Add SQLite 3 realtime support

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@335129 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/res_config_sqlite3.conf.sample

+; Define a realtime database name to use in extconfig.conf
+;
+;[asterisk]
+;dbfile => /var/lib/asterisk/realtime.sqlite3
+;
+; debug - Turn on debugging information
+;debug=yes
+;
+; requirements - At startup, each realtime family will make requirements
+;   on the backend.  There are several strategies for handling requirements:
+;     warn        - Warn if the required column does not exist.
+;     createclose - Create columns as close to the requirements as possible.
+;     createchar  - Create char columns only
+;
+;requirements=warn
+;
+; batch - SQLite 3 write performance can be greatly improved by wrapping
+;   multiple writes in transactions. This option specifies the duration in
+;   milliseconds of auto-generated transactions. Any changes made during an
+;   unfinished transaction will be immediately available to the same database
+;   connection, but any external connections could see a delay up to the value
+;   of this setting. It is also possible that if asterisk crashes, any changes
+;   made during this time could be lost. Due to the nearly 100x performance
+;   benefit, the default is 100 ms. Set to 0 to disable batching.
+;
+;   PLEASE NOTE: If you need to write to the database from another connection
+;   you will need to set batch=0 as the transactions will cause the database
+;   to lock for writing.
+;
+;batch=1000
+

res/res_config_sqlite3.c

+/*
+ * Asterisk -- An open source telephony toolkit.
+ *
+ * Copyright (C) 2011, Terry Wilson
+ *
+ * Terry Wilson <twilson@digium.com>
+ *
+ * See http://www.asterisk.org for more information about
+ * the Asterisk project. Please do not directly contact
+ * any of the maintainers of this project for assistance;
+ * the project provides a web site, mailing lists and IRC
+ * channels for your use.
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License Version 2. See the LICENSE file
+ * at the top of the source tree.
+ *
+ * Please follow coding guidelines
+ * http://svn.digium.com/view/asterisk/trunk/doc/CODING-GUIDELINES
+ */
+
+/*! \file
+ *
+ * \brief SQLite 3 configuration engine
+ *
+ * \author\verbatim Terry Wilson <twilson@digium.com> \endverbatim
+ *
+ * This is a realtime configuration engine for the SQLite 3 Database
+ * \ingroup resources
+ */
+
+/*** MODULEINFO
+	<depend>sqlite3</depend>
+	<support_level>core</support_level>
+ ***/
+
+#include "asterisk.h"
+
+ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
+
+#include <sqlite3.h>
+
+#include "asterisk/module.h"
+#include "asterisk/config.h"
+#include "asterisk/paths.h"
+#include "asterisk/astobj2.h"
+#include "asterisk/lock.h"
+#include "asterisk/utils.h"
+#include "asterisk/app.h"
+
+/*** DOCUMENTATION
+ ***/
+
+static struct ast_config *realtime_sqlite3_load(const char *database, const char *table, const char *configfile, struct ast_config *config, struct ast_flags flags, const char *suggested_include_file, const char *who_asked);
+static struct ast_variable *realtime_sqlite3(const char *database, const char *table, va_list ap);
+static struct ast_config *realtime_sqlite3_multi(const char *database, const char *table, va_list ap);
+static int realtime_sqlite3_update(const char *database, const char *table, const char *keyfield, const char *entity, va_list ap);
+static int realtime_sqlite3_update2(const char *database, const char *table, va_list ap);
+static int realtime_sqlite3_store(const char *database, const char *table, va_list ap);
+static int realtime_sqlite3_destroy(const char *database, const char *table, const char *keyfield, const char *entity, va_list ap);
+static int realtime_sqlite3_require(const char *database, const char *table, va_list ap);
+static int realtime_sqlite3_unload(const char *database, const char *table);
+
+struct ast_config_engine sqlite3_config_engine = {
+	.name = "sqlite3",
+	.load_func = realtime_sqlite3_load,
+	.realtime_func = realtime_sqlite3,
+	.realtime_multi_func = realtime_sqlite3_multi,
+	.update_func = realtime_sqlite3_update,
+	.update2_func = realtime_sqlite3_update2,
+	.store_func = realtime_sqlite3_store,
+	.destroy_func = realtime_sqlite3_destroy,
+	.require_func = realtime_sqlite3_require,
