cmd_results_to_json: return copied string and properly free the json

The only user of this function would copy the string right away
to get rid of the const flag anyway, and freeing a const string
afterwards might work but is not meant to be done according to the
json-c API.

include/sway/commands.h

@@ -79,7 +79,7 @@ void free_cmd_results(struct cmd_results *results);
  *
  * Free the JSON string later on.
  */
-const char *cmd_results_to_json(struct cmd_results *results);
+char *cmd_results_to_json(struct cmd_results *results);
 
 struct cmd_results *add_color(const char *name,
 		char *buffer, const char *color);

sway/commands.c

@@ -527,7 +527,7 @@ void free_cmd_results(struct cmd_results *results) {
 	free(results);
 }
 
-const char *cmd_results_to_json(struct cmd_results *results) {
+char *cmd_results_to_json(struct cmd_results *results) {
 	json_object *result_array = json_object_new_array();
 	json_object *root = json_object_new_object();
 	json_object_object_add(root, "success",
@@ -542,9 +542,9 @@ const char *cmd_results_to_json(struct cmd_results *results) {
 	}
 	json_object_array_add(result_array, root);
 	const char *json = json_object_to_json_string(result_array);
-	free(result_array);
-	free(root);
-	return json;
+	char *res = strdup(json);
+	json_object_put(result_array);
+	return res;
 }
 
 /**

sway/ipc-server.c

@@ -481,11 +481,10 @@ void ipc_client_handle_command(struct ipc_client *client) {
 	case IPC_COMMAND:
 	{
 		struct cmd_results *results = execute_command(buf, NULL);
-		const char *json = cmd_results_to_json(results);
-		char reply[256];
-		int length = snprintf(reply, sizeof(reply), "%s", json);
+		char *json = cmd_results_to_json(results);
+		int length = strlen(json);
+		client_valid = ipc_send_reply(client, json, (uint32_t)length);
 		free(json);
-		client_valid = ipc_send_reply(client, reply, (uint32_t)length);
 		free_cmd_results(results);
 		goto exit_cleanup;
 	}