- NAME
- SYNOPSIS
- DESCRIPTION
- GZIP INTERFACE
- COMPRESS/UNCOMPRESS
- Deflate Interface
- Inflate Interface
- CHECKSUM FUNCTIONS
- Misc
- CONSTANTS
- SEE ALSO
- AUTHOR
- MODIFICATION HISTORY
- COPYRIGHT AND LICENSE
NAME
Compress::Zlib - Interface to zlib compression library
SYNOPSIS
use Compress::Zlib ; ($d, $status) = deflateInit( [OPT] ) ; $status = $d->deflate($input, $output) ; $status = $d->flush([$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]) ; $crc = crc32_combine($crc1, $crc2, $len2); $adler = adler32_combine($adler1, $adler2, $len2); my $version = Compress::Raw::Zlib::zlib_version();
DESCRIPTION
The Compress::Zlib module provides a Perl interface to the zlib compression library (see AUTHOR for details about where to get zlib).
The Compress::Zlib
module can be split into two general areas of functionality, namely a simple read/write interface to gzip files and a low-level in-memory compression/decompression interface.
Each of these areas will be discussed in the following sections.
Notes for users of Compress::Zlib version 1
The main change in Compress::Zlib
version 2.x is that it does not now interface directly to the zlib library. Instead it uses the IO::Compress::Gzip
and IO::Uncompress::Gunzip
modules for reading/writing gzip files, and the Compress::Raw::Zlib
module for some low-level zlib access.
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 AUTHOR). See GZIP INTERFACE
With the creation of the IO::Compress
and IO::Uncompress
modules no new features are planned for Compress::Zlib
- the new modules do everything that Compress::Zlib
does and then some. Development on Compress::Zlib
will be limited to bug fixes only.
If you are writing new code, your first port of call should be one of the new IO::Compress
or IO::Uncompress
modules.
GZIP INTERFACE
A number of functions are supplied in zlib for reading and writing gzip files that conform to RFC 1952. This module provides an interface to most of them.
If you have previously used Compress::Zlib
1.x, the following enhancements/changes have been made to the gzopen
interface:
- 1
-
If you want to open either STDIN or STDOUT with
gzopen
, you can now optionally use the special filename "-
" as a synonym for\*STDIN
and\*STDOUT
. - 2
-
In
Compress::Zlib
version 1.x,gzopen
used the zlib library to open the underlying file. This made things especially tricky when a Perl filehandle was passed togzopen
. Behind the scenes the numeric C file descriptor had to be extracted from the Perl filehandle and this passed to the zlib library.Apart from being non-portable to some operating systems, this made it difficult to use
gzopen
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.It also made it impossible to pass a perl filehandle that wasn't associated with a real filesystem file, like, say, an
IO::String
.In
Compress::Zlib
version 2.x, thegzopen
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. - 3
-
Addition of
gzseek
to provide a restrictedseek
interface. - 4.
-
Added
gztell
.
A more complete and flexible interface for reading/writing gzip files/buffers is included with the module IO-Compress-Zlib
. See IO::Compress::Gzip and IO::Uncompress::Gunzip for more details.
- $gz = gzopen($filename, $mode)
-
$gz = gzopen($filehandle, $mode)
This function opens either the gzip file
$filename
for reading or writing or attaches to the opened filehandle,$filehandle
. It returns an object on success andundef
on failure.When writing a gzip file this interface will always 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.
The second parameter,
$mode
, is used to specify whether the file is opened for reading or writing and to optionally specify a compression level and compression strategy when writing. The format of the$mode
parameter is similar to the mode parameter to the 'C' functionfopen
, so "rb" is used to open for reading, "wb" for writing and "ab" for appending (writing at the end of the file).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.
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.
So, for example, "wb9" means open for writing with the maximum compression using the default strategy and "wb4R" means open for writing with compression level 4 and run-length encoding.
Refer to the zlib documentation for the exact format of the
$mode
parameter. -
$bytesread = $gz->gzread($buffer [, $size]) ;
Reads
$size
bytes from the compressed file into$buffer
. If$size
is not specified, it will default to 4096. If the scalar$buffer
is not large enough, it will be extended automatically.Returns the number of bytes actually read. On EOF it returns 0 and in the case of an error, -1.
-
$bytesread = $gz->gzreadline($line) ;
Reads the next line from the compressed file into
$line
.Returns the number of bytes actually read. On EOF it returns 0 and in the case of an error, -1.
