[PATCH] libnftnl: Implement new buffer of TLV objects.

["Carlos Falgueras García" <carlosfg@riseup.net>]

These functions allow to create a buffer (nftnl_attrbuf) of TLV objects
(nftnl_attr). It is inspired by libmnl/src/attr.c. It can be used to store
several variable length user data into an object.

Example usage:
	```
	struct nftnl_attrbuf *attrbuf;
	struct nftnl_attr *attr;
	const char str[] = "Hello World!";

	attrbuf = nftnl_attrbuf_alloc(ATTRBUF_SIZE);
	if (!nftnl_attr_put_check(attrbuf, NFTNL_ATTR_TYPE_COMMENT,
				  strlen(str), str)
	) {
		fprintf(stderr, "Can't put attribute \"%s\"", str);
	}

	nftnl_attr_for_each(attr, attrbuf) {
		printf("%s\n", (char *)nftnl_attr_get_value(attr));
	}

	nftnl_attr_free(attrbuf);
	```

Signed-off-by: Carlos Falgueras García <carlosfg@riseup.net>
---
 include/Makefile.am          |   1 +
 include/attr.h               |  40 +++++++++++++
 include/libnftnl/Makefile.am |   1 +
 include/libnftnl/attr.h      |  59 +++++++++++++++++++
 src/Makefile.am              |   1 +
 src/attr.c                   | 132 +++++++++++++++++++++++++++++++++++++++++++
 src/libnftnl.map             |  16 ++++++
 7 files changed, 250 insertions(+)
 create mode 100644 include/attr.h
 create mode 100644 include/libnftnl/attr.h
 create mode 100644 src/attr.c

