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 - 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 }
496