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 }