1 /*
2 * Copyright (c) 1994, 2019, 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 import jdk.internal.util.ArraysSupport;
30
31 /**
32 * A <code>BufferedInputStream</code> adds
33 * functionality to another input stream-namely,
34 * the ability to buffer the input and to
35 * support the <code>mark</code> and <code>reset</code>
36 * methods. When the <code>BufferedInputStream</code>
37 * is created, an internal buffer array is
38 * created. As bytes from the stream are read
39 * or skipped, the internal buffer is refilled
40 * as necessary from the contained input stream,
41 * many bytes at a time. The <code>mark</code>
42 * operation remembers a point in the input
43 * stream and the <code>reset</code> operation
44 * causes all the bytes read since the most
45 * recent <code>mark</code> operation to be
46 * reread before new bytes are taken from
47 * the contained input stream.
48 *
49 * @author Arthur van Hoff
50 * @since 1.0
51 */
52 public
53 class BufferedInputStream extends FilterInputStream {
54
55 private static int DEFAULT_BUFFER_SIZE = 8192;
56
57 /**
58 * As this class is used early during bootstrap, it's motivated to use
59 * Unsafe.compareAndSetObject instead of AtomicReferenceFieldUpdater
60 * (or VarHandles) to reduce dependencies and improve startup time.
61 */
62 private static final Unsafe U = Unsafe.getUnsafe();
63
64 private static final long BUF_OFFSET
65 = U.objectFieldOffset(BufferedInputStream.class, "buf");
66
67 /**
68 * The internal buffer array where the data is stored. When necessary,
69 * it may be replaced by another array of
70 * a different size.
71 */
72 /*
73 * We null this out with a CAS on close(), which is necessary since
74 * closes can be asynchronous. We use nullness of buf[] as primary
75 * indicator that this stream is closed. (The "in" field is also
76 * nulled out on close.)
77 */
78 protected volatile byte[] buf;
79
80 /**
81 * The index one greater than the index of the last valid byte in
82 * the buffer.
83 * This value is always
84 * in the range <code>0</code> through <code>buf.length</code>;
85 * elements <code>buf[0]</code> through <code>buf[count-1]
86 * </code>contain buffered input data obtained
87 * from the underlying input stream.
88 */
89 protected int count;
90
91 /**
92 * The current position in the buffer. This is the index of the next
93 * character to be read from the <code>buf</code> array.
94 * <p>
95 * This value is always in the range <code>0</code>
96 * through <code>count</code>. If it is less
97 * than <code>count</code>, then <code>buf[pos]</code>
98 * is the next byte to be supplied as input;
99 * if it is equal to <code>count</code>, then
100 * the next <code>read</code> or <code>skip</code>
101 * operation will require more bytes to be
102 * read from the contained input stream.
103 *
104 * @see java.io.BufferedInputStream#buf
105 */
106 protected int pos;
107
108 /**
109 * The value of the <code>pos</code> field at the time the last
110 * <code>mark</code> method was called.
111 * <p>
112 * This value is always
113 * in the range <code>-1</code> through <code>pos</code>.
114 * If there is no marked position in the input
115 * stream, this field is <code>-1</code>. If
116 * there is a marked position in the input
117 * stream, then <code>buf[markpos]</code>
118 * is the first byte to be supplied as input
119 * after a <code>reset</code> operation. If
120 * <code>markpos</code> is not <code>-1</code>,
121 * then all bytes from positions <code>buf[markpos]</code>
122 * through <code>buf[pos-1]</code> must remain
123 * in the buffer array (though they may be
124 * moved to another place in the buffer array,
125 * with suitable adjustments to the values
126 * of <code>count</code>, <code>pos</code>,
127 * and <code>markpos</code>); they may not
128 * be discarded unless and until the difference
129 * between <code>pos</code> and <code>markpos</code>
130 * exceeds <code>marklimit</code>.
