Extending MySQL using the Component Infrastructure – part 4: error logging

This post is the fourth post of a series of articles on extending MySQL with the Component Infrastructure, the list above will be updated as new articles are published:

In this article we will add to our component the capability to add messages in error log (and performance_schema.error_log table) using the log builtins component service.

You will notice that this very easy and fast.

We start as usual with scan.h:

/* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is also distributed with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have included with MySQL.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License, version 2.0, for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#define LOG_COMPONENT_TAG "viruscan"
#include <mysql/components/component_implementation.h>
#include <mysql/components/services/log_builtins.h> /* LogComponentErr */
#include <mysqld_error.h> /* Errors */
extern REQUIRES_SERVICE_PLACEHOLDER(log_builtins);
extern REQUIRES_SERVICE_PLACEHOLDER(log_builtins_string);
extern SERVICE_TYPE(log_builtins) * log_bi;
extern SERVICE_TYPE(log_builtins_string) * log_bs;
view raw scan.h hosted with ❤ by GitHub

On line 22 and 23 we add the headers. mysqld_error.h is required to define ER_LOG_PRINTF_MSG.

Then we specify the services that we need.

We can then update scan.cc to also include those services and use them on 42 and 54:

/* Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is also distributed with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have included with MySQL.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License, version 2.0, for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#define LOG_COMPONENT_TAG "viruscan"
#define NO_SIGNATURE_CHANGE 0
#define SIGNATURE_CHANGE 1
#include <components/viruscan/scan.h>
REQUIRES_SERVICE_PLACEHOLDER(log_builtins);
REQUIRES_SERVICE_PLACEHOLDER(log_builtins_string);
SERVICE_TYPE(log_builtins) * log_bi;
SERVICE_TYPE(log_builtins_string) * log_bs;
static mysql_service_status_t viruscan_service_init() {
mysql_service_status_t result = 0;
log_bi = mysql_service_log_builtins;
log_bs = mysql_service_log_builtins_string;
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, "initializing…");
return result;
}
static mysql_service_status_t viruscan_service_deinit() {
mysql_service_status_t result = 0;
LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, "uninstalled.");
return result;
}
BEGIN_COMPONENT_PROVIDES(viruscan_service)
END_COMPONENT_PROVIDES();
BEGIN_COMPONENT_REQUIRES(viruscan_service)
REQUIRES_SERVICE(log_builtins),
REQUIRES_SERVICE(log_builtins_string),
END_COMPONENT_REQUIRES();
/* A list of metadata to describe the Component. */
BEGIN_COMPONENT_METADATA(viruscan_service)
METADATA("mysql.author", "Oracle Corporation"),
METADATA("mysql.license", "GPL"), METADATA("mysql.dev", "lefred"),
END_COMPONENT_METADATA();
/* Declaration of the Component. */
DECLARE_COMPONENT(viruscan_service,
"mysql:viruscan_service")
viruscan_service_init,
viruscan_service_deinit END_DECLARE_COMPONENT();
/* Defines list of Components contained in this library. Note that for now
we assume that library will have exactly one Component. */
DECLARE_LIBRARY_COMPONENTS &COMPONENT_REF(viruscan_service)
END_DECLARE_LIBRARY_COMPONENTS
view raw scan.cc hosted with ❤ by GitHub

We also need to tell that our component requires those services on line 60 and 61.

We can compile it again (using make component_viruscan), restart mtr and test it again:

And in error log file, we can also see the following lines:

2022-01-06T09:26:14.450784Z 8 [Note] [MY-011071] [Server] Component viruscan reported: 'initializing...'
2022-01-06T09:26:21.906295Z 8 [Note] [MY-011071] [Server] Component viruscan reported: 'uninstalled.'

On the next article, we will create our new privilege, stay tuned and enjoy MySQL!

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