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=head1 NAME

Dpkg::Compression - simple database of available compression methods

=head1 DESCRIPTION

This modules provides a few public functions and a public regex to
interact with the set of supported compression methods.

=cut

=head1 FUNCTIONS

=over 4

=item @list = compression_get_list()

Returns a list of supported compression methods (sorted alphabetically).

=cut

=item compression_is_supported($comp)

Returns a boolean indicating whether the give compression method is
known and supported.

=cut

=item compression_get_property($comp, $property)

Returns the requested property of the compression method. Returns undef if
either the property or the compression method doesn't exist. Valid
properties currently include "file_ext" for the file extension,
"default_level" for the default compression level,
"comp_prog" for the name of the compression program and "decomp_prog" for
the name of the decompression program.

This function is deprecated, please switch to one of the new specialized
getters instead.

=cut

=item compression_guess_from_filename($filename)

Returns the compression method that is likely used on the indicated
filename based on its file extension.

=cut

=item $regex = compression_get_file_extension_regex()

Returns a regex that matches a file extension of a file compressed with
one of the supported compression methods.

=cut

=item $ext = compression_get_file_extension($comp)

Return the file extension for the compressor $comp.

=cut

=item $comp = compression_get_default()

Return the default compression method. It is "xz" unless
compression_set_default() has been used to change it.

=cut

=item compression_set_default($comp)

Change the default compression method. Errors out if the
given compression method is not supported.

=cut

=item $level = compression_get_default_level()

Return the global default compression level used when compressing data if
it has been set, otherwise the default level for the default compressor.

It's "9" for "gzip" and "bzip2", "6" for "xz" and "lzma", unless
compression_set_default_level() has been used to change it.

=cut

=item compression_set_default_level($level)

Change the global default compression level. Passing undef as the level will
reset it to the global default compressor specific default, otherwise errors
out if the level is not valid (see compression_is_valid_level()).

=cut

=item $level = compression_get_level($comp)

Return the compression level used when compressing data with a specific
compressor. The value returned is the specific compression level if it has
been set, otherwise the global default compression level if it has been set,
falling back to the specific default compression level.

=cut

=item compression_set_level($comp, $level)

Change the compression level for a specific compressor. Passing undef as
the level will reset it to the specific default compressor level, otherwise
errors out if the level is not valid (see compression_is_valid_level()).

=cut

=item compression_is_valid_level($level)

Returns a boolean indicating whether $level is a valid compression level
(it must be either a number between 1 and 9 or "fast" or "best")

=cut

=item $threads = compression_get_threads()

Return the number of threads to use for compression and decompression.

=cut

=item compression_set_threads($threads)

Change the threads to use for compression and decompression. Passing C<undef>
or B<0> requests to use automatic mode, based on the current CPU cores on
the system.

=cut

=item @exec = compression_get_cmdline_compress($comp)

Returns a list ready to be passed to exec(), its first element is the
program name for compression and the following elements are parameters
for the program.

When executed the program will act as a filter between its standard input
and its standard output.

=cut

=item @exec = compression_get_cmdline_decompress($comp)

Returns a list ready to be passed to exec(), its first element is the
program name for decompression and the following elements are parameters
for the program.

When executed the program will act as a filter between its standard input
and its standard output.

=cut

=head1 CHANGES

=head2 Version 2.01 (dpkg 1.21.14)

New functions: compression_get_file_extension(), compression_get_level(),
compression_set_level(), compression_get_cmdline_compress(),
compression_get_cmdline_decompress(), compression_get_threads() and
compression_set_threads().

Deprecated functions: compression_get_property().

=head2 Version 2.00 (dpkg 1.20.0)

Hide variables: $default_compression, $default_compression_level
and $compression_re_file_ext.

=head2 Version 1.02 (dpkg 1.17.2)

New function: compression_get_file_extension_regex()

Deprecated variables: $default_compression, $default_compression_level
and $compression_re_file_ext

=head2 Version 1.01 (dpkg 1.16.1)

Default compression level is not global any more, it is per compressor type.

=head2 Version 1.00 (dpkg 1.15.6)

Mark the module as public.

=cut