udata: add TLV user data infrastructure

These functions allow to create a buffer (struct nftnl_udata_buf) of
user data attributes in TLV format (struct nftnl_udata). It is inspired
by libmnl/src/attr.c. It can be used to store several TLVs sequentially
into an object.

Example:

	struct nftnl_udata_buf *buf;
	struct nftnl_udata *attr;
	const char *str = "Hello World!";

	buf = nftnl_udata_buf_alloc(UDATA_SIZE);
	if (!buf) {
		perror("OOM");
		exit(EXIT_FAILURE);
	}

	if (!nftnl_udata_put_strz(buf, MY_TYPE, str)) {
		perror("Can't put attribute \"%s\"", str);
		exit(EXIT_FAILURE);
	}

	nftnl_udata_for_each(buf, attr)
		printf("%s\n", (char *)nftnl_udata_attr_value(attr));

	nftnl_udata_buf_free(buf);

Signed-off-by: Carlos Falgueras García <carlosfg@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 53 insertions, 0 deletions

diff --git a/include/libnftnl/Makefile.am b/include/libnftnl/Makefile.am
index 84f01b6..457ec95 100644
--- a/include/libnftnl/Makefile.am
+++ b/include/libnftnl/Makefile.am
@@ -7,4 +7,5 @@ pkginclude_HEADERS = batch.h		\
 		     set.h		\
 		     ruleset.h		\
 		     common.h		\
+		     udata.h		\
 		     gen.h
diff --git a/include/libnftnl/udata.h b/include/libnftnl/udata.h
new file mode 100644
index 0000000..312ce26
--- /dev/null
+++ b/include/libnftnl/udata.h
@@ -0,0 +1,52 @@
+#ifndef _LIBNFTNL_UDATA_H_
+#define _LIBNFTNL_UDATA_H_
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+/*
+ * nftnl user data attributes API
+ */
+struct nftnl_udata;
+struct nftnl_udata_buf;
+
+/* nftnl_udata_buf */
+struct nftnl_udata_buf *nftnl_udata_buf_alloc(uint32_t data_size);
+void nftnl_udata_buf_free(struct nftnl_udata_buf *buf);
+uint32_t nftnl_udata_buf_len(const struct nftnl_udata_buf *buf);
+void *nftnl_udata_buf_data(const struct nftnl_udata_buf *buf);
+void nftnl_udata_buf_put(struct nftnl_udata_buf *buf, const void *data,
+			 uint32_t len);
+struct nftnl_udata *nftnl_udata_start(const struct nftnl_udata_buf *buf);
+struct nftnl_udata *nftnl_udata_end(const struct nftnl_udata_buf *buf);
+
+/* putters */
+bool nftnl_udata_put(struct nftnl_udata_buf *buf, uint8_t type, uint32_t len,
+		     const void *value);
+bool nftnl_udata_put_strz(struct nftnl_udata_buf *buf, uint8_t type,
+			  const char *strz);
+
+/* nftnl_udata_attr */
+uint8_t nftnl_udata_type(const struct nftnl_udata *attr);
+uint8_t nftnl_udata_len(const struct nftnl_udata *attr);
+void *nftnl_udata_get(const struct nftnl_udata *attr);
+
+/* iterator */
+struct nftnl_udata *nftnl_udata_next(const struct nftnl_udata *attr);
+
+#define nftnl_udata_for_each(buf, attr)                       \
+	for ((attr) = nftnl_udata_start(buf);                 \
+	     (char *)(nftnl_udata_end(buf)) > (char *)(attr); \
+	     (attr) = nftnl_udata_next(attr))
+
+#define nftnl_udata_for_each_data(data, data_len, attr)  \
+	for ((attr) = (struct nftnl_udata *)(data);      \
+	     (char *)(data + data_len) > (char *)(attr); \
+	     (attr) = nftnl_udata_next(attr))
+
+typedef int (*nftnl_udata_cb_t)(const struct nftnl_udata *attr, void *data);
+int nftnl_udata_parse(const void *data, uint32_t data_len, nftnl_udata_cb_t cb,
+		      void *cb_data);
+
+#endif /* _LIBNFTNL_UDATA_H_ */