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

[Phil Sutter <phil@nwl.cc>]

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.

Cheers, Phil