luci-lib-jsonc: improve handling of integral numeric values

Properly deal with integral numeric values exceeding the int32_t range
by replacing the cast logic with more fine grained checks:

 - Lua numbers which are integers in the first place are directly converted
   to JSON integers

 - Finite double Lua numbers which are integral are converted to JSON
   integer values

 - All other numeric values are converted to JSON doubles

This should bring the handling of large integral value in line with the
documented behavior of turning non-fractional Lua numbers into JSON
integers.

Fixes: #6647
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 5 insertions, 3 deletions

diff --git a/libs/luci-lib-jsonc/src/jsonc.c b/libs/luci-lib-jsonc/src/jsonc.c
index 74839dd4f5..5abb738f5f 100644
--- a/libs/luci-lib-jsonc/src/jsonc.c
+++ b/libs/luci-lib-jsonc/src/jsonc.c
@@ -294,7 +294,7 @@ static bool visited(struct seen **sp, const void *ptr) {
 static struct json_object * _lua_to_json_rec(lua_State *L, int index,
                                              struct seen **seen)
 {
-	lua_Number nd, ni;
+	lua_Number nd;
 	struct json_object *obj;
 	const char *key;
 	int i, max;
@@ -364,10 +364,12 @@ static struct json_object * _lua_to_json_rec(lua_State *L, int index,
 		return json_object_new_boolean(lua_toboolean(L, index));
 
 	case LUA_TNUMBER:
+		if (lua_isinteger(L, index))
+			return json_object_new_int64(lua_tointeger(L, index));
+
 		nd = lua_tonumber(L, index);
-		ni = lua_tointeger(L, index);
 
-		if (nd == ni)
+		if (isfinite(nd) && trunc(nd) == nd)
 			return json_object_new_int64(nd);
 
 		return json_object_new_double(nd);