+	.unload_func = realtime_sqlite3_unload,
+};
+
+enum {
+	REALTIME_SQLITE3_REQ_WARN,
+	REALTIME_SQLITE3_REQ_CLOSE,
+	REALTIME_SQLITE3_REQ_CHAR,
+};
+
+struct realtime_sqlite3_db {
+	AST_DECLARE_STRING_FIELDS(
+		AST_STRING_FIELD(name);
+		AST_STRING_FIELD(filename);
+	);
+	sqlite3 *handle;
+	pthread_t syncthread;
+	ast_cond_t cond;
+	unsigned int requirements:2;
+	unsigned int dirty:1;
+	unsigned int debug:1;
+	unsigned int exiting:1;
+	unsigned int wakeup:1;
+	unsigned int batch;
+};
+
+struct ao2_container *databases;
+#define DB_BUCKETS 7
+
+AST_MUTEX_DEFINE_STATIC(config_lock);
+
+/* We need a separate buffer for each field we might use concurrently */
+AST_THREADSTORAGE(escape_table_buf);
+AST_THREADSTORAGE(escape_column_buf);
+AST_THREADSTORAGE(escape_value_buf);
+
+static int realtime_sqlite3_execute_handle(struct realtime_sqlite3_db *db, const char *sql, int (*callback)(void*, int, char **, char **), void *arg, int sync);
+void db_start_batch(struct realtime_sqlite3_db *db);
+void db_stop_batch(struct realtime_sqlite3_db *db);
+
+static inline const char *sqlite3_escape_string_helper(struct ast_threadstorage *ts, const char *param)
+{
+	size_t maxlen = strlen(param) * 2 + sizeof("\"\"");
+	/* It doesn't appear that sqlite3_snprintf will do more than double the
+	 * length of a string with %q as an option. %Q could double and possibly
+	 * add two quotes, and convert NULL pointers to the word "NULL", but we
+	 * don't allow those anyway. Just going to use %q for now. */
+	struct ast_str *buf = ast_str_thread_get(ts, maxlen);
+	char *tmp = ast_str_buffer(buf);
+	char q = ts == &escape_value_buf ? '\'' : '"';
+
+	ast_str_reset(buf);
+	*tmp++ = q; /* Initial quote */
+	while ((*tmp++ = *param++)) {
+		/* Did we just copy a quote? Then double it. */
+		if (*(tmp - 1) == q) {
+			*tmp++ = q;
+		}
+	}
+	*tmp = '\0'; /* Terminate past NULL from copy */
+	*(tmp - 1) = q; /* Replace original NULL with the quote */
+	ast_str_update(buf);
+
+	return ast_str_buffer(buf);
+}
+
+static inline const char *sqlite3_escape_table(const char *param)
+{
+	return sqlite3_escape_string_helper(&escape_table_buf, param);
+}
+
+static inline const char *sqlite3_escape_column(const char *param)
+{
+	return sqlite3_escape_string_helper(&escape_column_buf, param);
+}
+
+/* Not inlining this function because it uses strdupa and I don't know if the compiler would be dumb */
+static const char *sqlite3_escape_column_op(const char *param)
+{
+	size_t maxlen = strlen(param) * 2 + sizeof("\"\" =");
+	struct ast_str *buf = ast_str_thread_get(&escape_column_buf, maxlen);
+	char *tmp = ast_str_buffer(buf);
+	int space = 0;
+
+	ast_str_reset(buf);
+	*tmp++ = '"';
+	while ((*tmp++ = *param++)) {
+		/* If we have seen a space, don't double quotes. XXX If we ever make the column/op field
+		 * available to users via an API, we will definitely need to avoid allowing special
+		 * characters like ';' in the data past the space as it will be unquoted data */
+		if (space) {
+			continue;
+		}
+		if (*(tmp - 1) == ' ') {
+			*(tmp - 1) = '"';
+			*tmp++ = ' ';
+			space = 1;
+		} else if (*(tmp - 1) == '"') {
+			*tmp++ = '"';
+		}
+	}
+	if (!space) {
+		strcpy(tmp - 1, "\" =");
+	}
+
+	ast_str_update(buf);
+
+	return ast_str_buffer(buf);
+}
+
+static inline const char *sqlite3_escape_value(const char *param)
+{
+	return sqlite3_escape_string_helper(&escape_value_buf, param);
+}
+
+static int db_hash_fn(const void *obj, const int flags)
+{
+	const struct realtime_sqlite3_db *db = obj;
+
+	return ast_str_hash(flags & OBJ_KEY ? (const char *) obj : db->name);
+}
+
+static int db_cmp_fn(void *obj, void *arg, int flags) {
+	struct realtime_sqlite3_db *db = obj, *other = arg;
+	const char *name = arg;
+
+	return !strcasecmp(db->name, flags & OBJ_KEY ? name : other->name) ? CMP_MATCH | CMP_STOP : 0;
+}
+
+static void db_destructor(void *obj)
+{
+	struct realtime_sqlite3_db *db = obj;
+
+	ast_debug(1, "Destroying db: %s\n", db->name);
+	ast_string_field_free_memory(db);
+	db_stop_batch(db);
+	if (db->handle) {
+		ao2_lock(db);
+		sqlite3_close(db->handle);
+		ao2_unlock(db);
+	}
+}
+
+static struct realtime_sqlite3_db *find_database(const char *database)
+{
+	return ao2_find(databases, database, OBJ_KEY);
+}
+
+static void unref_db(struct realtime_sqlite3_db **db)
