified buffer size,
  181        * and saves its  argument, the input stream
  182        * <code>in</code>, for later use.  An internal
  183        * buffer array of length  <code>size</code>
  184        * is created and stored in <code>buf</code>.
  185        *
  186        * @param   in     the underlying input stream.
  187        * @param   size   the buffer size.
  188        * @exception IllegalArgumentException if size <= 0.
  189        */
  190       public BufferedInputStream(InputStream in, int size) {
  191           super(in);
  192           if (size <= 0) {
  193               throw new IllegalArgumentException("Buffer size <= 0");
  194           }
  195           buf = new byte[size];
  196       }
  197   
  198       /**
  199        * Fills the buffer with more data, taking into account
  200        * shuffling and other tricks for dealing with marks.
  201        * Assumes that it is being called by a synchronized method.
  202        * This method also assumes that all data has already been read in,
  203        * hence pos > count.
  204        */
  205       private void fill() throws IOException {
  206           byte[] buffer = getBufIfOpen();
  207           if (markpos < 0)
  208               pos = 0;            /* no mark: throw away the buffer */
  209           else if (pos >= buffer.length)  /* no room left in buffer */
  210               if (markpos > 0) {  /* can throw away early part of the buffer */
  211                   int sz = pos - markpos;
  212                   System.arraycopy(buffer, markpos, buffer, 0, sz);
  213                   pos = sz;
  214                   markpos = 0;
  215               } else if (buffer.length >= marklimit) {
  216                   markpos = -1;   /* buffer got too big, invalidate mark */
  217                   pos = 0;        /* drop buffer contents */
  218               } else {            /* grow buffer */
  219                   int nsz = pos * 2;
  220                   if (nsz > marklimit)
  221                       nsz = marklimit;
  222                   byte nbuf[] = new byte[nsz];
  223                   System.arraycopy(buffer, 0, nbuf, 0, pos);
  224                   if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
  225                       // Can't replace buf if there was an async close.
  226                       // Note: This would need to be changed if fill()
  227                       // is ever made accessible to multiple threads.
  228                       // But for now, the only way CAS can fail is via close.
  229                       // assert buf == null;
  230                       throw new IOException("Stream closed");
  231                   }
  232                   buffer = nbuf;
  233               }
  234           count = pos;
  235           int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
  236           if (n > 0)
  237               count = n + pos;
  238       }
  239   
  240       /**
  241        * See
  242        * the general contract of the <code>read</code>
  243        * method of <code>InputStream</code>.
  244        *
  245        * @return     the next byte of data, or <code>-1</code> if the end of the
  246        *             stream is reached.
  247        * @exception  IOException  if this input stream has been closed by
  248        *                          invoking its {@link #close()} method,
  249        *                          or an I/O error occurs.
  250        * @see        java.io.FilterInputStream#in
  251        */
  252       public synchronized int read() throws IOException {
  253           if (pos >= count) {
  254               fill();
  255               if (pos >= count)
  256                   return -1;
  257           }
  258           return getBufIfOpen()[pos++] & 0xff;
  259       }
  260   
  261       /**
  262        * Read characters into a portion of an array, reading from the underlying
  263        * stream at most once if necessary.
  264        */
  265       private int read1(byte[] b, int off, int len) throws IOException {
  266           int avail = count - pos;
  267           if (avail <= 0) {
  268               /* If the requested length is at least as large as the buffer, and
  269                  if there is no mark/reset activity, do not bother to copy the
  270                  bytes into the local buffer.  In this way buffered streams will
  271                  cascade harmlessly. */
  272               if (len >= getBufIfOpen().length && markpos < 0) {
  273                   return getInIfOpen().read(b, off, len);
  274               }
  275               fill();
  276               avail = count - pos;
  277               if (avail <= 0) return -1;
  278           }
  279           int cnt = (avail < len) ? avail : len;
  280           System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
  281           pos += cnt;
  282           return cnt;
  283       }
  284   
  285       /**
  286        * Reads bytes from this byte-input stream into the specified byte array,
  287        * starting at the given offset.
  288        *
  289        * <p> This method implements the general contract of the corresponding
  290        * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
  291        * the <code>{@link InputStream}</code> class.  As an additional
  292        * convenience, it attempts to read as many bytes as possible by repeatedly
  293        * invoking the <code>read</code> method of the underlying stream.  This
  294        * iterated <code>read</code> continues until one of the following
  295        * conditions becomes true: <ul>
  296        *
  297        *   <li> The specified number of bytes have been read,
  298        *
  299        *   <li> The <code>read</code> method of the underlying stream returns
  300        *   <code>-1</code>, indicating end-of-file, or
  301        *
  302        *   <li> The <code>available</code> method of the underlying stream
  303        *   returns zero, indicating that further input requests would block.
  304        *
  305        * </ul> If the first <code>read</code> on the underlying stream returns
  306        * <code>-1</code> to indicate end-of-file then this method returns
  307        * <code>-1</code>.  Otherwise this method returns the number of bytes
  308        * actually read.
  309        *
  310        * <p> Subclasses of this class are encouraged, but not required, to
  311        * attempt to read as many bytes as possible in the same fashion.
  312        *
  313        * @param      b     destination buffer.
  314        * @param      off   offset at which to start storing bytes.
  315        * @param      len   maximum number of bytes to read.
  316        * @return     the number of bytes read, or <code>-1</code> if the end of
  317        *             the stream has been reached.
  318        * @exception  IOException  if this input stream has been closed by
  319        *                          invoking its {@link #close()} method,
  320        *                          or an I/O error occurs.
