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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
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package javax.imageio.stream;

import java.util.ArrayList;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;


Package-visible class consolidating common code for
MemoryCacheImageInputStream and
MemoryCacheImageOutputStream.
This class keeps an ArrayList of 8K blocks,
loaded sequentially.  Blocks may only be disposed of
from the index 0 forward.  As blocks are freed, the
corresponding entries in the array list are set to
null, but no compacting is performed.
This allows the index for each block to never change,
and the length of the cache is always the same as the
total amount of data ever cached.  Cached data is
therefore always contiguous from the point of last
disposal to the current length.

 The total number of blocks resident in the cache must not
exceed Integer.MAX_VALUE.  In practice, the limit of
available memory will be exceeded long before this becomes an
issue, since a full cache would contain 8192*2^31 = 16 terabytes of
data.
A MemoryCache may be reused after a call
to reset().

/**
 * Package-visible class consolidating common code for
 * <code>MemoryCacheImageInputStream</code> and
 * <code>MemoryCacheImageOutputStream</code>.
 * This class keeps an <code>ArrayList</code> of 8K blocks,
 * loaded sequentially.  Blocks may only be disposed of
 * from the index 0 forward.  As blocks are freed, the
 * corresponding entries in the array list are set to
 * <code>null</code>, but no compacting is performed.
 * This allows the index for each block to never change,
 * and the length of the cache is always the same as the
 * total amount of data ever cached.  Cached data is
 * therefore always contiguous from the point of last
 * disposal to the current length.
 *
 * <p> The total number of blocks resident in the cache must not
 * exceed <code>Integer.MAX_VALUE</code>.  In practice, the limit of
 * available memory will be exceeded long before this becomes an
 * issue, since a full cache would contain 8192*2^31 = 16 terabytes of
 * data.
 *
 * A <code>MemoryCache</code> may be reused after a call
 * to <code>reset()</code>.
 */
class MemoryCache {

    private static final int BUFFER_LENGTH = 8192;

    private ArrayList cache = new ArrayList();

    private long cacheStart = 0L;

    
The largest position ever written to the cache.

/**
     * The largest position ever written to the cache.
     */
    private long length = 0L;

    private byte[] getCacheBlock(long blockNum) throws IOException {
        long blockOffset = blockNum - cacheStart;
        if (blockOffset > Integer.MAX_VALUE) {
            // This can only happen when the cache hits 16 terabytes of
            // contiguous data...
            throw new IOException("Cache addressing limit exceeded!");
        }
        return (byte[])cache.get((int)blockOffset);
    }

    
Ensures that at least pos bytes are cached,
or the end of the source is reached.  The return value
is equal to the smaller of pos and the
length of the source.

/**
     * Ensures that at least <code>pos</code> bytes are cached,
     * or the end of the source is reached.  The return value
     * is equal to the smaller of <code>pos</code> and the
     * length of the source.
     */
    public long loadFromStream(InputStream stream, long pos)
        throws IOException {
        // We've already got enough data cached
        if (pos < length) {
            return pos;
        }

        int offset = (int)(length % BUFFER_LENGTH);
        byte [] buf = null;

        long len = pos - length;
        if (offset != 0) {
            buf = getCacheBlock(length/BUFFER_LENGTH);
        }

        while (len > 0) {
            if (buf == null) {
                try {
                    buf = new byte[BUFFER_LENGTH];
                } catch (OutOfMemoryError e) {
                    throw new IOException("No memory left for cache!");
                }
                offset = 0;
            }

            int left = BUFFER_LENGTH - offset;
            int nbytes = (int)Math.min(len, (long)left);
            nbytes = stream.read(buf, offset, nbytes);
            if (nbytes == -1) {
                return length; // EOF
            }

            if (offset == 0) {
                cache.add(buf);
            }

            len -= nbytes;
            length += nbytes;
            offset += nbytes;

            if (offset >= BUFFER_LENGTH) {
                // we've filled the current buffer, so a new one will be
                // allocated next time around (and offset will be reset to 0)
                buf = null;
            }
        }