131 *
132 * @see java.io.BufferedInputStream#mark(int)
133 * @see java.io.BufferedInputStream#pos
134 */
135 protected int markpos = -1;
136
137 /**
138 * The maximum read ahead allowed after a call to the
139 * <code>mark</code> method before subsequent calls to the
140 * <code>reset</code> method fail.
141 * Whenever the difference between <code>pos</code>
142 * and <code>markpos</code> exceeds <code>marklimit</code>,
143 * then the mark may be dropped by setting
144 * <code>markpos</code> to <code>-1</code>.
145 *
146 * @see java.io.BufferedInputStream#mark(int)
147 * @see java.io.BufferedInputStream#reset()
148 */
149 protected int marklimit;
150
151 /**
152 * Check to make sure that underlying input stream has not been
153 * nulled out due to close; if not return it;
154 */
155 private InputStream getInIfOpen() throws IOException {
156 InputStream input = in;
157 if (input == null)
158 throw new IOException("Stream closed");
159 return input;
160 }
161
162 /**
163 * Check to make sure that buffer has not been nulled out due to
164 * close; if not return it;
165 */
166 private byte[] getBufIfOpen() throws IOException {
167 byte[] buffer = buf;
168 if (buffer == null)
169 throw new IOException("Stream closed");
170 return buffer;
171 }
172
173 /**
174 * Creates a <code>BufferedInputStream</code>
175 * and saves its argument, the input stream
176 * <code>in</code>, for later use. An internal
177 * buffer array is created and stored in <code>buf</code>.
178 *
179 * @param in the underlying input stream.
180 */
181 public BufferedInputStream(InputStream in) {
182 this(in, DEFAULT_BUFFER_SIZE);
183 }
184
185 /**
186 * Creates a <code>BufferedInputStream</code>
187 * with the specified buffer size,
188 * and saves its argument, the input stream
189 * <code>in</code>, for later use. An internal
190 * buffer array of length <code>size</code>
191 * is created and stored in <code>buf</code>.
192 *
193 * @param in the underlying input stream.
194 * @param size the buffer size.
195 * @exception IllegalArgumentException if {@code size <= 0}.
196 */
197 public BufferedInputStream(InputStream in, int size) {
198 super(in);
199 if (size <= 0) {
200 throw new IllegalArgumentException("Buffer size <= 0");
201 }
202 buf = new byte[size];
203 }
204
205 /**
206 * Fills the buffer with more data, taking into account
207 * shuffling and other tricks for dealing with marks.
208 * Assumes that it is being called by a synchronized method.
209 * This method also assumes that all data has already been read in,
210 * hence pos > count.
211 */
212 private void fill() throws IOException {
213 byte[] buffer = getBufIfOpen();
214 if (markpos < 0)
215 pos = 0; /* no mark: throw away the buffer */
216 else if (pos >= buffer.length) { /* no room left in buffer */
217 if (markpos > 0) { /* can throw away early part of the buffer */
218 int sz = pos - markpos;
219 System.arraycopy(buffer, markpos, buffer, 0, sz);
220 pos = sz;
221 markpos = 0;
222 } else if (buffer.length >= marklimit) {
223 markpos = -1; /* buffer got too big, invalidate mark */
224 pos = 0; /* drop buffer contents */
225 } else { /* grow buffer */
226 int nsz = ArraysSupport.newLength(pos,
227 1, /* minimum growth */
228 pos /* preferred growth */);
229 if (nsz > marklimit)
230 nsz = marklimit;
231 byte[] nbuf = new byte[nsz];
232 System.arraycopy(buffer, 0, nbuf, 0, pos);
233 if (!U.compareAndSetReference(this, BUF_OFFSET, buffer, nbuf)) {
234 // Can't replace buf if there was an async close.
235 // Note: This would need to be changed if fill()
236 // is ever made accessible to multiple threads.
237 // But for now, the only way CAS can fail is via close.
238 // assert buf == null;
239 throw new IOException("Stream closed");
240 }
241 buffer = nbuf;
242 }
243 }
244 count = pos;
245 int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
246 if (n > 0)
247 count = n + pos;
248 }
249
250 /**
251 * See
252 * the general contract of the <code>read</code>
253 * method of <code>InputStream</code>.
