JSON: Add support for echo option

The basic principle is to not return a JSON object freshly created from
netlink responses, but just update the existing user-provided one to
make sure callers get back exactly what they expect.

To achieve that, keep the parsed JSON object around in a global variable
('cur_root') and provide a custom callback to insert handles into it
from received netlink messages. The tricky bit here is updating rules
since unique identification is problematic. Therefore drop possibly
present handles from input and later assume updates are received in
order so the first rule not having a handle set is the right one.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/json.h b/include/json.h
index d2dc92d9..8d45c3c3 100644
--- a/include/json.h
+++ b/include/json.h
@@ -7,6 +7,7 @@ struct chain;
 struct cmd;
 struct expr;
 struct netlink_ctx;
+struct nlmsghdr;
 struct rule;
 struct set;
 struct obj;
@@ -103,6 +104,10 @@ void monitor_print_obj_json(struct netlink_mon_handler *monh,
 void monitor_print_rule_json(struct netlink_mon_handler *monh,
 			     const char *cmd, struct rule *r);
 
+int json_events_cb(const struct nlmsghdr *nlh,
+		   struct netlink_mon_handler *monh);
+void json_print_echo(struct nft_ctx *ctx);
+
 #else /* ! HAVE_LIBJANSSON */
 
 typedef void json_t;
@@ -234,6 +239,16 @@ static inline void monitor_print_rule_json(struct netlink_mon_handler *monh,
 	/* empty */
 }
 
+static inline int json_events_cb(const struct nlmsghdr *nlh)
+{
+	return -1;
+}
+
+static inline void json_print_echo(struct nft_ctx *ctx)
+{
+	/* empty */
+}
+
 #endif /* HAVE_LIBJANSSON */
 
 #endif /* NFTABLES_JSON_H */