[Dancer-users] Follow-up: extending the serializer

[David Precious]

On Wednesday 08 June 2011 00:03:44 Mr. Puneet Kishor wrote:
> On Jun 7, 2011, at 4:51 PM, Mr. Puneet Kishor wrote:
> > I am trying to write a new serializer plugin called
> > `Dancer::Serializer::Tgz` modeled after Data::Dumper, JSON, etc. The
> > idea is that, in conjunction with `Dancer::Plugin::REST` and
> > `Dancer::Serializer::Mutable`, the user would be able to request data in
> > .tgz format on demand like so --
> > 
> > $ curl http://example.com/employees.tgz
> > 
> > Here is my baby code, and it gives me a rather unhelpful "an internal
> > error occurred". What am I doing wrong?
> 
> After much fiddling, I was able to see the following errors --
> 
> in my Apache error log, I get
> 
> Deep recursion on subroutine "Dancer::Error::render" at ../Dancer.pm line
> 312. Deep recursion on subroutine "Dancer::Error::_render_serialized" at
> ../Dancer/Error.pm line 167. Deep recursion on subroutine
> "Dancer::Serializer::Tgz::serialize" at ../Dancer/Error.pm line 177. Deep
> recursion on subroutine "Dancer::_send_file" ../Dancer.pm line 140.

I suspect that the call to send_file() is generating an error of some sort - 
which gets passed to the serializer to serialize... recursion ahoy.
 
> 
> If I uncomment the `sub content_type {'application/gzip'}` I also get
> 
> Subroutine content_type redefined at ../Dancer/Serializer/Tgz.pm line 43.

Ah - you've got "use Dancer ':syntax';" before "use base 
'Dancer::Serializer::Abstract';", so Dancer has already exported the 
content_type() keyword into your package.

You can probably fix it with:

use Dancer qw(:syntax !content_type);


 
> Also, if I comment the `send_file` command in serialize(), I actually do
> get a result.tgz. If I untar that result.tgz, I see the following text
> 
> {
>    "error" : "Serializer (Dancer::Serializer::Tgz) failed at serializing
> Dancer::Error=HASH(0x100a93008):\nencountered object
> 'Dancer::Error=HASH(0x100a93008)', but neither allow_blessed nor
> convert_blessed settings are enabled at (eval 71) line 153.\n" }
> 
> What am I doing wrong?

For debugging, I'd have the serializer log what it's about to serialize; it 
seems there's an error somewhere, and it's received a Dancer::Error object, 
and tried to serialize it with to_json() which then complained that 
convert_blessed isn't enabled.

Or you could add a bit of code to special-case serialisation of D::E objects, 
e.g.:

if (ref $entity eq 'Dancer::Error') {
    $entity = { error => $entity->message };
}

That might reveal the real problem.


-- 
David Precious  ("bigpresh")
http://www.preshweb.co.uk/

   "Programming is like sex. One mistake and you have to support
   it for the rest of your life". (Michael Sinz)