Extending MySQL using the Component Infrastructure – part 10: status variables - lefred blog: tribulations of a MySQL Evangelist

Today we are already at the post number ten of the series of articles related to extending MySQL with the Component Infrastructure, the list above will be updated as new articles are published:

Today we will keep improving our component by adding some status variables.

What I have in mind is to add the following status variables:

clamav_signatures (integer): the amount of signatures loaded
clamav_engine_version (varchar): the ClamAV Engine Version
virus_found (integer): counter of detected viruses

Once again, we will use a MySQL Component Service to handle our status variables: the Status Variable Registration service.

In scan.h we will add the required include file and the required service placeholder, lines 30 and 49:

	/* 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 */
	#include <mysql/components/services/dynamic_privilege.h>
	#include <mysql/components/services/udf_metadata.h>
	#include <mysql/components/services/udf_registration.h>
	#include <mysql/components/services/security_context.h>
	#include <mysql/components/services/mysql_current_thread_reader.h>
	#include <mysql/components/services/mysql_runtime_error_service.h>
	#include <mysql/components/services/component_status_var_service.h>

	#include <list>
	#include <string>

	#include <clamav.h>

	extern REQUIRES_SERVICE_PLACEHOLDER(log_builtins);
	extern REQUIRES_SERVICE_PLACEHOLDER(log_builtins_string);
	extern REQUIRES_SERVICE_PLACEHOLDER(dynamic_privilege_register);
	extern REQUIRES_SERVICE_PLACEHOLDER(udf_registration);
	extern REQUIRES_SERVICE_PLACEHOLDER(mysql_udf_metadata);

	extern REQUIRES_SERVICE_PLACEHOLDER(mysql_thd_security_context);
	extern REQUIRES_SERVICE_PLACEHOLDER(global_grants_check);
	extern REQUIRES_SERVICE_PLACEHOLDER(mysql_current_thread_reader);

	extern REQUIRES_SERVICE_PLACEHOLDER(mysql_runtime_error);

	extern REQUIRES_SERVICE_PLACEHOLDER(status_variable_registration);

	extern SERVICE_TYPE(log_builtins) * log_bi;
	extern SERVICE_TYPE(log_builtins_string) * log_bs;

view raw scan.h hosted with ❤ by GitHub

Now we can modify the code of our component, scan.cc. We start as usually by adding the service placeholder (line 39) and we add the status_variable_registration service to the required services on line 424:

	/* 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);
	REQUIRES_SERVICE_PLACEHOLDER(dynamic_privilege_register);
	REQUIRES_SERVICE_PLACEHOLDER(udf_registration);
	REQUIRES_SERVICE_PLACEHOLDER(mysql_udf_metadata);
	REQUIRES_SERVICE_PLACEHOLDER(mysql_thd_security_context);
	REQUIRES_SERVICE_PLACEHOLDER(global_grants_check);
	REQUIRES_SERVICE_PLACEHOLDER(mysql_current_thread_reader);
	REQUIRES_SERVICE_PLACEHOLDER(mysql_runtime_error);
	REQUIRES_SERVICE_PLACEHOLDER(status_variable_registration);

	SERVICE_TYPE(log_builtins) * log_bi;
	SERVICE_TYPE(log_builtins_string) * log_bs;

	static const char *SCAN_PRIVILEGE_NAME = "VIRUS_SCAN";

	static unsigned int signature_status = 0;
	static unsigned int virusfound_status = 0;
	static char clamav_version[10] = "";

	static SHOW_VAR viruscan_status_variables[] = {
	{"viruscan.clamav_signatures", (char *)&signature_status, SHOW_INT,
	SHOW_SCOPE_GLOBAL},
	{"viruscan.clamav_engine_version", (char *)&clamav_version, SHOW_CHAR,
	SHOW_SCOPE_GLOBAL},
	{"viruscan.virus_found", (char *)&virusfound_status, SHOW_INT,
	SHOW_SCOPE_GLOBAL},
	{nullptr, nullptr, SHOW_LONG, SHOW_SCOPE_GLOBAL}
	};

	struct scan_result scan_data(const char *data, size_t data_size);

