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