Run legacy applications which depend on environment variables.

plack-middleware-env.pl

package Plack::Middleware::ENV;
use strict;
use warnings;
use parent qw(Plack::Middleware);

sub call {
    my ($self, $env) = @_;
    my @fields = grep { m/^(?:HTTP.*|REMOTE_ADDR)$/ } keys %$env;
    local @ENV{@fields} = @$env{@fields};
    return $self->app->($env);
}

1;

package main;
use Test::More;
use Plack::Builder;

$INC{'Plack/Middleware/ENV.pm'} = __FILE__;

my $app = builder {
    enable 'Plack::Middleware::ENV';

    sub {
        is $ENV{HTTP_USER_AGENT}, 'MyAgent/1.0';
    };
};

$app->({ HTTP_USER_AGENT => 'MyAgent/1.0' });

done_testing;