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<?php

/**

 * ADOdb Load Balancer

 *

 * ADOdbLoadBalancer is a class that allows the user to do read/write splitting

 * and load balancing across multiple servers. It can handle and load balance

 * any number of write capable (AKA: master) or readonly (AKA: slave) connections,

 * including dealing with connection failures and retrying queries on a different

 * connection instead.

 *

 * This file is part of ADOdb, a Database Abstraction Layer library for PHP.

 *

 * @package ADOdb

 * @link https://adodb.org Project's web site and documentation

 * @link https://github.com/ADOdb/ADOdb Source code and issue tracker

 *

 * The ADOdb Library is dual-licensed, released under both the BSD 3-Clause

 * and the GNU Lesser General Public Licence (LGPL) v2.1 or, at your option,

 * any later version. This means you can use it in proprietary products.

 * See the LICENSE.md file distributed with this source code for details.

 * @license BSD-3-Clause

 * @license LGPL-2.1-or-later

 *

 * @copyright 2016 Mike Benoit and the ADOdb community

 */

/**

 * Class ADOdbLoadBalancer

 */

class ADOdbLoadBalancer

{

    /**

     * @var bool    Once a write or readonly connection is made, stick to that connection for the entire request.

     */

    public $enable_sticky_sessions = true;

    /**

     * @var bool|array    All connections to each database.

     */

    protected $connections = [];

    /**

     * @var bool|array    Just connections to the write capable database.

     */

    protected $connections_write = [];

    /**

     * @var bool|array    Just connections to the readonly database.

     */

    protected $connections_readonly = [];

    /**

     * @var array    Counts of all connections and their types.

     */

    protected $total_connections = array('all' => 0, 'write' => 0, 'readonly' => 0);

    /**

     * @var array    Weights of all connections for each type.

     */

    protected $total_connection_weights = array('all' => 0, 'write' => 0, 'readonly' => 0);

    /**

     * @var bool    When in transactions, always use this connection.

     */

    protected $pinned_connection_id = false;

    /**

     * @var array    Last connection_id for each database type.

     */

    protected $last_connection_id = array('write' => false, 'readonly' => false, 'all' => false);

    /**

     * @var bool    Session variables that must be maintained across all connections, ie: SET TIME ZONE.

     */

    protected $session_variables = [];

    /**

     * @var bool    Called immediately after connecting to any DB.

     */

    protected $user_defined_session_init_sql = [];

    /**

     * Defines SQL queries that are executed each time a new database connection is established.

     *

     * @param  $sql

     * @return bool

     */

    public function setSessionInitSQL($sql)

    {

        $this->user_defined_session_init_sql[] = $sql;

        return true;

    }

    /**

     * Adds a new database connection to the pool, but no actual connection is made until its needed.

     *

     * @param  $obj

     * @return bool

     * @throws Exception

     */

    public function addConnection($obj)

    {

        if ($obj instanceof ADOdbLoadBalancerConnection) {

            $this->connections[] = $obj;

            end($this->connections);

            $i = key($this->connections);

            $this->total_connections[$obj->type]++;

            $this->total_connections['all']++;

            $this->total_connection_weights[$obj->type] += abs($obj->weight);

            $this->total_connection_weights['all'] += abs($obj->weight);

            if ($obj->type == 'write') {

                $this->connections_write[] = $i;

            } else {

                $this->connections_readonly[] = $i;

            }

            return true;

        }

        throw new Exception('Connection object is not an instance of ADOdbLoadBalancerConnection');

    }

    /**

     * Removes a database connection from the pool.

     *

     * @param  $i

     * @return bool

     */

    public function removeConnection($i)

    {

        if (isset($this->connections[$i])) {

               $obj = $this->connections[ $i ];

               $this->total_connections[ $obj->type ]--;

               $this->total_connections['all']--;

               $this->total_connection_weights[ $obj->type ] -= abs($obj->weight);

               $this->total_connection_weights['all'] -= abs($obj->weight);

            if ($obj->type == 'write') {

                unset($this->connections_write[array_search($i, $this->connections_write)]);

                // Reindex array.

                $this->connections_write = array_values($this->connections_write);

            } else {

                unset($this->connections_readonly[array_search($i, $this->connections_readonly)]);

                // Reindex array.

