Compress::Zlib - Interface to zlib compression library |
Compress::Zlib - Interface to zlib compression library
use Compress::Zlib ;
($d, $status) = deflateInit( [OPT] ) ; ($out, $status) = $d->deflate($buffer) ; ($out, $status) = $d->flush() ; $d->dict_adler() ;
($i, $status) = inflateInit( [OPT] ) ; ($out, $status) = $i->inflate($buffer) ; $i->dict_adler() ;
$dest = compress($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) ; $status = $gz->gzclose() ; $errstring = $gz->gzerror() ; $gzerrno
$dest = Compress::Zlib::memGzip($buffer) ; $dest = Compress::Zlib::memGunzip($buffer) ;
$crc = adler32($buffer [,$crc]) ; $crc = crc32($buffer [,$crc]) ;
ZLIB_VERSION
The Compress::Zlib module provides a Perl interface to the zlib compression library (see AUTHOR for details about where to get zlib). Most of the functionality provided by zlib is available in Compress::Zlib.
The module can be split into two general areas of functionality, namely in-memory compression/decompression and read/write access to gzip files. Each of these areas will be discussed separately below.
The interface Compress::Zlib provides to the in-memory deflate (and inflate) functions has been modified to fit into a Perl model.
The main difference is that for both inflation and deflation, the Perl interface will always consume the complete input buffer before returning. Also the output buffer returned will be automatically grown to fit the amount of output available.
Here is a definition of the interface available:
Initialises a deflation stream.
It combines the features of the zlib functions deflateInit, deflateInit2 and deflateSetDictionary.
If successful, it will return the initialised deflation stream, $d
and $status of Z_OK
in a list context. In scalar context it
returns the deflation stream, $d, only.
If not successful, the returned deflation stream ($d) will be undef and $status will hold the exact zlib error code.
The function optionally takes a number of named options specified as
-Name=>value
pairs. This allows individual options to be
tailored without having to specify them all in the parameter list.
For backward compatibility, it is also possible to pass the parameters as a reference to a hash containing the name=>value pairs.
The function takes one optional parameter, a reference to a hash. The contents of the hash allow the deflation interface to be tailored.
Here is a list of the valid options:
Z_BEST_SPEED
, Z_BEST_COMPRESSION
, and Z_DEFAULT_COMPRESSION
.
The default is -Level =>Z_DEFAULT_COMPRESSION
.
-Method =>Z_DEFLATED
.
Defaults to -WindowBits =>MAX_WBITS
.
Defaults to -MemLevel =>MAX_MEM_LEVEL
.
Z_DEFAULT_STRATEGY
, Z_FILTERED
and Z_HUFFMAN_ONLY
.
The default is -Strategy =>Z_DEFAULT_STRATEGY
.
$d-
dict_adler()>.
The default is no dictionary.
The default is 4096.
Here is an example of using the deflateInit optional parameter list to override the default buffer size and compression level. All other options will take their default values.
deflateInit( -Bufsize => 300, -Level => Z_BEST_SPEED ) ;
Deflates the contents of $buffer. The buffer can either be a scalar
or a scalar reference. When finished, $buffer will be
completely processed (assuming there were no errors). If the deflation
was successful it returns the deflated output, $out, and a status
value, $status, of Z_OK
.
On error, $out will be undef and $status will contain the zlib error code.
In a scalar context deflate will return $out only.
As with the deflate function in zlib, it is not necessarily the case that any output will be produced by this method. So don't rely on the fact that $out is empty for an error test.
Finishes the deflation. Any pending output will be returned via $out.
$status will have a value Z_OK
if successful.
In a scalar context flush will return $out only.
Note that flushing can degrade the compression ratio, so it should only be used to terminate a decompression.
By default the flush_type
used is Z_FINISH
. Other valid values
for flush_type
are Z_NO_FLUSH, Z_PARTIAL_FLUSH, Z_SYNC_FLUSH
and Z_FULL_FLUSH. It is strongly recommended that you only set the
flush_type
parameter if you fully understand what it does. See the
zlib
documentation for details.