254 *
255 * @return the next byte of data, or <code>-1</code> if the end of the
256 * stream is reached.
257 * @exception IOException if this input stream has been closed by
258 * invoking its {@link #close()} method,
259 * or an I/O error occurs.
260 * @see java.io.FilterInputStream#in
261 */
262 public synchronized int read() throws IOException {
263 if (pos >= count) {
264 fill();
265 if (pos >= count)
266 return -1;
267 }
268 return getBufIfOpen()[pos++] & 0xff;
269 }
270
271 /**
272 * Read characters into a portion of an array, reading from the underlying
273 * stream at most once if necessary.
274 */
275 private int read1(byte[] b, int off, int len) throws IOException {
276 int avail = count - pos;
277 if (avail <= 0) {
278 /* If the requested length is at least as large as the buffer, and
279 if there is no mark/reset activity, do not bother to copy the
280 bytes into the local buffer. In this way buffered streams will
281 cascade harmlessly. */
282 if (len >= getBufIfOpen().length && markpos < 0) {
283 return getInIfOpen().read(b, off, len);
284 }
285 fill();
286 avail = count - pos;
287 if (avail <= 0) return -1;
288 }
289 int cnt = (avail < len) ? avail : len;
290 System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
291 pos += cnt;
292 return cnt;
293 }
294
295 /**
296 * Reads bytes from this byte-input stream into the specified byte array,
297 * starting at the given offset.
298 *
299 * <p> This method implements the general contract of the corresponding
300 * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
301 * the <code>{@link InputStream}</code> class. As an additional
302 * convenience, it attempts to read as many bytes as possible by repeatedly
303 * invoking the <code>read</code> method of the underlying stream. This
304 * iterated <code>read</code> continues until one of the following
305 * conditions becomes true: <ul>
306 *
307 * <li> The specified number of bytes have been read,
308 *
309 * <li> The <code>read</code> method of the underlying stream returns
310 * <code>-1</code>, indicating end-of-file, or
311 *
312 * <li> The <code>available</code> method of the underlying stream
313 * returns zero, indicating that further input requests would block.
314 *
315 * </ul> If the first <code>read</code> on the underlying stream returns
316 * <code>-1</code> to indicate end-of-file then this method returns
317 * <code>-1</code>. Otherwise this method returns the number of bytes
318 * actually read.
319 *
320 * <p> Subclasses of this class are encouraged, but not required, to
321 * attempt to read as many bytes as possible in the same fashion.
322 *
323 * @param b destination buffer.
324 * @param off offset at which to start storing bytes.
325 * @param len maximum number of bytes to read.
326 * @return the number of bytes read, or <code>-1</code> if the end of
327 * the stream has been reached.
328 * @exception IOException if this input stream has been closed by
329 * invoking its {@link #close()} method,
330 * or an I/O error occurs.
331 */
332 public synchronized int read(byte b[], int off, int len)
333 throws IOException
334 {
335 getBufIfOpen(); // Check for closed stream
336 if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
337 throw new IndexOutOfBoundsException();
338 } else if (len == 0) {
339 return 0;
340 }
341
342 int n = 0;
343 for (;;) {
344 int nread = read1(b, off + n, len - n);
345 if (nread <= 0)
346 return (n == 0) ? nread : n;
347 n += nread;
348 if (n >= len)
349 return n;
350 // if not closed but no bytes available, return
351 InputStream input = in;
352 if (input != null && input.available() <= 0)
353 return n;
354 }
355 }
356
357 /**
358 * See the general contract of the <code>skip</code>
359 * method of <code>InputStream</code>.
360 *
361 * @throws IOException if this input stream has been closed by
362 * invoking its {@link #close()} method,
363 * {@code in.skip(n)} throws an IOException,
364 * or an I/O error occurs.
