src: add command tag in JSON/XML export support

Currently, we can't do incremental updates via JSON/XML.

This patch enriches the existing output to indicate the kind of
update that you want to perform.

So, if we have a ruleset like:

table ip filter {
	chain input {
		type filter hook input priority 0;
	}
}

The new output looks like:

{"nftables":[{"add":[{"table":{"name":"filter",...}}]}]}
              ^^^^^

Where we explicitly indicate that we want to add a table.

We support all the actions that we can do with nft, they are:

 - Add, delete and flush tables and chains.
 - Add, delete, replace and insert rules.
 - Add and delete sets.
 - Add and delete set elements.
 - Flush ruleset.

You only need to add the command tag:

	{"nftables":[{"delete":[{...}, {...},...}]}]}
		       ^^^^^^^^

The possible command tags that you can use are "add", "delete", "insert",
"replace" and "flush".

- Flush table or chain, eg.:

	{"nftables":[{"flush":[{"table":{"name":...}}]}]}

- Delete table, chain, set or rule:

	{"nftables":[{"delete":[{"chain":{"name":...}]}]}

- Replace a rule (you have to  specify the handle):

	{"nftables":[{"replace":[{"rule":{...}}]}]}

- Insert a rule:

	{"nftables":[{"insert":[{"rule":{...}}]}]}

Signed-off-by: Alvaro Neira Ayuso <alvaroneay@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/buffer.c b/src/buffer.c
index 4cedb9e..97567db 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -90,6 +90,30 @@ int nft_buf_close(struct nft_buf *b, int type, const char *tag)
 	}
 }
 
+int nft_buf_open_array(struct nft_buf *b, int type, const char *tag)
+{
+	switch (type) {
+	case NFT_OUTPUT_JSON:
+		return nft_buf_put(b, "{\"%s\":[", tag);
+	case NFT_OUTPUT_XML:
+		return nft_buf_put(b, "<%s>", tag);
+	default:
+		return 0;
+	}
+}
+
+int nft_buf_close_array(struct nft_buf *b, int type, const char *tag)
+{
+	switch (type) {
+	case NFT_OUTPUT_JSON:
+		return nft_buf_put(b, "]}");
+	case NFT_OUTPUT_XML:
+		return nft_buf_put(b, "</%s>", tag);
+	default:
+		return 0;
+	}
+}
+
 int nft_buf_u32(struct nft_buf *b, int type, uint32_t value, const char *tag)
 {
 	switch (type) {