	/*
	* Holds the data of a virus scan
	*/
	struct scan_result
	{
	int return_code;
	const char *virus_name;
	long unsigned int scanned;
	};

	/*
	* Global variable to access the ClamAV engine
	*/
	struct cl_engine *engine = NULL;
	char *signatureDir;
	struct cl_stat signatureStat;

	class udf_list {
	typedef std::list<std::string> udf_list_t;

	public:
	~udf_list() { unregister(); }
	bool add_scalar(const char *func_name, enum Item_result return_type,
	Udf_func_any func, Udf_func_init init_func = NULL,
	Udf_func_deinit deinit_func = NULL) {
	if (!mysql_service_udf_registration->udf_register(
	func_name, return_type, func, init_func, deinit_func)) {
	set.push_back(func_name);
	return false;
	}
	return true;
	}

	bool unregister() {
	udf_list_t delete_set;
	/* try to unregister all of the udfs */
	for (auto udf : set) {
	int was_present = 0;
	if (!mysql_service_udf_registration->udf_unregister(udf.c_str(),
	&was_present) \|\|
	!was_present)
	delete_set.push_back(udf);
	}

	/* remove the unregistered ones from the list */
	for (auto udf : delete_set) set.remove(udf);

	/* success: empty set */
	if (set.empty()) return false;

	/* failure: entries still in the set */
	return true;
	}

	private:
	udf_list_t set;
	} * list;

	unsigned int reload_engine()
	{
	unsigned int signatureNum = 0;
	int rv;

	if (engine != NULL)
	{
	cl_engine_free(engine);
	}

	engine = cl_engine_new();

	memset(&signatureStat, 0, sizeof(struct cl_stat));
	signatureDir = const_cast<char*>(cl_retdbdir());
	cl_statinidir(signatureDir, &signatureStat);
	/*
	* Load the signatures from signatureDir, we use only the default dir
	*/
	rv = cl_load(signatureDir, engine, &signatureNum, CL_DB_STDOPT);
	char buf[1024];
	if (CL_SUCCESS != rv)
	{
	snprintf(buf, 1024, "failure loading clamav databases: %s", cl_strerror(rv));
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
	}

	rv = cl_engine_compile(engine);
	if (CL_SUCCESS != rv)
	{
	snprintf(buf, 1024, "cannot create clamav engine: %s", cl_strerror(rv));
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
	cl_engine_free(engine);
	}

	snprintf(buf, 1024, "clamav engine loaded with signatureNum %d from %s", signatureNum, signatureDir);
	LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, buf);
	signature_status = signatureNum;
	return signatureNum;
	}

	int register_status_variables() {
	if (mysql_service_status_variable_registration->register_variable(
	(SHOW_VAR *)&viruscan_status_variables)) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, "Failed to register status variable");
	return 1;
	}
	LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, "Status variable(s) registered");
	return 0;
	}

	int unregister_status_variables() {
	if (mysql_service_status_variable_registration->unregister_variable(
	(SHOW_VAR *)&viruscan_status_variables)) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, "Failed to unregister status variable");
	return 1;
	}
	LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, "Status variable(s) unregistered");
	return 0;
	}


	namespace udf_impl {

	struct scan_result scan_data(const char *data, size_t data_size)
	{
	struct scan_result result = {0, "", 0};
	cl_fmap_t *map;

	map = cl_fmap_open_memory(data, data_size);
	/* scan file descriptor */
	static struct cl_scan_options cl_scan_options;
	memset(&cl_scan_options, 0, sizeof(struct cl_scan_options));
	cl_scan_options.parse \|= ~0; /* enable all parsers */
	cl_scan_options.general \|= CL_SCAN_GENERAL_ALLMATCHES;
	result.return_code = cl_scanmap_callback(map,
	NULL,
	&result.virus_name,
	&result.scanned,
	engine,
	&cl_scan_options,
	NULL);

