NAME

Compress::Zlib - Interface to zlib compression library

SYNOPSIS

use Compress::Zlib 2 ;

($d, $status) = new Compress::Zlib::Deflate( [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) = new Compress::Zlib::Inflate( [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

# Compress::Zlib 1.x legacy interface

($d, $status) = deflateInit( [OPT] ) ;
($out, $status) = $d->deflate($buffer) ;
$status = $d->deflateParams([OPT]) ;
($out, $status) = $d->flush() ;
$d->dict_adler() ;
$d->total_in() ;
$d->total_out() ;
$d->msg() ;

($i, $status) = inflateInit( [OPT] ) ;
($out, $status) = $i->inflate($buffer) ;
$status = $i->inflateSync($buffer) ;
$i->dict_adler() ;
$i->total_in() ;
$i->total_out() ;
$i->msg() ;

DESCRIPTION

The Compress::Zlib module provides a Perl interface to the zlib compression library (see "AUTHOR" for details about where to get zlib). The zlib library allows reading and writing of compressed data streams that conform to RFC1950, RFC1951 and RFC1952 (aka gzip). Most of the zlib functionality is available in Compress::Zlib.

Unless you are working with legacy code, or you need to work directly with the low-level zlib interface, it is recommended that applications use one of the newer IO::* interfaces provided with this module.

The Compress::Zlib module can be split into two general areas of functionality, namely a low-level in-memory compression/decompression interface and a simple read/write interface to gzip files.

Each of these areas will be discussed separately below.

GZIP INTERFACE

A number of functions are supplied in zlib for reading and writing gzip files that conform to RFC1952. This module provides an interface to most of them.

If you are upgrading from Compress::Zlib 1.x, the following enhancements have been made to the gzopen interface:

If you want to to open either STDIN or STDOUT with gzopen, you can now optionally use the special filename "-" as a synonym for \*STDIN and \*STDOUT.
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 to gzopen. 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.

In Compress::Zlib version 2.x, the gzopen interface has been completely rewritten to use the IO::Gzip for writing gzip files and IO::Gunzip for reading gzip files.
Addition of gzseek to provide a restricted seek interface.
Added gztell.

A more complete and flexible interface for reading/writing gzip files/buffers is included with this module. See IO::Gzip and IO::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 and undef 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 the information stored in the gzip header (like the original filename or a comment) use IO::Gzip instead.

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' function fopen, so "rb" is used to open for reading and "wb" for writing.

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 and gzreadline.

In addition, gzreadline fully supports the use of of the variable $/ ($INPUT_RECORD_SEPARATOR or $RS when English is in use) to determine what constitutes an end of line. Both paragraph mode and file slurp mode are supported.

$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 is Z_FINISH. Other valid values for $flush_type are Z_NO_FLUSH, Z_SYNC_FLUSH, Z_FULL_FLUSH and Z_BLOCK. It is strongly recommended that you only set the flush_type parameter if you fully understand the implications of what it does - overuse of flush can seriously degrade the level of compression achieved. See the zlib documentation for details.

Returns 1 on success, 0 on failure.

$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 1 on success, 0 on failure.

$gz->gzsetparams($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, 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.

$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 unlike gzerror(), 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. 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.

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) ;

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.

See IO::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) ;

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.

See IO::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, and Z_DEFAULT_COMPRESSION. If $level is not specified Z_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.

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.

Compress::Zlib::Deflate

This section defines an interface that allows in-memory compression using the deflate interface provided by zlib.

Note: The interface defined in this section is different from version 1.x of this module. The original deflate interface is still available for backward compatibility and is documented in the section "Compress::Zlib 1.x Deflate Interface".

Here is a definition of the interface available:

($d, $status) = new Compress::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.

The default is -Level => Z_DEFAULT_COMPRESSION.

-Method

Defines the compression method. The only valid value at present (and the default) is -Method => Z_DEFLATED.

