[cgiapp] RFC: first-class support for PSGI in CGI::Application

[Mark Stosberg]

> The final result might look like this:
> 
>     use WebApp;
>     use CGI::PSGI;
> 
>     my $handler = sub {
>         my $env = shift;
>         my $webapp = WebApp->new({ QUERY => CGI::PSGI->new($env) });
>         $webapp->run_as_psgi;
>     };

I've considered this more, I want to submit a second draft of a
proposal. First-class PSGI support should address all of the following
aspects:

1. Passing in and setting up the PSGI env
2. Returning the PSGI required return format
3. Accessing the environment in an abstracted way. 
4. Wrapping the whole application as a coderef which does steps 1-3.

My initial proposal addressed the the return format, leaving setup and
"env" access to CGI::PSGI, and letting the user deal with 4, the final
wrapper. 

Michael Peters rightly pointed that arguments to new({}) is how we make
all the other modifications to what happens in run(), and Miyagawa
suggested that we provide a shortcut to generate the final wrapper as
well, CGI::Application::PSGI does.

So, some proposal refinements:

1. We should add an "env" method as an abstract way to access the
environment. In non-PSGI code, this would just access \%ENV. Using
this, internal code and plugins could access the environment in a way
that would work with our without PSGI. With CGI::PSGI, we could access
this already through $self->query->env, and perhaps $self->env will
just be an alias for that. As a related example, we have this bug
report:
https://rt.cpan.org/Public/Bug/Display.html?id=54762
Adding a env() method to CGI::Application would help address it
somewhat. 

2. We add a wrapper method which should take the same arguments as new,
but will default to setting up CGI::PSGI correctly and also calling run.
So, running a CGI::Application project on PSGI could be as simple as
this:

WebApp->psgi_app({ ... args to new() ... });

If you want to manually construct the code ref, of course you still
can. 

Anyone else have further thoughts on PSGI integration?

   Mark


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