lib: json: add JSON_OBJ_DESCR_*_NAMED variants

The set of valid JSON field names is larger than the set of C
identifiers. This can result in structure field names which pack
decoded JSON values which necessarily differ from the field names in
the JSON.

Support this by adding _NAMED variants to each of the JSON_OBJ_DESCR_*
helper macros. For example, JSON_OBJ_DESCR_PRIM_NAMED allows users to
declare a descriptor field for a primitive type, whose structure field
name is different from the JSON field name.

Signed-off-by: Marti Bolivar <[email protected]>

Author: Marti Bolivar

lib/json/json.h

@@ -172,6 +172,95 @@ typedef int (*json_append_bytes_t)(const u8_t *bytes, size_t len,
 		.n_elements = (max_len_), \
 	}
 
+/**
+ * @brief Variant of JSON_OBJ_DESCR_PRIM that can be used when the
+ *        structure and JSON field names differ.
+ *
+ * This is useful when the JSON field is not a valid C identifier.
+ *
+ * @param struct_ Struct packing the values.
+ *
+ * @param json_field_name_ String, field name in JSON strings
+ *
+ * @param struct_field_name_ Field name in the struct
+ *
+ * @param type_ Token type for JSON value corresponding to a primitive
+ * type.
+ *
+ * @see JSON_OBJ_DESCR_PRIM
+ */
+#define JSON_OBJ_DESCR_PRIM_NAMED(struct_, json_field_name_, \
+				  struct_field_name_, type_) \
+	{ \
+		.field_name = (json_field_name_), \
+		.field_name_len = sizeof(json_field_name_) - 1, \
+		.offset = offsetof(struct_, struct_field_name_), \
+		.type = type_, \
+	}
+
+/**
+ * @brief Variant of JSON_OBJ_DESCR_OBJECT that can be used when the
+ *        structure and JSON field names differ.
+ *
+ * This is useful when the JSON field is not a valid C identifier.
+ *
+ * @param struct_ Struct packing the values
+ *
+ * @param json_field_name_ String, field name in JSON strings
+ *
+ * @param struct_field_name_ Field name in the struct
+ *
+ * @param sub_descr_ Array of json_obj_descr describing the subobject
+ *
+ * @see JSON_OBJ_DESCR_OBJECT
+ */
+#define JSON_OBJ_DESCR_OBJECT_NAMED(struct_, json_field_name_, \
+				    struct_field_name_, sub_descr_) \
+	{ \
+		.field_name = (json_field_name_), \
+		.field_name_len = (sizeof(json_field_name_) - 1), \
+		.offset = offsetof(struct_, struct_field_name_), \
+		.type = JSON_TOK_OBJECT_START, \
+		.sub_descr = sub_descr_, \
+		.sub_descr_len = ARRAY_SIZE(sub_descr_) \
+	}
+
+/**
+ * @brief Variant of JSON_OBJ_DESCR_ARRAY that can be used when the
+ *        structure and JSON field names differ.
+ *
+ * This is useful when the JSON field is not a valid C identifier.
+ *
+ * @param struct_ Struct packing the values
+ *
+ * @param json_field_name_ String, field name in JSON strings
+ *
+ * @param struct_field_name_ Field name in the struct
+ *
+ * @param max_len_ Maximum number of elements in array
+ *
+ * @param len_field_ Field name in the struct for the number of elements
+ * in the array
+ *
+ * @param elem_type_ Element type
+ *
+ * @see JSON_OBJ_DESCR_ARRAY
+ */
+#define JSON_OBJ_DESCR_ARRAY_NAMED(struct_, json_field_name_,\
+				   struct_field_name_, max_len_, len_field_, \
+				   elem_type_) \
+	{ \
+		.field_name = (json_field_name_), \
+		.field_name_len = sizeof(json_field_name_) - 1, \
+		.offset = offsetof(struct_, struct_field_name_), \
+		.type = JSON_TOK_LIST_START, \
+		.element_descr = &(struct json_obj_descr) { \
+			.type = elem_type_, \
+			.offset = offsetof(struct_, len_field_), \
+		}, \
+		.n_elements = (max_len_), \
+	}
+
 /**
  * @brief Parses the JSON-encoded object pointer to by @param json, with
  * size @param len, according to the descriptor pointed to by @param descr.