dpkg/scripts/Dpkg/Compression.pm

# Copyright © 2010 Raphaël Hertzog <hertzog@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

package Dpkg::Compression;

use strict;
use warnings;

our $VERSION = '1.01';

use Dpkg::ErrorHandling;
use Dpkg::Gettext;

use base qw(Exporter);
our @EXPORT = qw($compression_re_file_ext compression_get_list
		 compression_is_supported compression_get_property
		 compression_guess_from_filename
		 compression_get_default compression_set_default
		 compression_get_default_level
		 compression_set_default_level
		 compression_is_valid_level);

=encoding utf8

=head1 NAME

Dpkg::Compression - simple database of available compression methods

=head1 DESCRIPTION

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

=head1 EXPORTED VARIABLES

=over 4

=cut

my $COMP = {
    gzip => {
	file_ext => 'gz',
	comp_prog => [ 'gzip', '--no-name', '--rsyncable' ],
	decomp_prog => [ 'gunzip' ],
	default_level => 9,
    },
    bzip2 => {
	file_ext => 'bz2',
	comp_prog => [ 'bzip2' ],
	decomp_prog => [ 'bunzip2' ],
	default_level => 9,
    },
    lzma => {
	file_ext => 'lzma',
	comp_prog => [ 'xz', '--format=lzma' ],
	decomp_prog => [ 'unxz', '--format=lzma' ],
	default_level => 6,
    },
    xz => {
	file_ext => 'xz',
	comp_prog => [ 'xz' ],
	decomp_prog => [ 'unxz' ],
	default_level => 6,
    },
};

our $default_compression = 'gzip';
our $default_compression_level = undef;

=item $compression_re_file_ext

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

=back

=cut

my $regex = join '|', map { $_->{file_ext} } values %$COMP;
our $compression_re_file_ext = qr/(?:$regex)/;

=head1 EXPORTED FUNCTIONS

=over 4

=item my @list = compression_get_list()

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

=cut

sub compression_get_list {
    my @list = sort keys %$COMP;
    return @list;
}

=item compression_is_supported($comp)

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

=cut

sub compression_is_supported {
    return exists $COMP->{$_[0]};
}

=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.

=cut

sub compression_get_property {
    my ($comp, $property) = @_;
    return unless compression_is_supported($comp);
    return $COMP->{$comp}{$property} if exists $COMP->{$comp}{$property};
    return;
}

=item compression_guess_from_filename($filename)

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

=cut

sub compression_guess_from_filename {
    my $filename = shift;
    foreach my $comp (compression_get_list()) {
	my $ext = compression_get_property($comp, 'file_ext');
        if ($filename =~ /^(.*)\.\Q$ext\E$/) {
	    return $comp;
        }
    }
    return;
}

=item my $comp = compression_get_default()

Return the default compression method. It's "gzip" unless
C<compression_set_default> has been used to change it.

=item compression_set_default($comp)

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

=cut

sub compression_get_default {
    return $default_compression;
}

sub compression_set_default {
    my ($method) = @_;
    error(_g('%s is not a supported compression'), $method)
            unless compression_is_supported($method);
    $default_compression = $method;
}

=item my $level = compression_get_default_level()

Return the default compression level used when compressing data. It's "9"
for "gzip" and "bzip2", "6" for "xz" and "lzma", unless
C<compression_set_default_level> has been used to change it.

=item compression_set_default_level($level)

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

=cut

sub compression_get_default_level {
    if (defined $default_compression_level) {
        return $default_compression_level;
    } else {
        return compression_get_property($default_compression, 'default_level');
    }
}

sub compression_set_default_level {
    my ($level) = @_;
    error(_g('%s is not a compression level'), $level)
            unless !defined($level) or compression_is_valid_level($level);
    $default_compression_level = $level;
}

=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

sub compression_is_valid_level {
    my ($level) = @_;
    return $level =~ /^([1-9]|fast|best)$/;
}

=back

=head1 AUTHOR

Raphaël Hertzog <hertzog@debian.org>.

=cut

1;