json: Improve tolerance to uncovered C members during JSON encoding

This enhancement fix encoding of JSON objects for which descriptors do not covers all members of the C structure represented. Introduce SIZEOF_FIELD helper macro Fixes #50976 Signed-off-by: Lucas Dietrich <[email protected]>
zephyrproject-rtos · Apr 3, 2023 · de6b69c · de6b69c
1 parent 4256cd4
commit de6b69c
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Showing 4 changed files with 42 additions and 14 deletions.
diff --git a/include/zephyr/data/json.h b/include/zephyr/data/json.h
@@ -109,7 +109,8 @@ struct json_obj_descr {
 	union {
 		struct {
 			const struct json_obj_descr *sub_descr;
-			size_t sub_descr_len;
+			uint16_t sub_descr_len;
+			uint16_t sub_struct_size;
 		} object;
 		struct {
 			const struct json_obj_descr *element_descr;
@@ -201,6 +202,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 			.object = { \
 				.sub_descr = sub_descr_, \
 				.sub_descr_len = ARRAY_SIZE(sub_descr_), \
+				.sub_struct_size = sizeof(struct_), \
 			}, \
 		}, \
 	}
@@ -245,11 +247,12 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
  * @param elem_descr_ Element descriptor, pointer to a descriptor array
  * @param elem_descr_len_ Number of elements in elem_descr_
  */
-#define Z_JSON_DESCR_OBJ(elem_descr_, elem_descr_len_) \
+#define Z_JSON_DESCR_OBJ(elem_descr_, elem_descr_len_, struct_size_) \
 	{ \
 		.object = { \
 			.sub_descr = elem_descr_, \
 			.sub_descr_len = elem_descr_len_, \
+			.sub_struct_size = struct_size_, \
 		}, \
 	}
 
@@ -338,7 +341,8 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 			.array = { \
 				.element_descr = Z_JSON_ELEMENT_DESCR(struct_, len_field_, \
 					JSON_TOK_OBJECT_START, \
-					Z_JSON_DESCR_OBJ(elem_descr_, elem_descr_len_)), \
+					Z_JSON_DESCR_OBJ(elem_descr_, elem_descr_len_, \
+						SIZEOF_FIELD(struct_, field_name_[0]))), \
 				.n_elements = (max_len_), \
 			}, \
 		}, \
@@ -456,6 +460,7 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 			.object = { \
 				.sub_descr = sub_descr_, \
 				.sub_descr_len = ARRAY_SIZE(sub_descr_), \
+				.sub_struct_size = sizeof(struct_), \
 			}, \
 		}, \
 	}
@@ -548,7 +553,8 @@ typedef int (*json_append_bytes_t)(const char *bytes, size_t len,
 			.array = { \
 				.element_descr = Z_JSON_ELEMENT_DESCR(struct_, len_field_, \
 					JSON_TOK_OBJECT_START, \
-					Z_JSON_DESCR_OBJ(elem_descr_, elem_descr_len_)), \
+					Z_JSON_DESCR_OBJ(elem_descr_, elem_descr_len_, \
+						SIZEOF_FIELD(struct_, field_name_[0])), \
 				.n_elements = (max_len_), \
 			}, \
 		}, \

diff --git a/include/zephyr/sys/util.h b/include/zephyr/sys/util.h
@@ -210,6 +210,26 @@ extern "C" {
 #define CONTAINER_OF(ptr, type, field) \
 	((type *)(((char *)(ptr)) - offsetof(type, field)))
 
+/**
+ * @brief Get the size of a field in a structure type
+ *
+ * Example:
+ *
+ *	struct foo {
+ *		int bar;
+ *		char baz;
+ *	};
+ *
+ *	size_t size_of_baz = SIZEOF_FIELD(struct foo, baz);
+ *
+ * Above, @p size_of_baz is equal to sizeof(char).
+ *
+ * @param type the type of the structure containing the field
+ * @param member the name of the field in the structure
+ * @return the size of the field in bytes
+ */
+#define SIZEOF_FIELD(type, member) sizeof(((type *)0)->member)
+
 /**
  * @brief Value of @p x rounded up to the next multiple of @p align,
  *        which must be a power of 2.

diff --git a/lib/os/json.c b/lib/os/json.c
@@ -522,16 +522,7 @@ static ptrdiff_t get_elem_size(const struct json_obj_descr *descr)
 	case JSON_TOK_ARRAY_START:
 		return descr->array.n_elements * get_elem_size(descr->array.element_descr);
 	case JSON_TOK_OBJECT_START: {
-		ptrdiff_t total = 0;
-		size_t i;
-
-		for (i = 0; i < descr->object.sub_descr_len; i++) {
-			ptrdiff_t s = get_elem_size(&descr->object.sub_descr[i]);
-
-			total += ROUND_UP(s, 1 << descr->align_shift);
-		}
-
-		return total;
+		return descr->object.sub_struct_size;
 	}
 	default:
 		return -EINVAL;
@@ -549,6 +540,8 @@ static int arr_parse(struct json_obj *obj,
 
 	if (val) {
 		elements = (size_t *)((char *)val + elem_descr->offset);
+	} else {
+		field = (char *)field + elem_descr->offset;
 	}
 
 	__ASSERT_NO_MSG(elem_size > 0);

diff --git a/tests/lib/json/src/main.c b/tests/lib/json/src/main.c
@@ -11,6 +11,7 @@
 
 struct test_nested {
 	int nested_int;
+	uint32_t _unused_member;
 	bool nested_bool;
 	const char *nested_string;
 };
@@ -19,6 +20,7 @@ struct test_struct {
 	const char *some_string;
 	int some_int;
 	bool some_bool;
+	uint32_t _unused_member;
 	struct test_nested some_nested_struct;
 	int some_array[16];
 	size_t some_array_len;
@@ -30,17 +32,20 @@ struct test_struct {
 };
 
 struct elt {
+	uint32_t _unused_member;
 	const char *name;
 	int height;
 };
 
 struct obj_array {
 	struct elt elements[10];
+	uint32_t _unused_member;
 	size_t num_elements;
 };
 
 struct test_int_limits {
 	int int_max;
+	uint32_t _unused_member;
 	int int_cero;
 	int int_min;
 };
@@ -88,11 +93,15 @@ static const struct json_obj_descr obj_limits_descr[] = {
 };
 
 struct array {
+	uint32_t _unused_member1;
+	uint32_t _unused_member2;
 	struct elt objects;
 };
 
 struct obj_array_array {
+	uint32_t _unused_member1;
 	struct array objects_array[4];
+	uint32_t _unused_member2;
 	size_t objects_array_len;
 };