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 (in == null) {
200 throw new NullPointerException();
201 }
202 if (size <= 0) {
203 throw new IllegalArgumentException("Buffer size <= 0");
204 }
205 buf = new byte[size];
206 }
207
208 /**
209 * Fills the buffer with more data, taking into account
210 * shuffling and other tricks for dealing with marks.
211 * Assumes that it is being called by a synchronized method.
212 * This method also assumes that all data has already been read in,
213 * hence pos > count.
214 */
215 private void fill() throws IOException {
216 byte[] buffer = getBufIfOpen();
217 if (markpos < 0)
218 pos = 0; /* no mark: throw away the buffer */
219 else if (pos >= buffer.length) { /* no room left in buffer */
220 if (markpos > 0) { /* can throw away early part of the buffer */
221 int sz = pos - markpos;
222 System.arraycopy(buffer, markpos, buffer, 0, sz);
223 pos = sz;
224 markpos = 0;
225 } else if (buffer.length >= marklimit) {
226 markpos = -1; /* buffer got too big, invalidate mark */
227 pos = 0; /* drop buffer contents */
228 } else { /* grow buffer */
229 int nsz = ArraysSupport.newLength(pos,
230 1, /* minimum growth */
231 pos /* preferred growth */);
232 if (nsz > marklimit)
233 nsz = marklimit;
234 byte[] nbuf = new byte[nsz];
235 System.arraycopy(buffer, 0, nbuf, 0, pos);
236 if (!U.compareAndSetReference(this, BUF_OFFSET, buffer, nbuf)) {
237 // Can't replace buf if there was an async close.
238 // Note: This would need to be changed if fill()
239 // is ever made accessible to multiple threads.
240 // But for now, the only way CAS can fail is via close.
241 // assert buf == null;
242 throw new IOException("Stream closed");
243 }
244 buffer = nbuf;
245 }
246 }
247 count = pos;
248 int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
249 if (n > 0)
250 count = n + pos;
251 }
252
253 /**
254 * See
255 * the general contract of the <code>read</code>
256 * method of <code>InputStream</code>.
257 *
258 * @return the next byte of data, or <code>-1</code> if the end of the
259 * stream is reached.
260 * @exception IOException if this input stream has been closed by
261 * invoking its {@link #close()} method,
262 * or an I/O error occurs.
263 * @see java.io.FilterInputStream#in
264 */
265 public synchronized int read() throws IOException {
266 if (pos >= count) {
267 fill();
268 if (pos >= count)
269 return -1;
270 }
271 return getBufIfOpen()[pos++] & 0xff;
272 }
273
274 /**
275 * Read characters into a portion of an array, reading from the underlying
276 * stream at most once if necessary.
277 */
278 private int read1(byte[] b, int off, int len) throws IOException {
279 int avail = count - pos;
280 if (avail <= 0) {
281 /* If the requested length is at least as large as the buffer, and
282 if there is no mark/reset activity, do not bother to copy the
283 bytes into the local buffer. In this way buffered streams will
284 cascade harmlessly. */
285 if (len >= getBufIfOpen().length && markpos < 0) {
286 return getInIfOpen().read(b, off, len);
287 }
288 fill();
289 avail = count - pos;
290 if (avail <= 0) return -1;
291 }
292 int cnt = (avail < len) ? avail : len;
293 System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
294 pos += cnt;
295 return cnt;
296 }
297
298 /**
299 * Reads bytes from this byte-input stream into the specified byte array,
300 * starting at the given offset.
301 *
302 * <p> This method implements the general contract of the corresponding
303 * <code>{@link InputStream#read(byte[], int, int) read}</code> method of
304 * the <code>{@link InputStream}</code> class. As an additional
305 * convenience, it attempts to read as many bytes as possible by repeatedly
306 * invoking the <code>read</code> method of the underlying stream. This
307 * iterated <code>read</code> continues until one of the following
308 * conditions becomes true: <ul>
309 *
310 * <li> The specified number of bytes have been read,
311 *
312 * <li> The <code>read</code> method of the underlying stream returns
313 * <code>-1</code>, indicating end-of-file, or
314 *
315 * <li> The <code>available</code> method of the underlying stream
316 * returns zero, indicating that further input requests would block.
317 *
318 * </ul> If the first <code>read</code> on the underlying stream returns
319 * <code>-1</code> to indicate end-of-file then this method returns
320 * <code>-1</code>. Otherwise this method returns the number of bytes
321 * actually read.
322 *
323 * <p> Subclasses of this class are encouraged, but not required, to
324 * attempt to read as many bytes as possible in the same fashion.
325 *
326 * @param b destination buffer.
327 * @param off offset at which to start storing bytes.
328 * @param len maximum number of bytes to read.
329 * @return the number of bytes read, or <code>-1</code> if the end of
330 * the stream has been reached.
331 * @exception IOException if this input stream has been closed by
332 * invoking its {@link #close()} method,
333 * or an I/O error occurs.
