compress::zlib.3

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.\" ========================================================================
.\"
.IX Title "Compress::Zlib 3"
.TH Compress::Zlib 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Compress::Zlib \- Interface to zlib compression library
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Compress::Zlib ;
\&
\&    ($d, $status) = deflateInit( [OPT] ) ;
\&    $status = $d\->deflate($input, $output) ;
\&    $status = $d\->flush($output [, $flush_type]) ;
\&    $d\->deflateParams(OPTS) ;
\&    $d\->deflateTune(OPTS) ;
\&    $d\->dict_adler() ;
\&    $d\->crc32() ;
\&    $d\->adler32() ;
\&    $d\->total_in() ;
\&    $d\->total_out() ;
\&    $d\->msg() ;
\&    $d\->get_Strategy();
\&    $d\->get_Level();
\&    $d\->get_BufSize();
\&
\&    ($i, $status) = inflateInit( [OPT] ) ;
\&    $status = $i\->inflate($input, $output [, $eof]) ;
\&    $status = $i\->inflateSync($input) ;
\&    $i\->dict_adler() ;
\&    $d\->crc32() ;
\&    $d\->adler32() ;
\&    $i\->total_in() ;
\&    $i\->total_out() ;
\&    $i\->msg() ;
\&    $d\->get_BufSize();
\&
\&    $dest = compress($source) ;
\&    $dest = uncompress($source) ;
\&
\&    $gz = gzopen($filename or filehandle, $mode) ;
\&    $bytesread = $gz\->gzread($buffer [,$size]) ;
\&    $bytesread = $gz\->gzreadline($line) ;
\&    $byteswritten = $gz\->gzwrite($buffer) ;
\&    $status = $gz\->gzflush($flush) ;
\&    $offset = $gz\->gztell() ;
\&    $status = $gz\->gzseek($offset, $whence) ;
\&    $status = $gz\->gzclose() ;
\&    $status = $gz\->gzeof() ;
\&    $status = $gz\->gzsetparams($level, $strategy) ;
\&    $errstring = $gz\->gzerror() ; 
\&    $gzerrno
\&
\&    $dest = Compress::Zlib::memGzip($buffer) ;
\&    $dest = Compress::Zlib::memGunzip($buffer) ;
\&
\&    $crc = adler32($buffer [,$crc]) ;
\&    $crc = crc32($buffer [,$crc]) ;
\&
\&    $crc = adler32_combine($crc1, $crc2, $len2)l
\&    $crc = crc32_combine($adler1, $adler2, $len2)
\&
\&    ZLIB_VERSION
\&    ZLIB_VERNUM
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fICompress::Zlib\fR module provides a Perl interface to the \fIzlib\fR
compression library (see \*(L"\s-1AUTHOR\s0\*(R" for details about where to get
\&\fIzlib\fR).
.PP
The \f(CW\*(C`Compress::Zlib\*(C'\fR module can be split into two general areas of
functionality, namely a simple read/write interface to \fIgzip\fR files
and a low-level in-memory compression/decompression interface.
.PP
Each of these areas will be discussed in the following sections.
.Sh "Notes for users of Compress::Zlib version 1"
.IX Subsection "Notes for users of Compress::Zlib version 1"
The main change in \f(CW\*(C`Compress::Zlib\*(C'\fR version 2.x is that it does not now
interface directly to the zlib library. Instead it uses the
\&\f(CW\*(C`IO::Compress::Gzip\*(C'\fR and \f(CW\*(C`IO::Uncompress::Gunzip\*(C'\fR modules for
reading/writing gzip files, and the \f(CW\*(C`Compress::Raw::Zlib\*(C'\fR module for some
low-level zlib access.
.PP
The interface provided by version 2 of this module should be 100% backward
compatible with version 1. If you find a difference in the expected
behaviour please contact the author (See \*(L"\s-1AUTHOR\s0\*(R"). See \*(L"\s-1GZIP\s0 \s-1INTERFACE\s0\*(R"
.PP
With the creation of the \f(CW\*(C`IO::Compress\*(C'\fR and \f(CW\*(C`IO::Uncompress\*(C'\fR modules no
new features are planned for \f(CW\*(C`Compress::Zlib\*(C'\fR \- the new modules do
everything that \f(CW\*(C`Compress::Zlib\*(C'\fR does and then some. Development on
\&\f(CW\*(C`Compress::Zlib\*(C'\fR will be limited to bug fixes only.
.PP
If you are writing new code, your first port of call should be one of the
new \f(CW\*(C`IO::Compress\*(C'\fR or \f(CW\*(C`IO::Uncompress\*(C'\fR modules.
.SH "GZIP INTERFACE"
.IX Header "GZIP INTERFACE"
A number of functions are supplied in \fIzlib\fR for reading and writing
\&\fIgzip\fR files that conform to \s-1RFC\s0 1952. This module provides an interface
to most of them.
.PP
If you have previously used \f(CW\*(C`Compress::Zlib\*(C'\fR 1.x, the following
enhancements/changes have been made to the \f(CW\*(C`gzopen\*(C'\fR interface:
.IP "1." 5
If you want to to open either \s-1STDIN\s0 or \s-1STDOUT\s0 with \f(CW\*(C`gzopen\*(C'\fR, you can now
optionally use the special filename "\f(CW\*(C`\-\*(C'\fR" as a synonym for \f(CW\*(C`\e*STDIN\*(C'\fR and
\&\f(CW\*(C`\e*STDOUT\*(C'\fR.
