Adding a trailing slash to request uri, as other servlet containers do

In servlet containers such as Tomcat and JBoss Web, when accessing a uri such as localhost/portal it would add a trailing slash to make the request localhost/portal/.

GateIn uses various routing rules to determine what to display which relies on the trailing slash being present such that:

req.getRequestURI().substring(req.getContextPath().length());

returns "/" instead of "".

If this violates the spec, or is something that undertow doesn't wish to include, what is the best approach to add a trailing slash to such requests?