Backport JSON parser improvement (#81)

* json: Skip unknown fields on parsing

Skip child objects and arrays that are not specified in the given object
descriptor when parsing a JSON input string.
This patch adds support for extra child arrays which previously were not
supported by the parser as opposed to additional child objects.

Fixes zephyrproject-rtos#47988

Signed-off-by: Markus Fuchs <[email protected]>

* tests: lib: json: Add tests for parsing inputs with extra fields

Add tests for both extra objects and extra arrays nested in JSON objects.
Fields in extra nested objects should be ignored and also not manipulate
subsequent fields with the same name.

Signed-off-by: Markus Fuchs <[email protected]>

---------

Signed-off-by: Markus Fuchs <[email protected]>
Co-authored-by: Markus Fuchs <[email protected]>

Author: berendo

lib/os/json.c

@@ -388,6 +388,33 @@ static int arr_next(struct json_obj *json, struct token *value)
 	return element_token(value->type);
 }
 
+static int skip_field(struct json_obj *obj, struct json_obj_key_value *kv)
+{
+	int field_count = 1;
+
+	if (kv->value.type == JSON_TOK_OBJECT_START ||
+	    kv->value.type == JSON_TOK_LIST_START) {
+		while (field_count > 0 && lexer_next(&obj->lexer, &kv->value)) {
+			switch (kv->value.type) {
+			case JSON_TOK_OBJECT_START:
+			case JSON_TOK_LIST_START:
+				field_count++;
+				break;
+			case JSON_TOK_OBJECT_END:
+			case JSON_TOK_LIST_END:
+				field_count--;
+				break;
+			case JSON_TOK_ERROR:
+				return -EINVAL;
+			default:
+				break;
+			}
+		}
+	}
+
+	return 0;
+}
+
 static int decode_num(const struct token *token, int32_t *num)
 {
 	/* FIXME: strtod() is not available in newlib/minimal libc,
@@ -585,6 +612,14 @@ static int obj_parse(struct json_obj *obj, const struct json_obj_descr *descr,
 			decoded_fields |= 1<<i;
 			break;
 		}
+
+		/* Skip field, if no descriptor was found */
+		if (i >= descr_len) {
+			ret = skip_field(obj, &kv);
+			if (ret < 0) {
+				return ret;
+			}
+		}
 	}
 
 	return -EINVAL;

tests/lib/json/src/main.c

@@ -164,8 +164,11 @@ static void test_json_decoding(void)
 		"\"some_nested_struct\":{    "
 		"\"nested_int\":-1234,\n\n"
 		"\"nested_bool\":false,\t"
-		"\"nested_string\":\"this should be escaped: \\t\"},"
-		"\"some_array\":[11,22, 33,\t45,\n299]"
+		"\"nested_string\":\"this should be escaped: \\t\","
+		"\"extra_nested_array\":[0,-1]},"
+		"\"extra_struct\":{\"nested_bool\":false},"
+		"\"extra_bool\":true,"
+		"\"some_array\":[11,22, 33,\t45,\n299],"
 		"\"another_b!@l\":true,"
 		"\"if\":false,"
 		"\"another-array\":[2,3,5,7],"