1 // Copyright 2005 and onwards Google Inc. 2 // 3 // Redistribution and use in source and binary forms, with or without 4 // modification, are permitted provided that the following conditions are 5 // met: 6 // 7 // * Redistributions of source code must retain the above copyright 8 // notice, this list of conditions and the following disclaimer. 9 // * Redistributions in binary form must reproduce the above 10 // copyright notice, this list of conditions and the following disclaimer 11 // in the documentation and/or other materials provided with the 12 // distribution. 13 // * Neither the name of Google Inc. nor the names of its 14 // contributors may be used to endorse or promote products derived from 15 // this software without specific prior written permission. 16 // 17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 18 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 19 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 20 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 21 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 22 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 23 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 27 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 // 29 // A light-weight compression algorithm. It is designed for speed of 30 // compression and decompression, rather than for the utmost in space 31 // savings. 32 // 33 // For getting better compression ratios when you are compressing data 34 // with long repeated sequences or compressing data that is similar to 35 // other data, while still compressing fast, you might look at first 36 // using BMDiff and then compressing the output of BMDiff with 37 // Snappy. 38 39 #ifndef UTIL_SNAPPY_SNAPPY_H__ 40 #define UTIL_SNAPPY_SNAPPY_H__ 41 42 #include <stddef.h> 43 #include <string> 44 45 #include "snappy-stubs-public.h" 46 47 namespace snappy { 48 class Source; 49 class Sink; 50 51 // ------------------------------------------------------------------------ 52 // Generic compression/decompression routines. 53 // ------------------------------------------------------------------------ 54 55 // Compress the bytes read from "*source" and append to "*sink". Return the 56 // number of bytes written. 57 size_t Compress(Source* source, Sink* sink); 58 59 // Find the uncompressed length of the given stream, as given by the header. 60 // Note that the true length could deviate from this; the stream could e.g. 61 // be truncated. 62 // 63 // Also note that this leaves "*source" in a state that is unsuitable for 64 // further operations, such as RawUncompress(). You will need to rewind 65 // or recreate the source yourself before attempting any further calls. 66 bool GetUncompressedLength(Source* source, uint32* result); 67 68 // ------------------------------------------------------------------------ 69 // Higher-level string based routines (should be sufficient for most users) 70 // ------------------------------------------------------------------------ 71 72 // Sets "*output" to the compressed version of "input[0,input_length-1]". 73 // Original contents of *output are lost. 74 // 75 // REQUIRES: "input[]" is not an alias of "*output". 76 size_t Compress(const char* input, size_t input_length, string* output); 77 78 // Decompresses "compressed[0,compressed_length-1]" to "*uncompressed". 79 // Original contents of "*uncompressed" are lost. 80 // 81 // REQUIRES: "compressed[]" is not an alias of "*uncompressed". 82 // 83 // returns false if the message is corrupted and could not be decompressed 84 bool Uncompress(const char* compressed, size_t compressed_length, 85 string* uncompressed); 86 87 88 // ------------------------------------------------------------------------ 89 // Lower-level character array based routines. May be useful for 90 // efficiency reasons in certain circumstances. 91 // ------------------------------------------------------------------------ 92 93 // REQUIRES: "compressed" must point to an area of memory that is at 94 // least "MaxCompressedLength(input_length)" bytes in length. 95 // 96 // Takes the data stored in "input[0..input_length]" and stores 97 // it in the array pointed to by "compressed". 98 // 99 // "*compressed_length" is set to the length of the compressed output. 100 // 101 // Example: 102 // char* output = new char[snappy::MaxCompressedLength(input_length)]; 103 // size_t output_length; 104 // RawCompress(input, input_length, output, &output_length); 105 // ... Process(output, output_length) ... 106 // delete [] output; 107 void RawCompress(const char* input, 108 size_t input_length, 109 char* compressed, 110 size_t* compressed_length); 111 112 // Given data in "compressed[0..compressed_length-1]" generated by 113 // calling the Snappy::Compress routine, this routine 114 // stores the uncompressed data to 115 // uncompressed[0..GetUncompressedLength(compressed)-1] 116 // returns false if the message is corrupted and could not be decrypted 117 bool RawUncompress(const char* compressed, size_t compressed_length, 118 char* uncompressed); 119 120 // Given data from the byte source 'compressed' generated by calling 121 // the Snappy::Compress routine, this routine stores the uncompressed 122 // data to 123 // uncompressed[0..GetUncompressedLength(compressed,compressed_length)-1] 124 // returns false if the message is corrupted and could not be decrypted 125 bool RawUncompress(Source* compressed, char* uncompressed); 126 127 // Given data in "compressed[0..compressed_length-1]" generated by 128 // calling the Snappy::Compress routine, this routine 129 // stores the uncompressed data to the iovec "iov". The number of physical 130 // buffers in "iov" is given by iov_cnt and their cumulative size 131 // must be at least GetUncompressedLength(compressed). The individual buffers 132 // in "iov" must not overlap with each other. 133 // 134 // returns false if the message is corrupted and could not be decrypted 135 bool RawUncompressToIOVec(const char* compressed, size_t compressed_length, 136 const struct iovec* iov, size_t iov_cnt); 137 138 // Given data from the byte source 'compressed' generated by calling 139 // the Snappy::Compress routine, this routine stores the uncompressed 140 // data to the iovec "iov". The number of physical 141 // buffers in "iov" is given by iov_cnt and their cumulative size 142 // must be at least GetUncompressedLength(compressed). The individual buffers 143 // in "iov" must not overlap with each other. 144 // 145 // returns false if the message is corrupted and could not be decrypted 146 bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov, 147 size_t iov_cnt); 148 149 // Returns the maximal size of the compressed representation of 150 // input data that is "source_bytes" bytes in length; 151 size_t MaxCompressedLength(size_t source_bytes); 152 153 // REQUIRES: "compressed[]" was produced by RawCompress() or Compress() 154 // Returns true and stores the length of the uncompressed data in 155 // *result normally. Returns false on parsing error. 156 // This operation takes O(1) time. 157 bool GetUncompressedLength(const char* compressed, size_t compressed_length, 158 size_t* result); 159 160 // Returns true iff the contents of "compressed[]" can be uncompressed 161 // successfully. Does not return the uncompressed data. Takes 162 // time proportional to compressed_length, but is usually at least 163 // a factor of four faster than actual decompression. 164 bool IsValidCompressedBuffer(const char* compressed, 165 size_t compressed_length); 166 167 // The size of a compression block. Note that many parts of the compression 168 // code assumes that kBlockSize <= 65536; in particular, the hash table 169 // can only store 16-bit offsets, and EmitCopy() also assumes the offset 170 // is 65535 bytes or less. Note also that if you change this, it will 171 // affect the framing format (see framing_format.txt). 172 // 173 // Note that there might be older data around that is compressed with larger 174 // block sizes, so the decompression code should not rely on the 175 // non-existence of long backreferences. 176 static const int kBlockLog = 16; 177 static const size_t kBlockSize = 1 << kBlockLog; 178 179 static const int kMaxHashTableBits = 14; 180 static const size_t kMaxHashTableSize = 1 << kMaxHashTableBits; 181 } // end namespace snappy 182 183 184 #endif // UTIL_SNAPPY_SNAPPY_H__ 185