[libnftnl PATCH v4 3/3] expr: log: Do not print unset values in xml

[Ana Rey <anarey@gmail.com>]

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

If we used this rule:
nft add rule ip test output log

We got this xml file:
<rule><family>ip</family>
<table>test</table>
<chain>output</chain>
<handle>88</handle>
<expr type="log">
        <prefix>(null)</prefix>
        <group>0</group>
        <snaplen>0</snaplen>
        <qthreshold>0</qthreshold>
</expr>
</rule>

And It was imposible import this file.

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

<rule><family>ip</family>
<table>test</table>
<chain>output</chain>
<handle>88</handle>
<expr type="log">
</expr>
</rule>

and It's possible import this xml file.

Signed-off-by: Ana Rey <anarey@gmail.com>
---
 src/expr/log.c | 49 +++++++++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/src/expr/log.c b/src/expr/log.c
index 392bb14..fda353b 100644
--- a/src/expr/log.c
+++ b/src/expr/log.c
@@ -216,25 +216,21 @@ static int nft_rule_expr_log_xml_parse(struct nft_rule_expr *e,
 
 	prefix = nft_mxml_str_parse(tree, "prefix", MXML_DESCEND_FIRST,
 				    NFT_XML_MAND, err);
-	if (prefix == NULL)
-		return -1;
-	nft_rule_expr_set_str(e, NFT_EXPR_LOG_PREFIX, prefix);
+	if (prefix != NULL)
+		nft_rule_expr_set_str(e, NFT_EXPR_LOG_PREFIX, prefix);
 
 	if (nft_mxml_num_parse(tree, "group", MXML_DESCEND_FIRST, BASE_DEC,
-			       &group, NFT_TYPE_U16, NFT_XML_MAND, err) < 0)
-		return -1;
-	nft_rule_expr_set_u16(e, NFT_EXPR_LOG_GROUP, group);
+			       &group, NFT_TYPE_U16, NFT_XML_MAND, err) == 0)
+		nft_rule_expr_set_u16(e, NFT_EXPR_LOG_GROUP, group);
 
 	if (nft_mxml_num_parse(tree, "snaplen", MXML_DESCEND_FIRST, BASE_DEC,
-			       &snaplen, NFT_TYPE_U32, NFT_XML_MAND, err) < 0)
-		return -1;
-	nft_rule_expr_set_u32(e, NFT_EXPR_LOG_SNAPLEN, snaplen);
+			       &snaplen, NFT_TYPE_U32, NFT_XML_MAND, err) == 0)
+		nft_rule_expr_set_u32(e, NFT_EXPR_LOG_SNAPLEN, snaplen);
 
 	if (nft_mxml_num_parse(tree, "qthreshold", MXML_DESCEND_FIRST, BASE_DEC,
 			       &qthreshold, NFT_TYPE_U16, NFT_XML_MAND,
-			       err) < 0)
-		return -1;
-	nft_rule_expr_set_u16(e, NFT_EXPR_LOG_QTHRESHOLD, qthreshold);
+			       err) == 0)
+		nft_rule_expr_set_u16(e, NFT_EXPR_LOG_QTHRESHOLD, qthreshold);
 
 	return 0;
 #else
@@ -256,14 +252,31 @@ static int nft_rule_expr_log_snprintf_default(char *buf, size_t len,
 static int nft_rule_expr_log_snprintf_xml(char *buf, size_t size,
 					  struct nft_rule_expr *e)
 {
+	int ret, len = size, offset = 0;
 	struct nft_expr_log *log = nft_expr_data(e);
 
-	return snprintf(buf, size, "<prefix>%s</prefix>"
-				   "<group>%u</group>"
-				   "<snaplen>%u</snaplen>"
-				   "<qthreshold>%u</qthreshold>",
-			log->prefix, log->group,
-			log->snaplen, log->qthreshold);
+	if (e->flags & (1 << NFT_EXPR_LOG_PREFIX)) {
+		ret = snprintf(buf+offset, len, "<prefix>%s</prefix>",
+			       log->prefix);
+		SNPRINTF_BUFFER_SIZE(ret, size, len, offset);
+	}
+	if (e->flags & (1 << NFT_EXPR_LOG_GROUP)) {
+		ret = snprintf(buf+offset, len, "<group>%u</group>",
+			       log->group);
+		SNPRINTF_BUFFER_SIZE(ret, size, len, offset);
+	}
+	if (e->flags & (1 << NFT_EXPR_LOG_SNAPLEN)) {
+		ret = snprintf(buf+offset, len, "<snaplen>%u</snaplen>",
+			       log->snaplen);
+		SNPRINTF_BUFFER_SIZE(ret, size, len, offset);
+	}
+	if (e->flags & (1 << NFT_EXPR_LOG_QTHRESHOLD)) {
+		ret = snprintf(buf+offset, len, "<qthreshold>%u</qthreshold>",
+			       log->qthreshold);
+		SNPRINTF_BUFFER_SIZE(ret, size, len, offset);
+	}
+
+	return offset;
 }
 
 static int nft_rule_expr_log_snprintf_json(char *buf, size_t len,
-- 
2.0.0.rc2