+{
+	ao2_ref(*db, -1);
+	*db = NULL;
+}
+
+static int stop_batch_cb(void *obj, void *arg, int flags)
+{
+	struct realtime_sqlite3_db *db = obj;
+
+	db_stop_batch(db);
+	return CMP_MATCH;
+}
+
+static int mark_dirty_cb(void *obj, void *arg, int flags)
+{
+	struct realtime_sqlite3_db *db = obj;
+	db->dirty = 1;
+	return CMP_MATCH;
+}
+
+static void mark_all_databases_dirty(void)
+{
+	ao2_callback(databases, OBJ_MULTIPLE | OBJ_NODATA, mark_dirty_cb, NULL);
+}
+
+static int is_dirty_cb(void *obj, void *arg, int flags)
+{
+	struct realtime_sqlite3_db *db = obj;
+	if (db->dirty) {
+		db_stop_batch(db);
+		return CMP_MATCH;
+	}
+	return 0;
+}
+
+static void unlink_dirty_databases(void)
+{
+	ao2_callback(databases, OBJ_MULTIPLE | OBJ_NODATA | OBJ_UNLINK, is_dirty_cb, NULL);
+}
+
+static int str_to_requirements(const char *data)
+{
+	if (!strcasecmp(data, "createclose")) {
+		return REALTIME_SQLITE3_REQ_CLOSE;
+	} else if (!strcasecmp(data, "createchar")) {
+		return REALTIME_SQLITE3_REQ_CHAR;
+	}
+	/* default */
+	return REALTIME_SQLITE3_REQ_WARN;
+}
+
+/*! \note Since this is called while a query is executing, we should already hold the db lock */
+static void trace_cb(void *arg, const char *sql)
+{
+	struct realtime_sqlite3_db *db = arg;
+	ast_debug(3, "DB: %s SQL: %s\n", db->name, sql);
+}
+
+/*! \brief Wrap commands in transactions increased write performance */
+static void *db_sync_thread(void *data)
+{
+	struct realtime_sqlite3_db *db = data;
+	ao2_lock(db);
+	realtime_sqlite3_execute_handle(db, "BEGIN TRANSACTION", NULL, NULL, 0);
+	for (;;) {
+		if (!db->wakeup) {
+			ast_cond_wait(&db->cond, ao2_object_get_lockaddr(db));
+		}
+		db->wakeup = 0;
+		if (realtime_sqlite3_execute_handle(db, "COMMIT", NULL, NULL, 0) < 0) {
+			realtime_sqlite3_execute_handle(db, "ROLLBACK", NULL, NULL, 0);
+		}
+		if (db->exiting) {
+			ao2_unlock(db);
+			break;
+		}
+		realtime_sqlite3_execute_handle(db, "BEGIN TRANSACTION", NULL, NULL, 0);
+		ao2_unlock(db);
+		usleep(1000 * db->batch);
+		ao2_lock(db);
+	}
+
+	unref_db(&db);
+
+	return NULL;
+}
+
+/*! \brief Open a database and appropriately set debugging on the db handle */
+static int db_open(struct realtime_sqlite3_db *db)
+{
+	ao2_lock(db);
+	if (sqlite3_open(db->filename, &db->handle) != SQLITE_OK) {
+		ast_log(LOG_WARNING, "Could not open %s: %s\n", db->filename, sqlite3_errmsg(db->handle));
+		ao2_unlock(db);
+		return -1;
+	}
+
+	if (db->debug) {
+		sqlite3_trace(db->handle, trace_cb, db);
+	} else {
+		sqlite3_trace(db->handle, NULL, NULL);
+	}
+
+	ao2_unlock(db);
+
+	return 0;
+}
+
+static void db_sync(struct realtime_sqlite3_db *db)
+{
+	db->wakeup = 1;
+	ast_cond_signal(&db->cond);
+}
+
+void db_start_batch(struct realtime_sqlite3_db *db)
+{
+	if (db->batch) {
+		ast_cond_init(&db->cond, NULL);
+		ao2_ref(db, +1);
+		ast_pthread_create_background(&db->syncthread, NULL, db_sync_thread, db);
+	}
+}
+
+void db_stop_batch(struct realtime_sqlite3_db *db)
+{
+	if (db->batch) {
+		db->exiting = 1;
+		db_sync(db);
+		pthread_join(db->syncthread, NULL);
+	}
+}
+
+/*! \brief Create a db object based on a config category
+ * \note Opening the db handle and linking to databases must be handled outside of this function
+ */
+static struct realtime_sqlite3_db *new_realtime_sqlite3_db(struct ast_config *config, const char *cat)
+{
+	struct ast_variable *var;
+	struct realtime_sqlite3_db *db;
+
+	if (!(db = ao2_alloc(sizeof(*db), db_destructor))) {
+		return NULL;
+	}
+
+	if (ast_string_field_init(db, 64)) {
+		unref_db(&db);
+		return NULL;
+	}
+
+	/* Set defaults */
+	db->requirements = REALTIME_SQLITE3_REQ_WARN;
+	db->batch = 100;
+	ast_string_field_set(db, name, cat);
+
+	for (var = ast_variable_browse(config, cat); var; var = var->next) {
+		if (!strcasecmp(var->name, "dbfile")) {
+			ast_string_field_set(db, filename, var->value);
+		} else if (!strcasecmp(var->name, "requirements")) {
+			db->requirements = str_to_requirements(var->value);
+		} else if (!strcasecmp(var->name, "batch")) {
+			ast_app_parse_timelen(var->value, (int *) &db->batch, TIMELEN_MILLISECONDS);
+		} else if (!strcasecmp(var->name, "debug")) {
+			db->debug = ast_true(var->value);
+		}
+	}
+
+	if (ast_strlen_zero(db->filename)) {
+		ast_log(LOG_WARNING, "Must specify dbfile in res_config_sqlite3.conf\n");
+		unref_db(&db);
