1 /*

     2  * Copyright (c) 1994, 2016, 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 

    28 import jdk.internal.misc.Unsafe;

    29 

    30 /**

    31  * A <code>BufferedInputStream</code> adds

    32  * functionality to another input stream-namely,

    33  * the ability to buffer the input and to

    34  * support the <code>mark</code> and <code>reset</code>

    35  * methods. When  the <code>BufferedInputStream</code>

    36  * is created, an internal buffer array is

    37  * created. As bytes  from the stream are read

    38  * or skipped, the internal buffer is refilled

    39  * as necessary  from the contained input stream,

    40  * many bytes at a time. The <code>mark</code>

    41  * operation  remembers a point in the input

    42  * stream and the <code>reset</code> operation

    43  * causes all the  bytes read since the most

    44  * recent <code>mark</code> operation to be

    45  * reread before new bytes are  taken from

    46  * the contained input stream.

    47  *

    48  * @author  Arthur van Hoff

    49  * @since   1.0

    50  */

    51 public

    52 class BufferedInputStream extends FilterInputStream {

    53 

    54     private static int DEFAULT_BUFFER_SIZE = 8192;

    55 

    56     /**

    57      * The maximum size of array to allocate.

    58      * Some VMs reserve some header words in an array.

    59      * Attempts to allocate larger arrays may result in

    60      * OutOfMemoryError: Requested array size exceeds VM limit

    61      */

    62     private static int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;

    63 

    64     /**

    65      * As this class is used early during bootstrap, it's motivated to use

    66      * Unsafe.compareAndSetObject instead of AtomicReferenceFieldUpdater

    67      * (or VarHandles) to reduce dependencies and improve startup time.

    68      */

    69     private static final Unsafe U = Unsafe.getUnsafe();

    70 

    71     private static final long BUF_OFFSET

    72             = U.objectFieldOffset(BufferedInputStream.class, "buf");

    73 

    74     /**

    75      * The internal buffer array where the data is stored. When necessary,

    76      * it may be replaced by another array of

    77      * a different size.

    78      */

    79     /*

    80      * We null this out with a CAS on close(), which is necessary since

    81      * closes can be asynchronous. We use nullness of buf[] as primary

    82      * indicator that this stream is closed. (The "in" field is also

    83      * nulled out on close.)

    84      */

    85     protected volatile byte[] buf;

    86 

    87     /**

    88      * The index one greater than the index of the last valid byte in

    89      * the buffer.

    90      * This value is always

    91      * in the range <code>0</code> through <code>buf.length</code>;

    92      * elements <code>buf[0]</code>  through <code>buf[count-1]

    93      * </code>contain buffered input data obtained

    94      * from the underlying  input stream.

    95      */

    96     protected int count;

    97 

    98     /**

    99      * The current position in the buffer. This is the index of the next

   100      * character to be read from the <code>buf</code> array.

   101      * <p>

   102      * This value is always in the range <code>0</code>

   103      * through <code>count</code>. If it is less

   104      * than <code>count</code>, then  <code>buf[pos]</code>

   105      * is the next byte to be supplied as input;

   106      * if it is equal to <code>count</code>, then

   107      * the  next <code>read</code> or <code>skip</code>

   108      * operation will require more bytes to be

   109      * read from the contained  input stream.

   110      *

   111      * @see     java.io.BufferedInputStream#buf

   112      */

   113     protected int pos;

   114 

   115     /**

   116      * The value of the <code>pos</code> field at the time the last

   117      * <code>mark</code> method was called.

   118      * <p>

   119      * This value is always

   120      * in the range <code>-1</code> through <code>pos</code>.

   121      * If there is no marked position in  the input

   122      * stream, this field is <code>-1</code>. If

   123      * there is a marked position in the input

   124      * stream,  then <code>buf[markpos]</code>

   125      * is the first byte to be supplied as input

   126      * after a <code>reset</code> operation. If

   127      * <code>markpos</code> is not <code>-1</code>,

   128      * then all bytes from positions <code>buf[markpos]</code>

   129      * through  <code>buf[pos-1]</code> must remain

   130      * in the buffer array (though they may be

   131      * moved to  another place in the buffer array,

   132      * with suitable adjustments to the values

   133      * of <code>count</code>,  <code>pos</code>,

   134      * and <code>markpos</code>); they may not

   135      * be discarded unless and until the difference

   136      * between <code>pos</code> and <code>markpos</code>

   137      * exceeds <code>marklimit</code>.

