json: add spdk_json_free_object()

After decoding a JSON object we had to free the parsed
strings one-by-one. Not anymore.

Change-Id: I819f1d533e397aa9babca58b5500c38ac01a963d
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/2753
Reviewed-by: Mellanox Build Bot
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

CHANGELOG.md

@@ -84,6 +84,8 @@ through the JSON context provided via spdk_nvmf_target_opts->transport_specific.
 
 ## v20.07: SPDK CSI driver, new accel_fw commands, I/O abort support
 
+spdk_json_free_object() was added to free memory allocated by spdk_json_decode_object().
+
 ### accel
 
 A new API was added `spdk_accel_get_capabilities` that allows applications to

include/spdk/json.h

@@ -156,6 +156,9 @@ int spdk_json_decode_uint32(const struct spdk_json_val *val, void *out);
 int spdk_json_decode_uint64(const struct spdk_json_val *val, void *out);
 int spdk_json_decode_string(const struct spdk_json_val *val, void *out);
 
+void spdk_json_free_object(const struct spdk_json_object_decoder *decoders, size_t num_decoders,
+			   void *obj);
+
 /**
  * Get length of a value in number of values.
  *

lib/json/json_util.c

@@ -364,6 +364,29 @@ _json_decode_object(const struct spdk_json_val *values,
 	return invalid ? -1 : 0;
 }
 
+void
+spdk_json_free_object(const struct spdk_json_object_decoder *decoders, size_t num_decoders,
+		      void *obj)
+{
+	struct spdk_json_val invalid_val = {
+		.start = "",
+		.len = 0,
+		.type = SPDK_JSON_VAL_INVALID
+	};
+	size_t decidx;
+
+	for (decidx = 0; decidx < num_decoders; decidx++) {
+		const struct spdk_json_object_decoder *dec = &decoders[decidx];
+		void *field = (void *)((uintptr_t)obj + dec->offset);
+
+		/* decoding an invalid value will free the
+		 * previous memory without allocating it again.
+		 */
+		dec->decode_func(&invalid_val, field);
+	}
+}
+
+
 int
 spdk_json_decode_object(const struct spdk_json_val *values,
 			const struct spdk_json_object_decoder *decoders, size_t num_decoders, void *out)

lib/json/spdk_json.map

@@ -13,6 +13,8 @@
 	spdk_json_decode_uint64;
 	spdk_json_decode_string;
 
+	spdk_json_free_object;
+
 	spdk_json_val_len;
 	spdk_json_strequal;
 	spdk_json_strdup;

test/unit/lib/json/json_util.c/json_util_ut.c

@@ -251,6 +251,37 @@ test_decode_object(void)
 	free(output.my_name);
 }
 
+static void
+test_free_object(void)
+{
+	struct my_object {
+		char *my_name;
+		uint32_t my_int;
+		char *my_other_name;
+		char *empty_string;
+	};
+	struct spdk_json_object_decoder decoders[] = {
+		{"first", offsetof(struct my_object, my_name), spdk_json_decode_string, false},
+		{"second", offsetof(struct my_object, my_int), spdk_json_decode_uint32, false},
+		{"third", offsetof(struct my_object, my_other_name), spdk_json_decode_string, true},
+		{"fourth", offsetof(struct my_object, empty_string), spdk_json_decode_string, false},
+	};
+	struct my_object output = {
+		.my_name = strdup("hello"),
+		.my_int = 3,
+		.my_other_name = strdup("world"),
+		.empty_string = NULL
+	};
+
+	SPDK_CU_ASSERT_FATAL(output.my_name != NULL);
+	SPDK_CU_ASSERT_FATAL(output.my_other_name != NULL);
+
+	spdk_json_free_object(decoders, 4, &output);
+	CU_ASSERT(output.my_name == NULL);
+	CU_ASSERT(output.my_other_name == NULL);
+	CU_ASSERT(output.empty_string == NULL);
+}
+
 static void
 test_decode_array(void)
 {
@@ -942,6 +973,7 @@ int main(int argc, char **argv)
 	CU_ADD_TEST(suite, test_decode_string);
 	CU_ADD_TEST(suite, test_find);
 	CU_ADD_TEST(suite, test_iterating);
+	CU_ADD_TEST(suite, test_free_object);
 
 	CU_basic_set_mode(CU_BRM_VERBOSE);