DecompressingStreamBuf Class Reference

A stream buffer that decompresses another stream on demand. More...

#include <compressedstream.h>

Inheritance diagram for DecompressingStreamBuf:

Public Member Functions
	DecompressingStreamBuf (std::unique_ptr< std::istream > source, Compression type, std::uint64_t maxDecodedSize=defaultMaxDecompressedSize)
	Wrap source, which must be positioned at the first byte.
	DecompressingStreamBuf (const DecompressingStreamBuf &)=delete
DecompressingStreamBuf &	operator= (const DecompressingStreamBuf &)=delete
std::string	error () const
	The error encountered while decoding, if any.
bool	hitSizeLimit () const
std::uint64_t	decodedSize () const

Protected Member Functions
int_type	underflow () override
std::streamsize	xsgetn (char *s, std::streamsize count) override
pos_type	seekoff (off_type off, std::ios_base::seekdir dir, std::ios_base::openmode which=std::ios_base::in|std::ios_base::out) override
pos_type	seekpos (pos_type pos, std::ios_base::openmode which=std::ios_base::in|std::ios_base::out) override

Detailed Description

<avogadro/io/compressedstream.h>

Decoded bytes are produced lazily, a block at a time, and every block is retained, so the buffer is seekable in both directions even though the underlying codecs are not. Seeking forward decodes as far as the target; seeking to the end decodes everything. That matters because several readers measure a file by seeking to its end (DCD and TRR take block lengths from the file itself) and others rewind to re-read a record (MDL, Molden), so they would not work against a forward only stream.

The cost is memory: a reader that seeks to the end of a compressed trajectory holds the whole decompressed trajectory. That is what the size limit is for.

Constructor & Destructor Documentation

DecompressingStreamBuf()

DecompressingStreamBuf	(	std::unique_ptr< std::istream >	source,
		Compression	type,
		std::uint64_t	maxDecodedSize = defaultMaxDecompressedSize )

Parameters

source	The compressed stream. Ownership is taken, and it is read incrementally rather than all at once.
type	The codec, as determined by detectCompression().
maxDecodedSize	The ceiling on decoded bytes; 0 means no ceiling.

Member Function Documentation

error()

std::string error

(

)

const

Empty while all is well. A truncated file, a failed integrity check or a breach of the size limit all leave a message here. Callers must check this after reading, because a decoding failure surfaces to the reader as an ordinary end of stream, which most parsers treat as a short but valid file.

hitSizeLimit()

bool hitSizeLimit

(

)

const

Returns

True if decoding stopped because the size limit was reached.

decodedSize()

std::uint64_t decodedSize

(

)

const

Returns

The number of bytes decoded so far.

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

• compressedstream.h