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9758c9dfd7
This reads from an `iovec` array rather than from a `char` array as in `snappy::Compress`. PiperOrigin-RevId: 476930623
223 lines
10 KiB
C++
223 lines
10 KiB
C++
// Copyright 2005 and onwards Google Inc.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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// A light-weight compression algorithm. It is designed for speed of
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// compression and decompression, rather than for the utmost in space
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// savings.
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//
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// For getting better compression ratios when you are compressing data
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// with long repeated sequences or compressing data that is similar to
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// other data, while still compressing fast, you might look at first
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// using BMDiff and then compressing the output of BMDiff with
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// Snappy.
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#ifndef THIRD_PARTY_SNAPPY_SNAPPY_H__
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#define THIRD_PARTY_SNAPPY_SNAPPY_H__
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#include <stddef.h>
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#include <stdint.h>
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#include <string>
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#include "snappy-stubs-public.h"
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namespace snappy {
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class Source;
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class Sink;
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// ------------------------------------------------------------------------
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// Generic compression/decompression routines.
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// ------------------------------------------------------------------------
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// Compress the bytes read from "*source" and append to "*sink". Return the
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// number of bytes written.
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size_t Compress(Source* source, Sink* sink);
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// Find the uncompressed length of the given stream, as given by the header.
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// Note that the true length could deviate from this; the stream could e.g.
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// be truncated.
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//
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// Also note that this leaves "*source" in a state that is unsuitable for
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// further operations, such as RawUncompress(). You will need to rewind
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// or recreate the source yourself before attempting any further calls.
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bool GetUncompressedLength(Source* source, uint32_t* result);
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// ------------------------------------------------------------------------
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// Higher-level string based routines (should be sufficient for most users)
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// ------------------------------------------------------------------------
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// Sets "*compressed" to the compressed version of "input[0..input_length-1]".
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// Original contents of *compressed are lost.
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//
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// REQUIRES: "input[]" is not an alias of "*compressed".
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size_t Compress(const char* input, size_t input_length,
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std::string* compressed);
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// Same as `Compress` above but taking an `iovec` array as input. Note that
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// this function preprocesses the inputs to compute the sum of
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// `iov[0..iov_cnt-1].iov_len` before reading. To avoid this, use
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// `RawCompressFromIOVec` below.
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size_t CompressFromIOVec(const struct iovec* iov, size_t iov_cnt,
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std::string* compressed);
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// Decompresses "compressed[0..compressed_length-1]" to "*uncompressed".
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// Original contents of "*uncompressed" are lost.
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//
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// REQUIRES: "compressed[]" is not an alias of "*uncompressed".
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//
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// returns false if the message is corrupted and could not be decompressed
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bool Uncompress(const char* compressed, size_t compressed_length,
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std::string* uncompressed);
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// Decompresses "compressed" to "*uncompressed".
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//
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// returns false if the message is corrupted and could not be decompressed
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bool Uncompress(Source* compressed, Sink* uncompressed);
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// This routine uncompresses as much of the "compressed" as possible
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// into sink. It returns the number of valid bytes added to sink
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// (extra invalid bytes may have been added due to errors; the caller
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// should ignore those). The emitted data typically has length
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// GetUncompressedLength(), but may be shorter if an error is
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// encountered.
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size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed);
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// ------------------------------------------------------------------------
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// Lower-level character array based routines. May be useful for
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// efficiency reasons in certain circumstances.
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// ------------------------------------------------------------------------
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// REQUIRES: "compressed" must point to an area of memory that is at
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// least "MaxCompressedLength(input_length)" bytes in length.
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//
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// Takes the data stored in "input[0..input_length]" and stores
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// it in the array pointed to by "compressed".
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//
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// "*compressed_length" is set to the length of the compressed output.
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//
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// Example:
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// char* output = new char[snappy::MaxCompressedLength(input_length)];
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// size_t output_length;
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// RawCompress(input, input_length, output, &output_length);
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// ... Process(output, output_length) ...
