| CC: | Franck PORCHER <fporcher [...] smartech.pf> |
| Subject: | CGI::Session alters custom data and yield to a wrong behavior(CGI::Session bug report) |
| Date: | Sun, 08 Oct 2006 00:10:36 -1000 |
| To: | markstos [...] cpan.org, sherzodr [...] cpan.org, bug-Cgi-Session [...] rt.cpan.org |
| From: | Franck Porcher <fporcher [...] smartech.pf> |
Hello Mark & Sherzod
I just started yesterday to use CGI::Session (as an embedded component
of CGI::Forge ), and would like to report a wrong behavior.
-----------------------------------------------------
My environment :
CGI::Session : Version 4.14
uname -a : Linux perl.smartech.pf 2.6.16.4 #1 PREEMPT Mon Apr 17
15:12:40 TAHT 2006 i686 AMD Athlon(TM) XP 2800+ unknown GNU/Linux
perl -v : This is perl, v5.8.7 built for i386-linux
-----------------------------------------------------
My code (summarized) :
1 my $opt_dsn = ...
2 my $cgiquery = ...
3 my $s = CGI::Session->load('driver:file;serializer:default',
$cgiquery, $opt_dsn) or die;
4 $s = CGI::Session->new('driver:file;serializer:default', $cgiquery,
$opt_dsn) if $s->is_empty();
5 <END OF PROG>
-----------------------------------------------------
The suspicious behavior...
- The statement line 3 leads to the creation of a new CGI::Session
object, say A, and to the creation of a CGI::Session::Sriver::file
driver object, say B.
- Statement 4 resets $s, so A & B, no longer reachable are DESTROYed and
garbage collected.The destruction of A is caught in CGI/Session.pm to
automagically call CGI::Session::flush() which does nothing in this
case. A new CGI::Session object is created and assigned to $s, say C, which
shares the driver B (see log below).
- When the end of program is reached (line 5 above), C is caught to be
flushed by DESTROY. B having already disappeared out the scene, a
new driver is specially created at this time of death only to allow the
flushing (DESTROY >> flush() >> CGI::Session::_driver).
This new driver ignores $opt_dsn (for instance Directory => /my/temp),
so the flushing creates or updates session files
at the wrong place...
And it appears that
C->{_DRIVER_ARGS} is also gone,
-----------------------------------------------------
My analysis of the problem
Statement line 3 leads CGI::Session::Driver::new() to physically alter
its argument (here $opt_dsn) by turning it into a driver object (bless
$opt_dsn, <driver>).
So $opt_dsn data is no longer a private custom data structure : it has
turned into an object (B) elligible for a premature DESTROY
when it goes out of reach after statement 4 resets $s.
As such, and unfortunate as it is, the garbage collection of B is also
that of $opt_dsn, and that of $s->{_DRIVER_ARGS},
which proves to be unavailable (long gone) when used by
CGI::Session::_driver() to create a driver for the late flushing
(<driverClass>->new( $self->{_DRIVER_ARGS} ).
-------------------
My suggestion
My idea is that the custom data, here $opt_dsn, *should not* be altered
by the underlying CGI::Session logic.
My suggestion to restore a good behavior is to prevent
CGI::Session::Driver to turn its argument into an object.
This is easily done by patching CGI::Forge::Driver::new() as follows
( *bold* shows the suggested patch, /*bold italic*/ shows my other
"perturbations" ) :
sub new {
/*my ($class, $args) = @_;
croak "Invalid argument type passed to driver: " . Dumper($args) if
$args && ! ref $args;
$args ||= {};*/
# my $self = bless ($args, $class) # wrong : $args is a custom
data that shouldn't be altered
my $self = bless (*{%$args}*, $class); # Instead make it a
shallow-clone, and only alter the clone !
return $self if $self->init();
return $self->set_error( "%s->init() returned false", $class);
}
I've applied it to my CGI::Session version and the suspicious behavior
was removed.
Cheers, and good luck.
I hope that CGI::Session stays around up & running : it's a fine suite
of module. Thanks for contributing it.
Franck PORCHER
======================= LOGS==========================
/*Statement line 3 ...
*/Oct 7 16:32:21 perl logger: [CGISESSION::LOAD::1] SESSION:
CGI::Session=HASH(0x87808ac)
Oct 7 16:32:21 perl logger: [CGISESSION::_driver] SESSION:
CGI::Session=HASH(0x87808ac) DRIVER: *DRIVERARGS: _HASH(0x87b3a20)_*
Oct 7 16:32:21 perl logger: [DRIVER::INIT] DRIVER:*
CGI::Session::Driver::file=_HASH(0x87b3a20)_* DIRECTORY: .
Oct 7 16:32:21 perl logger: [CGISESSION::LOAD::2] SESSION:
CGI::Session=HASH(0x87808ac) DRIVER:
CGI::Session::Driver::file=HASH(0x87b3a20)
==> The 3 lines above show how $opt_dsn (*_HASH(0x87b3a20)_*) is turned
into an object (_*CGI::Session::Driver::file=HASH(0x87b3a20)*_)
/*Statement lien 4 (rest of $s) ...*/
Oct 7 16:32:21 perl logger: [*CGISESSION::DESTROY*] SESSION:
CGI::Session=HASH(0x87808ac) DRIVER:
Oct 7 16:32:21 perl logger: [*DRIVER::DESTROY*] DRIVER:
_*CGI::Session::Driver::file=HASH(0x87b3a20)*_
==> these 2 lines show that (blessed)$opt_dsn is DESTROYED prematurately..
--
Franck Porcher, Docteur ès Sciences (Paris VI), Informatique théorique
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