Zlib Streams

zlib compression through stream buffers and iostreams. More...

Classes
class	ZBuffer
	Stream buffer that inflates on read and deflates on write. More...
class	ZIStream
	Input stream that inflates zlib or gzip data. More...
class	ZOStream
	Output stream that deflates to zlib or gzip. More...
class	ZIOStream
	Bidirectional stream for zlib or gzip. More...

Detailed Description

These types put zlib in the stream model of Streams. A ZBuffer is a BasicStreamBuffer of char attached to a target std::ios. Reading the buffer inflates compressed bytes from the target. Writing the buffer deflates uncompressed bytes into the target. The stream wrappers own a ZBuffer and present it as an input stream, an output stream, or both.

ZBuffer::Format selects the on-wire layout. ZBuffer::Zlib is the zlib wrapper with an Adler-32 checksum. ZBuffer::Gzip is the gzip wrapper with a CRC-32 checksum, as in RFC 1952. The format is fixed at construction. It must match the data on the target; a gzip file attached as zlib, or the reverse, fails during inflate.

attach() sets the target stream. detach() drops it without finishing a compressed frame. reset() discards buffered data and returns the zlib state to the start of a new stream, and can take a new target at the same time. discard() throws away the buffer contents and resets the state while keeping the target. finish() flushes the remaining compressed bytes to the target and ends the zlib stream. After finish(), start a new stream with reset() before writing more.

zcount() is the total number of uncompressed bytes produced by inflate so far. It does not count compressed bytes written on the deflate path.

ZIStream, ZOStream and ZIOStream construct a ZBuffer, install it with setBuffer(), and forward attach(), detach(), reset() and finish() to it. ZIStream reads uncompressed bytes from a compressed std::istream. ZOStream writes uncompressed bytes to a compressed std::ostream. ZIOStream does both on a std::iostream. zBuffer() returns the owned buffer when a caller needs the buffer API directly.

std::ifstream file("data.gz", std::ios::binary);
Pt::ZIStream in(file, Pt::ZBuffer::Gzip);
std::string text;
in >> text;

The stream wrappers do not own the target. Keep the target alive until detach() or destruction. Call finish() on an output stream before relying on the target to contain a complete zlib or gzip frame. A format mismatch or a truncated frame surfaces as a stream error, typically a IOError.