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/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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*/
package java.io;
import jdk.internal.misc.Unsafe;
import jdk.internal.util.ArraysSupport;
/**
* A {@code BufferedInputStream} adds
* functionality to another input stream-namely,
* the ability to buffer the input and to
* support the {@code mark} and {@code reset}
* methods. When the {@code BufferedInputStream}
* is created, an internal buffer array is
* created. As bytes from the stream are read
* or skipped, the internal buffer is refilled
* as necessary from the contained input stream,
* many bytes at a time. The {@code mark}
* operation remembers a point in the input
* stream and the {@code reset} operation
* causes all the bytes read since the most
* recent {@code mark} operation to be
* reread before new bytes are taken from
* the contained input stream.
*
* @author Arthur van Hoff
* @since 1.0
*/
public class BufferedInputStream extends FilterInputStream {
private static int DEFAULT_BUFFER_SIZE = 8192;
/**
* As this class is used early during bootstrap, it's motivated to use
* Unsafe.compareAndSetObject instead of AtomicReferenceFieldUpdater
* (or VarHandles) to reduce dependencies and improve startup time.
*/
private static final Unsafe U = Unsafe.getUnsafe();
private static final long BUF_OFFSET
= U.objectFieldOffset(BufferedInputStream.class, "buf");
/**
* The internal buffer array where the data is stored. When necessary,
* it may be replaced by another array of
* a different size.
*/
/*
* We null this out with a CAS on close(), which is necessary since
* closes can be asynchronous. We use nullness of buf[] as primary
* indicator that this stream is closed. (The "in" field is also
* nulled out on close.)
*/
protected volatile byte[] buf;
/**
* The index one greater than the index of the last valid byte in
* the buffer.
* This value is always
* in the range {@code 0} through {@code buf.length};
* elements {@code buf[0]} through {@code buf[count-1]}
* contain buffered input data obtained
* from the underlying input stream.
*/
protected int count;
/**
* The current position in the buffer. This is the index of the next
* character to be read from the {@code buf} array.
*
* This value is always in the range {@code 0}
* through {@code count}. If it is less
* than {@code count}, then {@code buf[pos]}
* is the next byte to be supplied as input;
* if it is equal to {@code count}, then
* the next {@code read} or {@code skip}
* operation will require more bytes to be
* read from the contained input stream.
*
* @see java.io.BufferedInputStream#buf
*/
protected int pos;
/**
* The value of the {@code pos} field at the time the last
* {@code mark} method was called.
*
* This value is always
* in the range {@code -1} through {@code pos}.
* If there is no marked position in the input
* stream, this field is {@code -1}. If
* there is a marked position in the input
* stream, then {@code buf[markpos]}
* is the first byte to be supplied as input
* after a {@code reset} operation. If
* {@code markpos} is not {@code -1},
* then all bytes from positions {@code buf[markpos]}
* through {@code buf[pos-1]} must remain
* in the buffer array (though they may be
* moved to another place in the buffer array,
* with suitable adjustments to the values
* of {@code count}, {@code pos},
* and {@code markpos}); they may not
* be discarded unless and until the difference
* between {@code pos} and {@code markpos}
* exceeds {@code marklimit}.
*
* @see java.io.BufferedInputStream#mark(int)
* @see java.io.BufferedInputStream#pos
*/
protected int markpos = -1;
/**
* The maximum read ahead allowed after a call to the
* {@code mark} method before subsequent calls to the
* {@code reset} method fail.
* Whenever the difference between {@code pos}
* and {@code markpos} exceeds {@code marklimit},
* then the mark may be dropped by setting
* {@code markpos} to {@code -1}.
*
* @see java.io.BufferedInputStream#mark(int)
* @see java.io.BufferedInputStream#reset()
*/
protected int marklimit;
/**
* Check to make sure that underlying input stream has not been
* nulled out due to close; if not return it;
*/
private InputStream getInIfOpen() throws IOException {
InputStream input = in;
if (input == null)
throw new IOException("Stream closed");
return input;
}
/**
* Check to make sure that buffer has not been nulled out due to
* close; if not return it;
*/
private byte[] getBufIfOpen() throws IOException {
byte[] buffer = buf;
if (buffer == null)
throw new IOException("Stream closed");
return buffer;
}
/**
* Creates a {@code BufferedInputStream}
* and saves its argument, the input stream
* {@code in}, for later use. An internal
* buffer array is created and stored in {@code buf}.
