use strict; use warnings; use 5.020;
use utf8;

use Plack::Request;
use Encode;
use JSON::XS;

my $app = sub {
    my $req = Plack::Request->new($_[0]);
    my $input = decode 'UTF-8', $req->parameters->{'input'};
    [
        200,
        [ 'Content-Type', 'application/json; charset=UTF-8' ],
        [ encode_json { output => uc $input } ]
    ];
};

# To run as a true CGI script, include after the sub:
#use Plack::Handler::CGI;
#Plack::Handler::CGI->new->run($app);

# Or FastCGI for reverse proxy:
# plackup -s FCGI --listen /tmp/fcgi.sock myapp.psgi

# Or persistently for simple direct serve:
# plackup --host 127.0.0.1 --port 9090 script.pl