-WindowBits

For a definition of the meaning and valid values for WindowBits refer to the zlib documentation for deflateInit2.

Defaults to -WindowBits => MAX_WBITS.

-MemLevel

For a definition of the meaning and valid values for MemLevel refer to the zlib documentation for deflateInit2.

Defaults to -MemLevel => MAX_MEM_LEVEL.

-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.

The default is -Strategy =>Z_DEFAULT_STRATEGY.

-Dictionary

When a dictionary is specified Compress::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().

The default is no dictionary.

-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.

The default buffer size is 4096.

-AppendOutput

This option controls how data is written to the output buffer by the $d->deflate and $d->flush methods.

If the AppendOutput option is set to false, the output buffers in the $d->deflate and $d->flush methods will be truncated before uncompressed data is written to them.

If the option is set to true, uncompressed data will be appended to the output buffer in the $d->deflate and $d->flush methods.

This option defaults to false.

-CRC32

If set to true, a crc32 checksum of the uncompressed data will be calculated. Use the $d->crc32 method to retrieve this value.

This option defaults to false.

-ADLER32

If set to true, an adler32 checksum of the uncompressed data will be calculated. Use the $d->adler32 method to retrieve this value.

This option defaults to false.

Here is an example of using the Compress::Zlib::Deflate optional parameter list to override the default buffer size and compression level. All other options will take their default values.

my $d = new Compress::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.

$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::Zlib 2 ;

binmode STDIN;
binmode STDOUT;
my $x = new Compress::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::Zlib::Inflate

This section defines an interface that allows in-memory uncompression using the inflate interface provided by zlib.

Note: The interface defined in this section is different from version 1.x of this module. The original inflate interface is still available for backward compatibility and is documented in the section "Compress::Zlib 1.x Inflate Interface".

Here is a definition of the interface:

($i, $status) = new Compress::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 RFC1950 data stream, set WindowBits to a positive number.

To uncompress an RFC1951 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 -WindowBits =>MAX_WBITS.

-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.

Default is 4096.

-Dictionary

The default is no dictionary.

-AppendOutput

This option controls how data is written to the output buffer by the $i->inflate method.

If the option is set to false, the output buffer in the $i->inflate method will be truncated before uncompressed data is written to it.

If the option is set to true, uncompressed data will be appended to the output buffer by the $i->inflate method.

This option defaults to false.

-CRC32

If set to true, a crc32 checksum of the uncompressed data will be calculated. Use the $i->crc32 method to retrieve this value.

This option defaults to false.

-ADLER32

If set to true, an adler32 checksum of the uncompressed data will be calculated. Use the $i->adler32 method to retrieve this value.

This option defaults to false.

-ConsumeInput

If set to true, this option will remove compressed data from the input buffer of the the $i->inflate method as the inflate progresses.

This option can be useful when you are processing compressed data that is embedded in another file/buffer. In this case the data that immediately follows the compressed stream will be left in the input buffer.

This option defaults to true.

Here is an example of using an optional parameter to override the default buffer size.

my ($i, $status) = new Compress::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::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 (RFC1950) 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

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.
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 (RFC1951).
There is no data immediately after the compressed data stream.

If all of these are the case, then you need to set the $eof parameter to true on the final call (and only the final call) to $i->inflate.

If you have built this module with zlib >= 1.2.0, the $eof parameter is ignored. You can still set it if you want, but it won't be used behind the scenes.

$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.

$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.

Example

Here is an example of using inflate.

use strict ;
use warnings ;

use Compress::Zlib 2 ;

my $x = new Compress::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 
        if $status == Z_OK or $status == Z_STREAM_END ;

    last if $status != Z_OK ;
}

die "inflation failed\n"
    unless $status == Z_STREAM_END ;

Compress::Zlib 1.x Deflate Interface

This section defines the interface available in Compress::Zlib version 1.x 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, and Z_DEFAULT_COMPRESSION.