   138      *

   139      * @see     java.io.BufferedInputStream#mark(int)

   140      * @see     java.io.BufferedInputStream#pos

   141      */

   142     protected int markpos = -1;

   143 

   144     /**

   145      * The maximum read ahead allowed after a call to the

   146      * <code>mark</code> method before subsequent calls to the

   147      * <code>reset</code> method fail.

   148      * Whenever the difference between <code>pos</code>

   149      * and <code>markpos</code> exceeds <code>marklimit</code>,

   150      * then the  mark may be dropped by setting

   151      * <code>markpos</code> to <code>-1</code>.

   152      *

   153      * @see     java.io.BufferedInputStream#mark(int)

   154      * @see     java.io.BufferedInputStream#reset()

   155      */

   156     protected int marklimit;

   157 

   158     /**

   159      * Check to make sure that underlying input stream has not been

   160      * nulled out due to close; if not return it;

   161      */

   162     private InputStream getInIfOpen() throws IOException {

   163         InputStream input = in;

   164         if (input == null)

   165             throw new IOException("Stream closed");

   166         return input;

   167     }

   168 

   169     /**

   170      * Check to make sure that buffer has not been nulled out due to

   171      * close; if not return it;

   172      */

   173     private byte[] getBufIfOpen() throws IOException {

   174         byte[] buffer = buf;

   175         if (buffer == null)

   176             throw new IOException("Stream closed");

   177         return buffer;

   178     }

   179 

   180     /**

   181      * Creates a <code>BufferedInputStream</code>

   182      * and saves its  argument, the input stream

   183      * <code>in</code>, for later use. An internal

   184      * buffer array is created and  stored in <code>buf</code>.

   185      *

   186      * @param   in   the underlying input stream.

   187      */

   188     public BufferedInputStream(InputStream in) {

   189         this(in, DEFAULT_BUFFER_SIZE);

   190     }

   191 

   192     /**

   193      * Creates a <code>BufferedInputStream</code>

   194      * with the specified buffer size,

   195      * and saves its  argument, the input stream

   196      * <code>in</code>, for later use.  An internal

   197      * buffer array of length  <code>size</code>

   198      * is created and stored in <code>buf</code>.

   199      *

   200      * @param   in     the underlying input stream.

   201      * @param   size   the buffer size.

   202      * @exception IllegalArgumentException if {@code size <= 0}.

   203      */

   204     public BufferedInputStream(InputStream in, int size) {

   205         super(in);

   206         if (size <= 0) {

   207             throw new IllegalArgumentException("Buffer size <= 0");

   208         }

   209         buf = new byte[size];

   210     }

   211 

   212     /**

   213      * Fills the buffer with more data, taking into account

   214      * shuffling and other tricks for dealing with marks.

   215      * Assumes that it is being called by a synchronized method.

   216      * This method also assumes that all data has already been read in,

   217      * hence pos > count.

   218      */

   219     private void fill() throws IOException {

   220         byte[] buffer = getBufIfOpen();

   221         if (markpos < 0)

   222             pos = 0;            /* no mark: throw away the buffer */

   223         else if (pos >= buffer.length)  /* no room left in buffer */

   224             if (markpos > 0) {  /* can throw away early part of the buffer */

   225                 int sz = pos - markpos;

   226                 System.arraycopy(buffer, markpos, buffer, 0, sz);

   227                 pos = sz;

   228                 markpos = 0;

   229             } else if (buffer.length >= marklimit) {

   230                 markpos = -1;   /* buffer got too big, invalidate mark */

   231                 pos = 0;        /* drop buffer contents */

   232             } else if (buffer.length >= MAX_BUFFER_SIZE) {

   233                 throw new OutOfMemoryError("Required array size too large");

   234             } else {            /* grow buffer */

   235                 int nsz = (pos <= MAX_BUFFER_SIZE - pos) ?

   236                         pos * 2 : MAX_BUFFER_SIZE;

   237                 if (nsz > marklimit)

   238                     nsz = marklimit;

   239                 byte[] nbuf = new byte[nsz];

   240                 System.arraycopy(buffer, 0, nbuf, 0, pos);

   241                 if (!U.compareAndSetObject(this, BUF_OFFSET, buffer, nbuf)) {

   242                     // Can't replace buf if there was an async close.

   243                     // Note: This would need to be changed if fill()

   244                     // is ever made accessible to multiple threads.

   245                     // But for now, the only way CAS can fail is via close.

   246                     // assert buf == null;

   247                     throw new IOException("Stream closed");

   248                 }

   249                 buffer = nbuf;

   250             }

   251         count = pos;

   252         int n = getInIfOpen().read(buffer, pos, buffer.length - pos);

   253         if (n > 0)

   254             count = n + pos;

   255     }

   256 

   257     /**

   258      * See

   259      * the general contract of the <code>read</code>

   260      * method of <code>InputStream</code>.