Returns the adler32 value for the dictionary.
Here is a trivial example of using deflate. It simply reads standard input, deflates it and writes it to standard output.
use strict ; use warnings ;
use Compress::Zlib ;
binmode STDIN; binmode STDOUT; my $x = deflateInit() or die "Cannot create a deflation stream\n" ;
my ($output, $status) ; while (<>) { ($output, $status) = $x->deflate($_) ; $status == Z_OK or die "deflation failed\n" ; print $output ; } ($output, $status) = $x->flush() ; $status == Z_OK or die "deflation failed\n" ; print $output ;
Here is a definition of the interface:
Initialises an inflation stream.
In a list context it returns the inflation stream, $i, and the zlib status code ($status). In a scalar context it returns the inflation stream only.
If successful, $i will hold the inflation stream and $status will
be Z_OK
.
If not successful, $i will be undef and $status will hold the zlib error code.
The function optionally takes a number of named options specified as
-Name=>value
pairs. This allows individual options to be
tailored without having to specify them all in the parameter list.
For backward compatibility, it is also possible to pass the parameters as a reference to a hash containing the name=>value pairs.
The function takes one optional parameter, a reference to a hash. The contents of the hash allow the deflation interface to be tailored.
Here is a list of the valid options:
Defaults to -WindowBits =>MAX_WBITS
.
Default is 4096.
Here is an example of using the inflateInit optional parameter to override the default buffer size.
inflateInit( -Bufsize => 300 ) ;
Inflates the complete contents of $buffer. The buffer can either be a scalar or a scalar reference.
Returns Z_OK
if successful and Z_STREAM_END
if the end of the
compressed data has been successfully reached.
If not successful, $out will be undef and $status will hold
the zlib error code.
The $buffer
parameter is modified by inflate
. On completion it
will contain what remains of the input buffer after inflation. This
means that $buffer
will be an empty string when the return status is
Z_OK
. When the return status is Z_STREAM_END
the $buffer
parameter will contains what (if anything) was stored in the input
buffer after the deflated data stream.
This feature is useful when processing a file format that encapsulates a compressed data stream (e.g. gzip, zip).
Returns the adler32 value for the dictionary.
Here is an example of using inflate.
use strict ; use warnings ; use Compress::Zlib ; my $x = inflateInit() or die "Cannot create a inflation stream\n" ; my $input = '' ; binmode STDIN; binmode STDOUT; my ($output, $status) ; while (read(STDIN, $input, 4096)) { ($output, $status) = $x->inflate(\$input) ; print $output if $status == Z_OK or $status == Z_STREAM_END ; last if $status != Z_OK ; } die "inflation failed\n" unless $status == Z_STREAM_END ;
Two high-level functions are provided by zlib to perform in-memory compression. They are compress and uncompress. Two Perl subs are provided which provide similar functionality.
The source buffer can either be a scalar or a scalar reference.
The source buffer can either be a scalar or a scalar reference.
A number of functions are supplied in zlib for reading and writing gzip files. This module provides an interface to most of them. In general the interface provided by this module operates identically to the functions provided by zlib. Any differences are explained below.
As with the zlib equivalent, the mode parameter is used to specify both whether the file is opened for reading or writing and to optionally specify a a compression level. Refer to the zlib documentation for the exact format of the mode parameter.
If a reference to an open filehandle is passed in place of the filename, gzdopen will be called behind the scenes. The third example at the end of this section, gzstream, uses this feature.
Returns the number of bytes actually read. On EOF it returns 0 and in the case of an error, -1.
Returns the number of bytes actually read. On EOF it returns 0 and in the case of an error, -1.
It is legal to intermix calls to gzread and gzreadline.
At this time gzreadline ignores the variable $/
($INPUT_RECORD_SEPARATOR
or $RS
when English
is in use). The
end of a line is denoted by the C character '\n'
.
Refer to the zlib documentation for the valid values of $flush.