                $this->connections_readonly = array_values($this->connections_readonly);

            }

            // Remove any sticky connections as well.

            if ($this->last_connection_id[$obj->type] == $i) {

                $this->last_connection_id[$obj->type] = false;

            }

            unset($this->connections[$i]);

            return true;

        }

        return false;

    }

    /**

     * Returns a database connection of the specified type.

     *

     * Takes into account the connection weight for load balancing.

     *

     * @param  string $type Type of database connection, either: 'write' capable or 'readonly'

     * @return bool|int|string

     */

    public function getConnectionByWeight($type)

    {

        if ($type == 'readonly') {

            $total_weight = $this->total_connection_weights['all'];

        } else {

            $total_weight = $this->total_connection_weights['write'];

        }

        $i = false;

        if (is_array($this->connections)) {

            $n = 0;

            $num = mt_rand(0, $total_weight);

            foreach ($this->connections as $i => $connection_obj) {

                if ($connection_obj->weight > 0 && ($type == 'readonly' || $connection_obj->type == 'write')) {

                    $n += $connection_obj->weight;

                    if ($n >= $num) {

                        break;

                    }

                }

            }

        }

        return $i;

    }

    /**

     * Returns the proper database connection when taking into account sticky sessions and load balancing.

     *

     * @param  $type

     * @return bool|int|mixed|string

     */

    public function getLoadBalancedConnection($type)

    {

        if ($this->total_connections == 0) {

            $connection_id = 0;

        } else {

            if ($this->enable_sticky_sessions == true && $this->last_connection_id[$type] !== false) {

                $connection_id = $this->last_connection_id[$type];

            } else {

                if ($type == 'write' && $this->total_connections['write'] == 1) {

                    $connection_id = $this->connections_write[0];

                } else {

                    $connection_id = $this->getConnectionByWeight($type);

                }

            }

        }

        return $connection_id;

    }

    /**

     * Returns the ADODB connection object by connection_id.

     *

     * Ensures that it's connected and the session variables are executed.

     *

     * @param  $connection_id

     * @return bool|ADOConnection

     * @throws Exception

     */

    public function getConnectionById($connection_id)

    {

        if (isset($this->connections[$connection_id])) {

            $connection_obj = $this->connections[$connection_id];

            /** @var ADOConnection $adodb_obj */

            $adodb_obj = $connection_obj->getADOdbObject();

            if (is_object($adodb_obj) && $adodb_obj->_connectionID == false) {

                try {

                    if ($connection_obj->persistent_connection == true) {

                        $adodb_obj->Pconnect(

                            $connection_obj->host,

                            $connection_obj->user,

                            $connection_obj->password,

                            $connection_obj->database

                        );

                    } else {

                        $adodb_obj->Connect(

                            $connection_obj->host,

                            $connection_obj->user,

                            $connection_obj->password,

                            $connection_obj->database

                        );

                    }

                } catch (Exception $e) {

                    // Connection error, see if there are other connections to try still.

                    throw $e; // No connections left, reThrow exception so application can catch it.

                }

                // Check to see if a connection test callback was defined, and if so execute it.

                // This is useful for testing replication lag and such to ensure the connection is suitable to be used.

                $test_connection_callback = $connection_obj->getConnectionTestCallback();

                if (is_callable($test_connection_callback)

                    && $test_connection_callback($connection_obj, $adodb_obj) !== TRUE

                ) {

                    return false;

                }

                if (is_array($this->user_defined_session_init_sql)) {

                    foreach ($this->user_defined_session_init_sql as $session_init_sql) {

                        $adodb_obj->Execute($session_init_sql);

                    }

                }

                $this->executeSessionVariables($adodb_obj);

            }

            return $adodb_obj;

        } else {

            throw new Exception('Unable to return Connection object...');

        }

    }

    /**

     * Returns the ADODB connection object by database type.

     *

     * Ensures that it's connected and the session variables are executed.

     *

     * @param  string $type

     * @param  null   $pin_connection

     * @return ADOConnection|bool

     * @throws Exception

     */

    public function getConnection($type = 'write', $pin_connection = null)

    {

        while (($type == 'write' && $this->total_connections['write'] > 0)

            || ($type == 'readonly' && $this->total_connections['all'] > 0)

        ) {

            if ($this->pinned_connection_id !== false) {

                $connection_id = $this->pinned_connection_id;

            } else {

                $connection_id = $this->getLoadBalancedConnection($type);

            }

            if ($connection_id !== false) {

                try {

                    $adodb_obj = $this->getConnectionById($connection_id);

                    if (is_object($adodb_obj)) {

                        break; //Found valid connection, continue with it.

