The retrieve sub in the module looks like this:

sub retrieve
{
    my( $self, $fileobj, $sourceid, $offset, $n, $f ) = @_;

    my $repository = $self->{session}->get_repository;
    $repository->log( "Attempting to set up user agent" ) if ($self->{debug}); # for testing
    if (create_ua( $self, $fileobj))
    {
        $repository->log( "Attempting to access HCP " . $self->{_url}->{$fileobj} ) if ($self->{debug}); # for testing
        my $ua = $self->{_ua}->{$fileobj};
        my $request = new HTTP::Request('GET',$self->{_url}->{$fileobj});   
        my $response = $ua->request( $request,$f ); # feed the response to the callback function
        $repository->log( "Have response" ) if ($self->{debug}); # for testing
        if( $response->is_error )
        {
            $repository->log( $response->as_string );
        }
        return $response->is_success;
    }
    else
    {
        $repository->log("Could not define LWP user agent: aborting file save\n");
        return 0;
    }
}