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