It is legal to intermix calls to
gzread
andgzreadline
.To maintain backward compatibility with version 1.x of this module
gzreadline
ignores the$/
variable - it always uses the string"\n"
as the line delimiter.If you want to read a gzip file a line at a time and have it respect the
$/
variable (or$INPUT_RECORD_SEPARATOR
, or$RS
whenEnglish
is in use) see IO::Uncompress::Gunzip. -
$byteswritten = $gz->gzwrite($buffer) ;
Writes the contents of
$buffer
to the compressed file. Returns the number of bytes actually written, or 0 on error. -
$status = $gz->gzflush($flush_type) ;
Flushes all pending output into the compressed file.
This method takes an optional parameter,
$flush_type
, that controls how the flushing will be carried out. By default the$flush_type
used isZ_FINISH
. Other valid values for$flush_type
areZ_NO_FLUSH
,Z_SYNC_FLUSH
,Z_FULL_FLUSH
andZ_BLOCK
. It is strongly recommended that you only set theflush_type
parameter if you fully understand the implications of what it does - overuse offlush
can seriously degrade the level of compression achieved. See thezlib
documentation for details.Returns 0 on success.
-
$offset = $gz->gztell() ;
Returns the uncompressed file offset.
-
$status = $gz->gzseek($offset, $whence) ;
Provides a sub-set of the
seek
functionality, with the restriction that it is only legal to seek forward in the compressed file. It is a fatal error to attempt to seek backward.When opened for writing, empty parts of the file will have NULL (0x00) bytes written to them.
The
$whence
parameter should be one of SEEK_SET, SEEK_CUR or SEEK_END.Returns 1 on success, 0 on failure.
-
$gz->gzclose
Closes the compressed file. Any pending data is flushed to the file before it is closed.
Returns 0 on success.
-
$gz->gzsetparams($level, $strategy
Change settings for the deflate stream
$gz
.The list of the valid options is shown below. Options not specified will remain unchanged.
Note: This method is only available if you are running zlib 1.0.6 or better.
-
$level
Defines the compression level. Valid values are 0 through 9,
Z_NO_COMPRESSION
,Z_BEST_SPEED
,Z_BEST_COMPRESSION
, andZ_DEFAULT_COMPRESSION
. -
$strategy
Defines the strategy used to tune the compression. The valid values are
Z_DEFAULT_STRATEGY
,Z_FILTERED
andZ_HUFFMAN_ONLY
.
-
$level
-
$gz->gzerror
Returns the zlib error message or number for the last operation associated with
$gz
. The return value will be the zlib error number when used in a numeric context and the zlib error message when used in a string context. The zlib error number constants, shown below, are available for use.Z_OK Z_STREAM_END Z_ERRNO Z_STREAM_ERROR Z_DATA_ERROR Z_MEM_ERROR Z_BUF_ERROR
-
$gzerrno
The
$gzerrno
scalar holds the error code associated with the most recent gzip routine. Note that unlikegzerror()
, the error is not associated with a particular file.As with
gzerror()
it returns an error number in numeric context and an error message in string context. Unlikegzerror()
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 returnedZ_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. Usegzerror()
to check for specific zlib errors. The gzcat example below shows how the variable can be used safely.
Examples
Here is an example script which uses the interface. It implements a gzcat function.
use strict ; use warnings ; use Compress::Zlib ; # use stdin if no files supplied @ARGV = '-' unless @ARGV ; foreach my $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 >= 1; my $pattern = shift ; # use stdin if no files supplied @ARGV = '-' unless @ARGV ; foreach my $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 data stream 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 ;
Compress::Zlib::memGzip
This function is used to create an in-memory gzip file with the minimum possible gzip header (exactly 10 bytes).
$dest = Compress::Zlib::memGzip($buffer) or die "Cannot compress: $gzerrno\n";
If successful, it returns the in-memory gzip file. Otherwise it returns undef
and the $gzerrno
variable will store the zlib error code.
The $buffer
parameter can either be a scalar or a scalar reference.
See IO::Compress::Gzip for an alternative way to carry out in-memory gzip compression.
Compress::Zlib::memGunzip
This function is used to uncompress an in-memory gzip file.
$dest = Compress::Zlib::memGunzip($buffer) or die "Cannot uncompress: $gzerrno\n";
If successful, it returns the uncompressed gzip file. Otherwise it returns undef
and the $gzerrno
variable will store the zlib error code.
The $buffer
parameter can either be a scalar or a scalar reference. The contents of the $buffer
parameter are destroyed after calling this function.
