Re: [PATCH nft v4] src: enable json echo output when reading native syntax

[Phil Sutter <phil@nwl.cc>]

On Tue, Aug 04, 2020 at 12:38:46PM +0200, Jose M. Guisado Gomez wrote:
> This patch fixes a bug in which nft did not print any output when
> specifying --echo and --json and reading nft native syntax.
> 
> This patch respects behavior when input is json, in which the output
> would be the identical input plus the handles.
> 
> Adds a json_echo member inside struct nft_ctx to build and store the json object
> containing the json command objects, the object is built using a mock
> monitor to reuse monitor json code. This json object is only used when
> we are sure we have not read json from input.
> 
> Fixes: https://bugzilla.netfilter.org/show_bug.cgi?id=1446
> 
> Signed-off-by: Jose M. Guisado Gomez <guigom@riseup.net>
> ---
> v4 respects previous behavior for json echo when reading json input too
> 
>  include/nftables.h |  1 +
>  src/json.c         | 13 ++++++++++---
>  src/monitor.c      | 37 +++++++++++++++++++++++++++++--------
>  src/parser_json.c  | 24 +++++++++++++++++-------
>  4 files changed, 57 insertions(+), 18 deletions(-)

Why not just:

--- a/src/monitor.c
+++ b/src/monitor.c
@@ -922,8 +922,11 @@ int netlink_echo_callback(const struct nlmsghdr *nlh, void *data)
        if (!nft_output_echo(&echo_monh.ctx->nft->output))
                return MNL_CB_OK;
 
-       if (nft_output_json(&ctx->nft->output))
-               return json_events_cb(nlh, &echo_monh);
+       if (nft_output_json(&ctx->nft->output)) {
+               if (ctx->nft->json_root)
+                       return json_events_cb(nlh, &echo_monh);
+               echo_monh.format = NFTNL_OUTPUT_JSON;
+       }
 
        return netlink_events_cb(nlh, &echo_monh);
 }

At a first glance, this seems to work just fine.

Cheers, Phil