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Plack Handbook - Use plack request

Sunday, September 7, 2014, 9:33 PM

Day 14: Use Plack::Request

Plack is not a framework per se, but is more of a toolkit that contains PSGI server implementations as well as utilities like plackup, Plack::Test and Middleware components.

Since Plack project is a revolution from HTTP::Engine, there seems a demand to write a quick web application in Request/Response style handler API. Plack::Request gives you a nice Object Oriented API around PSGI environment hash and response array, just like Rack's Rack::Request and Response objects. It could also be used as a library when writing a new middleware component, and a base class for requests/responses when you write a new web application framework based on Plack.

Use Plack::Request and Response

Plack::Request is a wrapper around PSGI environment, and the code goes like this:

 use Plack::Request;

 my $app = sub {
     my $req = Plack::Request->new(shift);

     my $name = $req->param('name');
     my $res  = $req->new_response(200);
     $res->content_type('text/html');
     $res->content("<html><body>Hello World</body></html>");

     return $res->finalize;
 };

The only thing you need to change, if you're migrating from HTTP::Engine, is the first line of the application to create a Plack::Request out of PSGI env (shift) and then call finalize to get an array reference out of Response object.

Many other methods like path_info, uri, param, redirect etc. work like HTTP::Engine::Request and Response object which is very similar to Catalyst 's Request and Response object.

Plack::Request and Plack

Plack::Request is available as part of Plack on CPAN. Your framework can use Plack::Request to handle parameters and can also make it run on other PSGI server implementations such as mod_psgi.

Use Plack::Request or not?

Directly using Plack::Request in the .psgi code is quite handy to quickly write and test your code but not really recommended for a large scale application. It's exactly like writing a 1000 lines of .cgi script where you could factor out the application code into a module (.pm files). The same thing applies to .psgi file: it's best to create an application class by using and possibly extending Plack::Request, and then have just a few lines of code in .psgi file with Plack::Builder to configure middleware components.

Plack::Request is also supposed to be used from a web application framework to adapt to PSGI interface.