1 /*
   2  * Copyright (c) 1994, 2013, 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   1.0
  49  */
  50 public
  51 class BufferedInputStream extends FilterInputStream {
  52 
  53     private static int DEFAULT_BUFFER_SIZE = 8192;
  54 
  55     /**
  56      * The maximum size of array to allocate.
  57      * Some VMs reserve some header words in an array.
  58      * Attempts to allocate larger arrays may result in
  59      * OutOfMemoryError: Requested array size exceeds VM limit
  60      */
  61     private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
  62 
  63     /**
  64      * The internal buffer array where the data is stored. When necessary,
  65      * it may be replaced by another array of
  66      * a different size.
  67      */
  68     protected volatile byte buf[];
  69 
  70     /**
  71      * Atomic updater to provide compareAndSet for buf. This is
  72      * necessary because closes can be asynchronous. We use nullness
  73      * of buf[] as primary indicator that this stream is closed. (The
  74      * "in" field is also nulled out on close.)
  75      */
  76     private static final
  77         AtomicReferenceFieldUpdater<BufferedInputStream, byte[]> bufUpdater =
  78         AtomicReferenceFieldUpdater.newUpdater
  79         (BufferedInputStream.class,  byte[].class, "buf");
  80 
  81     /**
  82      * The index one greater than the index of the last valid byte in
  83      * the buffer.
  84      * This value is always
  85      * in the range <code>0</code> through <code>buf.length</code>;
  86      * elements <code>buf[0]</code>  through <code>buf[count-1]
  87      * </code>contain buffered input data obtained
  88      * from the underlying  input stream.
  89      */
  90     protected int count;
  91 
  92     /**
  93      * The current position in the buffer. This is the index of the next
  94      * character to be read from the <code>buf</code> array.
  95      * <p>
  96      * This value is always in the range <code>0</code>
  97      * through <code>count</code>. If it is less
  98      * than <code>count</code>, then  <code>buf[pos]</code>
  99      * is the next byte to be supplied as input;
 100      * if it is equal to <code>count</code>, then
 101      * the  next <code>read</code> or <code>skip</code>
 102      * operation will require more bytes to be
 103      * read from the contained  input stream.
 104      *
 105      * @see     java.io.BufferedInputStream#buf
 106      */
 107     protected int pos;
 108 
 109     /**
 110      * The value of the <code>pos</code> field at the time the last
 111      * <code>mark</code> method was called.
 112      * <p>
 113      * This value is always
 114      * in the range <code>-1</code> through <code>pos</code>.
 115      * If there is no marked position in  the input
 116      * stream, this field is <code>-1</code>. If
 117      * there is a marked position in the input
 118      * stream,  then <code>buf[markpos]</code>
 119      * is the first byte to be supplied as input
 120      * after a <code>reset</code> operation. If
 121      * <code>markpos</code> is not <code>-1</code>,
 122      * then all bytes from positions <code>buf[markpos]</code>
 123      * through  <code>buf[pos-1]</code> must remain
 124      * in the buffer array (though they may be
 125      * moved to  another place in the buffer array,
 126      * with suitable adjustments to the values
 127      * of <code>count</code>,  <code>pos</code>,
 128      * and <code>markpos</code>); they may not
 129      * be discarded unless and until the difference
 130      * between <code>pos</code> and <code>markpos</code>
 131      * exceeds <code>marklimit</code>.
 132      *
 133      * @see     java.io.BufferedInputStream#mark(int)
 134      * @see     java.io.BufferedInputStream#pos
 135      */
 136     protected int markpos = -1;
 137 
 138     /**
 139      * The maximum read ahead allowed after a call to the
 140      * <code>mark</code> method before subsequent calls to the
 141      * <code>reset</code> method fail.
 142      * Whenever the difference between <code>pos</code>
 143      * and <code>markpos</code> exceeds <code>marklimit</code>,
 144      * then the  mark may be dropped by setting
 145      * <code>markpos</code> to <code>-1</code>.
