UA.pm

has 'request_builder' => (
    is       => 'ro',
    isa      => 'CodeRef',
    traits   => ['Code'],
    handles  => { request => 'execute' },
    default  => sub {
        my ($self) = @_;
        weaken $self;
        return sub {
            my ($method, $uri, $headers, $cb) = @_;
            $headers ||= [];
            my $guard;
            weaken $guard;
            $guard = http_request $method => $uri, @$headers, sub {
                $self->delete_request($guard);
                $cb->(@_);
            };
            $self->insert_request($guard);
            return $guard;
        };
    },
);