The getserv function has remained mostly unchanged since
1ed. These checks are for handling string local ports
or lack thereof. This was used by datakit at the time,
where 'ports' were service strings. This made the default
datakit service 'login' when a connector did not give
a specific service. The checks for directory traversal also
seemed specifically to guard against a connector from providing
a malicious service string. With datakit gone all current protocols
use numerics as ports so these checks and defaults become uneeded.
1ed reference:
https://github.com/plan9foundation/plan9/tree/1e-1992-09-21
5f49f8ac9c