snippet.pl

use MooseX::Declare;

role Validation {
    requires qw/ GET HEAD responseCode responseContent /;
    after GET { confess 'URL does not exist' if $self->responseCode eq 404 };
};

class App with(Validation) {
    use Moose::Util::TypeConstraints;
    use REST::Client;
    my @REST_METHODS = qw/ GET HEAD responseCode responseContent /;
    has client => (
        isa        => duck_type( \@REST_METHODS ),
        handles    => \@REST_METHODS,
        lazy_build => 1,
    );
    method _build_client { REST::Client->new }
};

Moose is just awesome. Here we are delegating to the GET method from REST::Client (actually any class that can do all of the @REST_METHODS) and validating the response code in a role (so the validation can be as complex as you need it to be). In this case the validation is just inspecting the REST::Client delegatee after the GET is complete.