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Compress::Raw::Zlib(3perl) | Perl Programmers Reference Guide | Compress::Raw::Zlib(3perl) |
NAME¶
Compress::Raw::Zlib - Low-Level Interface to zlib compression librarySYNOPSIS¶
use Compress::Raw::Zlib ; ($d, $status) = new Compress::Raw::Zlib::Deflate( [OPT] ) ; $status = $d->deflate($input, $output) ; $status = $d->flush($output [, $flush_type]) ; $d->deflateReset() ; $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) = new Compress::Raw::Zlib::Inflate( [OPT] ) ; $status = $i->inflate($input, $output [, $eof]) ; $status = $i->inflateSync($input) ; $i->inflateReset() ; $i->dict_adler() ; $d->crc32() ; $d->adler32() ; $i->total_in() ; $i->total_out() ; $i->msg() ; $d->get_BufSize(); $crc = adler32($buffer [,$crc]) ; $crc = crc32($buffer [,$crc]) ; $crc = adler32_combine($crc1, $crc2, $len2)l $crc = crc32_combine($adler1, $adler2, $len2) my $version = Compress::Raw::Zlib::zlib_version();
DESCRIPTION¶
The Compress::Raw::Zlib module provides a Perl interface to the zlib compression library (see "AUTHOR" for details about where to get zlib).Compress::Raw::Zlib::Deflate¶
This section defines an interface that allows in-memory compression using the deflate interface provided by zlib. Here is a definition of the interface available:($d, $status) = new Compress::Raw::Zlib::Deflate( [OPT] ) ¶
Initialises a deflation object. If you are familiar with the zlib library, it combines the features of the zlib functions "deflateInit", "deflateInit2" and "deflateSetDictionary". If successful, it will return the initialised deflation object, $d and a $status of "Z_OK" in a list context. In scalar context it returns the deflation object, $d, only. If not successful, the returned deflation object, $d, will be undef and $status will hold the a zlib error code. The function optionally takes a number of named options specified as "Name => value" pairs. This allows individual options to be tailored without having to specify them all in the parameter list. For backward compatibility, it is also possible to pass the parameters as a reference to a hash containing the name=>value pairs. Below is a list of the valid options:- -Level
- Defines the compression level. Valid values are 0 through
9, "Z_NO_COMPRESSION", "Z_BEST_SPEED",
"Z_BEST_COMPRESSION", and "Z_DEFAULT_COMPRESSION".
- -Method
- Defines the compression method. The only valid value at present (and the default) is "Z_DEFLATED".
- -WindowBits
- To compress an RFC 1950 data stream, set
"WindowBits" to a positive number between 8 and 15.
- -MemLevel
- For a definition of the meaning and valid values for
"MemLevel" refer to the zlib documentation for
deflateInit2.
- -Strategy
- Defines the strategy used to tune the compression. The
valid values are "Z_DEFAULT_STRATEGY", "Z_FILTERED",
"Z_RLE", "Z_FIXED" and "Z_HUFFMAN_ONLY".
- -Dictionary
- When a dictionary is specified Compress::Raw::Zlib
will automatically call "deflateSetDictionary" directly after
calling "deflateInit". The Adler32 value for the dictionary can
be obtained by calling the method "$d->dict_adler()".
- -Bufsize
- Sets the initial size for the output buffer used by the
"$d->deflate" and "$d->flush" methods. If the
buffer has to be reallocated to increase the size, it will grow in
increments of "Bufsize".
- -AppendOutput
- This option controls how data is written to the output
buffer by the "$d->deflate" and "$d->flush"
methods.
- -CRC32
- If set to true, a crc32 checksum of the uncompressed data
will be calculated. Use the "$d->crc32" method to retrieve
this value.