The default is -Level =>Z_DEFAULT_COMPRESSION.

-Method

Defines the compression method. The only valid value at present (and the default) is -Method =>Z_DEFLATED.

-WindowBits

To create an RFC1950 data stream, set WindowBits to a positive number.

To create an RFC1951 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 -WindowBits =>MAX_WBITS.

-MemLevel

For a definition of the meaning and valid values for MemLevel refer to the zlib documentation for deflateInit2.

Defaults to -MemLevel =>MAX_MEM_LEVEL.

-Strategy

Defines the strategy used to tune the compression. The valid values are Z_DEFAULT_STRATEGY, Z_FILTERED and Z_HUFFMAN_ONLY.

The default is -Strategy =>Z_DEFAULT_STRATEGY.

-Dictionary

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([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.

$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, 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.

$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 ;

Compress::Zlib 1.x Inflate Interface

This section defines the interface available in Compress::Zlib version 1.x that allows in-memory uncompression using the deflate interface provided by zlib.

Here is a definition of the interface:

($i, $status) = inflateInit()

Initializes 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:

-WindowBits

To uncompress an RFC1950 data stream, set WindowBits to a positive number.

To uncompress an RFC1951 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 -WindowBits =>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 ;

ACCESSING ZIP FILES

Although it is possible (with some effort on your part) 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 the Archive::Zip module on CPAN at

http://www.cpan.org/modules/by-module/Archive/Archive-Zip-*.tar.gz

CONSTANTS

All the zlib constants are automatically imported when you make use of Compress::Zlib.

AUTHOR

The Compress::Zlib module was written by Paul Marquess, pmqs@cpan.org. The latest copy of the module can be found on CPAN in modules/by-module/Compress/Compress-Zlib-x.x.tar.gz.

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.

MODIFICATION HISTORY

See the Changes file.

COPYRIGHT AND LICENSE

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cpanm

cpanm Env

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perl -MCPAN -e shell
install Env

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NAME

SYNOPSIS

DESCRIPTION

GZIP INTERFACE

Examples

Compress::Zlib::memGzip

Compress::Zlib::memGunzip

COMPRESS/UNCOMPRESS

CHECKSUM FUNCTIONS

Compress::Zlib::Deflate

($d, $status) = new Compress::Zlib::Deflate( [OPT] )

$status = $d->deflate($input, $output)

$status = $d->flush($output [, $flush_type])

$status = $d->deflateParams([OPT])

$status = $d->deflateTune($good_length, $max_lazy, $nice_length, $max_chain)

$d->dict_adler()

$d->crc32()

$d->adler32()

$d->msg()

$d->total_in()

$d->total_out()

$d->get_Strategy()

$d->get_Level()

$d->get_BufSize()

Example

Compress::Zlib::Inflate

($i, $status) = new Compress::Zlib::Inflate( [OPT] )

$status = $i->inflate($input, $output [,$eof])

$status = $i->inflateSync($input)

$i->dict_adler()

$i->crc32()

$i->adler32()

$i->msg()

$i->total_in()

$i->total_out()

$d->get_BufSize()

Example

Compress::Zlib 1.x Deflate Interface

($d, $status) = deflateInit( [OPT] )

($out, $status) = $d->deflate($buffer)

($out, $status) = $d->flush([flush_type])

$status = $d->deflateParams([OPT])

$d->dict_adler()

$d->msg()

$d->total_in()

$d->total_out()

Example

Compress::Zlib 1.x Inflate Interface

($i, $status) = inflateInit()

($out, $status) = $i->inflate($buffer)

$status = $i->inflateSync($buffer)

$i->dict_adler()

$i->msg()

$i->total_in()

$i->total_out()

Example

ACCESSING ZIP FILES

CONSTANTS

SEE ALSO

AUTHOR

MODIFICATION HISTORY

COPYRIGHT AND LICENSE

Module Install Instructions