+		return NULL;
+	}
+
+	return db;
+}
+
+/*! \brief Update an existing db object based on config data
+ * \param db The database object to update
+ * \param config The configuration data with which to update the db
+ * \param cat The config category (which becomes db->name)
+ */
+static int update_realtime_sqlite3_db(struct realtime_sqlite3_db *db, struct ast_config *config, const char *cat)
+{
+	struct realtime_sqlite3_db *new;
+
+	if (!(new = new_realtime_sqlite3_db(config, cat))) {
+		return -1;
+	}
+
+	/* Copy fields that don't need anything special done on change */
+	db->requirements = new->requirements;
+
+	/* Handle changes that require immediate behavior modification */
+	if (db->debug != new->debug) {
+		if (db->debug) {
+			sqlite3_trace(db->handle, NULL, NULL);
+		} else {
+			sqlite3_trace(db->handle, trace_cb, db);
+		}
+		db->debug = new->debug;
+	}
+
+	if (strcmp(db->filename, new->filename)) {
+		sqlite3_close(db->handle);
+		ast_string_field_set(db, filename, new->filename);
+		db_open(db); /* Also handles setting appropriate debug on new handle */
+	}
+
+	if (db->batch != new->batch) {
+		if (db->batch == 0) {
+			db->batch = new->batch;
+			db_start_batch(db);
+		} else if (new->batch == 0) {
+			db->batch = new->batch;
+			db_stop_batch(db);
+		}
+		db->batch = new->batch;
+	}
+
+	db->dirty = 0;
+	unref_db(&new);
+
+	return 0;
+}
+
+/*! \brief Create a varlist from a single sqlite3 result row */
+static int row_to_varlist(void *arg, int num_columns, char **values, char **columns)
+{
+	struct ast_variable **head = arg, *tail;
+	int i;
+	struct ast_variable *new;
+
+	if (!(new = ast_variable_new(columns[0], S_OR(values[0], ""), ""))) {
+		return SQLITE_ABORT;
+	}
+	*head = tail = new;
+
+	for (i = 1; i < num_columns; i++) {
+		if (!(new = ast_variable_new(columns[i], S_OR(values[i], ""), ""))) {
+			ast_variables_destroy(*head);
+			*head = NULL;
+			return SQLITE_ABORT;
+		}
+		tail->next = new;
+		tail = new;
+	}
+
+	return 0;
+}
+
+/*! \brief Callback for creating an ast_config from a successive sqlite3 result rows */
+static int append_row_to_cfg(void *arg, int num_columns, char **values, char **columns)
+{
+	struct ast_config *cfg = arg;
+	struct ast_category *cat;
+	int i;
+
+	if (!(cat = ast_category_new("", "", 99999))) {
+		return SQLITE_ABORT;
+	}
+
+	for (i = 0; i < num_columns; i++) {
+		struct ast_variable *var;
+		if (!(var = ast_variable_new(columns[i], S_OR(values[i], ""), ""))) {
+			ast_log(LOG_ERROR, "Could not create new variable for '%s: %s', throwing away list\n", columns[i], values[i]);
+			continue;
+		}
+		ast_variable_append(cat, var);
+	}
+	ast_category_append(cfg, cat);
+
+	return 0;
+}
+
+/*!
+ * Structure sent to the SQLite 3 callback function for static configuration.
+ *
+ * \see static_realtime_cb()
+ */
+struct cfg_entry_args {
+	struct ast_config *cfg;
+	struct ast_category *cat;
+	char *cat_name;
+	struct ast_flags flags;
+	const char *who_asked;
+};
+
+/*! Exeute an SQL statement given the database object
+ *
+ * \retval -1 ERROR
+ * \retval > -1 Number of rows changed
+ */
+static int realtime_sqlite3_execute_handle(struct realtime_sqlite3_db *db, const char *sql, int (*callback)(void*, int, char **, char **), void *arg, int sync)
+{
+	int res = 0;
+	char *errmsg;
+
+	ao2_lock(db);
+	if (sqlite3_exec(db->handle, sql, callback, arg, &errmsg) != SQLITE_OK) {
+		ast_log(LOG_WARNING, "Could not execute '%s': %s\n", sql, errmsg);
+		sqlite3_free(errmsg);
+		res = -1;
+	} else {
+		res = sqlite3_changes(db->handle);
+	}
+	ao2_unlock(db);
+
+	if (sync) {
+		db_sync(db);
+	}
+
+	return res;
+}
+
+/*! Exeute an SQL statement give the database name
+ *
+ * \retval -1 ERROR
+ * \retval > -1 Number of rows changed
+ */
+static int realtime_sqlite3_execute(const char *database, const char *sql, int (*callback)(void*, int, char **, char **), void *arg, int sync)
+{
+	struct realtime_sqlite3_db *db;
+	int res;
+
+	if (!(db = find_database(database))) {
+		ast_log(LOG_WARNING, "Could not find database: %s\n", database);
+		return -1;
+	}
+
+	res = realtime_sqlite3_execute_handle(db, sql, callback, arg, sync);
+	ao2_ref(db, -1);
+
+	return res;
+}
+
+/*! \note It is important that the COL_* enum matches the order of the columns selected in static_sql */