  321        */
  322       public synchronized int read(byte b[], int off, int len)
  323           throws IOException
  324       {
  325           getBufIfOpen(); // Check for closed stream
  326           if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
  327               throw new IndexOutOfBoundsException();
  328           } else if (len == 0) {
  329               return 0;
  330           }
  331   
  332           int n = 0;
  333           for (;;) {
  334               int nread = read1(b, off + n, len - n);
  335               if (nread <= 0)
  336                   return (n == 0) ? nread : n;
  337               n += nread;
  338               if (n >= len)
  339                   return n;
  340               // if not closed but no bytes available, return
  341               InputStream input = in;
  342               if (input != null && input.available() <= 0)
  343                   return n;
  344           }
  345       }
  346   
  347       /**
  348        * See the general contract of the <code>skip</code>
  349        * method of <code>InputStream</code>.
  350        *
  351        * @exception  IOException  if the stream does not support seek,
  352        *                          or if this input stream has been closed by
  353        *                          invoking its {@link #close()} method, or an
  354        *                          I/O error occurs.
  355        */
  356       public synchronized long skip(long n) throws IOException {
  357           getBufIfOpen(); // Check for closed stream
  358           if (n <= 0) {
  359               return 0;
  360           }
  361           long avail = count - pos;
  362   
  363           if (avail <= 0) {
  364               // If no mark position set then don't keep in buffer
  365               if (markpos <0)
  366                   return getInIfOpen().skip(n);
  367   
  368               // Fill in buffer to save bytes for reset
  369               fill();
  370               avail = count - pos;
  371               if (avail <= 0)
  372                   return 0;
  373           }
  374   
  375           long skipped = (avail < n) ? avail : n;
  376           pos += skipped;
  377           return skipped;
  378       }
  379   
  380       /**
  381        * Returns an estimate of the number of bytes that can be read (or
  382        * skipped over) from this input stream without blocking by the next
  383        * invocation of a method for this input stream. The next invocation might be
  384        * the same thread or another thread.  A single read or skip of this
  385        * many bytes will not block, but may read or skip fewer bytes.
  386        * <p>
  387        * This method returns the sum of the number of bytes remaining to be read in
  388        * the buffer (<code>count&nbsp;- pos</code>) and the result of calling the
  389        * {@link java.io.FilterInputStream#in in}.available().
  390        *
  391        * @return     an estimate of the number of bytes that can be read (or skipped
  392        *             over) from this input stream without blocking.
  393        * @exception  IOException  if this input stream has been closed by
  394        *                          invoking its {@link #close()} method,
  395        *                          or an I/O error occurs.
  396        */
  397       public synchronized int available() throws IOException {
  398           int n = count - pos;
  399           int avail = getInIfOpen().available();
  400           return n > (Integer.MAX_VALUE - avail)
  401                       ? Integer.MAX_VALUE
  402                       : n + avail;
  403       }
  404   
  405       /**
  406        * See the general contract of the <code>mark</code>
  407        * method of <code>InputStream</code>.
  408        *
  409        * @param   readlimit   the maximum limit of bytes that can be read before
  410        *                      the mark position becomes invalid.
  411        * @see     java.io.BufferedInputStream#reset()
  412        */
  413       public synchronized void mark(int readlimit) {
  414           marklimit = readlimit;
  415           markpos = pos;
  416       }
  417   
  418       /**
  419        * See the general contract of the <code>reset</code>
  420        * method of <code>InputStream</code>.
  421        * <p>
  422        * If <code>markpos</code> is <code>-1</code>
  423        * (no mark has been set or the mark has been
  424        * invalidated), an <code>IOException</code>
  425        * is thrown. Otherwise, <code>pos</code> is
  426        * set equal to <code>markpos</code>.
  427        *
  428        * @exception  IOException  if this stream has not been marked or,
  429        *                  if the mark has been invalidated, or the stream
  430        *                  has been closed by invoking its {@link #close()}
  431        *                  method, or an I/O error occurs.
  432        * @see        java.io.BufferedInputStream#mark(int)
  433        */
  434       public synchronized void reset() throws IOException {
  435           getBufIfOpen(); // Cause exception if closed
  436           if (markpos < 0)
  437               throw new IOException("Resetting to invalid mark");
  438           pos = markpos;
  439       }
  440   
  441       /**
  442        * Tests if this input stream supports the <code>mark</code>
  443        * and <code>reset</code> methods. The <code>markSupported</code>
  444        * method of <code>BufferedInputStream</code> returns
  445        * <code>true</code>.
  446        *
  447        * @return  a <code>boolean</code> indicating if this stream type supports
  448        *          the <code>mark</code> and <code>reset</code> methods.
  449        * @see     java.io.InputStream#mark(int)
  450        * @see     java.io.InputStream#reset()
  451        */
  452       public boolean markSupported() {
  453           return true;
  454       }
  455   
  456       /**
  457        * Closes this input stream and releases any system resources
  458        * associated with the stream.
  459        * Once the stream has been closed, further read(), available(), reset(),
  460        * or skip() invocations will throw an IOException.
  461        * Closing a previously closed stream has no effect.
  462        *
  463        * @exception  IOException  if an I/O error occurs.
  464        */
  465       public void close() throws IOException {
  466           byte[] buffer;
  467           while ( (buffer = buf) != null) {
  468               if (bufUpdater.compareAndSet(this, buffer, null)) {
  469                   InputStream input = in;
  470                   in = null;
  471                   if (input != null)
  472                       input.close();
  473                   return;
  474               }
  475               // Else retry in case a new buf was CASed in fill()
  476           }
  477       }
  478   }

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