[PATCH/RFC 1/2] libubox: blobmsg: introduce BLOBMSG_CAST_INT64

[Daniel Golle]

When dealing with 64-bit integers in JSON documents, blobmsg_parse
becomes useless as blobmsg-json only uses BLOBMSG_TYPE_INT64 if the
value exceeds the range of a 32-bit integer, otherwise
BLOBMSG_TYPE_INT32 is used. This is because blobmsg-json parses the
JSON document ad-hoc without knowing the schema in advance and hence
a result of the design of blobmsg-json (and the absence of JSON
schema definitions).
In practise, this made code less readable as instead of using
blobmsg_parse() one had to to deal with *all* attributes manually just
to catch fields which can be both, BLOBMSG_TYPE_INT32 or
BLOBMSG_TYPE_INT64, but are always dealt with as uint64_t in code as
they potentially could exceed the 32-bit range.

To resolve this issue, introduce as special wildcard attribute
type BLOBMSG_CAST_INT64 which should only be used in policies used
by blobmsg_parse(). If used for an attribute in the policy,
blobmsg_parse shall accept all integer types and allow the user
to retrieve the value using the blobmsg_cast_u64() function which
is also introduced by this commit.

Signed-off-by: Daniel Golle <daniel at makrotopia.org>
---
 blobmsg.c |  8 ++++++++
 blobmsg.h | 17 +++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/blobmsg.c b/blobmsg.c
index 7da4183..93172ab 100644
--- a/blobmsg.c
+++ b/blobmsg.c
@@ -195,9 +195,17 @@ int blobmsg_parse(const struct blobmsg_policy *policy, int policy_len,
 				continue;
 
 			if (policy[i].type != BLOBMSG_TYPE_UNSPEC &&
+			    policy[i].type != BLOBMSG_CAST_INT64 &&
 			    blob_id(attr) != policy[i].type)
 				continue;
 
+			if (policy[i].type == BLOBMSG_CAST_INT64 &&
+			    (blob_id(attr) != BLOBMSG_TYPE_INT64 &&
+			     blob_id(attr) != BLOBMSG_TYPE_INT32 &&
+			     blob_id(attr) != BLOBMSG_TYPE_INT16 &&
+			     blob_id(attr) != BLOBMSG_TYPE_INT8))
+				continue;
+
 			if (blobmsg_namelen(hdr) != pslen[i])
 				continue;
 
diff --git a/blobmsg.h b/blobmsg.h
index 4565082..afb5a36 100644
--- a/blobmsg.h
+++ b/blobmsg.h
@@ -35,6 +35,7 @@ enum blobmsg_type {
 	__BLOBMSG_TYPE_LAST,
 	BLOBMSG_TYPE_LAST = __BLOBMSG_TYPE_LAST - 1,
 	BLOBMSG_TYPE_BOOL = BLOBMSG_TYPE_INT8,
+	BLOBMSG_CAST_INT64,
 };
 
 struct blobmsg_hdr {
@@ -288,6 +289,22 @@ static inline uint64_t blobmsg_get_u64(struct blob_attr *attr)
 	return tmp;
 }
 
+static inline uint64_t blobmsg_cast_u64(struct blob_attr *attr)
+{
+	uint64_t tmp = 0;
+
+	if (blobmsg_type(attr) == BLOBMSG_TYPE_INT64)
+		tmp = blobmsg_get_u64(attr);
+	else if (blobmsg_type(attr) == BLOBMSG_TYPE_INT32)
+		tmp = blobmsg_get_u32(attr);
+	else if (blobmsg_type(attr) == BLOBMSG_TYPE_INT16)
+		tmp = blobmsg_get_u16(attr);
+	else if (blobmsg_type(attr) == BLOBMSG_TYPE_INT8)
+		tmp = blobmsg_get_u8(attr);
+
+	return tmp;
+}
+
 static inline double blobmsg_get_double(struct blob_attr *attr)
 {
 	union {
-- 
2.28.0