	cl_fmap_close(map);
	return result;
	}

	bool have_virus_scan_privilege(void *opaque_thd) {
	// get the security context of the thread
	Security_context_handle ctx = nullptr;
	if (mysql_service_mysql_thd_security_context->get(opaque_thd, &ctx) \|\| !ctx) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG,
	"problem trying to get security context");
	return false;
	}

	if (mysql_service_global_grants_check->has_global_grant(
	ctx, SCAN_PRIVILEGE_NAME, strlen(SCAN_PRIVILEGE_NAME)))
	return true;

	return false;
	}

	const char udf_init = "udf_init", my_udf = "my_udf",
	my_udf_clear = "my_clear", my_udf_add = "my_udf_add";

	static bool viruscan_udf_init(UDF_INIT initid, UDF_ARGS , char *) {
	const char* name = "utf8mb4";
	char value = const_cast<char>(name);
	initid->ptr = const_cast<char *>(udf_init);
	if (mysql_service_mysql_udf_metadata->result_set(
	initid, "charset",
	const_cast<char *>(value))) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, "failed to set result charset");
	return false;
	}
	return 0;
	}

	static void viruscan_udf_deinit(__attribute__((unused)) UDF_INIT *initid) {
	assert(initid->ptr == udf_init \|\| initid->ptr == my_udf);
	}

	const char viruscan_udf(UDF_INIT , UDF_ARGS args, char outp,
	unsigned long length, char is_null, char *error) {

	MYSQL_THD thd;
	mysql_service_mysql_current_thread_reader->get(&thd);
	struct scan_result result;
	char buf[1024];

	if(!have_virus_scan_privilege(thd)) {
	mysql_error_service_printf(
	ER_SPECIFIC_ACCESS_DENIED_ERROR, 0,
	SCAN_PRIVILEGE_NAME);
	*error = 1;
	*is_null = 1;
	return 0;
	}

	result = scan_data(args->args[0], args->lengths[0]);
	if (result.return_code == 0) {
	strncpy(outp, "clean: no virus found", *length);
	} else {
	strncpy(outp, result.virus_name, *length);
	snprintf(buf, 1024, "Virus found: %s !!", result.virus_name);
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
	virusfound_status++;
	}

	*length = strlen(outp);
	return const_cast<char *>(outp);
	}

	static bool virusreload_udf_init(UDF_INIT initid, UDF_ARGS , char *) {
	const char* name = "utf8mb4";
	char value = const_cast<char>(name);
	initid->ptr = const_cast<char *>(udf_init);
	if (mysql_service_mysql_udf_metadata->result_set(
	initid, "charset",
	const_cast<char *>(value))) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, "failed to set result charset");
	return false;
	}
	return 0;
	}

	static void virusreload_udf_deinit(__attribute__((unused)) UDF_INIT *initid) {
	assert(initid->ptr == udf_init \|\| initid->ptr == my_udf);
	}

	const char virusreload_udf(UDF_INIT , UDF_ARGS args, char outp,
	unsigned long length, char is_null, char *error) {

	MYSQL_THD thd;
	mysql_service_mysql_current_thread_reader->get(&thd);

	unsigned int signatureNum = 0;

	if(!have_virus_scan_privilege(thd)) {
	mysql_error_service_printf(
	ER_SPECIFIC_ACCESS_DENIED_ERROR, 0,
	SCAN_PRIVILEGE_NAME);
	*error = 1;
	*is_null = 1;
	return 0;
	}

	if (args->arg_count > 0) {
	snprintf(outp, *length, "ERROR: this function doesn't require any parameter !");
	*length = strlen(outp);
	return const_cast<char *>(outp);
	}
	snprintf(outp, *length, "No need to reload ClamAV engine");

	if(cl_statchkdir(&signatureStat) == SIGNATURE_CHANGE) {
	signatureNum = reload_engine();
	cl_statfree(&signatureStat);
	cl_statinidir(cl_retdbdir(), &signatureStat);
	snprintf(outp, *length, "ClamAV engine reloaded with new virus database: %d signatures", signatureNum);
	}

