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[p5sagit/p5-mst-13.2.git] / ext / Compress / Zlib / pod / FAQ.pod

=head1 NAME

Compress::Zlib::FAQ -- Frequently Asked Questions about Compress::Zlib 

=head1 DESCRIPTION

Common questions answered.



=head2 Compatibility with Unix compress/uncompress.

Although C<Compress::Zlib> has a pair of functions called C<compress>
and C<uncompress>, they are I<not> the same as the Unix programs of the
same name. The C<Compress::Zlib> library is not compatible with Unix
C<compress>.

If you have the C<uncompress> program available, you can use this to
read compressed files

    open F, "uncompress -c $filename |";
    while (<F>)
    {
        ...

If you have the C<gunzip> program available, you can use this to read
compressed files

    open F, "gunzip -c $filename |";
    while (<F>)
    {
        ...

and this to write compress files if you have the C<compress> program
available

    open F, "| compress -c $filename ";
    print F "data";
    ...
    close F ;

=head2 Accessing .tar.Z files

The C<Archive::Tar> module can optionally use C<Compress::Zlib> (via
the C<IO::Zlib> module) to access tar files that have been compressed
with C<gzip>. Unfortunately tar files compressed with the Unix C<compress>
utility cannot be read by C<Compress::Zlib> and so cannot be directly
accesses by C<Archive::Tar>.

If the C<uncompress> or C<gunzip> programs are available, you can use
one of these workarounds to read C<.tar.Z> files from C<Archive::Tar>

Firstly with C<uncompress>

    use strict;
    use warnings;
    use Archive::Tar;

    open F, "uncompress -c $filename |";
    my $tar = Archive::Tar->new(*F);
    ...

and this with C<gunzip>

    use strict;
    use warnings;
    use Archive::Tar;

    open F, "gunzip -c $filename |";
    my $tar = Archive::Tar->new(*F);
    ...

Similarly, if the C<compress> program is available, you can use this to
write a C<.tar.Z> file

    use strict;
    use warnings;
    use Archive::Tar;
    use IO::File;

    my $fh = new IO::File "| compress -c >$filename";
    my $tar = Archive::Tar->new();
    ...
    $tar->write($fh);
    $fh->close ;


=head2 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 C<Archive::Zip> module on CPAN at

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

Assuming you don't want to use this module to access zip files there
are a number of undocumented features in the zlib library you need to
be aware of.

=over 5

=item 1.

When calling B<inflateInit> or B<deflateInit> the B<WindowBits> parameter
must be set to C<-MAX_WBITS>. This disables the creation of the zlib
header.

=item 2.

The zlib function B<inflate>, and so the B<inflate> method supplied in
this module, assume that there is at least one trailing byte after the
compressed data stream. Normally this isn't a problem because both
the gzip and zip file formats will guarantee that there is data directly
after the compressed data stream.

=back












=head2 Zlib Library Version Support

By default C<Compress::Zlib> will build with a private copy of version 1.2.3 of the zlib library. (See the F<README> file for details of how
to override this behavior)

If you decide to use a different version of the zlib library, you need to be
aware of the following issues

=over 5

=item *

First off, you must have zlib 1.0.5 or better.

=item *

You need to have zlib 1.2.1 or better if you want to use the C<-Merge> option
with C<IO::Compress::Gzip>, C<IO::Compress::Deflate> and C<IO::Compress::RawDeflate>.



=back




=head1 SEE ALSO

L<Compress::Zlib>, L<IO::Compress::Gzip>, L<IO::Uncompress::Gunzip>, L<IO::Compress::Deflate>, L<IO::Uncompress::Inflate>, L<IO::Compress::RawDeflate>, L<IO::Uncompress::RawInflate>, L<IO::Uncompress::AnyInflate>

L<Compress::Zlib::FAQ|Compress::Zlib::FAQ>

L<File::GlobMapper|File::GlobMapper>, L<Archive::Tar|Archive::Zip>,
L<IO::Zlib|IO::Zlib>

For RFC 1950, 1951 and 1952 see 
F<http://www.faqs.org/rfcs/rfc1950.html>,
F<http://www.faqs.org/rfcs/rfc1951.html> and
F<http://www.faqs.org/rfcs/rfc1952.html>

The primary site for the gzip program is F<http://www.gzip.org>.

=head1 AUTHOR

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

The I<zlib> compression library was written by Jean-loup Gailly
F<gzip@prep.ai.mit.edu> and Mark Adler F<madler@alumni.caltech.edu>.

The primary site for the I<zlib> compression library is
F<http://www.zlib.org>.

=head1 MODIFICATION HISTORY

See the Changes file.

=head1 COPYRIGHT AND LICENSE
 

Copyright (c) 2005 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.