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// delete [] output;
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void RawCompress(const char* input,
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size_t input_length,
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char* compressed,
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size_t* compressed_length);
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// Same as `RawCompress` above but taking an `iovec` array as input. Note that
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// `uncompressed_length` is the total number of bytes to be read from the
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// elements of `iov` (_not_ the number of elements in `iov`).
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void RawCompressFromIOVec(const struct iovec* iov, size_t uncompressed_length,
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char* compressed, size_t* compressed_length);
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// Given data in "compressed[0..compressed_length-1]" generated by
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// calling the Snappy::Compress routine, this routine
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// stores the uncompressed data to
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// uncompressed[0..GetUncompressedLength(compressed)-1]
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// returns false if the message is corrupted and could not be decrypted
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bool RawUncompress(const char* compressed, size_t compressed_length,
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char* uncompressed);
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// Given data from the byte source 'compressed' generated by calling
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// the Snappy::Compress routine, this routine stores the uncompressed
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// data to
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// uncompressed[0..GetUncompressedLength(compressed,compressed_length)-1]
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// returns false if the message is corrupted and could not be decrypted
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bool RawUncompress(Source* compressed, char* uncompressed);
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// Given data in "compressed[0..compressed_length-1]" generated by
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// calling the Snappy::Compress routine, this routine
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// stores the uncompressed data to the iovec "iov". The number of physical
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// buffers in "iov" is given by iov_cnt and their cumulative size
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// must be at least GetUncompressedLength(compressed). The individual buffers
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// in "iov" must not overlap with each other.
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//
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// returns false if the message is corrupted and could not be decrypted
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bool RawUncompressToIOVec(const char* compressed, size_t compressed_length,
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const struct iovec* iov, size_t iov_cnt);
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// Given data from the byte source 'compressed' generated by calling
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// the Snappy::Compress routine, this routine stores the uncompressed
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// data to the iovec "iov". The number of physical
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// buffers in "iov" is given by iov_cnt and their cumulative size
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// must be at least GetUncompressedLength(compressed). The individual buffers
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// in "iov" must not overlap with each other.
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//
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// returns false if the message is corrupted and could not be decrypted
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bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov,
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size_t iov_cnt);
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// Returns the maximal size of the compressed representation of
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// input data that is "source_bytes" bytes in length;
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size_t MaxCompressedLength(size_t source_bytes);
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// REQUIRES: "compressed[]" was produced by RawCompress() or Compress()
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// Returns true and stores the length of the uncompressed data in
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// *result normally. Returns false on parsing error.
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// This operation takes O(1) time.
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bool GetUncompressedLength(const char* compressed, size_t compressed_length,
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size_t* result);
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// Returns true iff the contents of "compressed[]" can be uncompressed
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// successfully. Does not return the uncompressed data. Takes
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// time proportional to compressed_length, but is usually at least
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// a factor of four faster than actual decompression.
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bool IsValidCompressedBuffer(const char* compressed,
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size_t compressed_length);
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// Returns true iff the contents of "compressed" can be uncompressed
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// successfully. Does not return the uncompressed data. Takes
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// time proportional to *compressed length, but is usually at least
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// a factor of four faster than actual decompression.
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// On success, consumes all of *compressed. On failure, consumes an
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// unspecified prefix of *compressed.
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bool IsValidCompressed(Source* compressed);
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// The size of a compression block. Note that many parts of the compression
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// code assumes that kBlockSize <= 65536; in particular, the hash table
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// can only store 16-bit offsets, and EmitCopy() also assumes the offset
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// is 65535 bytes or less. Note also that if you change this, it will
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// affect the framing format (see framing_format.txt).
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//
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// Note that there might be older data around that is compressed with larger
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// block sizes, so the decompression code should not rely on the
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// non-existence of long backreferences.
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static constexpr int kBlockLog = 16;
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static constexpr size_t kBlockSize = 1 << kBlockLog;
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static constexpr int kMinHashTableBits = 8;
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static constexpr size_t kMinHashTableSize = 1 << kMinHashTableBits;
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static constexpr int kMaxHashTableBits = 14;
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static constexpr size_t kMaxHashTableSize = 1 << kMaxHashTableBits;
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} // end namespace snappy
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#endif // THIRD_PARTY_SNAPPY_SNAPPY_H__
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