Re: [nft PATCH 2/2] monitor: Make JSON output respect output_fp

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

On Thu, Nov 16, 2017 at 09:06:29AM +0100, Phil Sutter wrote:
> This introduces a rather nasty macro to call nftnl_*_fprintf() only if
> output_fp is valid. On the other hand, it allows to pull the common
> parts (format argument, event conversion) into a single place.
> 
> Signed-off-by: Phil Sutter <phil@nwl.cc>
> ---
>  src/netlink.c | 38 ++++++++++++++++++--------------------
>  1 file changed, 18 insertions(+), 20 deletions(-)
> 
> diff --git a/src/netlink.c b/src/netlink.c
> index 845eeeffd7387..81b92ac1e2d7c 100644
> --- a/src/netlink.c
> +++ b/src/netlink.c
> @@ -40,6 +40,12 @@
>  #include <iface.h>
>  
>  #define nft_mon_print(monh, ...) nft_print(monh->ctx->octx, __VA_ARGS__)
> +#define nftnl_mon_print(monh, type, obj, event)				\
> +	if (monh->ctx->octx->output_fp) {				\
> +		nftnl_##type##_fprintf(monh->ctx->octx->output_fp,	\
> +				       obj, monh->format,		\
> +				       netlink_msg2nftnl_of(event));	\
> +	}

Wait.

Can't we just change nftnl_*_fprintf to do nothing if output_fp is
NULL.

That should be safe.