Source code
Revision control
Copy as Markdown
Other Tools
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
/* Various simple compression/decompression functions. */
#ifndef mozilla_Compression_h_
#define mozilla_Compression_h_
#include "mozilla/Assertions.h"
#include "mozilla/Types.h"
#include "mozilla/ResultVariant.h"
#include "mozilla/Span.h"
#include "mozilla/UniquePtr.h"
struct LZ4F_cctx_s; // compression context
struct LZ4F_dctx_s; // decompression context
namespace mozilla {
namespace Compression {
/**
* LZ4 is a very fast byte-wise compression algorithm.
*
* Compared to Google's Snappy it is faster to compress and decompress and
* generally produces output of about the same size.
*
* Compared to zlib it compresses at about 10x the speed, decompresses at about
* 4x the speed and produces output of about 1.5x the size.
*/
class LZ4 {
public:
/**
* Compresses |aInputSize| bytes from |aSource| into |aDest|. Destination
* buffer must be already allocated, and must be sized to handle worst cases
* situations (input data not compressible). Worst case size evaluation is
* provided by function maxCompressedSize()
*
* @param aInputSize is the input size. Max supported value is ~1.9GB
* @return the number of bytes written in buffer |aDest|
*/
static MFBT_API size_t compress(const char* aSource, size_t aInputSize,
char* aDest);
/**
* Compress |aInputSize| bytes from |aSource| into an output buffer
* |aDest| of maximum size |aMaxOutputSize|. If it cannot achieve it,
* compression will stop, and result of the function will be zero,
* |aDest| will still be written to, but since the number of input
* bytes consumed is not returned the result is not usable.
*
* This function never writes outside of provided output buffer.
*
* @param aInputSize is the input size. Max supported value is ~1.9GB
* @param aMaxOutputSize is the size of the destination buffer (which must
* be already allocated)
* @return the number of bytes written in buffer |aDest| or 0 if the
* compression fails
*/
static MFBT_API size_t compressLimitedOutput(const char* aSource,
size_t aInputSize, char* aDest,
size_t aMaxOutputSize);
/**
* If the source stream is malformed, the function will stop decoding
* and return false.
*
* This function never writes beyond aDest + aMaxOutputSize, and is
* therefore protected against malicious data packets.
*
* Note: Destination buffer must be already allocated. This version is
* slightly slower than the decompress without the aMaxOutputSize.
*
* @param aInputSize is the length of the input compressed data
* @param aMaxOutputSize is the size of the destination buffer (which must be
* already allocated)
* @param aOutputSize the actual number of bytes decoded in the destination
* buffer (necessarily <= aMaxOutputSize)
* @return true on success, false on failure
*/
[[nodiscard]] static MFBT_API bool decompress(const char* aSource,
size_t aInputSize, char* aDest,
size_t aMaxOutputSize,
size_t* aOutputSize);
/**
* If the source stream is malformed, the function will stop decoding
* and return false.
*
* This function never writes beyond aDest + aMaxOutputSize, and is
* therefore protected against malicious data packets. It also ignores
* unconsumed input upon reaching aMaxOutputSize and can therefore be used
* for partial decompression.
*
* Note: Destination buffer must be already allocated. This version is
* slightly slower than the decompress without the aMaxOutputSize.
*
* @param aInputSize is the length of the input compressed data
* @param aMaxOutputSize is the size of the destination buffer (which must be
* already allocated)
* @param aOutputSize the actual number of bytes decoded in the destination
* buffer (necessarily <= aMaxOutputSize)
* @return true on success, false on failure
*/
[[nodiscard]] static MFBT_API bool decompressPartial(const char* aSource,
size_t aInputSize,
char* aDest,
size_t aMaxOutputSize,
size_t* aOutputSize);
/*
* Provides the maximum size that LZ4 may output in a "worst case"
* scenario (input data not compressible) primarily useful for memory
* allocation of output buffer.
* note : this function is limited by "int" range (2^31-1)
*
* @param aInputSize is the input size. Max supported value is ~1.9GB
* @return maximum output size in a "worst case" scenario
*/
static inline size_t maxCompressedSize(size_t aInputSize) {
size_t max = (aInputSize + (aInputSize / 255) + 16);
MOZ_ASSERT(max > aInputSize);
return max;
}
};
/**
* Context for LZ4 Frame-based streaming compression. Use this if you
* want to incrementally compress something or if you want to compress
* something such that another application can read it.
*/
class LZ4FrameCompressionContext final {
public:
MFBT_API LZ4FrameCompressionContext(int aCompressionLevel, size_t aMaxSrcSize,
bool aChecksum, bool aStableSrc = false);
MFBT_API ~LZ4FrameCompressionContext();
size_t GetRequiredWriteBufferLength() { return mWriteBufLen; }
/**
* Begin streaming frame-based compression.
*
* @return a Result with a Span containing the frame header, or an lz4 error
* code (size_t).
*/
MFBT_API Result<Span<const char>, size_t> BeginCompressing(
Span<char> aWriteBuffer);
/**
* Continue streaming frame-based compression with the provided input.
*
* @param aInput input buffer to be compressed.
* @return a Result with a Span containing compressed output, or an lz4 error
* code (size_t).
*/
MFBT_API Result<Span<const char>, size_t> ContinueCompressing(
Span<const char> aInput);
/**
* Finalize streaming frame-based compression with the provided input.
*
* @return a Result with a Span containing compressed output and the frame
* footer, or an lz4 error code (size_t).
*/
MFBT_API Result<Span<const char>, size_t> EndCompressing();
private:
LZ4F_cctx_s* mContext;
int mCompressionLevel;
bool mGenerateChecksum;
bool mStableSrc;
size_t mMaxSrcSize;
size_t mWriteBufLen;
Span<char> mWriteBuffer;
};
struct LZ4FrameDecompressionResult {
size_t mSizeRead;
size_t mSizeWritten;
bool mFinished;
};
/**
* Context for LZ4 Frame-based streaming decompression. Use this if you
* want to decompress something compressed by LZ4FrameCompressionContext
* or by another application.
*/
class LZ4FrameDecompressionContext final {
public:
explicit MFBT_API LZ4FrameDecompressionContext(bool aStableDest = false);
MFBT_API ~LZ4FrameDecompressionContext();
/**
* Decompress a buffer/part of a buffer compressed with
* LZ4FrameCompressionContext or another application.
*
* @param aOutput output buffer to be write results into.
* @param aInput input buffer to be decompressed.
* @return a Result with information on bytes read/written and whether we
* completely decompressed the input into the output, or an lz4 error code
* (size_t).
*/
MFBT_API Result<LZ4FrameDecompressionResult, size_t> Decompress(
Span<char> aOutput, Span<const char> aInput);
private:
LZ4F_dctx_s* mContext;
bool mStableDest;
};
} /* namespace Compression */
} /* namespace mozilla */
#endif /* mozilla_Compression_h_ */