 146      *
 147      * @see     java.io.BufferedInputStream#mark(int)
 148      * @see     java.io.BufferedInputStream#reset()
 149      */
 150     protected int marklimit;
 151 
 152     /**
 153      * Check to make sure that underlying input stream has not been
 154      * nulled out due to close; if not return it;
 155      */
 156     private InputStream getInIfOpen() throws IOException {
 157         InputStream input = in;
 158         if (input == null)
 159             throw new IOException("Stream closed");
 160         return input;
 161     }
 162 
 163     /**
 164      * Check to make sure that buffer has not been nulled out due to
 165      * close; if not return it;
 166      */
 167     private byte[] getBufIfOpen() throws IOException {
 168         byte[] buffer = buf;
 169         if (buffer == null)
 170             throw new IOException("Stream closed");
 171         return buffer;
 172     }
 173 
 174     /**
 175      * Creates a <code>BufferedInputStream</code>
 176      * and saves its  argument, the input stream
 177      * <code>in</code>, for later use. An internal
 178      * buffer array is created and  stored in <code>buf</code>.
 179      *
 180      * @param   in   the underlying input stream.
 181      */
 182     public BufferedInputStream(InputStream in) {
 183         this(in, DEFAULT_BUFFER_SIZE);
 184     }
 185 
 186     /**
 187      * Creates a <code>BufferedInputStream</code>
 188      * with the specified buffer size,
 189      * and saves its  argument, the input stream
 190      * <code>in</code>, for later use.  An internal
 191      * buffer array of length  <code>size</code>
 192      * is created and stored in <code>buf</code>.
 193      *
 194      * @param   in     the underlying input stream.
 195      * @param   size   the buffer size.
 196      * @exception IllegalArgumentException if {@code size <= 0}.
 197      */
 198     public BufferedInputStream(InputStream in, int size) {
 199         super(in);
 200         if (size <= 0) {
 201             throw new IllegalArgumentException("Buffer size <= 0");
 202         }
 203         buf = new byte[size];
 204     }
 205 
 206     /**
 207      * Fills the buffer with more data, taking into account
 208      * shuffling and other tricks for dealing with marks.
 209      * Assumes that it is being called by a synchronized method.
 210      * This method also assumes that all data has already been read in,
 211      * hence pos > count.
 212      */
 213     private void fill() throws IOException {
 214         byte[] buffer = getBufIfOpen();
 215         if (markpos < 0)
 216             pos = 0;            /* no mark: throw away the buffer */
 217         else if (pos >= buffer.length)  /* no room left in buffer */
 218             if (markpos > 0) {  /* can throw away early part of the buffer */
 219                 int sz = pos - markpos;
 220                 System.arraycopy(buffer, markpos, buffer, 0, sz);
 221                 pos = sz;
 222                 markpos = 0;
 223             } else if (buffer.length >= marklimit) {
 224                 markpos = -1;   /* buffer got too big, invalidate mark */
 225                 pos = 0;        /* drop buffer contents */
 226             } else if (buffer.length >= MAX_BUFFER_SIZE) {
 227                 throw new OutOfMemoryError("Required array size too large");
 228             } else {            /* grow buffer */
 229                 int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?
 230                         pos * 2 : MAX_BUFFER_SIZE;
 231                 if (nsz > marklimit)
 232                     nsz = marklimit;
 233                 byte nbuf[] = new byte[nsz];
 234                 System.arraycopy(buffer, 0, nbuf, 0, pos);
 235                 if (!bufUpdater.compareAndSet(this, buffer, nbuf)) {
 236                     // Can't replace buf if there was an async close.
 237                     // Note: This would need to be changed if fill()
 238                     // is ever made accessible to multiple threads.
 239                     // But for now, the only way CAS can fail is via close.
 240                     // assert buf == null;
 241                     throw new IOException("Stream closed");
 242                 }
 243                 buffer = nbuf;
 244             }
 245         count = pos;
 246         int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
 247         if (n > 0)
 248             count = n + pos;
 249     }
 250 
 251     /**
 252      * See
 253      * the general contract of the <code>read</code>
 254      * method of <code>InputStream</code>.
 255      *
 256      * @return     the next byte of data, or <code>-1</code> if the end of the
 257      *             stream is reached.
 258      * @exception  IOException  if this input stream has been closed by
 259      *                          invoking its {@link #close()} method,
 260      *                          or an I/O error occurs.