*
* @param in the underlying input stream.
*/
public BufferedInputStream(InputStream in) {
this(in, DEFAULT_BUFFER_SIZE);
}
/**
* Creates a {@code BufferedInputStream}
* with the specified buffer size,
* and saves its argument, the input stream
* {@code in}, for later use. An internal
* buffer array of length {@code size}
* is created and stored in {@code buf}.
*
* @param in the underlying input stream.
* @param size the buffer size.
* @throws IllegalArgumentException if {@code size <= 0}.
*/
public BufferedInputStream(InputStream in, int size) {
super(in);
if (size <= 0) {
throw new IllegalArgumentException("Buffer size <= 0");
}
buf = new byte[size];
}
/**
* Fills the buffer with more data, taking into account
* shuffling and other tricks for dealing with marks.
* Assumes that it is being called by a synchronized method.
* This method also assumes that all data has already been read in,
* hence pos > count.
*/
private void fill() throws IOException {
byte[] buffer = getBufIfOpen();
if (markpos < 0)
pos = 0; /* no mark: throw away the buffer */
else if (pos >= buffer.length) { /* no room left in buffer */
if (markpos > 0) { /* can throw away early part of the buffer */
int sz = pos - markpos;
System.arraycopy(buffer, markpos, buffer, 0, sz);
pos = sz;
markpos = 0;
} else if (buffer.length >= marklimit) {
markpos = -1; /* buffer got too big, invalidate mark */
pos = 0; /* drop buffer contents */
} else { /* grow buffer */
int nsz = ArraysSupport.newLength(pos,
1, /* minimum growth */
pos /* preferred growth */);
if (nsz > marklimit)
nsz = marklimit;
byte[] nbuf = new byte[nsz];
System.arraycopy(buffer, 0, nbuf, 0, pos);
if (!U.compareAndSetReference(this, BUF_OFFSET, buffer, nbuf)) {
// Can't replace buf if there was an async close.
// Note: This would need to be changed if fill()
// is ever made accessible to multiple threads.
// But for now, the only way CAS can fail is via close.
// assert buf == null;
throw new IOException("Stream closed");
}
buffer = nbuf;
}
}
count = pos;
int n = getInIfOpen().read(buffer, pos, buffer.length - pos);
if (n > 0)
count = n + pos;
}
/**
* See
* the general contract of the {@code read}
* method of {@code InputStream}.
*
* @return the next byte of data, or {@code -1} if the end of the
* stream is reached.
* @throws IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* or an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public synchronized int read() throws IOException {
if (pos >= count) {
fill();
if (pos >= count)
return -1;
}
return getBufIfOpen()[pos++] & 0xff;
}
/**
* Read characters into a portion of an array, reading from the underlying
* stream at most once if necessary.
*/
private int read1(byte[] b, int off, int len) throws IOException {
int avail = count - pos;
if (avail <= 0) {
/* If the requested length is at least as large as the buffer, and
if there is no mark/reset activity, do not bother to copy the
bytes into the local buffer. In this way buffered streams will
cascade harmlessly. */
if (len >= getBufIfOpen().length && markpos < 0) {
return getInIfOpen().read(b, off, len);
}
fill();
avail = count - pos;
if (avail <= 0) return -1;
}
int cnt = (avail < len) ? avail : len;
System.arraycopy(getBufIfOpen(), pos, b, off, cnt);
pos += cnt;
return cnt;
}
/**
* Reads bytes from this byte-input stream into the specified byte array,
* starting at the given offset.
*
*
This method implements the general contract of the corresponding
* {@link InputStream#read(byte[], int, int) read} method of
* the {@link InputStream} class. As an additional
* convenience, it attempts to read as many bytes as possible by repeatedly
* invoking the {@code read} method of the underlying stream. This
* iterated {@code read} continues until one of the following
* conditions becomes true:
*
* - The specified number of bytes have been read,
*
*
- The {@code read} method of the underlying stream returns
* {@code -1}, indicating end-of-file, or
*
*
- The {@code available} method of the underlying stream
* returns zero, indicating that further input requests would block.
