vrs::Decompressor Class Reference

Decompressor helper class, to decompresses data at a target location. More...

#include <Decompressor.h>

Classes
class	Lz4Decompressor
	Decompressor for lz4 data. More...
class	ZstdDecompressor
	Decompressor for zstd data. More...

Public Member Functions
void	setCompressionType (CompressionType compressionType)
CompressionType	getCompressionType () const
size_t	getRecommendedInputBufferSize () const
int	decompress (void *destination, uint32_t destinationSize, uint32_t &outReadSize)
void *	allocateCompressedDataBuffer (size_t requestSize)
size_t	getRemainingCompressedDataBufferSize () const
int	initFrame (FileHandler &file, size_t &outFrameSize, size_t &inOutMaxReadSize)
int	readFrame (FileHandler &file, void *dst, size_t frameSize, size_t &inOutMaxReadSize)
void	reset ()
	Forget any remaining compressed data, get ready for a new frame.

Detailed Description

Decompressor helper class, to decompresses data at a target location.

The data to decompress must be in the internal buffer. Use getBuffer(size) to allocate memory for the internal buffer reserving at least size bytes and get a pointer where to write the data, probably reading from disk directly in that internal buffer. Call decompress to decompress a full record to the DataReference location. The whole record will be decompressed & written at the target location without intermediate memory copy.

Member Function Documentation

allocateCompressedDataBuffer()

void * vrs::Decompressor::allocateCompressedDataBuffer

(

size_t

requestSize

)

Get a buffer of a specific size where to write the data to be decoded. The decompressor will assume that the buffer will be filed to the requested size.

Parameters

requestSize

Size to allocate.

Returns

Pointer to the buffer.

decompress()

int vrs::Decompressor::decompress	(	void *	destination,
		uint32_t	destinationSize,
		uint32_t &	outReadSize
	)

Decompress a maximum of destinationSize bytes of data, at the pointed to destination, and return the number of bytes read in outReadSize.

Returns

0 if no error occurred, a file system error code otherwise.

getRemainingCompressedDataBufferSize()

size_t vrs::Decompressor::getRemainingCompressedDataBufferSize ( ) const

inline

Tell how many bytes we haven't yet decoded from our compressed data buffer.

Returns

Number of bytes.

initFrame()

int vrs::Decompressor::initFrame	(	FileHandler &	file,
		size_t &	outFrameSize,
		size_t &	inOutMaxReadSize
	)

Frame compression APIs, to read compressed frames from a file. 1/ call reset() (if the compressor was used before). 2/ call initFrame to know how large the uncompressed frame is. 3/ allocate enough memory for the whole frame. 4/ read the whole frame in the buffer 5/ if reading more than one successive frames, do not call reset, go straight back to 2/

Start to read a frame, by sniffing the upcoming frame's size.

Parameters

file	A file open for reading, at the position of the frame.
frameSize	On success, set to the size in bytes of the upcoming frame.
maxReadSize	Max number of bytes of compressed frames data. If there are multiple frames, or the size of the compressed frame(s) is unknown, this number maybe the remaining file size. This number is updated as needed, if data is read from the file and placed in an internal decode buffer.

Returns

0 for success, or an error code. This could happen if you try to read data that isn't a compressed frame. Note that the file might be read past the end of the compressed frame, but not beyond the incoming value of inOutMaxReadSize. So when reading successive frames, do not reset the compression object between frames. Instead, just call initFrame again, after successfully reading a frame.

readFrame()

int vrs::Decompressor::readFrame	(	FileHandler &	file,
		void *	dst,
		size_t	frameSize,
		size_t &	inOutMaxReadSize
	)

Read a compressed frame, all at once.

Parameters

file	A file open for reading, at the position of the frame.
dst	A pointer to an allocated buffer large enough for the whole frame.
frameSize	The size of the frame, as returned by initFrame. The buffer must be large enough to read the whole frame at once.
maxReadSize	Max number of bytes of compressed frames data left.

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The documentation for this class was generated from the following files:

• vrs/Decompressor.h
• vrs/Decompressor.cpp