 261      * @see        java.io.FilterInputStream#in
 262      */
 263     public synchronized int read() throws IOException {
 264         if (pos >= count) {
 265             fill();
 266             if (pos >= count)
 267                 return -1;
 268         }
 269         return getBufIfOpen()[pos++] & 0xff;
 270     }
 271 
 272     /**
 273      * Read characters into a portion of an array, reading from the underlying
 274      * stream at most once if necessary.
 275      */
 276     private int read1(byte[] b, int off, int len) throws IOException {
 277         int avail = count - pos;
 278         if (avail <= 0) {
 279             /* If the requested length is at least as large as the buffer, and
 280                if there is no mark/reset activity, do not bother to copy the
 281                bytes into the local buffer.  In this way buffered streams will
 282                cascade harmlessly. */
 283             if (len >= getBufIfOpen().length && markpos < 0) {
 284                 return getInIfOpen().read(b, off, len);
 285             }
 286             fill();
 287             avail = count - pos;
 288             if (avail <= 0) return -1;
 289         }
 290         int cnt = (avail < len) ? avail : len;
 291         System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
 292         pos += cnt;
 293         return cnt;
 294     }
 295 
 296     /**
 297      * Reads bytes from this byte-input stream into the specified byte array,
 298      * starting at the given offset.
 299      *
 300      * <p> This method implements the general contract of the corresponding
 301      * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
 302      * the <code>{@link InputStream}</code> class.  As an additional
 303      * convenience, it attempts to read as many bytes as possible by repeatedly
 304      * invoking the <code>read</code> method of the underlying stream.  This
 305      * iterated <code>read</code> continues until one of the following
 306      * conditions becomes true: <ul>
 307      *
 308      *   <li> The specified number of bytes have been read,
 309      *
 310      *   <li> The <code>read</code> method of the underlying stream returns
 311      *   <code>-1</code>, indicating end-of-file, or
 312      *
 313      *   <li> The <code>available</code> method of the underlying stream
 314      *   returns zero, indicating that further input requests would block.
 315      *
 316      * </ul> If the first <code>read</code> on the underlying stream returns
 317      * <code>-1</code> to indicate end-of-file then this method returns
 318      * <code>-1</code>.  Otherwise this method returns the number of bytes
 319      * actually read.
 320      *
 321      * <p> Subclasses of this class are encouraged, but not required, to
 322      * attempt to read as many bytes as possible in the same fashion.
 323      *
 324      * @param      b     destination buffer.
 325      * @param      off   offset at which to start storing bytes.
 326      * @param      len   maximum number of bytes to read.
 327      * @return     the number of bytes read, or <code>-1</code> if the end of
 328      *             the stream has been reached.
 329      * @exception  IOException  if this input stream has been closed by
 330      *                          invoking its {@link #close()} method,
 331      *                          or an I/O error occurs.
 332      */
 333     public synchronized int read(byte b[], int off, int len)
 334         throws IOException
 335     {
 336         getBufIfOpen(); // Check for closed stream
 337         if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
 338             throw new IndexOutOfBoundsException();
 339         } else if (len == 0) {
 340             return 0;
 341         }
 342 
 343         int n = 0;
 344         for (;;) {
 345             int nread = read1(b, off + n, len - n);
 346             if (nread <= 0)
 347                 return (n == 0) ? nread : n;
 348             n += nread;
 349             if (n >= len)
 350                 return n;
 351             // if not closed but no bytes available, return
 352             InputStream input = in;
 353             if (input != null && input.available() <= 0)
 354                 return n;
 355         }
 356     }
 357 
 358     /**
 359      * See the general contract of the <code>skip</code>
 360      * method of <code>InputStream</code>.
 361      *
 362      * @exception  IOException  if the stream does not support seek,
 363      *                          or if this input stream has been closed by
 364      *                          invoking its {@link #close()} method, or an
 365      *                          I/O error occurs.