	*length = strlen(outp);
	return const_cast<char *>(outp);
	}


	} /* namespace udf_impl */


	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…");

	register_status_variables();

	int rv;
	rv = cl_init(CL_INIT_DEFAULT);
	char buf[1024];
	if (CL_SUCCESS != rv) {
	snprintf(buf, 1024, "can't initialize libclamav: %s", cl_strerror(rv));
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG, buf);
	} else {
	// Print the version of ClamAV engine
	strncpy(clamav_version, cl_retver(), sizeof(clamav_version)-1);
	snprintf(buf, 1024, "ClamAV %s intialized", clamav_version);
	LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG, buf);
	}

	struct cl_engine *cl_engine_new(void);
	reload_engine();

	// Registration of the privilege
	if (mysql_service_dynamic_privilege_register->register_privilege(SCAN_PRIVILEGE_NAME, strlen(SCAN_PRIVILEGE_NAME))) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG,
	"could not register privilege 'VIRUS_SCAN'.");
	result = 1;
	} else {
	LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG,
	"new privilege 'VIRUS_SCAN' has been registered successfully.");
	}

	list = new udf_list();

	if (list->add_scalar("virus_scan", Item_result::STRING_RESULT,
	(Udf_func_any)udf_impl::viruscan_udf,
	udf_impl::viruscan_udf_init,
	udf_impl::viruscan_udf_deinit)) {
	delete list;
	return 1; /* failure: one of the UDF registrations failed */
	}

	if (list->add_scalar("virus_reload_engine", Item_result::STRING_RESULT,
	(Udf_func_any)udf_impl::virusreload_udf,
	udf_impl::virusreload_udf_init,
	udf_impl::virusreload_udf_deinit)) {
	delete list;
	return 1; /* failure: one of the UDF registrations failed */
	}

	return result;
	}

	static mysql_service_status_t viruscan_service_deinit() {
	mysql_service_status_t result = 0;

	cl_engine_free(engine);

	unregister_status_variables();

	if (mysql_service_dynamic_privilege_register->unregister_privilege(SCAN_PRIVILEGE_NAME, strlen(SCAN_PRIVILEGE_NAME))) {
	LogComponentErr(ERROR_LEVEL, ER_LOG_PRINTF_MSG,
	"could not unregister privilege 'VIRUS_SCAN'.");
	result = 1;
	} else {
	LogComponentErr(INFORMATION_LEVEL, ER_LOG_PRINTF_MSG,
	"privilege 'VIRUS_SCAN' has been unregistered successfully.");
	}

	if (list->unregister()) return 1; /* failure: some UDFs still in use */

	delete list;

	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),
	REQUIRES_SERVICE(dynamic_privilege_register),
	REQUIRES_SERVICE(mysql_udf_metadata),
	REQUIRES_SERVICE(udf_registration),
	REQUIRES_SERVICE(mysql_thd_security_context),
	REQUIRES_SERVICE(global_grants_check),
	REQUIRES_SERVICE(mysql_current_thread_reader),
	REQUIRES_SERVICE(mysql_runtime_error),
	REQUIRES_SERVICE(status_variable_registration),
	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

Then on line 46, 47 and 48, we create 3 variables that will contain the value of the new status variables.

We also create an array containing the information about the status variables, like their name, their type and their scope. Then we use that array to register our status variables on line 160 (and we unregister on line 170).

Finally, we assign values to the variables as we need (lines 156, 266 and 347).

You can also notice that I changed all sprintf() and strcpy() to use functions limiting the size to avoid overflow: snprintf()and strncpy().

Let’s test our freshly new created status variables:

Great !

Today we learned how to created status variables using the MySQL Component Infrastructure.

In the next article, we will see how to add a Performance_Schema table for our component.

I hope you enjoy this series and as usual, happy coding !

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Extending MySQL using the Component Infrastructure – part 10: status variables

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