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$OpenBSD: OpenBSD::Ustar.pod,v 1.4 2005/06/13 12:54:11 espie Exp $
=head1 NAME
OpenBSD::Ustar - simple access to Ustar C<tar(1)> archives
=head1 SYNOPSIS
use OpenBSD::Ustar;
# for reading
open(my $in, "<", $arcname);
$rdarc = OpenBSD::Ustar->new($in, $destdir);
while (my $o = $rdarc->next()) {
# decide whether we want to extract it, change object attributes
$o->create();
}
close($in);
# for writing
open(my $out, ">", $arcname);
$wrarc = OpenBSD::Ustar->new($fh, $destdir);
# loop
my $o = $wrarc->prepare($filename);
# tweak some entry parameters
$o->write();
close($out);
=head1 DESCRIPTION
C<OpenBSD::Ustar> provides an API to read or write archives compatible with
C<tar(1)>
For the time being, it can only handle the USTAR archive format.
A filehandle C<$fh> is associated with an C<OpenBSD::Ustar> object through
C<new>. For archive reading, the filehandle should support
C<read>. C<OpenBSD::UStar> does not rely on C<seek> or C<rewind> in order
to be usable on pipe outputs. For archive writing, the filehandle should
support C<print>.
Note that read and write support are mutually exclusive, though there is
no need to specify the mode used at creation time; it is implicitly
provided by the underlying filehandle.
Read access to an archive object C<$rdarc> occurs through a loop that
repeatedly calls C<$o = $rdarc-E<gt>next()> to obtain the next archive entry.
It returns an archive entry object C<$o> that can be
queried to decide whether to extract this entry or not.
Write access to an archive object C<$wrarc> occurs through a user-directed
loop: obtain an archive entry through C<$o = $wrarc-E<gt>prepare($filename)>,
which can be tweaked manually and then written to the archive.
Most client software will specialize C<OpenBSD::Ustar> to their own needs.
Note however that C<OpenBSD::Ustar> is not designed for inheritance.
Composition (putting a C<OpenBSD::Ustar> object inside your class) and
forwarding methods (writing C<create> or C<next> methods that call the
corresponding C<OpenBSD::Ustar> method) are the correct way to use this API.
Note that C<OpenBSD::Ustar> does not do any caching. The client
code is responsible for retrieving and storing archives if it
needs to scan through them multiple times in a row.
Actual extraction is performed through C<$o-E<gt>extract()> and is not
mandatory. Thus, client code can control whether it wants to extract archive
elements or not.
Actual writing is performed through C<$o-E<gt>write()> and is not mandatory
either.
Client code may decide to abort archive extraction early, or to run it through
until C<$arc-E<gt>next()> returns false. The C<OpenBSD::Ustar> object doesn't
hold any resources and doesn't need any specific clean-up. However, client
code is responsible for closing the underlying filehandle and
terminating any associated pipe process.
An object C<$o> returned through C<next> or through C<prepare> holds all
the characteristics of the archive header:
=over 20
=item C<$o-E<gt>IsDir()>
true if archive entry is a directory
=item C<$o-E<gt>IsFile()>
true if archive entry is a file
=item C<$o-E<gt>IsLink()>
true if archive entry is any kind of link
=item C<$o-E<gt>IsSymLink()>
true if archive entry is a symbolic link
=item C<$o-E<gt>IsHardLink()>
true if archive entry is a hard link
=item C<$o-E<gt>{name}>
filename
=item C<$o-E<gt>{mode}>
C<chmod(2)> mode
=item C<$o-E<gt>{mtime}>
C<utime(2)> modification time
=item C<$o-E<gt>{uid}>
owner user ID
=item C<$o-E<gt>{gid}>
owner group ID
=item C<$o-E<gt>{uname}>
owner user name
=item C<$o-E<gt>{gname}>
owner group name
=item C<$o-E<gt>{linkname}>
name of the source link, if applicable
=back
The fields C<name>, C<mode>, C<mtime>, C<uid>, C<gid> and C<linkname>
can be altered before calling C<$o-E<gt>create()> or C<$o-E<gt>write()>,
and will properly influence the resulting file.
The relationship between C<uid> and C<uname>, and C<gid> and C<gname>
conforms to the USTAR format usual behavior.
In addition, client code may define C<$o-E<gt>{cwd}> in a way similar
to C<tar(1)>'s C<-C> option to affect the creation of hard links.
All creation commands happen relative to the C<$destdir> that was used
for creating the C<$arc> C<OpenBSD::Ustar> object.
During writing, hard link status is determined according to already written
archive entries: a name that references a file which has already been written
will be granted hard link status.
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