 366      */
 367     public synchronized long skip(long n) throws IOException {
 368         getBufIfOpen(); // Check for closed stream
 369         if (n <= 0) {
 370             return 0;
 371         }
 372         long avail = count - pos;
 373 
 374         if (avail <= 0) {
 375             // If no mark position set then don't keep in buffer
 376             if (markpos <0)
 377                 return getInIfOpen().skip(n);
 378 
 379             // Fill in buffer to save bytes for reset
 380             fill();
 381             avail = count - pos;
 382             if (avail <= 0)
 383                 return 0;
 384         }
 385 
 386         long skipped = (avail < n) ? avail : n;
 387         pos += skipped;
 388         return skipped;
 389     }
 390 
 391     /**
 392      * Returns an estimate of the number of bytes that can be read (or
 393      * skipped over) from this input stream without blocking by the next
 394      * invocation of a method for this input stream. The next invocation might be
 395      * the same thread or another thread.  A single read or skip of this
 396      * many bytes will not block, but may read or skip fewer bytes.
 397      * <p>
 398      * This method returns the sum of the number of bytes remaining to be read in
 399      * the buffer (<code>count&nbsp;- pos</code>) and the result of calling the
 400      * {@link java.io.FilterInputStream#in in}.available().
 401      *
 402      * @return     an estimate of the number of bytes that can be read (or skipped
 403      *             over) from this input stream without blocking.
 404      * @exception  IOException  if this input stream has been closed by
 405      *                          invoking its {@link #close()} method,
 406      *                          or an I/O error occurs.
 407      */
 408     public synchronized int available() throws IOException {
 409         int n = count - pos;
 410         int avail = getInIfOpen().available();
 411         return n > (Integer.MAX_VALUE - avail)
 412                     ? Integer.MAX_VALUE
 413                     : n + avail;
 414     }
 415 
 416     /**
 417      * See the general contract of the <code>mark</code>
 418      * method of <code>InputStream</code>.
 419      *
 420      * @param   readlimit   the maximum limit of bytes that can be read before
 421      *                      the mark position becomes invalid.
 422      * @see     java.io.BufferedInputStream#reset()
 423      */
 424     public synchronized void mark(int readlimit) {
 425         marklimit = readlimit;
 426         markpos = pos;
 427     }
 428 
 429     /**
 430      * See the general contract of the <code>reset</code>
 431      * method of <code>InputStream</code>.
 432      * <p>
 433      * If <code>markpos</code> is <code>-1</code>
 434      * (no mark has been set or the mark has been
 435      * invalidated), an <code>IOException</code>
 436      * is thrown. Otherwise, <code>pos</code> is
 437      * set equal to <code>markpos</code>.
 438      *
 439      * @exception  IOException  if this stream has not been marked or,
 440      *                  if the mark has been invalidated, or the stream
 441      *                  has been closed by invoking its {@link #close()}
 442      *                  method, or an I/O error occurs.
 443      * @see        java.io.BufferedInputStream#mark(int)
 444      */
 445     public synchronized void reset() throws IOException {
 446         getBufIfOpen(); // Cause exception if closed
 447         if (markpos < 0)
 448             throw new IOException("Resetting to invalid mark");
 449         pos = markpos;
 450     }
 451 
 452     /**
 453      * Tests if this input stream supports the <code>mark</code>
 454      * and <code>reset</code> methods. The <code>markSupported</code>
 455      * method of <code>BufferedInputStream</code> returns
 456      * <code>true</code>.
 457      *
 458      * @return  a <code>boolean</code> indicating if this stream type supports
 459      *          the <code>mark</code> and <code>reset</code> methods.
 460      * @see     java.io.InputStream#mark(int)
 461      * @see     java.io.InputStream#reset()
 462      */
 463     public boolean markSupported() {
 464         return true;
 465     }
 466 
 467     /**
 468      * Closes this input stream and releases any system resources
 469      * associated with the stream.
 470      * Once the stream has been closed, further read(), available(), reset(),
 471      * or skip() invocations will throw an IOException.
 472      * Closing a previously closed stream has no effect.
 473      *
 474      * @exception  IOException  if an I/O error occurs.
 475      */
 476     public void close() throws IOException {
 477         byte[] buffer;
 478         while ( (buffer = buf) != null) {
 479             if (bufUpdater.compareAndSet(this, buffer, null)) {
 480                 InputStream input = in;
 481                 in = null;
 482                 if (input != null)
 483                     input.close();
 484                 return;
 485             }
 486             // Else retry in case a new buf was CASed in fill()
 487         }
 488     }
 489 }