expr: log: Do not print unset values in json

It changes the parse and the snprint functions to omit unset values.

Also, It fixes an unnecessary comma after key-value pair type.
This comma is not necessary if there is not more key-value pairs in this expr.

Example:
"expr":[{"type":"log"}]

If It uses this rule:
nft add rule ip test output log

It gets this json file:

[...]
{"expr":[{"type":"log","prefix":"(null)","group":0,"snaplen":0,"qthreshold":0}]}
[...]

Now, That rule creates this json file without null values:

{"expr":[{"type":"log"}]}

Signed-off-by: Ana Rey <anarey@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/rule.c b/src/rule.c
index ac88abb..88e9f71 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -816,6 +816,15 @@ static int nft_rule_snprintf_json(char *buf, size_t size, struct nft_rule *r,
 		ret = expr->ops->snprintf(buf+offset, len, type, flags, expr);
 		SNPRINTF_BUFFER_SIZE(ret, size, len, offset);
 
+		/*
+		 * Remove comma from the first element if there is type
+		 * key-value pair only. Example: "expr":[{"type":"log"}]
+		 */
+		if (ret == 0) {
+			offset--;
+			len--;
+		}
+
 		ret = snprintf(buf+offset, len, "},");
 		SNPRINTF_BUFFER_SIZE(ret, size, len, offset);