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Java ports and bindings of the LZ4 compression algorithm and the xxHash hashing algorithm
package net.jpountz.lz4;
/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.Checksum;
import net.jpountz.util.SafeUtils;
import net.jpountz.xxhash.StreamingXXHash32;
import net.jpountz.xxhash.XXHashFactory;
/**
* Streaming LZ4 (not compatible with the LZ4 Frame format).
* This class compresses data into fixed-size blocks of compressed data.
* This class uses its own format and is not compatible with the LZ4 Frame format.
* For interoperability with other LZ4 tools, use {@link LZ4FrameOutputStream},
* which is compatible with the LZ4 Frame format. This class remains for backward compatibility.
* @see LZ4BlockInputStream
* @see LZ4FrameOutputStream
*/
public class LZ4BlockOutputStream extends FilterOutputStream {
static final byte[] MAGIC = new byte[] { 'L', 'Z', '4', 'B', 'l', 'o', 'c', 'k' };
static final int MAGIC_LENGTH = MAGIC.length;
static final int HEADER_LENGTH =
MAGIC_LENGTH // magic bytes
+ 1 // token
+ 4 // compressed length
+ 4 // decompressed length
+ 4; // checksum
static final int COMPRESSION_LEVEL_BASE = 10;
static final int MIN_BLOCK_SIZE = 64;
static final int MAX_BLOCK_SIZE = 1 << (COMPRESSION_LEVEL_BASE + 0x0F);
static final int COMPRESSION_METHOD_RAW = 0x10;
static final int COMPRESSION_METHOD_LZ4 = 0x20;
static final int DEFAULT_SEED = 0x9747b28c;
private static int compressionLevel(int blockSize) {
if (blockSize < MIN_BLOCK_SIZE) {
throw new IllegalArgumentException("blockSize must be >= " + MIN_BLOCK_SIZE + ", got " + blockSize);
} else if (blockSize > MAX_BLOCK_SIZE) {
throw new IllegalArgumentException("blockSize must be <= " + MAX_BLOCK_SIZE + ", got " + blockSize);
}
int compressionLevel = 32 - Integer.numberOfLeadingZeros(blockSize - 1); // ceil of log2
assert (1 << compressionLevel) >= blockSize;
assert blockSize * 2 > (1 << compressionLevel);
compressionLevel = Math.max(0, compressionLevel - COMPRESSION_LEVEL_BASE);
assert compressionLevel >= 0 && compressionLevel <= 0x0F;
return compressionLevel;
}
private final int blockSize;
private final int compressionLevel;
private final LZ4Compressor compressor;
private final Checksum checksum;
private final byte[] buffer;
private final byte[] compressedBuffer;
private final boolean syncFlush;
private boolean finished;
private int o;
/**
* Creates a new {@link OutputStream} with configurable block size. Large
* blocks require more memory at compression and decompression time but
* should improve the compression ratio.
*
* @param out the {@link OutputStream} to feed
* @param blockSize the maximum number of bytes to try to compress at once,
* must be >= 64 and <= 32 M
* @param compressor the {@link LZ4Compressor} instance to use to compress
* data
* @param checksum the {@link Checksum} instance to use to check data for
* integrity.
* @param syncFlush true if pending data should also be flushed on {@link #flush()}
*/
public LZ4BlockOutputStream(OutputStream out, int blockSize, LZ4Compressor compressor, Checksum checksum, boolean syncFlush) {
super(out);
this.blockSize = blockSize;
this.compressor = compressor;
this.checksum = checksum;
this.compressionLevel = compressionLevel(blockSize);
this.buffer = new byte[blockSize];
final int compressedBlockSize = HEADER_LENGTH + compressor.maxCompressedLength(blockSize);
this.compressedBuffer = new byte[compressedBlockSize];
this.syncFlush = syncFlush;
o = 0;
finished = false;
System.arraycopy(MAGIC, 0, compressedBuffer, 0, MAGIC_LENGTH);
}
/**
* Creates a new instance which checks stream integrity using
* {@link StreamingXXHash32} and doesn't sync flush.
*
* @param out the {@link OutputStream} to feed
* @param blockSize the maximum number of bytes to try to compress at once,
* must be >= 64 and <= 32 M
* @param compressor the {@link LZ4Compressor} instance to use to compress
* data
*
* @see #LZ4BlockOutputStream(OutputStream, int, LZ4Compressor, Checksum, boolean)
* @see StreamingXXHash32#asChecksum()
*/
public LZ4BlockOutputStream(OutputStream out, int blockSize, LZ4Compressor compressor) {
this(out, blockSize, compressor, XXHashFactory.fastestInstance().newStreamingHash32(DEFAULT_SEED).asChecksum(), false);
}
/**
* Creates a new instance which compresses with the standard LZ4 compression
* algorithm.
