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Apache Commons Compress software defines an API for working with
compression and archive formats. These include: bzip2, gzip, pack200,
lzma, xz, Snappy, traditional Unix Compress, DEFLATE, DEFLATE64, LZ4,
Brotli, Zstandard and ar, cpio, jar, tar, zip, dump, 7z, arj.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
package org.apache.commons.compress.compressors.gzip;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.charset.StandardCharsets;
import java.util.zip.CRC32;
import java.util.zip.Deflater;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;
import org.apache.commons.compress.compressors.CompressorOutputStream;
/**
* Compressed output stream using the gzip format. This implementation improves
* over the standard {@link GZIPOutputStream} class by allowing
* the configuration of the compression level and the header metadata (file name,
* comment, modification time, operating system and extra flags).
*
* @see GZIP File Format Specification
*/
public class GzipCompressorOutputStream extends CompressorOutputStream {
/** Header flag indicating a file name follows the header */
private static final int FNAME = 1 << 3;
/** Header flag indicating a comment follows the header */
private static final int FCOMMENT = 1 << 4;
/** The underlying stream */
private final OutputStream out;
/** Deflater used to compress the data */
private final Deflater deflater;
/** The buffer receiving the compressed data from the deflater */
private final byte[] deflateBuffer;
/** Indicates if the stream has been closed */
private boolean closed;
/** The checksum of the uncompressed data */
private final CRC32 crc = new CRC32();
/**
* Creates a gzip compressed output stream with the default parameters.
* @param out the stream to compress to
* @throws IOException if writing fails
*/
public GzipCompressorOutputStream(final OutputStream out) throws IOException {
this(out, new GzipParameters());
}
/**
* Creates a gzip compressed output stream with the specified parameters.
* @param out the stream to compress to
* @param parameters the parameters to use
* @throws IOException if writing fails
*
* @since 1.7
*/
public GzipCompressorOutputStream(final OutputStream out, final GzipParameters parameters) throws IOException {
this.out = out;
this.deflater = new Deflater(parameters.getCompressionLevel(), true);
this.deflater.setStrategy(parameters.getDeflateStrategy());
this.deflateBuffer = new byte[parameters.getBufferSize()];
writeHeader(parameters);
}
@Override
public void close() throws IOException {
if (!closed) {
try {
finish();
} finally {
deflater.end();
out.close();
closed = true;
}
}
}
private void deflate() throws IOException {
final int length = deflater.deflate(deflateBuffer, 0, deflateBuffer.length);
if (length > 0) {
out.write(deflateBuffer, 0, length);
}
}
/**
* Finishes writing compressed data to the underlying stream without closing it.
*
* @since 1.7
* @throws IOException on error
*/
public void finish() throws IOException {
if (!deflater.finished()) {
deflater.finish();
while (!deflater.finished()) {
deflate();
}
writeTrailer();
}
}
/**
* {@inheritDoc}
*
* @since 1.7
*/
@Override
public void flush() throws IOException {
out.flush();
}
/**
* Gets the bytes encoded in the {@value GzipUtils#GZIP_ENCODING} Charset.
*
* If the string cannot be encoded directly with {@value GzipUtils#GZIP_ENCODING}, then use URI-style percent encoding.
*
*
* @param string The string to encode.
* @return
* @throws IOException
*/
private byte[] getBytes(final String string) throws IOException {
if (GzipUtils.GZIP_ENCODING.newEncoder().canEncode(string)) {
return string.getBytes(GzipUtils.GZIP_ENCODING);
}
try {
return new URI(null, null, string, null).toASCIIString().getBytes(StandardCharsets.US_ASCII);
} catch (final URISyntaxException e) {
throw new IOException(string, e);
}
}
/**
* {@inheritDoc}
*
* @since 1.1
*/
@Override
public void write(final byte[] buffer) throws IOException {
write(buffer, 0, buffer.length);
}
/**
* {@inheritDoc}
*
* @since 1.1
*/
@Override
public void write(final byte[] buffer, final int offset, final int length) throws IOException {
if (deflater.finished()) {
throw new IOException("Cannot write more data, the end of the compressed data stream has been reached");
}
if (length > 0) {
deflater.setInput(buffer, offset, length);
while (!deflater.needsInput()) {
deflate();
}
crc.update(buffer, offset, length);
}
}
@Override
public void write(final int b) throws IOException {
write(new byte[] { (byte) (b & 0xff) }, 0, 1);
}
private void writeHeader(final GzipParameters parameters) throws IOException {
final String filename = parameters.getFilename();
final String comment = parameters.getComment();
final ByteBuffer buffer = ByteBuffer.allocate(10);
buffer.order(ByteOrder.LITTLE_ENDIAN);
buffer.putShort((short) GZIPInputStream.GZIP_MAGIC);
buffer.put((byte) Deflater.DEFLATED); // compression method (8: deflate)
buffer.put((byte) ((filename != null ? FNAME : 0) | (comment != null ? FCOMMENT : 0))); // flags
buffer.putInt((int) (parameters.getModificationTime() / 1000));
// extra flags
final int compressionLevel = parameters.getCompressionLevel();
if (compressionLevel == Deflater.BEST_COMPRESSION) {
buffer.put((byte) 2);
} else if (compressionLevel == Deflater.BEST_SPEED) {
buffer.put((byte) 4);
} else {
buffer.put((byte) 0);
}
buffer.put((byte) parameters.getOperatingSystem());
out.write(buffer.array());
if (filename != null) {
out.write(getBytes(filename));
out.write(0);
}
if (comment != null) {
out.write(getBytes(comment));
out.write(0);
}
}
private void writeTrailer() throws IOException {
final ByteBuffer buffer = ByteBuffer.allocate(8);
buffer.order(ByteOrder.LITTLE_ENDIAN);
buffer.putInt((int) crc.getValue());
buffer.putInt(deflater.getTotalIn());
out.write(buffer.array());
}
}