Re: [libnftnl PATCH] Partially revert "rule, set_elem: remove trailing \n in userdata snprintf"

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Tue, Oct 01, 2024 at 02:39:52PM +0200, Phil Sutter wrote:
> Hi Pablo,
> 
> On Tue, Oct 01, 2024 at 01:23:58PM +0200, Pablo Neira Ayuso wrote:
> > On Tue, Oct 01, 2024 at 01:20:54PM +0200, Phil Sutter wrote:
> > > This reverts the rule-facing part of commit
> > > c759027a526ac09ce413dc88c308a4ed98b33416.
> > > 
> > > It can't be right: Rules without userdata are printed with a trailing
> > > newline, so this commit made behaviour inconsistent.
> > 
> > Did you run tests/py with this? It is the primary user for this.
> 
> It doesn't cover this because there's no test containing a rule with a
> comment. I just added a respective test, but only to notice it does not
> matter because nft-test.py compares rules' payload individually per-rule
> and thus does not care whether output has a trailing newline or not.
> 
> I noticed it when testing the iptables compat ext stuff. You can easily
> reproduce it like so:
> 
> | # nft --check --debug=netlink 'table t { chain c { accept comment mycomment; accept; accept;};}'
> | ip (null) (null) use 0
> | ip t c
> |   [ immediate reg 0 accept ]
> |   userdata = { \x00\x0amycomment\x00 }
> | ip t c
> |   [ immediate reg 0 accept ]
> | 
> | ip t c
> |   [ immediate reg 0 accept ]
> 
> Note the missing empty line after the first rule.

None of the existing libnftnl _snprintf functions terminate string
with line break, right?. I mean, for consistency with other existing
_snprintf functions. Maybe fix nft instead?