- -ADLER32
- If set to true, an adler32 checksum of the uncompressed
data will be calculated. Use the "$d->adler32" method to
retrieve this value.
my $d = new Compress::Raw::Zlib::Deflate ( -Bufsize => 300, -Level => Z_BEST_SPEED ) ;
$status = $d->deflate($input, $output)¶
Deflates the contents of $input and writes the compressed data to $output. The $input and $output parameters can be either scalars or scalar references. When finished, $input will be completely processed (assuming there were no errors). If the deflation was successful it writes the deflated data to $output and returns a status value of "Z_OK". On error, it returns a zlib error code. If the "AppendOutput" option is set to true in the constructor for the $d object, the compressed data will be appended to $output. If it is false, $output will be truncated before any compressed data is written to it. Note: This method will not necessarily write compressed data to $output every time it is called. So do not assume that there has been an error if the contents of $output is empty on returning from this method. As long as the return code from the method is "Z_OK", the deflate has succeeded.$status = $d->flush($output [, $flush_type]) ¶
Typically used to finish the deflation. Any pending output will be written to $output. Returns "Z_OK" if successful. 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. If the "AppendOutput" option is set to true in the constructor for the $d object, the compressed data will be appended to $output. If it is false, $output will be truncated before any compressed data is written to it.$status = $d->deflateReset() ¶
This method will reset the deflation object $d. It can be used when you are compressing multiple data streams and want to use the same object to compress each of them. It should only be used once the previous data stream has been flushed successfully, i.e. a call to "$d->flush(Z_FINISH)" has returned "Z_OK". Returns "Z_OK" if successful.$status = $d->deflateParams([OPT])¶
Change settings for the deflate object $d. The list of the valid options is shown below. Options not specified will remain unchanged.- -Level
- Defines the compression level. Valid values are 0 through 9, "Z_NO_COMPRESSION", "Z_BEST_SPEED", "Z_BEST_COMPRESSION", and "Z_DEFAULT_COMPRESSION".
- -Strategy
- Defines the strategy used to tune the compression. The valid values are "Z_DEFAULT_STRATEGY", "Z_FILTERED" and "Z_HUFFMAN_ONLY".
- -BufSize
- Sets the initial size for the output buffer used by the "$d->deflate" and "$d->flush" methods. If the buffer has to be reallocated to increase the size, it will grow in increments of "Bufsize".
$status = $d->deflateTune($good_length, $max_lazy, $nice_length, $max_chain)¶
Tune the internal settings for the deflate object $d. This option is only available if you are running zlib 1.2.2.3 or better. Refer to the documentation in zlib.h for instructions on how to fly "deflateTune".$d->dict_adler()¶
Returns the adler32 value for the dictionary.$d->crc32()¶
Returns the crc32 value for the uncompressed data to date. If the "CRC32" option is not enabled in the constructor for this object, this method will always return 0;$d->adler32()¶
Returns the adler32 value for the uncompressed data to date.$d->msg()¶
Returns the last error message generated by zlib.$d->total_in()¶
Returns the total number of bytes uncompressed bytes input to deflate.$d->total_out()¶
Returns the total number of compressed bytes output from deflate.$d->get_Strategy()¶
Returns the deflation strategy currently used. Valid values are "Z_DEFAULT_STRATEGY", "Z_FILTERED" and "Z_HUFFMAN_ONLY".$d->get_Level()¶
Returns the compression level being used.$d->get_BufSize()¶
Returns the buffer size used to carry out the compression.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::Raw::Zlib ; binmode STDIN; binmode STDOUT; my $x = new Compress::Raw::Zlib::Deflate or die "Cannot create a deflation stream\n" ; my ($output, $status) ; while (<>) { $status = $x->deflate($_, $output) ; $status == Z_OK or die "deflation failed\n" ; print $output ; } $status = $x->flush($output) ; $status == Z_OK or die "deflation failed\n" ; print $output ;
Compress::Raw::Zlib::Inflate¶
This section defines an interface that allows in-memory uncompression using the inflate interface provided by zlib. Here is a definition of the interface:($i, $status) = new Compress::Raw::Zlib::Inflate( [OPT] ) ¶
Initialises an inflation object. In a list context it returns the inflation object, $i, and the zlib status code ($status). In a scalar context it returns the inflation object only. If successful, $i will hold the inflation object and $status will be "Z_OK". If not successful, $i will be undef and $status will hold the zlib error code. The function optionally takes a number of named options specified as "-Name => value" pairs. This allows individual options to be tailored without having to specify them all in the parameter list. For backward compatibility, it is also possible to pass the parameters as a reference to a hash containing the "name=>value" pairs. Here is a list of the valid options:- -WindowBits
- To uncompress an RFC 1950 data stream, set
"WindowBits" to a positive number between 8 and 15.