                    } else {

                        throw new Exception('ADODB Connection Object does not exist. Perhaps LoadBalancer Database Connection Test Failed?');

                    }

                } catch (Exception $e) {

                    // Connection error, see if there are other connections to try still.

                    $this->removeConnection($connection_id);

                    if (   ($type == 'write' && $this->total_connections['write'] == 0)

                        || ($type == 'readonly' && $this->total_connections['all'] == 0)

                    ) {

                        throw $e;

                    }

                }

            } else {

                throw new Exception('Connection ID is invalid!');

            }

        }

        if (!isset($connection_id)) {

            throw new Exception('No connection available to use at this time! Type: ' . $type);

        }

        $this->last_connection_id[$type] = $connection_id;

        if ($pin_connection === true) {

            $this->pinned_connection_id = $connection_id;

        } elseif ($pin_connection === false && $adodb_obj->transOff <= 1) {

            // UnPin connection only if we are 1 level deep in a transaction.

            $this->pinned_connection_id = false;

            // When unpinning connection, reset last_connection_id so readonly

            // queries don't get stuck on the write capable connection.

            $this->last_connection_id['write'] = false;

            $this->last_connection_id['readonly'] = false;

        }

        return $adodb_obj;

    }

    /**

     * This is a hack to work around pass by reference error.

     *

     * Parameter 1 to ADOConnection::GetInsertSQL() expected to be a reference,

     * value given in adodb-loadbalancer.inc.php on line 83

     *

     * @param  $arr

     * @return array

     */

    private function makeValuesReferenced($arr)

    {

        $refs = array();

        foreach ($arr as $key => $value) {

            $refs[$key] = &$arr[$key];

        }

        return $refs;

    }

    /**

     * Allow setting session variables that are maintained across connections.

     *

     * Its important that these are set using name/value, so it can determine

     * if the same variable is set multiple times causing bloat/clutter when

     * new connections are established. For example if the time_zone is set to

     * many different ones through the course of a single connection, a new

     * connection should only set it to the most recent value.

     *

     * @param  $name

     * @param  $value

     * @param  bool  $execute_immediately

     * @return array|bool|mixed

     * @throws Exception

     */

    public function setSessionVariable($name, $value, $execute_immediately = true)

    {

        $this->session_variables[$name] = $value;

        if ($execute_immediately == true) {

            return $this->executeSessionVariables();

        } else {

            return true;

        }

    }

    /**

     * Executes the session variables on a given ADODB object.

     *

     * @param  ADOConnection|bool $adodb_obj

     * @return array|bool|mixed

     * @throws Exception

     */

    private function executeSessionVariables($adodb_obj = false)

    {

        if (is_array($this->session_variables) && count($this->session_variables) > 0) {

            $sql = '';

            foreach ($this->session_variables as $name => $value) {

                // $sql .= 'SET SESSION '. $name .' '. $value;

                // MySQL uses: SET SESSION foo_bar='foo'

                // PGSQL uses: SET SESSION foo_bar 'foo'

                // So leave it up to the user to pass the proper value with '=' if needed.

                // This may be a candidate to move into ADOdb proper.

                $sql .= 'SET SESSION ' . $name . ' ' . $value;

            }

            if ($adodb_obj !== false) {

                return $adodb_obj->Execute($sql);

            } else {

                return $this->ClusterExecute($sql);

            }

        }

        return false;

    }

    /**

     * Executes the same SQL QUERY on the entire cluster of connections.

     * Would be used for things like SET SESSION TIME ZONE calls and such.

     *

     * @param  $sql

     * @param  bool $inputarr

     * @param  bool $return_all_results

     * @param  bool $existing_connections_only

     * @return array|bool|mixed

     * @throws Exception

     */

    public function clusterExecute(

        $sql,

        $inputarr = false,

        $return_all_results = false,

        $existing_connections_only = true

    ) {

        if (is_array($this->connections) && count($this->connections) > 0) {

            foreach ($this->connections as $key => $connection_obj) {

                if ($existing_connections_only == false

                    || ($existing_connections_only == true

                        && $connection_obj->getADOdbObject()->_connectionID !== false

                    )

                ) {

                    $adodb_obj = $this->getConnectionById($key);

                    if (is_object($adodb_obj)) {

                        $result_arr[] = $adodb_obj->Execute($sql, $inputarr);

                    }

                }

            }

            if (isset($result_arr) && $return_all_results == true) {

                return $result_arr;

            } else {

                // Loop through all results checking to see if they match, if they do return the first one

                // otherwise return an array of all results.

                if (isset($result_arr)) {

                    foreach ($result_arr as $result) {

                        if ($result == false) {

                            return $result_arr;

                        }

                    }

                    return $result_arr[0];

                } else {

                    // When using lazy connections, there are cases where

                    // setSessionVariable() is called early on, but there are

                    // no connections to execute the queries on yet.