+static const char *static_sql = "SELECT category, var_name, var_val FROM \"%q\" WHERE filename = %Q AND commented = 0 ORDER BY cat_metric ASC, var_metric ASC";
+enum {
+	COL_CATEGORY,
+	COL_VAR_NAME,
+	COL_VAR_VAL,
+	COL_COLUMNS,
+};
+
+static int static_realtime_cb(void *arg, int num_columns, char **values, char **columns)
+{
+	struct cfg_entry_args *args = arg;
+	struct ast_variable *var;
+
+	if (!strcmp(values[COL_VAR_NAME], "#include")) {
+		struct ast_config *cfg;
+		char *val;
+
+		val = values[COL_VAR_VAL];
+		if (!(cfg = ast_config_internal_load(val, args->cfg, args->flags, "", args->who_asked))) {
+			ast_log(LOG_WARNING, "Unable to include %s\n", val);
+			return SQLITE_ABORT;
+		} else {
+			args->cfg = cfg;
+			return 0;
+		}
+	}
+
+	if (!args->cat_name || strcmp(args->cat_name, values[COL_CATEGORY])) {
+		if (!(args->cat = ast_category_new(values[COL_CATEGORY], "", 99999))) {
+			ast_log(LOG_WARNING, "Unable to allocate category\n");
+			return SQLITE_ABORT;
+		}
+
+		ast_free(args->cat_name);
+
+		if (!(args->cat_name = ast_strdup(values[COL_CATEGORY]))) {
+			ast_category_destroy(args->cat);
+			return SQLITE_ABORT;
+		}
+
+		ast_category_append(args->cfg, args->cat);
+	}
+
+	if (!(var = ast_variable_new(values[COL_VAR_NAME], values[COL_VAR_VAL], ""))) {
+		ast_log(LOG_WARNING, "Unable to allocate variable");
+		return SQLITE_ABORT;
+	}
+
+	ast_variable_append(args->cat, var);
+
+	return 0;
+}
+
+/*! \brief Realtime callback for static realtime
+ * \return ast_config on success, NULL on failure
+ */
+static struct ast_config *realtime_sqlite3_load(const char *database, const char *table, const char *configfile, struct ast_config *config, struct ast_flags flags, const char *suggested_include_file, const char *who_asked)
+{
+	char *sql;
+	struct cfg_entry_args args;
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return NULL;
+	}
+
+	if (!(sql = sqlite3_mprintf(static_sql, table, configfile))) {
+		ast_log(LOG_WARNING, "Couldn't allocate query\n");
+		return NULL;
+	};
+
+	args.cfg = config;
+	args.cat = NULL;
+	args.cat_name = NULL;
+	args.flags = flags;
+	args.who_asked = who_asked;
+
+	realtime_sqlite3_execute(database, sql, static_realtime_cb, &args, 0);
+
+	sqlite3_free(sql);
+
+	return config;
+}
+
+/*! \brief Helper function for single and multi-row realtime load functions */
+static int realtime_sqlite3_helper(const char *database, const char *table, va_list ap, int is_multi, void *arg)
+{
+	struct ast_str *sql;
+	const char *param, *value;
+	int first = 1;
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return -1;
+	}
+
+	if (!(sql = ast_str_create(128))) {
+		return -1;
+	}
+
+	while ((param = va_arg(ap, const char *)) && (value = va_arg(ap, const char *))) {
+		if (first) {
+			ast_str_set(&sql, 0, "SELECT * FROM %s WHERE %s %s", sqlite3_escape_table(table),
+					sqlite3_escape_column_op(param), sqlite3_escape_value(value));
+			first = 0;
+		} else {
+			ast_str_append(&sql, 0, " AND %s %s", sqlite3_escape_column_op(param),
+					sqlite3_escape_value(value));
+		}
+	}
+
+	if (!is_multi) {
+		ast_str_append(&sql, 0, "%s", " LIMIT 1");
+	}
+
+	if (realtime_sqlite3_execute(database, ast_str_buffer(sql), is_multi ? append_row_to_cfg : row_to_varlist, arg, 0) < 0) {
+		ast_free(sql);
+		return -1;
+	}
+
+	ast_free(sql);
+
+	return 0;
+}
+
+/*! \brief Realtime callback for a single row query
+ * \return ast_variable list for single result on success, NULL on empty/failure
+ */
+static struct ast_variable *realtime_sqlite3(const char *database, const char *table, va_list ap)
+{
+	struct ast_variable *result_row = NULL;
+
+	realtime_sqlite3_helper(database, table, ap, 0, &result_row);
+
+	return result_row;
+}
+
+/*! \brief Realtime callback for a multi-row query
+ * \return ast_config containing possibly many results on success, NULL on empty/failure
+ */
+static struct ast_config *realtime_sqlite3_multi(const char *database, const char *table, va_list ap)
+{
+	struct ast_config *cfg;
+
+	if (!(cfg = ast_config_new())) {
+		return NULL;
+	}
+
+	if (realtime_sqlite3_helper(database, table, ap, 1, cfg)) {
+		ast_config_destroy(cfg);
+		return NULL;
+	}
+
+	return cfg;
+}
+
+/*! \brief Realtime callback for updating a row based on a single criteria
+ * \return Number of rows affected or -1 on error
+ */
