Newbie plack mistake

gistfile1.pl

# shebang

use constant USER => 'xxxx';
use constant PASS => 'xxxx';

# libraries
use CGI::PSGI;
use Data::Dumper;
use File::Glob qw(:globally :nocase);
use JSON;
use MongoDB;
use Plack::App::URLMap;

# globals or reused
my ( $key, $value );
my $now = time;
my $setid = join( '.', $now, SERVER, int( rand() * 100000 ) );

my $connection =
  MongoDB::Connection->new( host => 'dbh01.mongolab.com', port => 27017 );
$connection->authenticate( 'blog1', 'USER', 'PASS' );

my $database = $connection->blog1;

# Not sure exactly what this does!
# Try http://advent.plackperl.org/2009/12/day-16-adding-jsonp-support-to-your-app.html
#use Plack::Builder;
#builder {
#    enable "JSONP";
#    $app;
#};


# My usual
#sub debug {
#    DEBUG and print "DEBUG: @_\n";
#    DEBUG_SAVE and print STDERR @_, "\n";
#}

# Write JSON
my $app1 = sub {

    my $env        = shift;
    my $q          = CGI::PSGI->new($env);
    my $collection = $database->post;
    
    # debug(Dumper($q->param));
    # post forms here
    # return redirect
    # return JSON
    my $body = JSON::encode_json( { hello => 'world', } );
    return [ 200, [ 'Content-Type', 'application/json' ], [$body] ];
};

# Read JSON
my $app2 = sub {

    my $env        = shift;
    my $q          = CGI::PSGI->new($env);
    my $collection = $database->post;

    # check params here

    # return JSON
    my $body = JSON::encode_json( { hello => 'world', } );
    return [ 200, [ 'Content-Type', 'application/json' ], [$body] ];
};

my $app3 = sub {

    my $env        = shift;
    my $q          = CGI::PSGI->new($env);
    my $collection = $database->user;

};

my $app4 = sub {

    my $env        = shift;
    my $q          = CGI::PSGI->new($env);
    my $collection = $database->stat;

};

my $app = Plack::App::URLMap->new;
$app->mount( "/write" => $app1 );
$app->mount( "/read"  => $app2 );
$app->mount( "/user"  => $app3 );
$app->mount( "/stat"  => $app4 );

I forgot app->to_app at the end.