- -Bufsize
- Sets the initial size for the output buffer used by the
"$i->inflate" method. If the output buffer in this method has
to be reallocated to increase the size, it will grow in increments of
"Bufsize".
- -Dictionary
- The default is no dictionary.
- -AppendOutput
- This option controls how data is written to the output
buffer by the "$i->inflate" method.
- -CRC32
- If set to true, a crc32 checksum of the uncompressed data
will be calculated. Use the "$i->crc32" method to retrieve
this value.
- -ADLER32
- If set to true, an adler32 checksum of the uncompressed
data will be calculated. Use the "$i->adler32" method to
retrieve this value.
- -ConsumeInput
- If set to true, this option will remove compressed data
from the input buffer of the "$i->inflate" method as the
inflate progresses.
- -LimitOutput
- The "LimitOutput" option changes the behavior of
the "$i->inflate" method so that the amount of memory used by
the output buffer can be limited.
my ($i, $status) = new Compress::Raw::Zlib::Inflate( -Bufsize => 300 ) ;
$status = $i->inflate($input, $output [,$eof]) ¶
Inflates the complete contents of $input and writes the uncompressed data to $output. The $input and $output parameters can either be scalars or scalar references. Returns "Z_OK" if successful and "Z_STREAM_END" if the end of the compressed data has been successfully reached. If not successful $status will hold the zlib error code. If the "ConsumeInput" option has been set to true when the "Compress::Raw::Zlib::Inflate" object is created, the $input parameter is modified by "inflate". On completion it will contain what remains of the input buffer after inflation. In practice, this means that when the return status is "Z_OK" the $input parameter will contain an empty string, and when the return status is "Z_STREAM_END" the $input 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) and there is useful data immediately after the deflation stream. If the "AppendOutput" option is set to true in the constructor for this object, the uncompressed data will be appended to $output. If it is false, $output will be truncated before any uncompressed data is written to it. The $eof parameter needs a bit of explanation. Prior to version 1.2.0, zlib assumed that there was at least one trailing byte immediately after the compressed data stream when it was carrying out decompression. This normally isn't a problem because the majority of zlib applications guarantee that there will be data directly after the compressed data stream. For example, both gzip (RFC 1950) and zip both define trailing data that follows the compressed data stream. The $eof parameter only needs to be used if all of the following conditions apply- 1.
- You are either using a copy of zlib that is older than version 1.2.0 or you want your application code to be able to run with as many different versions of zlib as possible.
- 2.
- You have set the "WindowBits" parameter to "-MAX_WBITS" in the constructor for this object, i.e. you are uncompressing a raw deflated data stream (RFC 1951).
- 3.
- There is no data immediately after the compressed data stream.
$status = $i->inflateSync($input)¶
This method can be used to attempt to recover good data from a compressed data stream that is partially corrupt. It scans $input 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 $input will be have all data up to the flush point removed. This data can then be passed to the "$i->inflate" method to be uncompressed. 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. Note full flush points are not present by default in compressed data streams. They must have been added explicitly when the data stream was created by calling "Compress::Deflate::flush" with "Z_FULL_FLUSH".$status = $i->inflateReset() ¶
This method will reset the inflation object $i. It can be used when you are uncompressing multiple data streams and want to use the same object to uncompress each of them. Returns "Z_OK" if successful.$i->dict_adler()¶
Returns the adler32 value for the dictionary.$i->crc32()¶
Returns the crc32 value for the uncompressed data to date. If the "CRC32" option is not enabled in the constructor for this object, this method will always return 0;$i->adler32()¶
Returns the adler32 value for the uncompressed data to date. If the "ADLER32" option is not enabled in the constructor for this object, this method will always return 0;$i->msg()¶
Returns the last error message generated by zlib.$i->total_in()¶
Returns the total number of bytes compressed bytes input to inflate.$i->total_out()¶
Returns the total number of uncompressed bytes output from inflate.$d->get_BufSize()¶
Returns the buffer size used to carry out the decompression.Examples¶
Here is an example of using "inflate".use strict ; use warnings ; use Compress::Raw::Zlib; my $x = new Compress::Raw::Zlib::Inflate() or die "Cannot create a inflation stream\n" ; my $input = '' ; binmode STDIN; binmode STDOUT; my ($output, $status) ; while (read(STDIN, $input, 4096)) { $status = $x->inflate($input, $output) ; print $output ; last if $status != Z_OK ; } die "inflation failed\n" unless $status == Z_STREAM_END ;The next example show how to use the "LimitOutput" option. Notice the use of two nested loops in this case. The outer loop reads the data from the input source - STDIN and the inner loop repeatedly calls "inflate" until $input is exhausted, we get an error, or the end of the stream is reached. One point worth remembering is by using the "LimitOutput" option you also get "ConsumeInput" set as well - this makes the code below much simpler.