                    // This captures that case and forces a RETURN TRUE to occur.

                    // As likely the queries will be executed as soon as a

                    // connection is established.

                    return true;

                }

            }

        }

        return false;

    }

    /**

     * Determines if a SQL query is read-only or not.

     *

     * @param  string $sql SQL Query to test.

     * @return bool

     */

    public function isReadOnlyQuery($sql)

    {

        if (   stripos($sql, 'SELECT') === 0

            && stripos($sql, 'FOR UPDATE') === false

            && stripos($sql, ' INTO ') === false

            && stripos($sql, 'LOCK IN') === false

        ) {

            return true;

        }

        return false;

    }

    /**

     * Use this instead of __call() as it significantly reduces the overhead of call_user_func_array().

     *

     * @param  $sql

     * @param  bool $inputarr

     * @return array|bool|mixed

     * @throws Exception

     */

    public function execute($sql, $inputarr = false)

    {

        $type = 'write';

        $pin_connection = null;

        // Prevent leading spaces from causing isReadOnlyQuery/stripos from failing.

        $sql = trim($sql);

        // SELECT queries that can write and therefore must be run on a write capable connection.

        // SELECT ... FOR UPDATE;

        // SELECT ... INTO ...

        // SELECT .. LOCK IN ... (MYSQL)

        if ($this->isReadOnlyQuery($sql) == true) {

            $type = 'readonly';

        } elseif (stripos($sql, 'SET') === 0) {

            // SET SQL statements should likely use setSessionVariable() instead,

            // so state is properly maintained across connections, especially when they are lazily created.

            return $this->ClusterExecute($sql, $inputarr);

        }

        $adodb_obj = $this->getConnection($type, $pin_connection);

        if ($adodb_obj !== false) {

            return $adodb_obj->Execute($sql, $inputarr);

        }

        return false;

    }

    /**

     * Magic method to intercept method and callback to the proper ADODB object for write/readonly connections.

     *

     * @param  string $method ADODB method to call.

     * @param  array  $args   Arguments to the ADODB method.

     * @return bool|mixed

     * @throws Exception

     */

    public function __call($method, $args)

    {

        $type = 'write';

        $pin_connection = null;

        // Intercept specific methods to determine if they are read-only or not.

        $method = strtolower($method);

        switch ($method) {

            // case 'execute': // This is the direct overloaded function above instead.

            case 'getone':

            case 'getrow':

            case 'getall':

            case 'getcol':

            case 'getassoc':

            case 'selectlimit':

                if ($this->isReadOnlyQuery(trim($args[0])) == true) {

                    $type = 'readonly';

                }

                break;

            case 'cachegetone':

            case 'cachegetrow':

            case 'cachegetall':

            case 'cachegetcol':

            case 'cachegetassoc':

            case 'cacheexecute':

            case 'cacheselect':

            case 'pageexecute':

            case 'cachepageexecute':

                $type = 'readonly';

                break;

                // case 'ignoreerrors':

                // 	// When ignoreerrors is called, PIN to the connection until its called again.

                // 	if (!isset($args[0]) || (isset($args[0]) && $args[0] == FALSE)) {

                // 		$pin_connection = TRUE;

                // 	} else {

                // 		$pin_connection = FALSE;

                // 	}

                // 	break;

                // Manual transactions

            case 'begintrans':

            case 'settransactionmode':

                    $pin_connection = true;

                break;

            case 'rollbacktrans':

            case 'committrans':

                $pin_connection = false;

                break;

                // Smart transactions

            case 'starttrans':

                $pin_connection = true;

                break;

            case 'completetrans':

            case 'failtrans':

                // getConnection() will only unpin the transaction if we're exiting the last nested transaction

                $pin_connection = false;

                break;

            // Functions that don't require any connection and therefore

            // shouldn't force a connection be established before they run.

            case 'qstr':

            case 'escape':

            case 'binddate':

            case 'bindtimestamp':

            case 'setfetchmode':

            case 'setcustommetatype':

                  $type = false; // No connection necessary.

                break;

            // Default to assuming write connection is required to be on the safe side.

            default:

                break;

        }

        if ($type === false) {

            if (is_array($this->connections) && count($this->connections) > 0) {

                foreach ($this->connections as $key => $connection_obj) {

                    $adodb_obj = $connection_obj->getADOdbObject();

                    return call_user_func_array(array($adodb_obj, $method), $this->makeValuesReferenced($args)); // Just makes the function call on the first object.