*
*
If the first {@code read} on the underlying stream returns
* {@code -1} to indicate end-of-file then this method returns
* {@code -1}. Otherwise this method returns the number of bytes
* actually read.
*
* Subclasses of this class are encouraged, but not required, to
* attempt to read as many bytes as possible in the same fashion.
*
* @param b destination buffer.
* @param off offset at which to start storing bytes.
* @param len maximum number of bytes to read.
* @return the number of bytes read, or {@code -1} if the end of
* the stream has been reached.
* @throws IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* or an I/O error occurs.
*/
public synchronized int read(byte b[], int off, int len)
throws IOException
{
getBufIfOpen(); // Check for closed stream
if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int n = 0;
for (;;) {
int nread = read1(b, off + n, len - n);
if (nread <= 0)
return (n == 0) ? nread : n;
n += nread;
if (n >= len)
return n;
// if not closed but no bytes available, return
InputStream input = in;
if (input != null && input.available() <= 0)
return n;
}
}
/**
* See the general contract of the {@code skip}
* method of {@code InputStream}.
*
* @throws IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* {@code in.skip(n)} throws an IOException,
* or an I/O error occurs.
*/
public synchronized long skip(long n) throws IOException {
getBufIfOpen(); // Check for closed stream
if (n <= 0) {
return 0;
}
long avail = count - pos;
if (avail <= 0) {
// If no mark position set then don't keep in buffer
if (markpos <0)
return getInIfOpen().skip(n);
// Fill in buffer to save bytes for reset
fill();
avail = count - pos;
if (avail <= 0)
return 0;
}
long skipped = (avail < n) ? avail : n;
pos += skipped;
return skipped;
}
/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* invocation of a method for this input stream. The next invocation might be
* the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
* This method returns the sum of the number of bytes remaining to be read in
* the buffer ({@code count - pos}) and the result of calling the
* {@link java.io.FilterInputStream#in in}{@code .available()}.
*
* @return an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking.
* @throws IOException if this input stream has been closed by
* invoking its {@link #close()} method,
* or an I/O error occurs.
*/
public synchronized int available() throws IOException {
int n = count - pos;
int avail = getInIfOpen().available();
return n > (Integer.MAX_VALUE - avail)
? Integer.MAX_VALUE
: n + avail;
}
/**
* See the general contract of the {@code mark}
* method of {@code InputStream}.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.BufferedInputStream#reset()
*/
public synchronized void mark(int readlimit) {
marklimit = readlimit;
markpos = pos;
}
/**
* See the general contract of the {@code reset}
* method of {@code InputStream}.
*
* If {@code markpos} is {@code -1}
* (no mark has been set or the mark has been
* invalidated), an {@code IOException}
* is thrown. Otherwise, {@code pos} is
* set equal to {@code markpos}.
*
* @throws IOException if this stream has not been marked or,
* if the mark has been invalidated, or the stream
* has been closed by invoking its {@link #close()}
* method, or an I/O error occurs.
* @see java.io.BufferedInputStream#mark(int)
*/
public synchronized void reset() throws IOException {
getBufIfOpen(); // Cause exception if closed
if (markpos < 0)
throw new IOException("Resetting to invalid mark");
pos = markpos;
}
/**
* Tests if this input stream supports the {@code mark}
* and {@code reset} methods. The {@code markSupported}
* method of {@code BufferedInputStream} returns
* {@code true}.
*
* @return a {@code boolean} indicating if this stream type supports
* the {@code mark} and {@code reset} methods.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
*/
public boolean markSupported() {
return true;
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
* Once the stream has been closed, further read(), available(), reset(),
* or skip() invocations will throw an IOException.
* Closing a previously closed stream has no effect.
*
* @throws IOException if an I/O error occurs.
*/
public void close() throws IOException {
byte[] buffer;
while ( (buffer = buf) != null) {
if (U.compareAndSetReference(this, BUF_OFFSET, buffer, null)) {
InputStream input = in;
in = null;
if (input != null)
input.close();
return;
}
// Else retry in case a new buf was CASed in fill()
}
}
}