sys/net/sock_util: add sock_tl_name2ep() to optionally perform DNS lookups

[benpicco]

Contribution description

This adds a new helper function sock_tl_name2ep() that will perform a DNS lookup if the sock_dns is used.
Otherwise it behaves exactly as sock_tl_str2ep()

Testing procedure

Tests were added to tests/netutils

Issues/PRs references

[miri64]

Can we make this its own function that then calls sock_tl_str2ep(), please? str2ep IMHO should only convert an actual string representing an address-port-pair to an endpoint. This way we do not muddy functionality and it is clearer what which function does. E.g. sock_tl_name2ep() or something.

[miri64]

(you also might not want to fallback to a name in some use case and explicitly want to call sock_tl_str2ep() without any implicit network operation)

[benpicco]

Can we make this its own function that then calls sock_tl_str2ep(), please?

Mind you that sock_tl_str2ep() is not called directly but always by a wrapper (sock_udp_str2ep()/sock_tcp_str2ep()).

The idea was that all users (e.g. suit_coap_get_blockwise_url()) will get this for 'free' when sock_dns is enabled.

[miri64]

Mind you that sock_tl_str2ep() is not called directly but always by a wrapper (sock_udp_str2ep()/sock_tcp_str2ep()).

I don't see how this is relevant... they are still the conversion functions from string to endpoint.

The idea was that all users (e.g. suit_coap_get_blockwise_url()) will get this for 'free' when sock_dns is enabled.

If you get something for free with unforeseen consequences, it is never really for free. IMHO we should change the usage of sock_udp_str2ep() in those instances to sock_udp_name2ep() where it is sensible. A classic example where it is not sensible, for instance, is when you want to set a DNS server's endpoint ;-).

[benpicco]

I added a new sock_tl_name2ep() function as well as UDP and TCP wrappers.
I would then convert users of sock_udp_str2ep() as a follow-up.

[kaspar030]

ACK (after that fix).

[benpicco]

Fix applied.
ping @miri64

[miri64]

LGTM

:checkmark: