Nut upsuser - Apr 2024 - RFE to extend "LISTEN" directive to support host-colon-port (as single token)

Cheers all,

  A recent discussion in the issue tracker brought up the idea to allow the
`LISTEN` keyword to also accept a single "host:port" token (e.g. if
there
is only one argument, with at least one colon, and the last colon is
followed only by numbers, split it into host and port) :
https://github.com/networkupstools/nut/issues/2424

  I see certain pros to the idea (may be more simple to use and consistent
with some other software setup), although I don't think it was an issue
ever brought up in discussions before.

  There are also certain cons, primarily about parsing such stuff reliably
and consistently in different code bases (now also with augeas and nutconf
to worry about). The actual "production" parsing in NUT data server
code
should be trivial.

  On a somewhat related note, should the port part be constrained to
numbers, or should it also pass through the naming database (resolve via
typically /etc/services on POSIX systems) if it is a non-numeric string,
similar to how we resolve host names into IP address numbers?

  What would the community say, is any of this worth spending time on?
Would anyone volunteer to roll up the sleeves for that? :)

Jim Klimov
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Jim Klimov via Nut-upsdev <nut-upsdev at alioth-lists.debian.net> writes:
>   A recent discussion in the issue tracker brought up the idea to allow the
> `LISTEN` keyword to also accept a single "host:port" token (e.g.
if there
> is only one argument, with at least one colon, and the last colon is
> followed only by numbers, split it into host and port) :
> https://github.com/networkupstools/nut/issues/2424
Is the point that people want to use different ports, and the current
situation lets you choose an address but not a port?

Assuming so, why would there be a restriction to a single host if there
is port, while one could have multiple listen addresses if not?  I would
think the : scheme should apply to each argument, with lack of : being
an implict :[normalport].

For me, the reason to use explicit listen is because you don't like *,
and if you are using IP addresses you might well want to listen to v4
and v6.

This raises the issue of whether "host" expands to all IP addresses
associated with a domain name.
>   There are also certain cons, primarily about parsing such stuff reliably
> and consistently in different code bases (now also with augeas and nutconf
> to worry about). The actual "production" parsing in NUT data
server code
> should be trivial.
I find this whole "our config needs to be generally machine readable but
we aren't just changing it to a machine-readable format" to be odd.  
If
we want to play in some world where that happens we should just flip to
yaml or something :-)
>   On a somewhat related note, should the port part be constrained to
> numbers, or should it also pass through the naming database (resolve via
> typically /etc/services on POSIX systems) if it is a non-numeric string,
> similar to how we resolve host names into IP address numbers?
sure, non-numeric port could go through getservbyname(3) and then fail
if not the expected protocol.  Don't talk about /etc/services but the
posix interface, except it's from 4.2BSD and I'm not sure it's been
specified by POSIX :-)

On the other hand, if you are using an alternate port, it's because you
are not doing the normal thing, and the idea that you specify 'ntp'
because you want nut on 123 doesn't really make sense.   And if you know
some name it's not hard to look it up by name.   So all in all, I vote
for no, it's a number.
>   What would the community say, is any of this worth spending time on?
> Would anyone volunteer to roll up the sleeves for that? :)
No and no, IMHO.   What is the problem being solved?  Are there actual
people who want to use a different port?  What are their reasons?
I can believe there might be a scenario, but it seems speculative.