diff --git a/include/Makefile.am b/include/Makefile.am
index be9eb9b..785ec15 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -12,4 +12,5 @@ noinst_HEADERS = internal.h	\
 		 expr.h		\
 		 json.h		\
 		 set_elem.h	\
+		 attr.h		\
 		 utils.h
diff --git a/include/attr.h b/include/attr.h
new file mode 100644
index 0000000..2a29fa0
--- /dev/null
+++ b/include/attr.h
@@ -0,0 +1,40 @@
+#ifndef _LIBNFTNL_ATTR_INTERNAL_H_
+#define _LIBNFTNL_ATTR_INTERNAL_H_
+
+#include <stdint.h>
+#include <stddef.h>
+
+/*
+ * TLV structures:
+ * nftnl_attr
+ *  <-------- HEADER --------> <------ PAYLOAD ------>
+ * +------------+-------------+- - - - - - - - - - - -+
+ * |    type    |     len     |         value         |
+ * |  (1 byte)  |   (1 byte)  |                       |
+ * +--------------------------+- - - - - - - - - - - -+
+ *  <-- sizeof(nftnl_attr) --> <-- nftnl_attr->len -->
+ */
+struct __attribute__((__packed__)) nftnl_attr {
+	uint8_t type;
+	uint8_t len;
+	unsigned char value[];
+};
+
+/*
+ *              +-------------------------------------------++
+ *              |           data[]                          ||
+ *              |             ||                            ||
+ *              |             \/                            \/
+ *  +-------+-------+- - - - -+-------+-------+ ... +-------+- - - - - - -+
+ *  | size  |  end  | padding |  TLV  |  TLV  |     |  TLV  |    Empty    |
+ *  +-------+-------+- - - - -+-------+-------+ ... +-------+- - - - - - -+
+ *                            |<- nftnl_attrbuf_get_len() ->|
+ *                            |<-------- nftnl_attrbuf_get_size() ------->|
+ */
+struct nftnl_attrbuf {
+	size_t size;
+	char  *end;
+	char   data[] __attribute__((aligned(64)));
+};
+
+#endif
diff --git a/include/libnftnl/Makefile.am b/include/libnftnl/Makefile.am
index 84f01b6..a3a6fb3 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		\
+		     attr.h		\
 		     gen.h
diff --git a/include/libnftnl/attr.h b/include/libnftnl/attr.h
new file mode 100644
index 0000000..a99185a
--- /dev/null
+++ b/include/libnftnl/attr.h
@@ -0,0 +1,59 @@
+#ifndef _LIBNFTNL_ATTR_H_
+#define _LIBNFTNL_ATTR_H_
+
+#include <stdio.h>
+#include <stdint.h>
+
+/*
+ * nftnl attributes API
+ */
+struct nftnl_attr;
+struct nftnl_attrbuf;
+
+/* nftnl_attrbuf */
+struct nftnl_attrbuf *nftnl_attrbuf_alloc(size_t data_size);
+void nftnl_attrbuf_free(struct nftnl_attrbuf *attrbuf);
+size_t nftnl_attrbuf_get_len(const struct nftnl_attrbuf *attrbuf);
+size_t nftnl_attrbuf_get_size(const struct nftnl_attrbuf *attrbuf);
+void *nftnl_attrbuf_get_data(const struct nftnl_attrbuf *attrbuf);
+void nftnl_attrbuf_copy_data(struct nftnl_attrbuf *attrbuf,
+			     const void *data, size_t len);
+struct nftnl_attr *nftnl_attrbuf_get_start(const struct nftnl_attrbuf *attrbuf);
+struct nftnl_attr *nftnl_attrbuf_get_end(const struct nftnl_attrbuf *attrbuf);
+
+/* TLV attribute getters */
+uint8_t nftnl_attr_get_type(const struct nftnl_attr *attr);
+uint8_t nftnl_attr_get_len(const struct nftnl_attr *attr);
+void *nftnl_attr_get_value(const struct nftnl_attr *attr);
+
+/* TLV attribute putters */
+struct nftnl_attr *nftnl_attr_put(struct nftnl_attrbuf *attrbuf,
+				  uint8_t type, uint8_t len, const void *value);
+struct nftnl_attr *nftnl_attr_put_check(struct nftnl_attrbuf *attrbuf,
+					uint8_t type, size_t len,
+					const void *value);
+
+enum nftnl_attr_data_type {
+	NFTNL_ATTR_TYPE_COMMENT,
+	__NFTNL_ATTR_TYPE_MAX,
+};
+#define NFTNL_ATTR_TYPE_MAX (__NFTNL_ATTR_TYPE_MAX - 1)
+
+/* TLV iterators */
+struct nftnl_attr *nftnl_attr_next(const struct nftnl_attr *attr);
+
+#define nftnl_attr_for_each(attr, attrbuf)                              \
+	for ((attr) = nftnl_attrbuf_get_start(attrbuf);                 \
+	     (char *)(nftnl_attrbuf_get_end(attrbuf)) > (char *)(attr); \
+	     (attr) = nftnl_attr_next(attr))
+
+/* TLV callback-based attribute parsers */
+#define NFTNL_CB_ERROR	-1
+#define NFTNL_CB_STOP	 0
+#define NFTNL_CB_OK	 1
+
+typedef int (*nftnl_attr_cb_t)(const struct nftnl_attr *attr, void *data);
+int nftnl_attr_parse(const struct nftnl_attrbuf *attrbuf, nftnl_attr_cb_t cb,
+		     void *data);
+
+#endif /* _LIBNFTNL_ATTR_H_ */
diff --git a/src/Makefile.am b/src/Makefile.am