365 */
366 public synchronized long skip(long n) throws IOException {
367 getBufIfOpen(); // Check for closed stream
368 if (n <= 0) {
369 return 0;
370 }
371 long avail = count - pos;
372
373 if (avail <= 0) {
374 // If no mark position set then don't keep in buffer
375 if (markpos <0)
376 return getInIfOpen().skip(n);
377
378 // Fill in buffer to save bytes for reset
379 fill();
380 avail = count - pos;
381 if (avail <= 0)
382 return 0;
383 }
384
385 long skipped = (avail < n) ? avail : n;
386 pos += skipped;
387 return skipped;
388 }
389
390 /**
391 * Returns an estimate of the number of bytes that can be read (or
392 * skipped over) from this input stream without blocking by the next
393 * invocation of a method for this input stream. The next invocation might be
394 * the same thread or another thread. A single read or skip of this
395 * many bytes will not block, but may read or skip fewer bytes.
396 * <p>
397 * This method returns the sum of the number of bytes remaining to be read in
398 * the buffer (<code>count - pos</code>) and the result of calling the
399 * {@link java.io.FilterInputStream#in in}.available().
400 *
401 * @return an estimate of the number of bytes that can be read (or skipped
402 * over) from this input stream without blocking.
403 * @exception IOException if this input stream has been closed by
404 * invoking its {@link #close()} method,
405 * or an I/O error occurs.
406 */
407 public synchronized int available() throws IOException {
408 int n = count - pos;
409 int avail = getInIfOpen().available();
410 return n > (Integer.MAX_VALUE - avail)
411 ? Integer.MAX_VALUE
412 : n + avail;
413 }
414
415 /**
416 * See the general contract of the <code>mark</code>
417 * method of <code>InputStream</code>.
418 *
419 * @param readlimit the maximum limit of bytes that can be read before
420 * the mark position becomes invalid.
421 * @see java.io.BufferedInputStream#reset()
422 */
423 public synchronized void mark(int readlimit) {
424 marklimit = readlimit;
425 markpos = pos;
426 }
427
428 /**
429 * See the general contract of the <code>reset</code>
430 * method of <code>InputStream</code>.
431 * <p>
432 * If <code>markpos</code> is <code>-1</code>
433 * (no mark has been set or the mark has been
434 * invalidated), an <code>IOException</code>
435 * is thrown. Otherwise, <code>pos</code> is
436 * set equal to <code>markpos</code>.
437 *
438 * @exception IOException if this stream has not been marked or,
439 * if the mark has been invalidated, or the stream
440 * has been closed by invoking its {@link #close()}
441 * method, or an I/O error occurs.
442 * @see java.io.BufferedInputStream#mark(int)
443 */
444 public synchronized void reset() throws IOException {
445 getBufIfOpen(); // Cause exception if closed
446 if (markpos < 0)
447 throw new IOException("Resetting to invalid mark");
448 pos = markpos;
449 }
450
451 /**
452 * Tests if this input stream supports the <code>mark</code>
453 * and <code>reset</code> methods. The <code>markSupported</code>
454 * method of <code>BufferedInputStream</code> returns
455 * <code>true</code>.
456 *
457 * @return a <code>boolean</code> indicating if this stream type supports
458 * the <code>mark</code> and <code>reset</code> methods.
459 * @see java.io.InputStream#mark(int)
460 * @see java.io.InputStream#reset()
461 */
462 public boolean markSupported() {
463 return true;
464 }
465
466 /**
467 * Closes this input stream and releases any system resources
468 * associated with the stream.
469 * Once the stream has been closed, further read(), available(), reset(),
470 * or skip() invocations will throw an IOException.
471 * Closing a previously closed stream has no effect.
472 *
473 * @exception IOException if an I/O error occurs.
474 */
475 public void close() throws IOException {
476 byte[] buffer;
477 while ( (buffer = buf) != null) {
478 if (U.compareAndSetReference(this, BUF_OFFSET, buffer, null)) {
479 InputStream input = in;
480 in = null;
481 if (input != null)
482 input.close();
483 return;
484 }
485 // Else retry in case a new buf was CASed in fill()
486 }
487 }
488 }