334 */
335 public synchronized int read(byte b[], int off, int len)
336 throws IOException
337 {
338 getBufIfOpen(); // Check for closed stream
339 if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
340 throw new IndexOutOfBoundsException();
341 } else if (len == 0) {
342 return 0;
343 }
344
345 int n = 0;
346 for (;;) {
347 int nread = read1(b, off + n, len - n);
348 if (nread <= 0)
349 return (n == 0) ? nread : n;
350 n += nread;
351 if (n >= len)
352 return n;
353 // if not closed but no bytes available, return
354 InputStream input = in;
355 if (input != null && input.available() <= 0)
356 return n;
357 }
358 }
359
360 /**
361 * See the general contract of the <code>skip</code>
362 * method of <code>InputStream</code>.
363 *
364 * @throws IOException if this input stream has been closed by
365 * invoking its {@link #close()} method,
366 * {@code in.skip(n)} throws an IOException,
367 * or an I/O error occurs.
368 */
369 public synchronized long skip(long n) throws IOException {
370 getBufIfOpen(); // Check for closed stream
371 if (n <= 0) {
372 return 0;
373 }
374 long avail = count - pos;
375
376 if (avail <= 0) {
377 // If no mark position set then don't keep in buffer
378 if (markpos <0)
379 return getInIfOpen().skip(n);
380
381 // Fill in buffer to save bytes for reset
382 fill();
383 avail = count - pos;
384 if (avail <= 0)
385 return 0;
386 }
387
388 long skipped = (avail < n) ? avail : n;
389 pos += skipped;
390 return skipped;
391 }
392
393 /**
394 * Returns an estimate of the number of bytes that can be read (or
395 * skipped over) from this input stream without blocking by the next
396 * invocation of a method for this input stream. The next invocation might be
397 * the same thread or another thread. A single read or skip of this
398 * many bytes will not block, but may read or skip fewer bytes.
399 * <p>
400 * This method returns the sum of the number of bytes remaining to be read in
401 * the buffer (<code>count - pos</code>) and the result of calling the
402 * {@link java.io.FilterInputStream#in in}.available().
403 *
404 * @return an estimate of the number of bytes that can be read (or skipped
405 * over) from this input stream without blocking.
406 * @exception IOException if this input stream has been closed by
407 * invoking its {@link #close()} method,
408 * or an I/O error occurs.
409 */
410 public synchronized int available() throws IOException {
411 int n = count - pos;
412 int avail = getInIfOpen().available();
413 return n > (Integer.MAX_VALUE - avail)
414 ? Integer.MAX_VALUE
415 : n + avail;
416 }
417
418 /**
419 * See the general contract of the <code>mark</code>
420 * method of <code>InputStream</code>.
421 *
422 * @param readlimit the maximum limit of bytes that can be read before
423 * the mark position becomes invalid.
424 * @see java.io.BufferedInputStream#reset()
425 */
426 public synchronized void mark(int readlimit) {
427 marklimit = readlimit;
428 markpos = pos;
429 }
430
431 /**
432 * See the general contract of the <code>reset</code>
433 * method of <code>InputStream</code>.
434 * <p>
435 * If <code>markpos</code> is <code>-1</code>
436 * (no mark has been set or the mark has been
437 * invalidated), an <code>IOException</code>
438 * is thrown. Otherwise, <code>pos</code> is
439 * set equal to <code>markpos</code>.
440 *
441 * @exception IOException if this stream has not been marked or,
442 * if the mark has been invalidated, or the stream
443 * has been closed by invoking its {@link #close()}
444 * method, or an I/O error occurs.
445 * @see java.io.BufferedInputStream#mark(int)
446 */
447 public synchronized void reset() throws IOException {
448 getBufIfOpen(); // Cause exception if closed
449 if (markpos < 0)
450 throw new IOException("Resetting to invalid mark");
451 pos = markpos;
452 }
453
454 /**
455 * Tests if this input stream supports the <code>mark</code>
456 * and <code>reset</code> methods. The <code>markSupported</code>
457 * method of <code>BufferedInputStream</code> returns
458 * <code>true</code>.
459 *
460 * @return a <code>boolean</code> indicating if this stream type supports
461 * the <code>mark</code> and <code>reset</code> methods.
462 * @see java.io.InputStream#mark(int)
463 * @see java.io.InputStream#reset()
464 */
465 public boolean markSupported() {
466 return true;
467 }
468
469 /**
470 * Closes this input stream and releases any system resources
471 * associated with the stream.
472 * Once the stream has been closed, further read(), available(), reset(),
473 * or skip() invocations will throw an IOException.
474 * Closing a previously closed stream has no effect.
475 *
476 * @exception IOException if an I/O error occurs.
477 */
478 public void close() throws IOException {
479 byte[] buffer;
480 while ( (buffer = buf) != null) {
481 if (U.compareAndSetReference(this, BUF_OFFSET, buffer, null)) {
482 InputStream input = in;
483 in = null;
484 if (input != null)
485 input.close();
486 return;
487 }
488 // Else retry in case a new buf was CASed in fill()
489 }
490 }
491 }