   261      *

   262      * @return     the next byte of data, or <code>-1</code> if the end of the

   263      *             stream is reached.

   264      * @exception  IOException  if this input stream has been closed by

   265      *                          invoking its {@link #close()} method,

   266      *                          or an I/O error occurs.

   267      * @see        java.io.FilterInputStream#in

   268      */

   269     public synchronized int read() throws IOException {

   270         if (pos >= count) {

   271             fill();

   272             if (pos >= count)

   273                 return -1;

   274         }

   275         return getBufIfOpen()[pos++] & 0xff;

   276     }

   277 

   278     /**

   279      * Read characters into a portion of an array, reading from the underlying

   280      * stream at most once if necessary.

   281      */

   282     private int read1(byte[] b, int off, int len) throws IOException {

   283         int avail = count - pos;

   284         if (avail <= 0) {

   285             /* If the requested length is at least as large as the buffer, and

   286                if there is no mark/reset activity, do not bother to copy the

   287                bytes into the local buffer.  In this way buffered streams will

   288                cascade harmlessly. */

   289             if (len >= getBufIfOpen().length && markpos < 0) {

   290                 return getInIfOpen().read(b, off, len);

   291             }

   292             fill();

   293             avail = count - pos;

   294             if (avail <= 0) return -1;

   295         }

   296         int cnt = (avail < len) ? avail : len;

   297         System.arraycopy(getBufIfOpen(), pos, b, off, cnt);

   298         pos += cnt;

   299         return cnt;

   300     }

   301 

   302     /**

   303      * Reads bytes from this byte-input stream into the specified byte array,

   304      * starting at the given offset.

   305      *

   306      * <p> This method implements the general contract of the corresponding

   307      * <code>{@link InputStream#read(byte[], int, int) read}</code> method of

   308      * the <code>{@link InputStream}</code> class.  As an additional

   309      * convenience, it attempts to read as many bytes as possible by repeatedly

   310      * invoking the <code>read</code> method of the underlying stream.  This

   311      * iterated <code>read</code> continues until one of the following

   312      * conditions becomes true: <ul>

   313      *

   314      *   <li> The specified number of bytes have been read,

   315      *

   316      *   <li> The <code>read</code> method of the underlying stream returns

   317      *   <code>-1</code>, indicating end-of-file, or

   318      *

   319      *   <li> The <code>available</code> method of the underlying stream

   320      *   returns zero, indicating that further input requests would block.

   321      *

   322      * </ul> If the first <code>read</code> on the underlying stream returns

   323      * <code>-1</code> to indicate end-of-file then this method returns

   324      * <code>-1</code>.  Otherwise this method returns the number of bytes

   325      * actually read.

   326      *

   327      * <p> Subclasses of this class are encouraged, but not required, to

   328      * attempt to read as many bytes as possible in the same fashion.

   329      *

   330      * @param      b     destination buffer.

   331      * @param      off   offset at which to start storing bytes.

   332      * @param      len   maximum number of bytes to read.

   333      * @return     the number of bytes read, or <code>-1</code> if the end of

   334      *             the stream has been reached.

   335      * @exception  IOException  if this input stream has been closed by

   336      *                          invoking its {@link #close()} method,

   337      *                          or an I/O error occurs.

   338      */

   339     public synchronized int read(byte b[], int off, int len)

   340         throws IOException

   341     {

   342         getBufIfOpen(); // Check for closed stream

   343         if ((off | len | (off + len) | (b.length - (off + len))) < 0) {

   344             throw new IndexOutOfBoundsException();

   345         } else if (len == 0) {

   346             return 0;

   347         }

   348 

   349         int n = 0;

   350         for (;;) {

   351             int nread = read1(b, off + n, len - n);

   352             if (nread <= 0)

   353                 return (n == 0) ? nread : n;

   354             n += nread;

   355             if (n >= len)

   356                 return n;

   357             // if not closed but no bytes available, return

   358             InputStream input = in;

   359             if (input != null && input.available() <= 0)

   360                 return n;

   361         }

   362     }

   363 

   364     /**

   365      * See the general contract of the <code>skip</code>

   366      * method of <code>InputStream</code>.

   367      *

   368      * @throws IOException  if this input stream has been closed by

   369      *                      invoking its {@link #close()} method,

   370      *                      {@code in.skip(n)} throws an IOException,

   371      *                      or an I/O error occurs.