        return pos;
    }

    
Writes out a portion of the cache to an OutputStream. This method preserves no state about the output stream, and does not dispose of any blocks containing bytes written. To dispose blocks, use disposeBefore(). 
Throws:
  • IndexOutOfBoundsException – if any portion of
the requested data is not in the cache (including if pos
is in a block already disposed), or if either pos or
len is < 0.
/**
     * Writes out a portion of the cache to an <code>OutputStream</code>.
     * This method preserves no state about the output stream, and does
     * not dispose of any blocks containing bytes written.  To dispose
     * blocks, use {@link #disposeBefore <code>disposeBefore()</code>}.
     *
     * @exception IndexOutOfBoundsException if any portion of
     * the requested data is not in the cache (including if <code>pos</code>
     * is in a block already disposed), or if either <code>pos</code> or
     * <code>len</code> is < 0.
     */
    public void writeToStream(OutputStream stream, long pos, long len)
        throws IOException {
        if (pos + len > length) {
            throw new IndexOutOfBoundsException("Argument out of cache");
        }
        if ((pos < 0) || (len < 0)) {
            throw new IndexOutOfBoundsException("Negative pos or len");
        }
        if (len == 0) {
            return;
        }

        long bufIndex = pos/BUFFER_LENGTH;
        if (bufIndex < cacheStart) {
            throw new IndexOutOfBoundsException("pos already disposed");
        }
        int offset = (int)(pos % BUFFER_LENGTH);

        byte[] buf = getCacheBlock(bufIndex++);
        while (len > 0) {
            if (buf == null) {
                buf = getCacheBlock(bufIndex++);
                offset = 0;
            }
            int nbytes = (int)Math.min(len, (long)(BUFFER_LENGTH - offset));
            stream.write(buf, offset, nbytes);
            buf = null;
            len -= nbytes;
        }
    }

    
Ensure that there is space to write a byte at the given position.

/**
     * Ensure that there is space to write a byte at the given position.
     */
    private void pad(long pos) throws IOException {
        long currIndex = cacheStart + cache.size() - 1;
        long lastIndex = pos/BUFFER_LENGTH;
        long numNewBuffers = lastIndex - currIndex;
        for (long i = 0; i < numNewBuffers; i++) {
            try {
                cache.add(new byte[BUFFER_LENGTH]);
            } catch (OutOfMemoryError e) {
                throw new IOException("No memory left for cache!");
            }
        }
    }

    
Overwrites and/or appends the cache from a byte array.
The length of the cache will be extended as needed to hold
the incoming data.

Params:
  • b – an array of bytes containing data to be written.
  • off – the starting offset withing the data array.
  • len – the number of bytes to be written.
  • pos – the cache position at which to begin writing.
Throws:
/**
     * Overwrites and/or appends the cache from a byte array.
     * The length of the cache will be extended as needed to hold
     * the incoming data.
     *
     * @param b an array of bytes containing data to be written.
     * @param off the starting offset withing the data array.
     * @param len the number of bytes to be written.
     * @param pos the cache position at which to begin writing.
     *
     * @exception NullPointerException if <code>b</code> is <code>null</code>.
     * @exception IndexOutOfBoundsException if <code>off</code>,
     * <code>len</code>, or <code>pos</code> are negative,
     * or if <code>off+len > b.length</code>.
     */
    public void write(byte[] b, int off, int len, long pos)
        throws IOException {
        if (b == null) {
            throw new NullPointerException("b == null!");
        }
        // Fix 4430357 - if off + len < 0, overflow occurred
        if ((off < 0) || (len < 0) || (pos < 0) ||
            (off + len > b.length) || (off + len < 0)) {
            throw new IndexOutOfBoundsException();
        }

        // Ensure there is space for the incoming data
        long lastPos = pos + len - 1;
        if (lastPos >= length) {
            pad(lastPos);
            length = lastPos + 1;
        }

        // Copy the data into the cache, block by block
        int offset = (int)(pos % BUFFER_LENGTH);
        while (len > 0) {
            byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
            int nbytes = Math.min(len, BUFFER_LENGTH - offset);
            System.arraycopy(b, off, buf, offset, nbytes);

            pos += nbytes;
            off += nbytes;
            len -= nbytes;
            offset = 0; // Always after the first time
        }
    }

    
Overwrites or appends a single byte to the cache.
The length of the cache will be extended as needed to hold
the incoming data.

