Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.commons.compress.compressors.snappy;
020
021import java.io.IOException;
022import java.io.OutputStream;
023
024import org.apache.commons.compress.compressors.CompressorOutputStream;
025import org.apache.commons.compress.compressors.lz77support.LZ77Compressor;
026import org.apache.commons.compress.compressors.lz77support.Parameters;
027import org.apache.commons.compress.utils.ByteUtils;
028
029/**
030 * CompressorOutputStream for the raw Snappy format.
031 *
032 * <p>
033 * This implementation uses an internal buffer in order to handle the back-references that are at the heart of the LZ77 algorithm. The size of the buffer must
034 * be at least as big as the biggest offset used in the compressed stream. The current version of the Snappy algorithm as defined by Google works on 32k blocks
035 * and doesn't contain offsets bigger than 32k which is the default block size used by this class.
036 * </p>
037 *
038 * <p>
039 * The raw Snappy format requires the uncompressed size to be written at the beginning of the stream using a varint representation, i.e. the number of bytes
040 * needed to write the information is not known before the uncompressed size is known. We've chosen to make the uncompressedSize a parameter of the constructor
041 * in favor of buffering the whole output until the size is known. When using the {@link FramedSnappyCompressorOutputStream} this limitation is taken care of by
042 * the warpping framing format.
043 * </p>
044 *
045 * @see <a href="https://github.com/google/snappy/blob/master/format_description.txt">Snappy compressed format description</a>
046 * @since 1.14
047 * @NotThreadSafe
048 */
049public class SnappyCompressorOutputStream extends CompressorOutputStream<OutputStream> {
050    // literal length is stored as (len - 1) either inside the tag
051    // (six bits minus four flags) or in 1 to 4 bytes after the tag
052    private static final int MAX_LITERAL_SIZE_WITHOUT_SIZE_BYTES = 60;
053    private static final int MAX_LITERAL_SIZE_WITH_ONE_SIZE_BYTE = 1 << 8;
054    private static final int MAX_LITERAL_SIZE_WITH_TWO_SIZE_BYTES = 1 << 16;
055
056    private static final int MAX_LITERAL_SIZE_WITH_THREE_SIZE_BYTES = 1 << 24;
057
058    private static final int ONE_SIZE_BYTE_MARKER = 60 << 2;
059
060    private static final int TWO_SIZE_BYTE_MARKER = 61 << 2;
061
062    private static final int THREE_SIZE_BYTE_MARKER = 62 << 2;
063
064    private static final int FOUR_SIZE_BYTE_MARKER = 63 << 2;
065
066    // Back-references ("copies") have their offset/size information
067    // in two, three or five bytes.
068    private static final int MIN_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE = 4;
069
070    private static final int MAX_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE = 11;
071
072    private static final int MAX_OFFSET_WITH_ONE_OFFSET_BYTE = 1 << 11 - 1;
073
074    private static final int MAX_OFFSET_WITH_TWO_OFFSET_BYTES = 1 << 16 - 1;
075
076    private static final int ONE_BYTE_COPY_TAG = 1;
077
078    private static final int TWO_BYTE_COPY_TAG = 2;
079    private static final int FOUR_BYTE_COPY_TAG = 3;
080    // technically the format could use shorter matches but with a
081    // length of three the offset would be encoded as at least two
082    // bytes in addition to the tag, so yield no compression at all
083    private static final int MIN_MATCH_LENGTH = 4;
084    // Snappy stores the match length in six bits of the tag
085    private static final int MAX_MATCH_LENGTH = 64;
086
087    /**
088     * Returns a builder correctly configured for the Snappy algorithm using the gven block size.
089     *
090     * @param blockSize the block size.
091     * @return a builder correctly configured for the Snappy algorithm using the gven block size
092     */
093    public static Parameters.Builder createParameterBuilder(final int blockSize) {
094        // the max offset and max literal length defined by the format
095        // are 2^32 - 1 and 2^32 respectively - with blockSize being
096        // an integer we will never exceed that
097        return Parameters.builder(blockSize).withMinBackReferenceLength(MIN_MATCH_LENGTH).withMaxBackReferenceLength(MAX_MATCH_LENGTH).withMaxOffset(blockSize)
098                .withMaxLiteralLength(blockSize);
099    }
100
101    private final LZ77Compressor compressor;
102    private final ByteUtils.ByteConsumer consumer;
103
104    // used in one-arg write method
105    private final byte[] oneByte = new byte[1];
106
107    private boolean finished;
108
109    /**
110     * Constructor using the default block size of 32k.
111     *
112     * @param os               the outputstream to write compressed data to
113     * @param uncompressedSize the uncompressed size of data
114     * @throws IOException if writing of the size fails
115     */
116    public SnappyCompressorOutputStream(final OutputStream os, final long uncompressedSize) throws IOException {
117        this(os, uncompressedSize, SnappyCompressorInputStream.DEFAULT_BLOCK_SIZE);
118    }
119
120    /**
121     * Constructor using a configurable block size.
122     *
123     * @param os               the outputstream to write compressed data to
124     * @param uncompressedSize the uncompressed size of data
125     * @param blockSize        the block size used - must be a power of two
126     * @throws IOException if writing of the size fails
127     */
128    public SnappyCompressorOutputStream(final OutputStream os, final long uncompressedSize, final int blockSize) throws IOException {
129        this(os, uncompressedSize, createParameterBuilder(blockSize).build());
130    }
131
132    /**
133     * Constructor providing full control over the underlying LZ77 compressor.
