Re: [PATCH nft 1/2] parser_json: use stdin buffer if available

[Phil Sutter <phil@nwl.cc>]

On Wed, Jul 10, 2024 at 03:53:52PM +0200, Phil Sutter wrote:
> Hi Pablo,
> 
> On Tue, Jul 09, 2024 at 04:59:52PM +0200, Pablo Neira Ayuso wrote:
> > Since 5c2b2b0a2ba7 ("src: error reporting with -f and read from stdin")
> > stdin is stored in a buffer, update json support to use it instead of
> > reading from /dev/stdin.
> > 
> > Some systems do not provide /dev/stdin symlink to /proc/self/fd/0
> > according to reporter (that mentions Yocto Linux as example).
> > 
> > Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> > ---
> >  src/parser_json.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/src/parser_json.c b/src/parser_json.c
> > index ee4657ee8044..4912d3608b2b 100644
> > --- a/src/parser_json.c
> > +++ b/src/parser_json.c
> > @@ -4357,6 +4357,13 @@ int nft_parse_json_filename(struct nft_ctx *nft, const char *filename,
> >  	json_error_t err;
> >  	int ret;
> >  
> > +	if (nft->stdin_buf) {
> > +		json_indesc.type = INDESC_STDIN;
> > +		json_indesc.name = "/dev/stdin";
> > +
> > +		return nft_parse_json_buffer(nft, nft->stdin_buf, msgs, cmds);
> > +	}
> 
> Is this sufficient? In nft_run_cmd_from_filename(), nft->stdin_buf is
> populated conditionally:
> 
> | if (!strcmp(filename, "/dev/stdin") &&
> |     !nft_output_json(&nft->output))
> |         nft->stdin_buf = stdin_to_buffer();
> 
> Later (in the wrapped __nft_run_cmd_from_filename()), we try JSON parsing
> conditionally:
> 
> | if (nft_output_json(&nft->output) || nft_input_json(&nft->input))
> |         rc = nft_parse_json_filename(nft, filename, &msgs, &cmds);
> 
> Things got complicated by commit 2034d8c60ed91 ("src: add input flag
> NFT_CTX_INPUT_JSON to enable JSON parsing") and my request to remain
> compatible, i.e. '-j' flag which enables JSON output shall continue to
> make JSON the assumed input format.
> 
> So long story short, I guess in order to cover all cases, we have to
> enable nft->stdin_buf population also if nft_input_json(...) returns
> true, i.e. cover for library users requesting JSON input (but standard
> output). WDYT?

On second review, I think the right change is to make
nft_run_cmd_from_filename() *always* populate nft->stdin_buf if
'filename' is '/dev/stdin', i.e. drop the !nft_output_json(...) clause.

Sorry for the confusion.

Cheers, Phil