Compress::Raw::Bzip2(3) Low-Level Interface to bzip2 compression library

SYNOPSIS


use Compress::Raw::Bzip2 ;
my ($bz, $status) = new Compress::Raw::Bzip2 [OPTS]
or die "Cannot create bzip2 object: $bzerno\n";

$status = $bz->bzdeflate($input, $output);
$status = $bz->bzflush($output);
$status = $bz->bzclose($output);
my ($bz, $status) = new Compress::Raw::Bunzip2 [OPTS]
or die "Cannot create bunzip2 object: $bzerno\n";

$status = $bz->bzinflate($input, $output);
my $version = Compress::Raw::Bzip2::bzlibversion();

DESCRIPTION

"Compress::Raw::Bzip2" provides an interface to the in-memory compression/uncompression functions from the bzip2 compression library.

Although the primary purpose for the existence of "Compress::Raw::Bzip2" is for use by the "IO::Compress::Bzip2" and "IO::Compress::Bunzip2" modules, it can be used on its own for simple compression/uncompression tasks.

Compression

($z, $status) = new Compress::Raw::Bzip2 $appendOutput, $blockSize100k, $workfactor;

Creates a new compression object.

If successful, it will return the initialised compression object, $z and a $status of "BZ_OK" in a list context. In scalar context it returns the deflation object, $z, only.

If not successful, the returned compression object, $z, will be undef and $status will hold the a bzip2 error code.

Below is a list of the valid options:

$appendOutput
Controls whether the compressed data is appended to the output buffer in the "bzdeflate", "bzflush" and "bzclose" methods.

Defaults to 1.

$blockSize100k
To quote the bzip2 documentation 

    blockSize100k specifies the block size to be used for compression. It
    should be a value between 1 and 9 inclusive, and the actual block size
    used is 100000 x this figure. 9 gives the best compression but takes
    most memory.

Defaults to 1.

$workfactor
To quote the bzip2 documentation 

    This parameter controls how the compression phase behaves when
    presented with worst case, highly repetitive, input data. If
    compression runs into difficulties caused by repetitive data, the
    library switches from the standard sorting algorithm to a fallback
    algorithm. The fallback is slower than the standard algorithm by
    perhaps a factor of three, but always behaves reasonably, no matter how
    bad the input.
    Lower values of workFactor reduce the amount of effort the standard
    algorithm will expend before resorting to the fallback. You should set
    this parameter carefully; too low, and many inputs will be handled by
    the fallback algorithm and so compress rather slowly, too high, and
    your average-to-worst case compression times can become very large. The
    default value of 30 gives reasonable behaviour over a wide range of
    circumstances.
    Allowable values range from 0 to 250 inclusive. 0 is a special case,
    equivalent to using the default value of 30.

Defaults to 0.

$status = $bz->bzdeflate($input, $output);

Reads the contents of $input, compresses it and writes the compressed data to $output.

Returns "BZ_RUN_OK" on success and a "bzip2" error code on failure.

If "appendOutput" is enabled in the constructor for the bzip2 object, the compressed data will be appended to $output. If not enabled, $output will be truncated before the compressed data is written to it.

$status = $bz->bzflush($output);

Flushes any pending compressed data to $output.

Returns "BZ_RUN_OK" on success and a "bzip2" error code on failure.

$status = $bz->bzclose($output);

Terminates the compressed data stream and flushes any pending compressed data to $output.

Returns "BZ_STREAM_END" on success and a "bzip2" error code on failure.

Example

Uncompression

($z, $status) = new Compress::Raw::Bunzip2 $appendOutput, $consumeInput, $small, $verbosity, $limitOutput;

If successful, it will return the initialised uncompression object, $z and a $status of "BZ_OK" in a list context. In scalar context it returns the deflation object, $z, only.

If not successful, the returned uncompression object, $z, will be undef and $status will hold the a bzip2 error code.

Below is a list of the valid options:

$appendOutput
Controls whether the compressed data is appended to the output buffer in the "bzinflate", "bzflush" and "bzclose" methods.

Defaults to 1.

$consumeInput
$small
To quote the bzip2 documentation 

    If small is nonzero, the library will use an alternative decompression
    algorithm which uses less memory but at the cost of decompressing more
    slowly (roughly speaking, half the speed, but the maximum memory
    requirement drops to around 2300k).

Defaults to 0.

$limitOutput
The "LimitOutput" option changes the behavior of the "$i->bzinflate" method so that the amount of memory used by the output buffer can be limited.

When "LimitOutput" is used the size of the output buffer used will either be the 16k or the amount of memory already allocated to $output, whichever is larger. Predicting the output size available is tricky, so don't rely on getting an exact output buffer size.

When "LimitOutout" is not specified "$i->bzinflate" will use as much memory as it takes to write all the uncompressed data it creates by uncompressing the input buffer.

If "LimitOutput" is enabled, the "ConsumeInput" option will also be enabled.

This option defaults to false.

$verbosity
This parameter is ignored.

Defaults to 0.

$status = $z->bzinflate($input, $output);

Uncompresses $input and writes the uncompressed data to $output.

Returns "BZ_OK" if the uncompression was successful, but the end of the compressed data stream has not been reached. Returns "BZ_STREAM_END" on successful uncompression and the end of the compression stream has been reached.

If "consumeInput" is enabled in the constructor for the bunzip2 object, $input will have all compressed data removed from it after uncompression. On "BZ_OK" return this will mean that $input will be an empty string; when "BZ_STREAM_END" $input will either be an empty string or will contain whatever data immediately followed the compressed data stream.

If "appendOutput" is enabled in the constructor for the bunzip2 object, the uncompressed data will be appended to $output. If not enabled, $output will be truncated before the uncompressed data is written to it.

Misc

my $version = Compress::Raw::Bzip2::bzlibversion();

Returns the version of the underlying bzip2 library.

Constants

The following bzip2 constants are exported by this module 

                BZ_RUN
                BZ_FLUSH
                BZ_FINISH
                BZ_OK
                BZ_RUN_OK
                BZ_FLUSH_OK
                BZ_FINISH_OK
                BZ_STREAM_END
                BZ_SEQUENCE_ERROR
                BZ_PARAM_ERROR
                BZ_MEM_ERROR
                BZ_DATA_ERROR
                BZ_DATA_ERROR_MAGIC
                BZ_IO_ERROR
                BZ_UNEXPECTED_EOF
                BZ_OUTBUFF_FULL
                BZ_CONFIG_ERROR

AUTHOR

This module was written by Paul Marquess, [email protected].

MODIFICATION HISTORY

See the Changes file.

COPYRIGHT AND LICENSE

Copyright (c) 2005-2015 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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