If $buffer
consists of multiple concatenated gzip data streams only the first will be uncompressed. Use gunzip
with the MultiStream
option in the IO::Uncompress::Gunzip
module if you need to deal with concatenated data streams.
See IO::Uncompress::Gunzip for an alternative way to carry out in-memory gzip uncompression.
COMPRESS/UNCOMPRESS
Two functions are provided to perform in-memory compression/uncompression of RFC 1950 data streams. They are called compress
and uncompress
.
-
$dest = compress($source [, $level] ) ;
Compresses
$source
. If successful it returns the compressed data. Otherwise it returns undef.The source buffer,
$source
, can either be a scalar or a scalar reference.The
$level
parameter defines the compression level. Valid values are 0 through 9,Z_NO_COMPRESSION
,Z_BEST_SPEED
,Z_BEST_COMPRESSION
, andZ_DEFAULT_COMPRESSION
. If$level
is not specifiedZ_DEFAULT_COMPRESSION
will be used. -
$dest = uncompress($source) ;
Uncompresses
$source
. If successful it returns the uncompressed data. Otherwise it returns undef.The source buffer can either be a scalar or a scalar reference.
Please note: the two functions defined above are not compatible with the Unix commands of the same name.
See IO::Deflate and IO::Inflate included with this distribution for an alternative interface for reading/writing RFC 1950 files/buffers.
Deflate Interface
This section defines an interface that allows in-memory compression using the deflate interface provided by zlib.
Here is a definition of the interface available:
($d, $status) = deflateInit( [OPT] )
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 $status
will hold the exact zlib error code.
The function optionally takes a number of named options specified as -Name=>value
pairs. This allows individual options to be tailored without having to specify them all in the parameter list.
For backward compatibility, it is also possible to pass the parameters as a reference to a hash containing the name=>value pairs.
The function takes one optional parameter, a reference to a hash. The contents of the hash allow the deflation interface to be tailored.
Here is a list of the valid options:
-
-Level
Defines the compression level. Valid values are 0 through 9,
Z_NO_COMPRESSION
,Z_BEST_SPEED
,Z_BEST_COMPRESSION
, andZ_DEFAULT_COMPRESSION
.The default is Z_DEFAULT_COMPRESSION.
-
-Method
Defines the compression method. The only valid value at present (and the default) is Z_DEFLATED.
-
-WindowBits
To create an RFC 1950 data stream, set
WindowBits
to a positive number.To create an RFC 1951 data stream, set
WindowBits
to-MAX_WBITS
.For a full definition of the meaning and valid values for
WindowBits
refer to the zlib documentation for deflateInit2.Defaults to MAX_WBITS.
-
-MemLevel
For a definition of the meaning and valid values for
MemLevel
refer to the zlib documentation for deflateInit2.Defaults to MAX_MEM_LEVEL.
-
-Strategy
Defines the strategy used to tune the compression. The valid values are
Z_DEFAULT_STRATEGY
,Z_FILTERED
andZ_HUFFMAN_ONLY
.The default is Z_DEFAULT_STRATEGY.
-
-Dictionary
When a dictionary is specified Compress::Zlib will automatically call
deflateSetDictionary
directly after callingdeflateInit
. The Adler32 value for the dictionary can be obtained by calling the method$d-
dict_adler()>.The default is no dictionary.
-
-Bufsize
Sets the initial size for the deflation buffer. If the buffer has to be reallocated to increase the size, it will grow in increments of
Bufsize
.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 ) ;
($out, $status) = $d->deflate($buffer)
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 $out
is empty for an error test.
($out, $status) = $d->flush() =head2 ($out, $status) = $d->flush($flush_type)
Typically used to finish 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 seriously degrade the compression ratio, so it should only be used to terminate a decompression (using Z_FINISH
) or when you want to create a full flush point (using Z_FULL_FLUSH
).
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 the implications of what it does. See the zlib
documentation for details.
$status = $d->deflateParams([OPT])
Change settings for the deflate stream $d
.
The list of the valid options is shown below. Options not specified will remain unchanged.
-
-Level
Defines the compression level. Valid values are 0 through 9,
Z_NO_COMPRESSION
,Z_BEST_SPEED
,Z_BEST_COMPRESSION
, andZ_DEFAULT_COMPRESSION
. -
-Strategy
Defines the strategy used to tune the compression. The valid values are
Z_DEFAULT_STRATEGY
,Z_FILTERED
andZ_HUFFMAN_ONLY
.
