#!/usr/bin/perl
use v5.10;
say ' This script explores how Plack::Request and CGI.pm interact with the global %ENV. ';
say;
say ' Does changing the globah hash after the object is created modify the object ';
say ' behavior? Do changes to the object cause the external environment to be ';
say ' modified? ';
say;
say ' Run it and press <enter> as prompted to see. Some of the answers for both';
say ' CGI.pm and Plack::Request may surprise you.';


use CGI;
use Plack::Request;
use strict;

$ENV{REMOTE_ADDR} = "initial global value";

  say;
  say;
  say 'Create objects with CGI->new() and Plack::Request->new(\%ENV)';

  my $q = CGI->new;
  my $r = Plack::Request->new(\%ENV);
  
  say;
  say 'Reality Check: Both CGI.pm and Plack::Request pick up REMOTE_ADDR from the environment:';
  say '  $ENV{REMOTE_ADDR} = "initial global value"; ';
  say '  CGI.pm, $q->remote_addr:      '.$q->remote_addr;
  say '  Plack::Request:  $r->address: '.$r->address;

  $ENV{REMOTE_ADDR} = 'changed global value after object was created.';

  say;
  say 'Now, modify the global %ENV hash after the object is created.';
  say ' ( press enter to see the results )'; <>;
  
  say '  $ENV{REMOTE_ADDR} = "changed global value after object was created."; ';
  say '  CGI.pm, $q->remote_addr:      '.$q->remote_addr;
  say '  Plack::Request:  $r->address: '.$r->address;
  say;
  say 'While isolation might be hoped for, they both picked up the changes.';

  say ' ( press enter to continue. )'; <>;
  say;
  say 'Another experiment is to modify the internal environment hash. ';
  say 'Plack::Request allows this, but CGI.pm does not.';
  say 'Will it cause the internal state to be modified? What about the global %ENV?';

  $r->env->{REMOTE_ADDR} = 'modified through internal hash';
  say ' ( press enter to see the results )'; <>;
  say '  $r->env->{REMOTE_ADDR} = "modified via internal environment."; ';
  say '  Plack::Request, $r->address:  '.$r->address;
  say '  $ENV{REMOTE_ADDR}:  '.$ENV{REMOTE_ADDR};
  say;
  say 'Perhaps surprisingly, Plack::Request is modifying the global environment through what';
  say 'appears to be a private copy of it.';
  say;
  say 'The Plack::Request documentation hints at this behavior in the docs for env():';
  say '  "This is a reference, so writing to this environment passes through';
  say '   during the whole PSGI request/response cycle."';
  say;
  say 'I think this could be even more explicit that "passes through" means that';
  say 'the hash passed in modified by reference.';
  say ' (press enter to continue);'; <>;

  say 'Now let\'s try another experiment, using a syntax to pass in a copy';
  say 'of the environment to Plack::Request: Plack::Request->new({ %ENV })';
  say 'This has no equivalent in CGI.pm, but they are still useful to compare';
  say 'to see this allows Plack::Request to achieve a different behavior.';

  $ENV{REMOTE_ADDR} = 'initial global value';
  $q = CGI->new;
  $r = Plack::Request->new({ %ENV });

  say ' $ENV{REMOTE_ADDR} = "initial global value";';
  say ' $q = CGI->new; ';
  say ' $r = Plack::Request->new({ %ENV }); ';

  say '  CGI.pm, $q->remote_addr:      '.$q->remote_addr;
  say '  Plack::Request:  $r->address: '.$r->address;

  say ' ( press enter to continue. )'; <>;
  say;

  $ENV{REMOTE_ADDR} = 'changed global value after object was created';

  say;
  say 'Now test again changing the external environment.';
  say ' ( press enter to see the results )'; <>;

  say '  $ENV{REMOTE_ADDR} = "changed global value after object was created"; ';
  say '  CGI.pm, $q->remote_addr:      '.$q->remote_addr;
  say '  Plack::Request:  $r->address: '.$r->address;
  say;
  say 'Now Plack::Request is \'protecting\' the internal object from global changes.';

  say ' ( press enter to continue. )'; <>;
  say;
  say 'Now, modify Plack::Request\'s internal environment (no CGI.pm equivalent).';

  $r->env->{REMOTE_ADDR} = 'modified via internal environment.';

  say;
  say 'Let\'s check if this changed the value internally and externally:';

# PSGI docs say: 'The application is free to modify the environment.'
  say ' ( press enter to see the results )'; <>;
  say '  $r->env->{REMOTE_ADDR} = "modified via internal environment."; ';
  say '  Plack::Request, $r->address:  '.$r->address;
  say '  $ENV{REMOTE_ADDR}:  '.$ENV{REMOTE_ADDR};
  say;
  say 'So, now Plack::Request did not modify the global environment.';
  say;
  say 'That\'s all. Were the answers what you expected?';
  say;
  say 'If you found this interesting, you also be interested to review my';
  say 'tests for the parameter related methods in Plack::Request';
  say 'They show inconsistency there about their read/write nature.';
  say  'https://github.com/markstos/Plack/commit/0aefed0900eeb2281eb0fe925bd18dfd60076b1e';

# written by Mark Stosberg <mark@stosberg.com>, 2011. Public domain.