                }

            }

        } else {

               $adodb_obj = $this->getConnection($type, $pin_connection);

            if (is_object($adodb_obj)) {

                $result = call_user_func_array(array($adodb_obj, $method), $this->makeValuesReferenced($args));

                return $result;

            }

        }

        return false;

    }

    /**

     * Magic method to proxy property getter calls back to the proper ADODB object currently in use.

     *

     * @param  $property

     * @return mixed

     * @throws Exception

     */

    public function __get($property)

    {

        if (is_array($this->connections) && count($this->connections) > 0) {

            foreach ($this->connections as $key => $connection_obj) {

                // Just returns the property from the first object.

                return $connection_obj->getADOdbObject()->$property;

            }

        }

        return false;

    }

    /**

     * Magic method to proxy property setter calls back to the proper ADODB object currently in use.

     *

     * @param  $property

     * @param  $value

     * @return mixed

     * @throws Exception

     */

    public function __set($property, $value)

    {

        // Special function to set object properties on all objects

        // without initiating a connection to the database.

        if (is_array($this->connections) && count($this->connections) > 0) {

            foreach ($this->connections as $key => $connection_obj) {

                $connection_obj->getADOdbObject()->$property = $value;

            }

               return true;

        }

        return false;

    }

    /**

     *  Override the __clone() magic method.

     */

    private function __clone()

    {

    }

}

/**

 * Class ADOdbLoadBalancerConnection

 */

class ADOdbLoadBalancerConnection

{

    /**

     * @var bool    ADOdb drive name.

     */

    protected $driver = false;

    /**

     * @var bool    ADODB object.

     */

    protected $adodb_obj = false;

    /**

     * @var callable    Closure

     */

    protected $connection_test_callback = NULL;

    /**

     * @var string    Type of connection, either 'write' capable or 'readonly'

     */

    public $type = 'write';

    /**

     * @var int        Weight of connection, lower receives less queries, higher receives more queries.

     */

    public $weight = 1;

    /**

     * @var bool    Determines if the connection persistent.

     */

    public $persistent_connection = false;

    /**

     * @var string    Database connection host

     */

    public $host = '';

    /**

     * @var string    Database connection user

     */

    public $user = '';

    /**

     * @var string    Database connection password

     */

    public $password = '';

    /**

     * @var string    Database connection database name

     */

    public $database = '';

    /**

     * ADOdbLoadBalancerConnection constructor to setup the ADODB object.

     *

     * @param $driver

     * @param string $type

     * @param int    $weight

     * @param bool   $persistent_connection

     * @param string $argHostname

     * @param string $argUsername

     * @param string $argPassword

     * @param string $argDatabaseName

     */

    public function __construct(

        $driver,

        $type = 'write',

        $weight = 1,

        $persistent_connection = false,

        $argHostname = '',

        $argUsername = '',

        $argPassword = '',

        $argDatabaseName = ''

    ) {

        if ($type !== 'write' && $type !== 'readonly') {

            return false;

        }

        $this->adodb_obj = ADONewConnection($driver);

        $this->type = $type;

        $this->weight = $weight;

        $this->persistent_connection = $persistent_connection;

        $this->host = $argHostname;

        $this->user = $argUsername;

        $this->password = $argPassword;

        $this->database = $argDatabaseName;

        return true;

    }

    /**

     * Anonymous function that is called and must return TRUE for the connection to be usable.*

     *   The first argument is the type of connection to test.

     *   Useful to check things like replication lag.

     * @param callable $callback

     * @return void

     */

    function setConnectionTestCallback($callback) {

        $this->connection_test_callback = $callback;

    }

    /**

     * @return callable|null

     */

    function getConnectionTestCallback() {

        return $this->connection_test_callback;

    }

    /**

     * Returns the ADODB object for this connection.

     *

     * @return bool

     */

    public function getADOdbObject()

    {

        return $this->adodb_obj;

    }

}