134     *
135     * @param out               the outputstream to write compressed data to
136     * @param uncompressedSize the uncompressed size of data
137     * @param params           the parameters to use by the compressor - note that the format itself imposes some limits like a maximum match length of 64 bytes
138     * @throws IOException if writing of the size fails
139     */
140    public SnappyCompressorOutputStream(final OutputStream out, final long uncompressedSize, final Parameters params) throws IOException {
141        super(out);
142        consumer = new ByteUtils.OutputStreamByteConsumer(out);
143        compressor = new LZ77Compressor(params, block -> {
144            switch (block.getType()) {
145            case LITERAL:
146                writeLiteralBlock((LZ77Compressor.LiteralBlock) block);
147                break;
148            case BACK_REFERENCE:
149                writeBackReference((LZ77Compressor.BackReference) block);
150                break;
151            case EOD:
152                break;
153            }
154        });
155        writeUncompressedSize(uncompressedSize);
156    }
157
158    @Override
159    public void close() throws IOException {
160        try {
161            finish();
162        } finally {
163            out.close();
164        }
165    }
166
167    /**
168     * Compresses all remaining data and writes it to the stream, doesn't close the underlying stream.
169     *
170     * @throws IOException if an error occurs
171     */
172    public void finish() throws IOException {
173        if (!finished) {
174            compressor.finish();
175            finished = true;
176        }
177    }
178
179    @Override
180    public void write(final byte[] data, final int off, final int len) throws IOException {
181        compressor.compress(data, off, len);
182    }
183
184    @Override
185    public void write(final int b) throws IOException {
186        oneByte[0] = (byte) (b & 0xff);
187        write(oneByte);
188    }
189
190    private void writeBackReference(final LZ77Compressor.BackReference block) throws IOException {
191        final int len = block.getLength();
192        final int offset = block.getOffset();
193        if (len >= MIN_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE && len <= MAX_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE && offset <= MAX_OFFSET_WITH_ONE_OFFSET_BYTE) {
194            writeBackReferenceWithOneOffsetByte(len, offset);
195        } else if (offset < MAX_OFFSET_WITH_TWO_OFFSET_BYTES) {
196            writeBackReferenceWithTwoOffsetBytes(len, offset);
197        } else {
198            writeBackReferenceWithFourOffsetBytes(len, offset);
199        }
200    }
201
202    private void writeBackReferenceWithFourOffsetBytes(final int len, final int offset) throws IOException {
203        writeBackReferenceWithLittleEndianOffset(FOUR_BYTE_COPY_TAG, 4, len, offset);
204    }
205
206    private void writeBackReferenceWithLittleEndianOffset(final int tag, final int offsetBytes, final int len, final int offset) throws IOException {
207        out.write(tag | len - 1 << 2);
208        writeLittleEndian(offsetBytes, offset);
209    }
210
211    private void writeBackReferenceWithOneOffsetByte(final int len, final int offset) throws IOException {
212        out.write(ONE_BYTE_COPY_TAG | len - 4 << 2 | (offset & 0x700) >> 3);
213        out.write(offset & 0xff);
214    }
215
216    private void writeBackReferenceWithTwoOffsetBytes(final int len, final int offset) throws IOException {
217        writeBackReferenceWithLittleEndianOffset(TWO_BYTE_COPY_TAG, 2, len, offset);
218    }
219
220    private void writeLiteralBlock(final LZ77Compressor.LiteralBlock block) throws IOException {
221        final int len = block.getLength();
222        if (len <= MAX_LITERAL_SIZE_WITHOUT_SIZE_BYTES) {
223            writeLiteralBlockNoSizeBytes(block, len);
224        } else if (len <= MAX_LITERAL_SIZE_WITH_ONE_SIZE_BYTE) {
225            writeLiteralBlockOneSizeByte(block, len);
226        } else if (len <= MAX_LITERAL_SIZE_WITH_TWO_SIZE_BYTES) {
227            writeLiteralBlockTwoSizeBytes(block, len);
228        } else if (len <= MAX_LITERAL_SIZE_WITH_THREE_SIZE_BYTES) {
229            writeLiteralBlockThreeSizeBytes(block, len);
230        } else {
231            writeLiteralBlockFourSizeBytes(block, len);
232        }
233    }
234
235    private void writeLiteralBlockFourSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
236        writeLiteralBlockWithSize(FOUR_SIZE_BYTE_MARKER, 4, len, block);
237    }
238
239    private void writeLiteralBlockNoSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
240        writeLiteralBlockWithSize(len - 1 << 2, 0, len, block);
241    }
242
243    private void writeLiteralBlockOneSizeByte(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
244        writeLiteralBlockWithSize(ONE_SIZE_BYTE_MARKER, 1, len, block);
245    }
246
247    private void writeLiteralBlockThreeSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
248        writeLiteralBlockWithSize(THREE_SIZE_BYTE_MARKER, 3, len, block);
249    }
250
251    private void writeLiteralBlockTwoSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
252        writeLiteralBlockWithSize(TWO_SIZE_BYTE_MARKER, 2, len, block);
253    }
254
255    private void writeLiteralBlockWithSize(final int tagByte, final int sizeBytes, final int len, final LZ77Compressor.LiteralBlock block) throws IOException {
256        out.write(tagByte);
257        writeLittleEndian(sizeBytes, len - 1);
258        out.write(block.getData(), block.getOffset(), len);
259    }
260
261    private void writeLittleEndian(final int numBytes, final int num) throws IOException {
262        ByteUtils.toLittleEndian(consumer, num, numBytes);
263    }
264
265    private void writeUncompressedSize(long uncompressedSize) throws IOException {
266        boolean more;
267        do {
268            int currentByte = (int) (uncompressedSize & 0x7F);
269            more = uncompressedSize > currentByte;
270            if (more) {
271                currentByte |= 0x80;
272            }
273            out.write(currentByte);
274            uncompressedSize >>= 7;
275        } while (more);
276    }
277}