    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>This implementation uses an internal buffer in order to handle
    033 * the back-references that are at the heart of the LZ77 algorithm.
    034 * The size of the buffer must be at least as big as the biggest
    035 * offset used in the compressed stream.  The current version of the
    036 * Snappy algorithm as defined by Google works on 32k blocks and
    037 * doesn't contain offsets bigger than 32k which is the default block
    038 * size used by this class.</p>
    039 *
    040 * <p>The raw Snappy format requires the uncompressed size to be
    041 * written at the beginning of the stream using a varint
    042 * representation, i.e. the number of bytes needed to write the
    043 * information is not known before the uncompressed size is
    044 * known. We've chosen to make the uncompressedSize a parameter of the
    045 * constructor in favor of buffering the whole output until the size
    046 * is known. When using the {@link FramedSnappyCompressorOutputStream}
    047 * this limitation is taken care of by the warpping framing
    048 * format.</p>
    049 *
    050 * @see <a href="https://github.com/google/snappy/blob/master/format_description.txt">Snappy compressed format description</a>
    051 * @since 1.14
    052 * @NotThreadSafe
    053 */
    054public class SnappyCompressorOutputStream extends CompressorOutputStream {
    055    // literal length is stored as (len - 1) either inside the tag
    056    // (six bits minus four flags) or in 1 to 4 bytes after the tag
    057    private static final int MAX_LITERAL_SIZE_WITHOUT_SIZE_BYTES = 60;
    058    private static final int MAX_LITERAL_SIZE_WITH_ONE_SIZE_BYTE = 1 << 8;
    059    private static final int MAX_LITERAL_SIZE_WITH_TWO_SIZE_BYTES = 1 << 16;
    060
    061    private static final int MAX_LITERAL_SIZE_WITH_THREE_SIZE_BYTES = 1 << 24;
    062
    063    private static final int ONE_SIZE_BYTE_MARKER = 60 << 2;
    064
    065    private static final int TWO_SIZE_BYTE_MARKER = 61 << 2;
    066
    067    private static final int THREE_SIZE_BYTE_MARKER = 62 << 2;
    068
    069    private static final int FOUR_SIZE_BYTE_MARKER = 63 << 2;
    070
    071    // Back-references ("copies") have their offset/size information
    072    // in two, three or five bytes.
    073    private static final int MIN_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE = 4;
    074
    075    private static final int MAX_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE = 11;
    076
    077    private static final int MAX_OFFSET_WITH_ONE_OFFSET_BYTE = 1 << 11 - 1;
    078
    079    private static final int MAX_OFFSET_WITH_TWO_OFFSET_BYTES = 1 << 16 - 1;
    080
    081    private static final int ONE_BYTE_COPY_TAG = 1;
    082
    083    private static final int TWO_BYTE_COPY_TAG = 2;
    084    private static final int FOUR_BYTE_COPY_TAG = 3;
    085    // technically the format could use shorter matches but with a
    086    // length of three the offset would be encoded as at least two
    087    // bytes in addition to the tag, so yield no compression at all
    088    private static final int MIN_MATCH_LENGTH = 4;
    089    // Snappy stores the match length in six bits of the tag
    090    private static final int MAX_MATCH_LENGTH = 64;
    091
    092    /**
    093     * Returns a builder correctly configured for the Snappy algorithm using the gven block size.
    094     * @param blockSize the block size.
    095     * @return a builder correctly configured for the Snappy algorithm using the gven block size
    096     */
    097    public static Parameters.Builder createParameterBuilder(final int blockSize) {
    098        // the max offset and max literal length defined by the format
    099        // are 2^32 - 1 and 2^32 respectively - with blockSize being
    100        // an integer we will never exceed that
    101        return Parameters.builder(blockSize)
    102            .withMinBackReferenceLength(MIN_MATCH_LENGTH)
    103            .withMaxBackReferenceLength(MAX_MATCH_LENGTH)
    104            .withMaxOffset(blockSize)
    105            .withMaxLiteralLength(blockSize);
    106    }
    107    private final LZ77Compressor compressor;
    108    private final OutputStream os;
    109    private final ByteUtils.ByteConsumer consumer;
    110
    111    // used in one-arg write method
    112    private final byte[] oneByte = new byte[1];
    113
    114    private boolean finished;
    115
    116    /**
    117     * Constructor using the default block size of 32k.