*
* @param out the {@link OutputStream} to feed
* @param blockSize the maximum number of bytes to try to compress at once,
* must be >= 64 and <= 32 M
*
* @see #LZ4BlockOutputStream(OutputStream, int, LZ4Compressor)
* @see LZ4Factory#fastCompressor()
*/
public LZ4BlockOutputStream(OutputStream out, int blockSize) {
this(out, blockSize, LZ4Factory.fastestInstance().fastCompressor());
}
/**
* Creates a new instance which compresses into blocks of 64 KB.
*
* @param out the {@link OutputStream} to feed
*
* @see #LZ4BlockOutputStream(OutputStream, int)
*/
public LZ4BlockOutputStream(OutputStream out) {
this(out, 1 << 16);
}
private void ensureNotFinished() {
if (finished) {
throw new IllegalStateException("This stream is already closed");
}
}
@Override
public void write(int b) throws IOException {
ensureNotFinished();
if (o == blockSize) {
flushBufferedData();
}
buffer[o++] = (byte) b;
}
@Override
public void write(byte[] b, int off, int len) throws IOException {
SafeUtils.checkRange(b, off, len);
ensureNotFinished();
while (o + len > blockSize) {
final int l = blockSize - o;
System.arraycopy(b, off, buffer, o, blockSize - o);
o = blockSize;
flushBufferedData();
off += l;
len -= l;
}
System.arraycopy(b, off, buffer, o, len);
o += len;
}
@Override
public void write(byte[] b) throws IOException {
ensureNotFinished();
write(b, 0, b.length);
}
@Override
public void close() throws IOException {
if (!finished) {
finish();
}
if (out != null) {
out.close();
out = null;
}
}
private void flushBufferedData() throws IOException {
if (o == 0) {
return;
}
checksum.reset();
checksum.update(buffer, 0, o);
final int check = (int) checksum.getValue();
int compressedLength = compressor.compress(buffer, 0, o, compressedBuffer, HEADER_LENGTH);
final int compressMethod;
if (compressedLength >= o) {
compressMethod = COMPRESSION_METHOD_RAW;
compressedLength = o;
System.arraycopy(buffer, 0, compressedBuffer, HEADER_LENGTH, o);
} else {
compressMethod = COMPRESSION_METHOD_LZ4;
}
compressedBuffer[MAGIC_LENGTH] = (byte) (compressMethod | compressionLevel);
writeIntLE(compressedLength, compressedBuffer, MAGIC_LENGTH + 1);
writeIntLE(o, compressedBuffer, MAGIC_LENGTH + 5);
writeIntLE(check, compressedBuffer, MAGIC_LENGTH + 9);
assert MAGIC_LENGTH + 13 == HEADER_LENGTH;
out.write(compressedBuffer, 0, HEADER_LENGTH + compressedLength);
o = 0;
}
/**
* Flushes this compressed {@link OutputStream}.
*
* If the stream has been created with syncFlush=true, pending
* data will be compressed and appended to the underlying {@link OutputStream}
* before calling {@link OutputStream#flush()} on the underlying stream.
* Otherwise, this method just flushes the underlying stream, so pending
* data might not be available for reading until {@link #finish()} or
* {@link #close()} is called.
*/
@Override
public void flush() throws IOException {
if (out != null) {
if (syncFlush) {
flushBufferedData();
}
out.flush();
}
}
/**
* Same as {@link #close()} except that it doesn't close the underlying stream.
* This can be useful if you want to keep on using the underlying stream.
*
* @throws IOException if an I/O error occurs.
*/
public void finish() throws IOException {
ensureNotFinished();
flushBufferedData();
compressedBuffer[MAGIC_LENGTH] = (byte) (COMPRESSION_METHOD_RAW | compressionLevel);
writeIntLE(0, compressedBuffer, MAGIC_LENGTH + 1);
writeIntLE(0, compressedBuffer, MAGIC_LENGTH + 5);
writeIntLE(0, compressedBuffer, MAGIC_LENGTH + 9);
assert MAGIC_LENGTH + 13 == HEADER_LENGTH;
out.write(compressedBuffer, 0, HEADER_LENGTH);
finished = true;
out.flush();
}
private static void writeIntLE(int i, byte[] buf, int off) {
buf[off++] = (byte) i;
buf[off++] = (byte) (i >>> 8);
buf[off++] = (byte) (i >>> 16);
buf[off++] = (byte) (i >>> 24);
}
@Override
public String toString() {
return getClass().getSimpleName() + "(out=" + out + ", blockSize=" + blockSize
+ ", compressor=" + compressor + ", checksum=" + checksum + ")";
}
}
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