   372      */

   373     public synchronized long skip(long n) throws IOException {

   374         getBufIfOpen(); // Check for closed stream

   375         if (n <= 0) {

   376             return 0;

   377         }

   378         long avail = count - pos;

   379 

   380         if (avail <= 0) {

   381             // If no mark position set then don't keep in buffer

   382             if (markpos <0)

   383                 return getInIfOpen().skip(n);

   384 

   385             // Fill in buffer to save bytes for reset

   386             fill();

   387             avail = count - pos;

   388             if (avail <= 0)

   389                 return 0;

   390         }

   391 

   392         long skipped = (avail < n) ? avail : n;

   393         pos += skipped;

   394         return skipped;

   395     }

   396 

   397     /**

   398      * Returns an estimate of the number of bytes that can be read (or

   399      * skipped over) from this input stream without blocking by the next

   400      * invocation of a method for this input stream. The next invocation might be

   401      * the same thread or another thread.  A single read or skip of this

   402      * many bytes will not block, but may read or skip fewer bytes.

   403      * <p>

   404      * This method returns the sum of the number of bytes remaining to be read in

   405      * the buffer (<code>count&nbsp;- pos</code>) and the result of calling the

   406      * {@link java.io.FilterInputStream#in in}.available().

   407      *

   408      * @return     an estimate of the number of bytes that can be read (or skipped

   409      *             over) from this input stream without blocking.

   410      * @exception  IOException  if this input stream has been closed by

   411      *                          invoking its {@link #close()} method,

   412      *                          or an I/O error occurs.

   413      */

   414     public synchronized int available() throws IOException {

   415         int n = count - pos;

   416         int avail = getInIfOpen().available();

   417         return n > (Integer.MAX_VALUE - avail)

   418                     ? Integer.MAX_VALUE

   419                     : n + avail;

   420     }

   421 

   422     /**

   423      * See the general contract of the <code>mark</code>

   424      * method of <code>InputStream</code>.

   425      *

   426      * @param   readlimit   the maximum limit of bytes that can be read before

   427      *                      the mark position becomes invalid.

   428      * @see     java.io.BufferedInputStream#reset()

   429      */

   430     public synchronized void mark(int readlimit) {

   431         marklimit = readlimit;

   432         markpos = pos;

   433     }

   434 

   435     /**

   436      * See the general contract of the <code>reset</code>

   437      * method of <code>InputStream</code>.

   438      * <p>

   439      * If <code>markpos</code> is <code>-1</code>

   440      * (no mark has been set or the mark has been

   441      * invalidated), an <code>IOException</code>

   442      * is thrown. Otherwise, <code>pos</code> is

   443      * set equal to <code>markpos</code>.

   444      *

   445      * @exception  IOException  if this stream has not been marked or,

   446      *                  if the mark has been invalidated, or the stream

   447      *                  has been closed by invoking its {@link #close()}

   448      *                  method, or an I/O error occurs.

   449      * @see        java.io.BufferedInputStream#mark(int)

   450      */

   451     public synchronized void reset() throws IOException {

   452         getBufIfOpen(); // Cause exception if closed

   453         if (markpos < 0)

   454             throw new IOException("Resetting to invalid mark");

   455         pos = markpos;

   456     }

   457 

   458     /**

   459      * Tests if this input stream supports the <code>mark</code>

   460      * and <code>reset</code> methods. The <code>markSupported</code>

   461      * method of <code>BufferedInputStream</code> returns

   462      * <code>true</code>.

   463      *

   464      * @return  a <code>boolean</code> indicating if this stream type supports

   465      *          the <code>mark</code> and <code>reset</code> methods.

   466      * @see     java.io.InputStream#mark(int)

   467      * @see     java.io.InputStream#reset()

   468      */

   469     public boolean markSupported() {

   470         return true;

   471     }

   472 

   473     /**

   474      * Closes this input stream and releases any system resources

   475      * associated with the stream.

   476      * Once the stream has been closed, further read(), available(), reset(),

   477      * or skip() invocations will throw an IOException.

   478      * Closing a previously closed stream has no effect.

   479      *

   480      * @exception  IOException  if an I/O error occurs.

   481      */

   482     public void close() throws IOException {

   483         byte[] buffer;

   484         while ( (buffer = buf) != null) {

   485             if (U.compareAndSetObject(this, BUF_OFFSET, buffer, null)) {

   486                 InputStream input = in;

   487                 in = null;

   488                 if (input != null)

   489                     input.close();

   490                 return;

   491             }

   492             // Else retry in case a new buf was CASed in fill()

   493         }

   494     }

   495 }