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

[Phil Sutter <phil@nwl.cc>]

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?

Cheers, Phil