.IP "2." 5
In \f(CW\*(C`Compress::Zlib\*(C'\fR version 1.x, \f(CW\*(C`gzopen\*(C'\fR used the zlib library to open
the underlying file. This made things especially tricky when a Perl
filehandle was passed to \f(CW\*(C`gzopen\*(C'\fR. Behind the scenes the numeric C file
descriptor had to be extracted from the Perl filehandle and this passed to
the zlib library.
.Sp
Apart from being non-portable to some operating systems, this made it
difficult to use \f(CW\*(C`gzopen\*(C'\fR in situations where you wanted to extract/create
a gzip data stream that is embedded in a larger file, without having to
resort to opening and closing the file multiple times.
.Sp
It also made it impossible to pass a perl filehandle that wasn't associated
with a real filesystem file, like, say, an \f(CW\*(C`IO::String\*(C'\fR.
.Sp
In \f(CW\*(C`Compress::Zlib\*(C'\fR version 2.x, the \f(CW\*(C`gzopen\*(C'\fR interface has been
completely rewritten to use the IO::Compress::Gzip
for writing gzip files and IO::Uncompress::Gunzip
for reading gzip files. None of the limitations mentioned above apply.
.IP "3." 5
Addition of \f(CW\*(C`gzseek\*(C'\fR to provide a restricted \f(CW\*(C`seek\*(C'\fR interface.
.IP "4." 5
Added \f(CW\*(C`gztell\*(C'\fR.
.PP
A more complete and flexible interface for reading/writing gzip
files/buffers is included with the module \f(CW\*(C`IO\-Compress\-Zlib\*(C'\fR. See
IO::Compress::Gzip and
IO::Uncompress::Gunzip for more details.
.ie n .IP "\fB\fB$gz\fB = gzopen($filename, \f(BI$mode\fB)\fR" 5
.el .IP "\fB\f(CB$gz\fB = gzopen($filename, \f(CB$mode\fB)\fR" 5
.IX Item "$gz = gzopen($filename, $mode)"
.PD 0
.ie n .IP "\fB\fB$gz\fB = gzopen($filehandle, \f(BI$mode\fB)\fR" 5
.el .IP "\fB\f(CB$gz\fB = gzopen($filehandle, \f(CB$mode\fB)\fR" 5
.IX Item "$gz = gzopen($filehandle, $mode)"
.PD
This function opens either the \fIgzip\fR file \f(CW$filename\fR for reading or
writing or attaches to the opened filehandle, \f(CW$filehandle\fR. 
It returns an object on success and \f(CW\*(C`undef\*(C'\fR on failure.
.Sp
When writing a gzip file this interface will \fIalways\fR create the smallest
possible gzip header (exactly 10 bytes). If you want greater control over
what gets stored in the gzip header (like the original filename or a
comment) use IO::Compress::Gzip instead. Similarly if
you want to read the contents of the gzip header use
IO::Uncompress::Gunzip.
.Sp
The second parameter, \f(CW$mode\fR, is used to specify whether the file is
opened for reading or writing and to optionally specify a compression
level and compression strategy when writing. The format of the \f(CW$mode\fR
parameter is similar to the mode parameter to the 'C' function \f(CW\*(C`fopen\*(C'\fR,
so \*(L"rb\*(R" is used to open for reading, \*(L"wb\*(R" for writing and \*(L"ab\*(R" for
appending (writing at the end of the file).
.Sp
To specify a compression level when writing, append a digit between 0
and 9 to the mode string \*(-- 0 means no compression and 9 means maximum
compression.
If no compression level is specified Z_DEFAULT_COMPRESSION is used.
.Sp
To specify the compression strategy when writing, append 'f' for filtered
data, 'h' for Huffman only compression, or 'R' for run-length encoding.
If no strategy is specified Z_DEFAULT_STRATEGY is used.
.Sp
So, for example, \*(L"wb9\*(R" means open for writing with the maximum compression
using the default strategy and \*(L"wb4R\*(R" means open for writing with compression
level 4 and run-length encoding.
.Sp
Refer to the \fIzlib\fR documentation for the exact format of the \f(CW$mode\fR
parameter.
.ie n .IP "\fB\fB$bytesread\fB = \f(BI$gz\fB\->gzread($buffer [, \f(CB$size\fB]) ;\fR" 5
.el .IP "\fB\f(CB$bytesread\fB = \f(CB$gz\fB\->gzread($buffer [, \f(CB$size\fB]) ;\fR" 5
.IX Item "$bytesread = $gz->gzread($buffer [, $size]) ;"
Reads \f(CW$size\fR bytes from the compressed file into \f(CW$buffer\fR. If
\&\f(CW$size\fR is not specified, it will default to 4096. If the scalar
\&\f(CW$buffer\fR is not large enough, it will be extended automatically.
.Sp
Returns the number of bytes actually read. On \s-1EOF\s0 it returns 0 and in
the case of an error, \-1.
.ie n .IP "\fB\fB$bytesread\fB = \f(BI$gz\fB\->gzreadline($line) ;\fR" 5
.el .IP "\fB\f(CB$bytesread\fB = \f(CB$gz\fB\->gzreadline($line) ;\fR" 5
.IX Item "$bytesread = $gz->gzreadline($line) ;"
Reads the next line from the compressed file into \f(CW$line\fR.
.Sp
Returns the number of bytes actually read. On \s-1EOF\s0 it returns 0 and in
the case of an error, \-1.