    118     *
    119     * @param os the outputstream to write compressed data to
    120     * @param uncompressedSize the uncompressed size of data
    121     * @throws IOException if writing of the size fails
    122     */
    123    public SnappyCompressorOutputStream(final OutputStream os, final long uncompressedSize) throws IOException {
    124        this(os, uncompressedSize, SnappyCompressorInputStream.DEFAULT_BLOCK_SIZE);
    125    }
    126
    127    /**
    128     * Constructor using a configurable block size.
    129     *
    130     * @param os the outputstream to write compressed data to
    131     * @param uncompressedSize the uncompressed size of data
    132     * @param blockSize the block size used - must be a power of two
    133     * @throws IOException if writing of the size fails
    134     */
    135    public SnappyCompressorOutputStream(final OutputStream os, final long uncompressedSize, final int blockSize)
    136        throws IOException {
    137        this(os, uncompressedSize, createParameterBuilder(blockSize).build());
    138    }
    139
    140    /**
    141     * Constructor providing full control over the underlying LZ77 compressor.
    142     *
    143     * @param os the outputstream to write compressed data to
    144     * @param uncompressedSize the uncompressed size of data
    145     * @param params the parameters to use by the compressor - note
    146     * that the format itself imposes some limits like a maximum match
    147     * length of 64 bytes
    148     * @throws IOException if writing of the size fails
    149     */
    150    public SnappyCompressorOutputStream(final OutputStream os, final long uncompressedSize, final Parameters params)
    151        throws IOException {
    152        this.os = os;
    153        consumer = new ByteUtils.OutputStreamByteConsumer(os);
    154        compressor = new LZ77Compressor(params, block -> {
    155            switch (block.getType()) {
    156            case LITERAL:
    157                writeLiteralBlock((LZ77Compressor.LiteralBlock) block);
    158                break;
    159            case BACK_REFERENCE:
    160                writeBackReference((LZ77Compressor.BackReference) block);
    161                break;
    162            case EOD:
    163                break;
    164            }
    165        });
    166        writeUncompressedSize(uncompressedSize);
    167    }
    168
    169    @Override
    170    public void close() throws IOException {
    171        try {
    172            finish();
    173        } finally {
    174            os.close();
    175        }
    176    }
    177
    178    /**
    179     * Compresses all remaining data and writes it to the stream,
    180     * doesn't close the underlying stream.
    181     * @throws IOException if an error occurs
    182     */
    183    public void finish() throws IOException {
    184        if (!finished) {
    185            compressor.finish();
    186            finished = true;
    187        }
    188    }
    189
    190    @Override
    191    public void write(final byte[] data, final int off, final int len) throws IOException {
    192        compressor.compress(data, off, len);
    193    }
    194
    195    @Override
    196    public void write(final int b) throws IOException {
    197        oneByte[0] = (byte) (b & 0xff);
    198        write(oneByte);
    199    }
    200    private void writeBackReference(final LZ77Compressor.BackReference block) throws IOException {
    201        final int len = block.getLength();
    202        final int offset = block.getOffset();
    203        if (len >= MIN_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE && len <= MAX_MATCH_LENGTH_WITH_ONE_OFFSET_BYTE
    204            && offset <= MAX_OFFSET_WITH_ONE_OFFSET_BYTE) {
    205            writeBackReferenceWithOneOffsetByte(len, offset);
    206        } else if (offset < MAX_OFFSET_WITH_TWO_OFFSET_BYTES) {
