Bug#490198: _load_pluggables can fail with hidden error

[Joey Hess]

Package: libcgi-session-perl
Version: 4.32-1
Severity: normal

This bug should be forwarded upstream. Sorry, too lazy to log into PAUSE
myself.

CGI::Session->new will occasionally fail for people like this:

<tschwinge> $ perl -e 'use CGI::Session; use CGI;$s=CGI::Session->new("driver:DB_File;serializer:default;id:static", CGI->new, { Filename => "foo"})'
<tschwinge> Can't locate object method "generate_id" via package "CGI::Session::ID::static" (perhaps you forgot to load "CGI::Session::ID::static"?) at /usr/share/perl5/CGI/Session.pm line 74.

Or this:

<tschwinge> $ perl -e 'use CGI::Session; use CGI;$s=CGI::Session->new("driver:DB_File;serializer:default", CGI->new, { Filename => "foo"})'
<tschwinge> Can't locate object method "generate_id" via package "CGI::Session::ID::" (perhaps you forgot to load "CGI::Session::ID::static"?) at /usr/share/perl5/CGI/Session.pm line 74.

The actual error is not what's shown, but this:

joeyh at gnubber:~$ perl -e 'use CGI::Session::Driver::db_file'

DB_File needs compatible versions of libdb & db.h
        you have db.h version 4.6.19 and libdb version 4.6.21
Compilation failed in require at /usr/share/perl5/CGI/Session/Driver/db_file.pm line 8.
BEGIN failed--compilation aborted at /usr/share/perl5/CGI/Session/Driver/db_file.pm line 8.
Compilation failed in require at -e line 1.

This is on a hurd system with some kind of messed up libraries, but that's not
really germane to this bug report.

The bug here is that the error message is useless. In _load_pluggables, 
if a module fails to load, it calls:

                return $self->set_error("couldn't load $mod_name: " . $msg);

This breaks out of the loop, before other pluggables can be loaded.

Then in new, it does this:

        my $id = $self->_id_generator()->generate_id(
                                                     $self->{_DRIVER_ARGS},
                                                     $self->{_CLAIMED_ID}
                                                     );


$self->_id_generator() in turn returns the module name, which has not been
loaded. Splat. 

The fix would probably involve testing the return value of load_pluggables
and propigating the error message out so that the caller of new can check it
with errstr().

Until this is fixed, callers of CGI::Session that want to use it robustly
need to eval CGI::Session->new ..

-- System Information:
Debian Release: lenny/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'stable')
Architecture: i386 (i686)

Kernel: Linux 2.6.25-2-686 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages libcgi-session-perl depends on:
ii  perl                          5.10.0-11  Larry Wall's Practical Extraction 

Versions of packages libcgi-session-perl recommends:
ii  libdbi-perl                   1.605-1    Perl5 database interface by Tim Bu

-- no debconf information

-- 
see shy jo
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