[Catalyst] Confused: how to handle system-level errors with fallback pages

[Stuart Watt]

  Looks like I was wrong in where the error occurred, although the main =

issue is unchanged. The problem is in finalize rather than prepare.

On 8/31/2010 10:08 AM, Bill Moseley wrote:
> Even the top-level handle_request is wrapped in an eval, but it tests =

> $@ instead of the return value of eval like it should.  Is it possible =

> something is clearing the $@ var?
>
> It's pretty easy to edit Catalyst.pm to check.
>
I hadn't seen the eval return value issue, although you're right. The =

error is reported on the console just fine. The problem is, that is the =

*only* place it is reported. The eval wrapper causes the finalize to be =

partially skipped.

Here's the stack trace at point of failure (more or less):

$ =3D ARM::Model::User::get_session_store_delegate(ref(ARM::Model::User), =

'fbc69cb40a085cae169b26034f64832d12a9c305') called from file =

`C:/perl/site/5.10.1/lib/Catalyst/Plugin/Session/Store/Delegate.pm' line 56
$ =3D =

Catalyst::Plugin::Session::Store::Delegate::get_session_store_delegate(ref(=
ARM), =

'fbc69cb40a085cae169b26034f64832d12a9c305') called from file =

`C:/perl/site/5.10.1/lib/Catalyst/Plugin/Session/Store/Delegate.pm' line 40
$ =3D =

Catalyst::Plugin::Session::Store::Delegate::session_store_delegate(ref(ARM)=
) =

called from file =

`C:/perl/site/5.10.1/lib/Catalyst/Plugin/Session/Store/Delegate.pm' line 94
. =3D =

Catalyst::Plugin::Session::Store::Delegate::store_session_data(ref(ARM), =

'expires:fbc69cb40a085cae169b26034f64832d12a9c305', 1283271921) called =

from file `C:/perl/site/5.10.1/lib/Catalyst/Plugin/Session.pm' line 148
. =3D Catalyst::Plugin::Session::_save_session_expires(ref(ARM)) called =

from file `C:/perl/site/5.10.1/lib/Catalyst/Plugin/Session.pm' line 106
. =3D Catalyst::Plugin::Session::finalize_headers(ref(ARM)) called from =

file `C:/perl/site/5.10.1/lib/Catalyst.pm' line 1762
$ =3D Catalyst::finalize(ref(ARM)) called from file =

`C:/perl/site/5.10.1/lib/Catalyst/Plugin/Compress/Deflate.pm' line 16
[other plugins here]
$ =3D Catalyst::Plugin::Session::PerUser::finalize(ref(ARM)) called from =

file =

`C:/perl/site/5.10.1/lib/MSWin32-x86-perlio/Class/MOP/Method/Wrapped.pm' =

line 48
...
$ =3D ARM::finalize(ref(ARM)) called from file =

`C:/perl/site/5.10.1/lib/Catalyst.pm' line 1927

So, the issue is: because I use =

Catalyst::Plugin::Session::Store::Delegate, my model methods are called =

in the finalize. These methods (based on my DBIC model class) die, and =

this drops all feedback, as finalize_headers is never completed and =

finalize_body never called. So I could overcome this by fixing my model =

to never fail - proxying off the DBIC class in some way to fake session =

handling on error. (Although I suspect this might be better part of =

Catalyst::Plugin::Session::Store::Delegate.)

The problem is: finalize_headers is normally called after =

finalize_error, so even if I detect an error, there seems to be no way =

to go back and display that error. It seems to me that my model code =

ought to be able to fail in a reasonable way and get something displayed.

--S

Stuart Watt
ARM Product Developer
Information Balance



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> Bill Moseley
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