+static int realtime_sqlite3_update(const char *database, const char *table, const char *keyfield, const char *entity, va_list ap)
+{
+	struct ast_str *sql;
+	const char *key, *value;
+	int first = 1, res;
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return -1;
+	}
+
+	if (!(sql = ast_str_create(128))) {
+		return -1;
+	}
+
+	while ((key = va_arg(ap, const char *)) && (value = va_arg(ap, const char *))) {
+		if (first) {
+			ast_str_set(&sql, 0, "UPDATE %s SET %s = %s",
+					sqlite3_escape_table(table), sqlite3_escape_column(key), sqlite3_escape_value(value));
+			first = 0;
+		} else {
+			ast_str_append(&sql, 0, ", %s = %s", sqlite3_escape_column(key), sqlite3_escape_value(value));
+		}
+	}
+
+	ast_str_append(&sql, 0, " WHERE %s %s", sqlite3_escape_column_op(keyfield), sqlite3_escape_value(entity));
+
+	res = realtime_sqlite3_execute(database, ast_str_buffer(sql), NULL, NULL, 1);
+	ast_free(sql);
+
+	return res;
+}
+
+/*! \brief Realtime callback for updating a row based on multiple criteria
+ * \return Number of rows affected or -1 on error
+ */
+static int realtime_sqlite3_update2(const char *database, const char *table, va_list ap)
+{
+	struct ast_str *sql;
+	struct ast_str *where_clause;
+	const char *key, *value;
+	int first = 1, res;
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return -1;
+	}
+
+	if (!(sql = ast_str_create(128))) {
+		return -1;
+	}
+
+	if (!(where_clause = ast_str_create(128))) {
+		ast_free(sql);
+		return -1;
+	}
+
+	while ((key = va_arg(ap, const char *)) && (value = va_arg(ap, const char *))) {
+		if (first) {
+			ast_str_set(&where_clause, 0, " WHERE %s %s", sqlite3_escape_column_op(key), sqlite3_escape_value(value));
+			first = 0;
+		} else {
+			ast_str_append(&where_clause, 0, " AND %s %s", sqlite3_escape_column_op(key), sqlite3_escape_value(value));
+		}
+	}
+
+	first = 1;
+	while ((key = va_arg(ap, const char *)) && (value = va_arg(ap, const char *))) {
+		if (first) {
+			ast_str_set(&sql, 0, "UPDATE %s SET %s = %s", sqlite3_escape_table(table), sqlite3_escape_column(key), sqlite3_escape_value(value));
+			first = 0;
+		} else {
+			ast_str_append(&sql, 0, ", %s = %s", sqlite3_escape_column(key), sqlite3_escape_value(value));
+		}
+	}
+
+	ast_str_append(&sql, 0, "%s", ast_str_buffer(where_clause));
+
+	res = realtime_sqlite3_execute(database, ast_str_buffer(sql), NULL, NULL, 1);
+
+	ast_free(sql);
+	ast_free(where_clause);
+
+	return res;
+}
+
+/*! \brief Realtime callback for inserting a row
+ * \return Number of rows affected or -1 on error
+ */
+static int realtime_sqlite3_store(const char *database, const char *table, va_list ap)
+{
+	struct ast_str *sql, *values;
+	const char *column, *value;
+	int first = 1, res;
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return -1;
+	}
+
+	if (!(sql = ast_str_create(128))) {
+		return -1;
+	}
+
+	if (!(values = ast_str_create(128))) {
+		ast_free(sql);
+		return -1;
+	}
+
+	while ((column = va_arg(ap, const char *)) && (value = va_arg(ap, const char *))) {
+		if (first) {
+			ast_str_set(&sql, 0, "INSERT INTO %s (%s", sqlite3_escape_table(table), sqlite3_escape_column(column));
+			ast_str_set(&values, 0, ") VALUES (%s", sqlite3_escape_value(value));
+			first = 0;
+		} else {
+			ast_str_append(&sql, 0, ", %s", sqlite3_escape_column(column));
+			ast_str_append(&values, 0, ", %s", sqlite3_escape_value(value));
+		}
+	}
+
+	ast_str_append(&sql, 0, "%s)", ast_str_buffer(values));
+
+	res = realtime_sqlite3_execute(database, ast_str_buffer(sql), NULL, NULL, 1);
+
+	ast_free(sql);
+	ast_free(values);
+
+	return res;
+}
+
+/*! \brief Realtime callback for deleting a row
+ * \return Number of rows affected or -1 on error
+ */
+static int realtime_sqlite3_destroy(const char *database, const char *table, const char *keyfield, const char *entity, va_list ap)
+{
+	struct ast_str *sql;
+	const char *param, *value;
+	int first = 1, res;
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return -1;
+	}
+
+	if (!(sql = ast_str_create(128))) {
+		return -1;
+	}
+
+	while ((param = va_arg(ap, const char *)) && (value = va_arg(ap, const char *))) {
+		if (first) {
+			ast_str_set(&sql, 0, "DELETE FROM %s WHERE %s %s", sqlite3_escape_table(table),
+					sqlite3_escape_column_op(param), sqlite3_escape_value(value));
+			first = 0;
+		} else {
