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 THIRD_PARTY_SNAPPY_SNAPPY_H__
40#define THIRD_PARTY_SNAPPY_SNAPPY_H__
41
42#include <cstddef>
43#include <string>
44
45#include "snappy-stubs-public.h"
46
47namespace 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 "*compressed" to the compressed version of "input[0,input_length-1]".
73 // Original contents of *compressed are lost.
74 //
75 // REQUIRES: "input[]" is not an alias of "*compressed".
76 size_t Compress(const char* input, size_t input_length,
77 std::string* compressed);
78
79 // Decompresses "compressed[0,compressed_length-1]" to "*uncompressed".
80 // Original contents of "*uncompressed" are lost.
81 //
82 // REQUIRES: "compressed[]" is not an alias of "*uncompressed".
83 //
84 // returns false if the message is corrupted and could not be decompressed
85 bool Uncompress(const char* compressed, size_t compressed_length,
86 std::string* uncompressed);
87
88 // Decompresses "compressed" to "*uncompressed".
89 //
90 // returns false if the message is corrupted and could not be decompressed
91 bool Uncompress(Source* compressed, Sink* uncompressed);
92
93 // This routine uncompresses as much of the "compressed" as possible
94 // into sink. It returns the number of valid bytes added to sink
95 // (extra invalid bytes may have been added due to errors; the caller
96 // should ignore those). The emitted data typically has length
97 // GetUncompressedLength(), but may be shorter if an error is
98 // encountered.
99 size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed);
100
101 // ------------------------------------------------------------------------
102 // Lower-level character array based routines. May be useful for
103 // efficiency reasons in certain circumstances.
104 // ------------------------------------------------------------------------
105
106 // REQUIRES: "compressed" must point to an area of memory that is at
107 // least "MaxCompressedLength(input_length)" bytes in length.
108 //
109 // Takes the data stored in "input[0..input_length]" and stores
110 // it in the array pointed to by "compressed".
111 //
112 // "*compressed_length" is set to the length of the compressed output.
113 //
114 // Example:
115 // char* output = new char[snappy::MaxCompressedLength(input_length)];
116 // size_t output_length;
117 // RawCompress(input, input_length, output, &output_length);
118 // ... Process(output, output_length) ...
119 // delete [] output;
120 void RawCompress(const char* input,
121 size_t input_length,
122 char* compressed,
123 size_t* compressed_length);
124
125 // Given data in "compressed[0..compressed_length-1]" generated by
126 // calling the Snappy::Compress routine, this routine
127 // stores the uncompressed data to
128 // uncompressed[0..GetUncompressedLength(compressed)-1]
129 // returns false if the message is corrupted and could not be decrypted
130 bool RawUncompress(const char* compressed, size_t compressed_length,
131 char* uncompressed);
132
133 // Given data from the byte source 'compressed' generated by calling
134 // the Snappy::Compress routine, this routine stores the uncompressed
135 // data to
136 // uncompressed[0..GetUncompressedLength(compressed,compressed_length)-1]
137 // returns false if the message is corrupted and could not be decrypted
138 bool RawUncompress(Source* compressed, char* uncompressed);
139
140 // Given data in "compressed[0..compressed_length-1]" generated by
141 // calling the Snappy::Compress routine, this routine
142 // stores the uncompressed data to the iovec "iov". The number of physical
143 // buffers in "iov" is given by iov_cnt and their cumulative size
144 // must be at least GetUncompressedLength(compressed). The individual buffers
145 // in "iov" must not overlap with each other.
146 //
147 // returns false if the message is corrupted and could not be decrypted
148 bool RawUncompressToIOVec(const char* compressed, size_t compressed_length,
149 const struct iovec* iov, size_t iov_cnt);
150
151 // Given data from the byte source 'compressed' generated by calling
152 // the Snappy::Compress routine, this routine stores the uncompressed
153 // data to the iovec "iov". The number of physical
154 // buffers in "iov" is given by iov_cnt and their cumulative size
155 // must be at least GetUncompressedLength(compressed). The individual buffers
156 // in "iov" must not overlap with each other.
157 //
158 // returns false if the message is corrupted and could not be decrypted
159 bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov,
160 size_t iov_cnt);
161
162 // Returns the maximal size of the compressed representation of
163 // input data that is "source_bytes" bytes in length;
164 size_t MaxCompressedLength(size_t source_bytes);
165
166 // REQUIRES: "compressed[]" was produced by RawCompress() or Compress()
167 // Returns true and stores the length of the uncompressed data in
168 // *result normally. Returns false on parsing error.
169 // This operation takes O(1) time.
170 bool GetUncompressedLength(const char* compressed, size_t compressed_length,
171 size_t* result);
172
173 // Returns true iff the contents of "compressed[]" can be uncompressed
174 // successfully. Does not return the uncompressed data. Takes
175 // time proportional to compressed_length, but is usually at least
176 // a factor of four faster than actual decompression.
177 bool IsValidCompressedBuffer(const char* compressed,
178 size_t compressed_length);
179
180 // Returns true iff the contents of "compressed" can be uncompressed
181 // successfully. Does not return the uncompressed data. Takes
182 // time proportional to *compressed length, but is usually at least
183 // a factor of four faster than actual decompression.
184 // On success, consumes all of *compressed. On failure, consumes an
185 // unspecified prefix of *compressed.
186 bool IsValidCompressed(Source* compressed);
187
188 // The size of a compression block. Note that many parts of the compression
189 // code assumes that kBlockSize <= 65536; in particular, the hash table
190 // can only store 16-bit offsets, and EmitCopy() also assumes the offset
191 // is 65535 bytes or less. Note also that if you change this, it will
192 // affect the framing format (see framing_format.txt).
193 //
194 // Note that there might be older data around that is compressed with larger
195 // block sizes, so the decompression code should not rely on the
196 // non-existence of long backreferences.
197 static constexpr int kBlockLog = 16;
198 static constexpr size_t kBlockSize = 1 << kBlockLog;
199
200 static constexpr int kMinHashTableBits = 8;
201 static constexpr size_t kMinHashTableSize = 1 << kMinHashTableBits;
202
203 static constexpr int kMaxHashTableBits = 14;
204 static constexpr size_t kMaxHashTableSize = 1 << kMaxHashTableBits;
205} // end namespace snappy
206
207#endif // THIRD_PARTY_SNAPPY_SNAPPY_H__
208