$OpenBSD: OpenBSD::PackingList.pod,v 1.7 2007/05/02 15:17:36 espie Exp $

=head1 NAME

OpenBSD::PackingList - C<pkg_add(1)> packing-list manipulations

=head1 SYNOPSIS

    use OpenBSD::PackingList;
    # different methods to create packing-lists
    my $p1 = OpenBSD::PackingList->new();	# empty
    my $p2 = OpenBSD::PackingList->read($fh);
    my $p3 = OpenBSD::PackingList->fromfile($filename);
    my $p4 = OpenBSD::PackingList->fromfile(\$scalar);
    my $p5 = OpenBSD::PackingList->from_installation($pkgname);

    # writing packing-lists
    $p2->write($fh);
    $p3->tofile($filename);
    $p4->to_installation();
    $p4->to_cache();

    # building up packing-lists
    OpenBSD::PackingElement::SUBCLASS->add($plist, @args);
    my $o = OpenBSD::PackingElement::SUBCLASS->new(@args);
    $o->add_object($plist);

    # tests and access
    $b = $p2->has($name);
    $b = $p2->get($name);
    # frequent accesses
    print $p3->pkgname, $p3->localbase, "\n";

    # processing packing-lists
    $p4->visit('method', @args);

    # auto visit
    $p4->method(@args);

    # signatures
    if ($p3->signature eq $p4->signature) {
    }

=head1 DESCRIPTION

C<OpenBSD::PackingList> is the only supported interface for access to
packing-list information. It includes conversion methods from an external
textual representation (file) into an internal structured representation.
Basically, a packing-list is a collection of strongly-typed objects. Some
of these objects are just properties of the package (like the package name,
or dependencies), some objects have long lists of properties (files come
with MD5 checksums, sizes, or linknames), some objects represent state
information (like file modes) and must be kept in the proper order.
The C<OpenBSD::PackingList> class handles all that.

Packing-lists can be obtained using the following methods: from an
opened file handle using C<OpenBSD::PackingList-E<gt>read($fh)>, from
an existing file using C<OpenBSD::PackingList-E<gt>fromfile($filename)>,
from a scalar in memory using C<OpenBSD::PackingList-E<gt>fromfile(\$scalar)>,
or from an installed package using 
C<OpenBSD::PackingList-E<gt>from_installation($pkgname)>.

Since building a full packing-list is a complex operation and can consume
a large amount of memory, those methods may take an extra argument in order to
obtain partial packing-lists with only some information:

=over 16

=item SharedItemsOnly

read only stuff that may be shared between packages, e.g., new users, 
groups and directories.

=item LibraryOnly

read only shared library entries.

=item FilesOnly

read only files without the associated annotations like size or MD5.

=item DependOnly

read only dependency information.

=item ExtraInfoOnly

read only the extra information field.

=item UpdateInfoOnly

read only what is needed to decide to update a package.

=back

A complete packing-list C<$plist> may be written to disk using the 
following methods:
C<$plist-E<gt>write($fh)> will write a packing-list to an
opened file handle C<$fh>, C<$plist-E<gt>tofile($filename)> will
write a packing-list to a file named C<$filename>, and 
C<$plist-E<gt>to_installation()> will write a packing-list during
registration of a package.

In addition C<$plist-E<gt>to_cache()> will register enough 
information from a package to let the framework believe the package has
been installed. This is used for the simulation modes of C<pkg_add(1)>
and friends.

Since a packing-list is structured information, reading a packing-list from
the disk and writing it back offers no guarantee the information will remain
in the same order.  It is a good way to validate packing-lists and normalize
them, though.

Building packing-lists entails cooperation with C<OpenBSD::PackingElement>.
Packing-lists are usually built by adding objects from an 
C<OpenBSD::PackingElement> subclass to the packing-list, either with
the C<add> constructor:  
C<OpenBSD::PackingElement::SUBCLASS-E<gt>add($plist, $args)>, which builds
a packing element and adds it to the packing-list in one operation, or with
the C<add_object> method, which takes an existing packing element and adds it
to the packing-list (note that C<add_object> only makes sense for subclasses
of C<OpenBSD::PackingElement::Object>).
See L<OpenBSD::PackingElement> for more details.

C<$plist-E<gt>pkgname()> retrieves a packing-list name (mandatory).
C<$plist-E<gt>signature()> retrieves a packing-list full signature, composed
of the package name and dependency information.

C<$plist-E<gt>visit($method, @args)> is a visitor pattern, calling
C<method(@args)> on each element of the packing-list in a specific order.

As a feature, if C<OpenBSD::PackingElement-E<gt>can(method)>, 
C<$plist-E<gt>method(@args)> will be turned into a visitor call automatically.