+			ast_str_append(&sql, 0, " AND %s %s", sqlite3_escape_column_op(param), sqlite3_escape_value(value));
+		}
+	}
+
+	res = realtime_sqlite3_execute(database, ast_str_buffer(sql), NULL, NULL, 1);
+
+	ast_free(sql);
+
+	return res;
+}
+
+/*! \brief Convert Asterisk realtime types to SQLite 3 types
+ * \note SQLite 3 has NULL, INTEGER, REAL, TEXT, and BLOB types. Any column other than
+ * an INTEGER PRIMARY KEY will actually store any kind of data due to its dynamic
+ * typing. When we create columns, we'll go ahead and use these base types instead
+ * of messing with column widths, etc. */
+
+static const char *get_sqlite_column_type(int type)
+{
+	switch(type) {
+	case RQ_INTEGER1 :
+	case RQ_UINTEGER1 :
+	case RQ_INTEGER2 :
+	case RQ_UINTEGER2 :
+	case RQ_INTEGER3 :
+	case RQ_UINTEGER3 :
+	case RQ_INTEGER4 :
+	case RQ_UINTEGER4 :
+	case RQ_INTEGER8 :
+		return "INTEGER";
+	case RQ_UINTEGER8 : /* SQLite3 stores INTEGER as signed 8-byte */
+	case RQ_CHAR :
+	case RQ_DATE :
+	case RQ_DATETIME :
+		return "TEXT";
+	case RQ_FLOAT :
+		return "REAL";
+	default :
+		return "TEXT";
+	}
+
+	return "TEXT";
+}
+
+/*! \brief Create a table if ast_realtime_require shows that we are configured to handle the data
+ */
+static int handle_missing_table(struct realtime_sqlite3_db *db, const char *table, va_list ap)
+{
+	const char *column;
+	int type, first = 1, res;
+	size_t sz;
+	struct ast_str *sql;
+
+	if (!(sql = ast_str_create(128))) {
+		return -1;
+	}
+
+	while ((column = va_arg(ap, typeof(column))) && (type = va_arg(ap, typeof(type))) && (sz = va_arg(ap, typeof(sz)))) {
+		if (first) {
+			ast_str_set(&sql, 0, "CREATE TABLE IF NOT EXISTS %s (%s %s", sqlite3_escape_table(table),
+					sqlite3_escape_column(column), get_sqlite_column_type(type));
+			first = 0;
+		} else {
+			ast_str_append(&sql, 0, ", %s %s", sqlite3_escape_column(column), get_sqlite_column_type(type));
+		}
+	}
+
+	ast_str_append(&sql, 0, ")");
+
+	res = realtime_sqlite3_execute_handle(db, ast_str_buffer(sql), NULL, NULL, 1) < 0 ? -1 : 0;
+	ast_free(sql);
+
+	return res;
+}
+
+/*! \brief If ast_realtime_require sends info about a column we don't have, create it
+ */
+static int handle_missing_column(struct realtime_sqlite3_db *db, const char *table, const char *column, int type, size_t sz)
+{
+	char *sql;
+	const char *sqltype = get_sqlite_column_type(type);
+	int res;
+
+	if (db->requirements == REALTIME_SQLITE3_REQ_WARN) {
+		ast_log(LOG_WARNING, "Missing column '%s' of type '%s' in %s.%s\n", column, sqltype, db->name, table);
+		return -1;
+	} else if (db->requirements == REALTIME_SQLITE3_REQ_CHAR) {
+		sqltype = "TEXT";
+	}
+
+	if (!(sql = sqlite3_mprintf("ALTER TABLE \"%q\" ADD COLUMN \"%q\" %s", table, column, sqltype))) {
+		return -1;
+	}
+
+	if (!(res = realtime_sqlite3_execute_handle(db, sql, NULL, NULL, 1) < 0 ? -1 : 0)) {
+		ast_log(LOG_NOTICE, "Creating column '%s' type %s for table %s\n", column, sqltype, table);
+	}
+
+	sqlite3_free(sql);
+
+	return res;
+}
+
+static int str_hash_fn(const void *obj, const int flags)
+{
+	return ast_str_hash((const char *) obj);
+}
+
+static int str_cmp_fn(void *obj, void *arg, int flags) {
+	return !strcasecmp((const char *) obj, (const char *) arg);
+}
+
+/*! \brief Callback for creating a hash of column names for comparison in realtime_sqlite3_require
+ */
+static int add_column_name(void *arg, int num_columns, char **values, char **columns)
+{
+	char *column;
+	struct ao2_container *cnames = arg;
+
+
+	if (!(column = ao2_alloc(strlen(values[1]) + 1, NULL))) {
+		return -1;
+	}
+
+	strcpy(column, values[1]);
+
+	ao2_link(cnames, column);
+	ao2_ref(column, -1);
+
+	return 0;
+}
+
+/*! \brief Callback for ast_realtime_require
+ * \retval 0 Required fields met specified standards
+ * \retval -1 One or more fields was missing or insufficient
+ */
+static int realtime_sqlite3_require(const char *database, const char *table, va_list ap)
+{
+	const char *column;
+	char *sql;
+	int type;
+	int res;
+	size_t sz;
+	struct ao2_container *columns;
+	struct realtime_sqlite3_db *db;
+
+	/* SQLite3 columns are dynamically typed, with type affinity. Built-in functions will
+	 * return the results as char * anyway. The only field that that cannot contain text
+	 * data is an INTEGER PRIMARY KEY, which must be a 64-bit signed integer. So, for
+	 * the purposes here we really only care whether the column exists and not what its
