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