Params:
  • b – an int whose 8 least significant bits
will be written.
  • pos – the cache position at which to begin writing.
Throws:
/**
     * Overwrites or appends a single byte to the cache.
     * The length of the cache will be extended as needed to hold
     * the incoming data.
     *
     * @param b an <code>int</code> whose 8 least significant bits
     * will be written.
     * @param pos the cache position at which to begin writing.
     *
     * @exception IndexOutOfBoundsException if <code>pos</code> is negative.
     */
    public void write(int b, long pos) throws IOException {
        if (pos < 0) {
            throw new ArrayIndexOutOfBoundsException("pos < 0");
        }

        // Ensure there is space for the incoming data
        if (pos >= length) {
            pad(pos);
            length = pos + 1;
        }

        // Insert the data.
        byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
        int offset = (int)(pos % BUFFER_LENGTH);
        buf[offset] = (byte)b;
    }

    
Returns the total length of data that has been cached,
regardless of whether any early blocks have been disposed.
This value will only ever increase.

/**
     * Returns the total length of data that has been cached,
     * regardless of whether any early blocks have been disposed.
     * This value will only ever increase.
     */
    public long getLength() {
        return length;
    }

    
Returns the single byte at the given position, as an
int.  Returns -1 if this position has
not been cached or has been disposed.

/**
     * Returns the single byte at the given position, as an
     * <code>int</code>.  Returns -1 if this position has
     * not been cached or has been disposed.
     */
    public int read(long pos) throws IOException {
        if (pos >= length) {
            return -1;
        }

        byte[] buf = getCacheBlock(pos/BUFFER_LENGTH);
        if (buf == null) {
            return -1;
        }

        return buf[(int)(pos % BUFFER_LENGTH)] & 0xff;
    }

    
Copy len bytes from the cache, starting
at cache position pos, into the array
b at offset off.

Throws:
  • NullPointerException – if b is null
  • IndexOutOfBoundsException – if off,
len or pos are negative or if
off + len > b.length or if any portion of the
requested data is not in the cache (including if
pos is in a block that has already been disposed).
/**
     * Copy <code>len</code> bytes from the cache, starting
     * at cache position <code>pos</code>, into the array
     * <code>b</code> at offset <code>off</code>.
     *
     * @exception NullPointerException if b is <code>null</code>
     * @exception IndexOutOfBoundsException if <code>off</code>,
     * <code>len</code> or <code>pos</code> are negative or if
     * <code>off + len > b.length</code> or if any portion of the
     * requested data is not in the cache (including if
     * <code>pos</code> is in a block that has already been disposed).
     */
    public void read(byte[] b, int off, int len, long pos)
        throws IOException {
        if (b == null) {
            throw new NullPointerException("b == null!");
        }
        // Fix 4430357 - if off + len < 0, overflow occurred
        if ((off < 0) || (len < 0) || (pos < 0) ||
            (off + len > b.length) || (off + len < 0)) {
            throw new IndexOutOfBoundsException();
        }
        if (pos + len > length) {
            throw new IndexOutOfBoundsException();
        }

        long index = pos/BUFFER_LENGTH;
        int offset = (int)pos % BUFFER_LENGTH;
        while (len > 0) {
            int nbytes = Math.min(len, BUFFER_LENGTH - offset);
            byte[] buf = getCacheBlock(index++);
            System.arraycopy(buf, offset, b, off, nbytes);

            len -= nbytes;
            off += nbytes;
            offset = 0; // Always after the first time
        }
    }

    
Free the blocks up to the position pos.
The byte at pos remains available.

Throws:
  • IndexOutOfBoundsException – if pos
is in a block that has already been disposed.
/**
     * Free the blocks up to the position <code>pos</code>.
     * The byte at <code>pos</code> remains available.
     *
     * @exception IndexOutOfBoundsException if <code>pos</code>
     * is in a block that has already been disposed.
     */
    public void disposeBefore(long pos) {
        long index = pos/BUFFER_LENGTH;
        if (index < cacheStart) {
            throw new IndexOutOfBoundsException("pos already disposed");
        }
        long numBlocks = Math.min(index - cacheStart, cache.size());
        for (long i = 0; i < numBlocks; i++) {
            cache.remove(0);
        }
        this.cacheStart = index;
    }

    
Erase the entire cache contents and reset the length to 0.
The cache object may subsequently be reused as though it had just
been allocated.

/**
     * Erase the entire cache contents and reset the length to 0.
     * The cache object may subsequently be reused as though it had just
     * been allocated.
     */
    public void reset() {
        cache.clear();
        cacheStart = 0;
        length = 0L;
    }
 }