+	 * type or length is. */
+
+	if (ast_strlen_zero(table)) {
+		ast_log(LOG_WARNING, "Must have a table to query!\n");
+		return -1;
+	}
+
+	if (!(db = find_database(database))) {
+		return -1;
+	}
+
+	if (!(columns = ao2_container_alloc(31, str_hash_fn, str_cmp_fn))) {
+		unref_db(&db);
+	   return -1;
+	}
+
+	if (!(sql = sqlite3_mprintf("PRAGMA table_info(\"%q\")", table))) {
+		unref_db(&db);
+		ao2_ref(columns, -1);
+		return -1;
+	}
+
+	if ((res = realtime_sqlite3_execute_handle(db, sql, add_column_name, columns, 0)) < 0) {
+		unref_db(&db);
+		ao2_ref(columns, -1);
+		sqlite3_free(sql);
+		return -1;
+	} else if (res == 0) {
+		/* Table does not exist */
+		sqlite3_free(sql);
+		res = handle_missing_table(db, table, ap);
+		ao2_ref(columns, -1);
+		unref_db(&db);
+		return res;
+	}
+
+	sqlite3_free(sql);
+
+	while ((column = va_arg(ap, typeof(column))) && (type = va_arg(ap, typeof(type))) && (sz = va_arg(ap, typeof(sz)))) {
+		char *found;
+		if (!(found = ao2_find(columns, column, OBJ_POINTER | OBJ_UNLINK))) {
+			if (handle_missing_column(db, table, column, type, sz)) {
+				unref_db(&db);
+				ao2_ref(columns, -1);
+				return -1;
+			}
+		} else {
+			ao2_ref(found, -1);
+		}
+	}
+
+	ao2_ref(columns, -1);
+	unref_db(&db);
+
+	return 0;
+}
+
+/*! \brief Callback for clearing any cached info
+ * \note We don't currently cache anything
+ * \retval 0 If any cache was purged
+ * \retval -1 If no cache was found
+ */
+static int realtime_sqlite3_unload(const char *database, const char *table)
+{
+	/* We currently do no caching */
+	return -1;
+}
+
+/*! \brief Parse the res_config_sqlite3 config file
+ */
+static int parse_config(int reload)
+{
+	struct ast_config *config;
+	struct ast_flags config_flags = { CONFIG_FLAG_NOREALTIME | (reload ? CONFIG_FLAG_FILEUNCHANGED : 0) };
+	static const char *config_filename = "res_config_sqlite3.conf";
+
+	config = ast_config_load(config_filename, config_flags);
+
+	if (config == CONFIG_STATUS_FILEUNCHANGED) {
+		ast_debug(1, "%s was unchanged, skipping parsing\n", config_filename);
+		return 0;
+	}
+
+	ast_mutex_lock(&config_lock);
+
+	if (config == CONFIG_STATUS_FILEMISSING || config == CONFIG_STATUS_FILEINVALID) {
+		ast_log(LOG_ERROR, "%s config file '%s'\n",
+			config == CONFIG_STATUS_FILEMISSING ? "Missing" : "Invalid", config_filename);
+	} else {
+		const char *cat;
+		struct realtime_sqlite3_db *db;
+
+		mark_all_databases_dirty();
+		for (cat = ast_category_browse(config, NULL); cat; cat = ast_category_browse(config, cat)) {
+			if (!strcasecmp(cat, "general")) {
+				continue;
+			}
+			if (!(db = find_database(cat))) {
+				if (!(db = new_realtime_sqlite3_db(config, cat))) {
+					ast_log(LOG_WARNING, "Could not allocate new db for '%s' - skipping.\n", cat);
+					continue;
+				}
+				if (db_open(db)) {
+					unref_db(&db);
+					continue;
+				}
+				db_start_batch(db);
+				ao2_link(databases, db);
+				unref_db(&db);
+			} else  {
+				if (update_realtime_sqlite3_db(db, config, cat)) {
+					unref_db(&db);
+					continue;
+				}
+				unref_db(&db);
+			}
+		}
+		unlink_dirty_databases();
+	}
+
+	ast_mutex_unlock(&config_lock);
+
+	ast_config_destroy(config);
+
+	return 0;
+}
+
+static int reload(void)
+{
+	parse_config(1);
+	return 0;
+}
+
+static int unload_module(void)
+{
+	ast_mutex_lock(&config_lock);
+	ao2_callback(databases, OBJ_MULTIPLE | OBJ_NODATA | OBJ_UNLINK, stop_batch_cb, NULL);
+	ao2_ref(databases, -1);
+	databases = NULL;
+	ast_config_engine_deregister(&sqlite3_config_engine);
+	ast_mutex_unlock(&config_lock);
+
+	return 0;
+}
+
+static int load_module(void)
+{
+	if (!((databases = ao2_container_alloc(DB_BUCKETS, db_hash_fn, db_cmp_fn)))) {
+		return AST_MODULE_LOAD_FAILURE;
+	}
+
+	if (parse_config(0)) {
+		ao2_ref(databases, -1);
+		return AST_MODULE_LOAD_FAILURE;
+	}
+
+	if (!(ast_config_engine_register(&sqlite3_config_engine))) {
+		ast_log(LOG_ERROR, "The config API must have changed, this shouldn't happen.\n");
+		ao2_ref(databases, -1);
+		return AST_MODULE_LOAD_FAILURE;
+	}
+
+	return AST_MODULE_LOAD_SUCCESS;
+}
+
+AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "SQLite 3 realtime config engine",
+	.load = load_module,
+	.unload = unload_module,
+	.reload = reload,
+	.load_pri = AST_MODPRI_REALTIME_DRIVER,
+);