use strict ; use warnings ; use Compress::Raw::Zlib; my $x = new Compress::Raw::Zlib::Inflate(LimitOutput => 1) or die "Cannot create a inflation stream\n" ; my $input = '' ; binmode STDIN; binmode STDOUT; my ($output, $status) ; OUTER: while (read(STDIN, $input, 4096)) { do { $status = $x->inflate($input, $output) ; print $output ; last OUTER unless $status == Z_OK || $status == Z_BUF_ERROR ; } while ($status == Z_OK && length $input); } 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.
$crc = adler32_combine($crc1, $crc2, $len2)l $crc = crc32_combine($adler1, $adler2, $len2)These functions allow checksums to be merged.
Misc¶
my $version = Compress::Raw::Zlib::zlib_version();¶
Returns the version of the zlib library.The LimitOutput option.¶
By default "$i->inflate($input, $output)" will uncompress all data in $input and write all of the uncompressed data it has generated to $output. This makes the interface to "inflate" much simpler - if the method has uncompressed $input successfully all compressed data in $input will have been dealt with. So if you are reading from an input source and uncompressing as you go the code will look something like thisuse strict ; use warnings ; use Compress::Raw::Zlib; my $x = new Compress::Raw::Zlib::Inflate() or die "Cannot create a inflation stream\n" ; my $input = '' ; my ($output, $status) ; while (read(STDIN, $input, 4096)) { $status = $x->inflate($input, $output) ; print $output ; last if $status != Z_OK ; } die "inflation failed\n" unless $status == Z_STREAM_END ;The points to note are
- •
- The main processing loop in the code handles reading of compressed data from STDIN.
- •
- The status code returned from "inflate" will only trigger termination of the main processing loop if it isn't "Z_OK". When "LimitOutput" has not been used the "Z_OK" status means means that the end of the compressed data stream has been reached or there has been an error in uncompression.
- •
- After the call to "inflate" all of the uncompressed data in $input will have been processed. This means the subsequent call to "read" can overwrite it's contents without any problem.
use strict ; use warnings ; use Compress::Raw::Zlib; my $x = new Compress::Raw::Zlib::Inflate(LimitOutput => 1) or die "Cannot create a inflation stream\n" ; my $input = '' ; binmode STDIN; binmode STDOUT; my ($output, $status) ; OUTER: while (read(STDIN, $input, 4096)) { do { $status = $x->inflate($input, $output) ; print $output ; last OUTER unless $status == Z_OK || $status == Z_BUF_ERROR ; } while ($status == Z_OK && length $input); } die "inflation failed\n" unless $status == Z_STREAM_END ;Points to note this time:
- •
- There are now two nested loops in the code: the outer loop for reading the compressed data from STDIN, as before; and the inner loop to carry out the uncompression.
- •
- There are two exit points from the inner uncompression
loop.
ACCESSING ZIP FILES¶
Although it is possible (with some effort on your part) to use this module to access .zip files, there are other perl modules available that will do all the hard work for you. Check out "Archive::Zip", "IO::Compress::Zip" and "IO::Uncompress::Unzip".CONSTANTS¶
All the zlib constants are automatically imported when you make use of Compress::Raw::Zlib.SEE ALSO¶
Compress::Zlib, 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 Compress::Zlib::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) 2005-2011 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.2011-09-26 | perl v5.14.2 |