Test for post type in request filter?

$request['post_type'] should contain the requested post type for any custom type. The default post type will have a name, but no post_type. Pages will have pagename and no post_type.

EDIT- determining custom post type based on taxonomy set in request:

function cpt_request_filters( $request ){
    if( ! is_admin() ){
        global $wp_taxonomies;
        foreach( $request as $tax_key => $value ){
            if( array_key_exists( $tax_key, $wp_taxonomies ) ){
                return cpt_parse_taxonomy_string( $request, $wp_taxonomies[$tax_key]->object_type[0], $tax_key );
            }
        }
    }
    return $request;
}
add_filter( 'request', 'cpt_request_filters' );