$d->dict_adler()
Returns the adler32 value for the dictionary.
$d->msg()
Returns the last error message generated by zlib.
$d->total_in()
Returns the total number of bytes uncompressed bytes input to deflate.
$d->total_out()
Returns the total number of compressed bytes output from deflate.
Example
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 $output ;
Inflate Interface
This section defines the interface available that allows in-memory uncompression using the deflate interface provided by zlib.
Here is a definition of the interface:
($i, $status) = inflateInit()
Initialises an inflation stream.
In a list context it returns the inflation stream, $i
, and the zlib status code in $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 $status
will hold the zlib error code.
The function optionally takes a number of named options specified as -Name=>value
pairs. This allows individual options to be tailored without having to specify them all in the parameter list.
For backward compatibility, it is also possible to pass the parameters as a reference to a hash containing the name=>value pairs.
The function takes one optional parameter, a reference to a hash. The contents of the hash allow the deflation interface to be tailored.
Here is a list of the valid options:
-
-WindowBits
To uncompress an RFC 1950 data stream, set
WindowBits
to a positive number.To uncompress an RFC 1951 data stream, set
WindowBits
to-MAX_WBITS
.For a full definition of the meaning and valid values for
WindowBits
refer to the zlib documentation for inflateInit2.Defaults to MAX_WBITS.
-
-Bufsize
Sets the initial size for the inflation buffer. If the buffer has to be reallocated to increase the size, it will grow in increments of
Bufsize
.Default is 4096.
-
-Dictionary
The default is no dictionary.
Here is an example of using the inflateInit
optional parameter to override the default buffer size.
inflateInit( -Bufsize => 300 ) ;
($out, $status) = $i->inflate($buffer)
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).
$status = $i->inflateSync($buffer)
Scans $buffer
until it reaches either a full flush point or the end of the buffer.
If a full flush point is found, Z_OK
is returned and $buffer
will be have all data up to the flush point removed. This can then be passed to the deflate
method.
Any other return code means that a flush point was not found. If more data is available, inflateSync
can be called repeatedly with more compressed data until the flush point is found.
$i->dict_adler()
Returns the adler32 value for the dictionary.
$i->msg()
Returns the last error message generated by zlib.
$i->total_in()
Returns the total number of bytes compressed bytes input to inflate.
$i->total_out()
Returns the total number of uncompressed bytes output from inflate.
Example
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 ;
CHECKSUM FUNCTIONS
Two functions are provided by zlib to calculate checksums. 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.
If you have built this module with zlib 1.2.3 or better, two more CRC-related functions are available.
$crc = crc32_combine($crc1, $crc2, $len2); $adler = adler32_combine($adler1, $adler2, $len2);
These functions allow checksums to be merged. Refer to the zlib documentation for more details.
Misc
my $version = Compress::Zlib::zlib_version();
Returns the version of the zlib library.
CONSTANTS
All the zlib constants are automatically imported when you make use of Compress::Zlib.
SEE ALSO
IO::Compress::Gzip, IO::Uncompress::Gunzip, IO::Compress::Deflate, IO::Uncompress::Inflate, IO::Compress::RawDeflate, IO::Uncompress::RawInflate, IO::Compress::Bzip2, IO::Uncompress::Bunzip2, IO::Compress::Lzma, IO::Uncompress::UnLzma, IO::Compress::Xz, IO::Uncompress::UnXz, IO::Compress::Lzop, IO::Uncompress::UnLzop, IO::Compress::Lzf, IO::Uncompress::UnLzf, IO::Uncompress::AnyInflate, IO::Uncompress::AnyUncompress
IO::Compress::FAQ
File::GlobMapper, Archive::Zip, Archive::Tar, IO::Zlib
For RFC 1950, 1951 and 1952 see http://www.faqs.org/rfcs/rfc1950.html, http://www.faqs.org/rfcs/rfc1951.html and http://www.faqs.org/rfcs/rfc1952.html
The zlib compression library was written by Jean-loup Gailly gzip@prep.ai.mit.edu and Mark Adler madler@alumni.caltech.edu.
The primary site for the zlib compression library is http://www.zlib.org.
The primary site for gzip is http://www.gzip.org.
AUTHOR
This module was written by Paul Marquess, pmqs@cpan.org.
MODIFICATION HISTORY
See the Changes file.
COPYRIGHT AND LICENSE
Copyright (c) 1995-2014 Paul Marquess. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
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