index a27e292..621dd69 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -19,6 +19,7 @@ libnftnl_la_SOURCES = utils.c		\
 		      ruleset.c		\
 		      mxml.c		\
 		      jansson.c		\
+		      attr.c		\
 		      expr.c		\
 		      expr_ops.c	\
 		      expr/bitwise.c	\
diff --git a/src/attr.c b/src/attr.c
new file mode 100644
index 0000000..82c63aa
--- /dev/null
+++ b/src/attr.c
@@ -0,0 +1,132 @@
+#include <libnftnl/attr.h>
+#include <attr.h>
+#include <utils.h>
+
+#include <stdlib.h>
+#include <stdint.h>
+
+
+struct nftnl_attrbuf *nftnl_attrbuf_alloc(size_t data_size)
+{
+	struct nftnl_attrbuf *attrbuf;
+
+	attrbuf = (struct nftnl_attrbuf *)
+		malloc(sizeof(struct nftnl_attrbuf) + data_size);
+	attrbuf->size = data_size;
+	attrbuf->end = attrbuf->data;
+
+	return attrbuf;
+}
+EXPORT_SYMBOL(nftnl_attrbuf_alloc);
+
+void nftnl_attrbuf_free(struct nftnl_attrbuf *attrbuf)
+{
+	attrbuf->size = 0;
+	attrbuf->end = NULL;
+	free((void *)attrbuf);
+}
+EXPORT_SYMBOL(nftnl_attrbuf_free);
+
+size_t nftnl_attrbuf_get_len(const struct nftnl_attrbuf *attrbuf)
+{
+	return (size_t)(attrbuf->end - attrbuf->data);
+}
+EXPORT_SYMBOL(nftnl_attrbuf_get_len);
+
+size_t nftnl_attrbuf_get_size(const struct nftnl_attrbuf *attrbuf)
+{
+	return attrbuf->size;
+}
+EXPORT_SYMBOL(nftnl_attrbuf_get_size);
+
+struct nftnl_attr *nftnl_attrbuf_get_start(const struct nftnl_attrbuf *attrbuf)
+{
+	return (struct nftnl_attr *)attrbuf->data;
+}
+EXPORT_SYMBOL(nftnl_attrbuf_get_start);
+
+struct nftnl_attr *nftnl_attrbuf_get_end(const struct nftnl_attrbuf *attrbuf)
+{
+	return (struct nftnl_attr *)attrbuf->end;
+}
+EXPORT_SYMBOL(nftnl_attrbuf_get_end);
+
+void *nftnl_attrbuf_get_data(const struct nftnl_attrbuf *attrbuf)
+{
+	return (void *)attrbuf->data;
+}
+EXPORT_SYMBOL(nftnl_attrbuf_get_data);
+
+void nftnl_attrbuf_copy_data(struct nftnl_attrbuf *attrbuf,
+			    const void *data, size_t len)
+{
+	memcpy(attrbuf->data, data, len <= attrbuf->size ? len : attrbuf->size);
+	attrbuf->end = attrbuf->data + len;
+}
+EXPORT_SYMBOL(nftnl_attrbuf_copy_data);
+
+uint8_t nftnl_attr_get_type(const struct nftnl_attr *attr)
+{
+	return attr->type;
+}
+EXPORT_SYMBOL(nftnl_attr_get_type);
+
+uint8_t nftnl_attr_get_len(const struct nftnl_attr *attr)
+{
+	return attr->len;
+}
+EXPORT_SYMBOL(nftnl_attr_get_len);
+
+void *nftnl_attr_get_value(const struct nftnl_attr *attr)
+{
+	return (void *)attr->value;
+}
+EXPORT_SYMBOL(nftnl_attr_get_value);
+
+struct nftnl_attr *nftnl_attr_put(struct nftnl_attrbuf *attrbuf,
+				  uint8_t type, uint8_t len, const void *value)
+{
+	struct nftnl_attr *attr = (struct nftnl_attr *)attrbuf->end;
+
+	attr->len  = len;
+	attr->type = type;
+	memcpy(attr->value, value, len);
+
+	attrbuf->end = (char *)nftnl_attr_next(attr);
+
+	return attr;
+}
+EXPORT_SYMBOL(nftnl_attr_put);
+
+struct nftnl_attr *nftnl_attr_put_check(struct nftnl_attrbuf *attrbuf,
+					uint8_t type, size_t len,
+					const void *value)
+{
+	/* Check if there is enough space */
+	if (attrbuf->size < len + sizeof(struct nftnl_attr))
+		return NULL;
+
+	return nftnl_attr_put(attrbuf, type, len, value);
+}
+EXPORT_SYMBOL(nftnl_attr_put_check);
+
+struct nftnl_attr *nftnl_attr_next(const struct nftnl_attr *attr)
+{
+	return (struct nftnl_attr *)&attr->value[attr->len];
+}
+EXPORT_SYMBOL(nftnl_attr_next);
+
+int nftnl_attr_parse(const struct nftnl_attrbuf *attrbuf, nftnl_attr_cb_t cb,
+		     void *data)
+{
+	int ret = NFTNL_CB_OK;
+	const struct nftnl_attr *attr;
+
+	nftnl_attr_for_each(attr, attrbuf) {
+		ret = cb(attr, data);
+		if (ret <= NFTNL_CB_STOP)
+			return ret;
+	}
+	return ret;
+}
+EXPORT_SYMBOL(nftnl_attr_parse);
diff --git a/src/libnftnl.map b/src/libnftnl.map
index 2e193b7..65bd37e 100644
--- a/src/libnftnl.map
+++ b/src/libnftnl.map
@@ -336,6 +336,22 @@ global:
   nftnl_set_snprintf;
   nftnl_set_fprintf;
 
+  nftnl_attrbuf_alloc;
+  nftnl_attrbuf_free;
+  nftnl_attrbuf_get_len;
+  nftnl_attrbuf_get_size;
+  nftnl_attrbuf_get_data;
+  nftnl_attrbuf_copy_data;
+  nftnl_attrbuf_get_start;
+  nftnl_attrbuf_get_end;
+  nftnl_attr_get_type;
+  nftnl_attr_get_len;
+  nftnl_attr_get_value;
+  nftnl_attr_put;
+  nftnl_attr_put_check;
+  nftnl_attr_next;
+  nftnl_attr_parse;
+
   nftnl_set_list_alloc;
   nftnl_set_list_free;
   nftnl_set_list_add;
-- 
2.7.0

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