Perl 5 version 24.3 documentation

Compress::Raw::Bzip2

NAME

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

SYNOPSIS

  1.     use Compress::Raw::Bzip2 ;
  3.     my ($bz, $status) = new Compress::Raw::Bzip2 [OPTS]
  4.         or die "Cannot create bzip2 object: $bzerno\n";
  5.     
  6.     $status = $bz->bzdeflate($input, $output);
  7.     $status = $bz->bzflush($output);
  8.     $status = $bz->bzclose($output);
  10.     my ($bz, $status) = new Compress::Raw::Bunzip2 [OPTS]
  11.         or die "Cannot create bunzip2 object: $bzerno\n";
  12.     
  13.     $status = $bz->bzinflate($input, $output);
  15.     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

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

    Defaults to 1.

  • $workfactor

    To quote the bzip2 documentation

    1.     This parameter controls how the compression phase behaves when
    2.     presented with worst case, highly repetitive, input data. If
    3.     compression runs into difficulties caused by repetitive data, the
    4.     library switches from the standard sorting algorithm to a fallback
    5.     algorithm. The fallback is slower than the standard algorithm by
    6.     perhaps a factor of three, but always behaves reasonably, no matter how
    7.     bad the input.
    9.     Lower values of workFactor reduce the amount of effort the standard
    10.     algorithm will expend before resorting to the fallback. You should set
    11.     this parameter carefully; too low, and many inputs will be handled by
    12.     the fallback algorithm and so compress rather slowly, too high, and
    13.     your average-to-worst case compression times can become very large. The
    14.     default value of 30 gives reasonable behaviour over a wide range of
    15.     circumstances.
    17.     Allowable values range from 0 to 250 inclusive. 0 is a special case,
    18.     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

    1.     If small is nonzero, the library will use an alternative decompression
    2.     algorithm which uses less memory but at the cost of decompressing more
    3.     slowly (roughly speaking, half the speed, but the maximum memory
    4.     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

  1. 		BZ_RUN
  2. 		BZ_FLUSH
  3. 		BZ_FINISH
  5. 		BZ_OK
  6. 		BZ_RUN_OK
  7. 		BZ_FLUSH_OK
  8. 		BZ_FINISH_OK
  9. 		BZ_STREAM_END
  10. 		BZ_SEQUENCE_ERROR
  11. 		BZ_PARAM_ERROR
  12. 		BZ_MEM_ERROR
  13. 		BZ_DATA_ERROR
  14. 		BZ_DATA_ERROR_MAGIC
  15. 		BZ_IO_ERROR
  16. 		BZ_UNEXPECTED_EOF
  17. 		BZ_OUTBUFF_FULL
  18. 		BZ_CONFIG_ERROR

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

IO::Compress::FAQ

File::GlobMapper, Archive::Zip, Archive::Tar, IO::Zlib

The primary site for the bzip2 program is http://www.bzip.org.

See the module Compress::Bzip2

AUTHOR

This module was written by Paul Marquess, pmqs@cpan.org.

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.