    207            writeBackReferenceWithTwoOffsetBytes(len, offset);
    208        } else {
    209            writeBackReferenceWithFourOffsetBytes(len, offset);
    210        }
    211    }
    212    private void writeBackReferenceWithFourOffsetBytes(final int len, final int offset) throws IOException {
    213        writeBackReferenceWithLittleEndianOffset(FOUR_BYTE_COPY_TAG, 4, len, offset);
    214    }
    215    private void writeBackReferenceWithLittleEndianOffset(final int tag, final int offsetBytes, final int len, final int offset)
    216        throws IOException {
    217        os.write(tag | ((len - 1) << 2));
    218        writeLittleEndian(offsetBytes, offset);
    219    }
    220
    221    private void writeBackReferenceWithOneOffsetByte(final int len, final int offset) throws IOException {
    222        os.write(ONE_BYTE_COPY_TAG | ((len - 4) << 2) | ((offset & 0x700) >> 3));
    223        os.write(offset & 0xff);
    224    }
    225    private void writeBackReferenceWithTwoOffsetBytes(final int len, final int offset) throws IOException {
    226        writeBackReferenceWithLittleEndianOffset(TWO_BYTE_COPY_TAG, 2, len, offset);
    227    }
    228    private void writeLiteralBlock(final LZ77Compressor.LiteralBlock block) throws IOException {
    229        final int len = block.getLength();
    230        if (len <= MAX_LITERAL_SIZE_WITHOUT_SIZE_BYTES) {
    231            writeLiteralBlockNoSizeBytes(block, len);
    232        } else if (len <= MAX_LITERAL_SIZE_WITH_ONE_SIZE_BYTE) {
    233            writeLiteralBlockOneSizeByte(block, len);
    234        } else if (len <= MAX_LITERAL_SIZE_WITH_TWO_SIZE_BYTES) {
    235            writeLiteralBlockTwoSizeBytes(block, len);
    236        } else if (len <= MAX_LITERAL_SIZE_WITH_THREE_SIZE_BYTES) {
    237            writeLiteralBlockThreeSizeBytes(block, len);
    238        } else {
    239            writeLiteralBlockFourSizeBytes(block, len);
    240        }
    241    }
    242
    243    private void writeLiteralBlockFourSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
    244        writeLiteralBlockWithSize(FOUR_SIZE_BYTE_MARKER, 4, len, block);
    245    }
    246
    247    private void writeLiteralBlockNoSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
    248        writeLiteralBlockWithSize(len - 1 << 2, 0, len, block);
    249    }
    250
    251    private void writeLiteralBlockOneSizeByte(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
    252        writeLiteralBlockWithSize(ONE_SIZE_BYTE_MARKER, 1, len, block);
    253    }
    254
    255    private void writeLiteralBlockThreeSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
    256        writeLiteralBlockWithSize(THREE_SIZE_BYTE_MARKER, 3, len, block);
    257    }
    258
    259    private void writeLiteralBlockTwoSizeBytes(final LZ77Compressor.LiteralBlock block, final int len) throws IOException {
    260        writeLiteralBlockWithSize(TWO_SIZE_BYTE_MARKER, 2, len, block);
    261    }
    262
    263    private void writeLiteralBlockWithSize(final int tagByte, final int sizeBytes, final int len, final LZ77Compressor.LiteralBlock block)
    264        throws IOException {
    265        os.write(tagByte);
    266        writeLittleEndian(sizeBytes, len - 1);
    267        os.write(block.getData(), block.getOffset(), len);
    268    }
    269    private void writeLittleEndian(final int numBytes, final int num) throws IOException {
    270        ByteUtils.toLittleEndian(consumer, num, numBytes);
    271    }
    272
    273    private void writeUncompressedSize(long uncompressedSize) throws IOException {
    274        boolean more;
    275        do {
    276            int currentByte = (int) (uncompressedSize & 0x7F);
    277            more = uncompressedSize > currentByte;
    278            if (more) {
    279                currentByte |= 0x80;
    280            }
    281            os.write(currentByte);
    282            uncompressedSize >>= 7;
    283        } while (more);
    284    }
    285}