Z_OK Z_STREAM_END Z_ERRNO Z_STREAM_ERROR Z_DATA_ERROR Z_MEM_ERROR Z_BUF_ERROR
As with gzerror() it returns an error number in numeric context and
an error message in string context. Unlike gzerror() though, the
error message will correspond to the zlib message when the error is
associated with zlib itself, or the UNIX error message when it is
not (i.e. zlib returned Z_ERRORNO
).
As there is an overlap between the error numbers used by zlib and UNIX, $gzerrno should only be used to check for the presence of an error in numeric context. Use gzerror() to check for specific zlib errors. The gzcat example below shows how the variable can be used safely.
Here is an example script which uses the interface. It implements a gzcat function.
use strict ; use warnings ; use Compress::Zlib ; die "Usage: gzcat file...\n" unless @ARGV ; my $file ; foreach $file (@ARGV) { my $buffer ; my $gz = gzopen($file, "rb") or die "Cannot open $file: $gzerrno\n" ; print $buffer while $gz->gzread($buffer) > 0 ; die "Error reading from $file: $gzerrno" . ($gzerrno+0) . "\n" if $gzerrno != Z_STREAM_END ; $gz->gzclose() ; }
Below is a script which makes use of gzreadline. It implements a very simple grep like script.
use strict ; use warnings ; use Compress::Zlib ; die "Usage: gzgrep pattern file...\n" unless @ARGV >= 2; my $pattern = shift ; my $file ; foreach $file (@ARGV) { my $gz = gzopen($file, "rb") or die "Cannot open $file: $gzerrno\n" ; while ($gz->gzreadline($_) > 0) { print if /$pattern/ ; } die "Error reading from $file: $gzerrno\n" if $gzerrno != Z_STREAM_END ; $gz->gzclose() ; }
This script, gzstream, does the opposite of the gzcat script above. It reads from standard input and writes a gzip file to standard output.
use strict ; use warnings ; use Compress::Zlib ; binmode STDOUT; # gzopen only sets it on the fd my $gz = gzopen(\*STDOUT, "wb") or die "Cannot open stdout: $gzerrno\n" ; while (<>) { $gz->gzwrite($_) or die "error writing: $gzerrno\n" ; }
$gz->gzclose ;
This function is used to create an in-memory gzip file. It creates a minimal gzip header.
$dest = Compress::Zlib::memGzip($buffer) ;
If successful, it returns the in-memory gzip file, otherwise it returns undef.
The buffer parameter can either be a scalar or a scalar reference.
This function is used to uncompress an in-memory gzip file.
$dest = Compress::Zlib::memGunzip($buffer) ;
If successful, it returns the uncompressed gzip file, otherwise it returns undef.
The buffer parameter can either be a scalar or a scalar reference. The contents of the buffer parameter are destroyed after calling this function.
Two functions are provided by zlib to calculate a checksum. For the Perl interface, the order of the two parameters in both functions has been reversed. This allows both running checksums and one off calculations to be done.
$crc = adler32($buffer [,$crc]) ; $crc = crc32($buffer [,$crc]) ;
The buffer parameters can either be a scalar or a scalar reference.
If the $crc parameters is undef
, the crc value will be reset.
Although it is possible to use this module to access .zip files, there is a module on CPAN that will do all the hard work for you. Check out
http://www.cpan.org/modules/by-module/Archive/Archive-Zip-*.tar.gz
Assuming you don't want to use this module to access zip files there are a number of undocumented features in the zlib library you need to be aware of.
-MAX_WBITS
. This disables the creation of the zlib
header.
The zlib function inflate, and so the inflate method supplied in
this module, assume that there is at least one trailing byte after the
compressed data stream. Normally this isn't a problem because both
the gzip and zip file formats will guarantee that there is data directly
after the compressed data stream.
All the zlib constants are automatically imported when you make use of Compress::Zlib.
The Compress::Zlib module was written by Paul Marquess, Paul.Marquess@btinternet.com. The latest copy of the module can be found on CPAN in modules/by-module/Compress/Compress-Zlib-x.x.tar.gz.
The primary site for the zlib compression library is http://www.gzip.org/zlib/.
See the README file.
Compress::Zlib - Interface to zlib compression library |