PHPSessionHandler: Implement SessionHandlerInterface

[mediawiki.git] / includes / objectcache / RedisBagOStuff.php

<?php
/**
 * Object caching using Redis (http://redis.io/).
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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 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 Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */

/**
 * Redis-based caching module for redis server >= 2.6.12
 *
 * @note: avoid use of Redis::MULTI transactions for twemproxy support
 */
class RedisBagOStuff extends BagOStuff {
        /** @var RedisConnectionPool */
        protected $redisPool;
        /** @var array List of server names */
        protected $servers;
        /** @var array Map of (tag => server name) */
        protected $serverTagMap;
        /** @var bool */
        protected $automaticFailover;

        /**
         * Construct a RedisBagOStuff object. Parameters are:
         *
         *   - servers: An array of server names. A server name may be a hostname,
         *     a hostname/port combination or the absolute path of a UNIX socket.
         *     If a hostname is specified but no port, the standard port number
         *     6379 will be used. Arrays keys can be used to specify the tag to
         *     hash on in place of the host/port. Required.
         *
         *   - connectTimeout: The timeout for new connections, in seconds. Optional,
         *     default is 1 second.
         *
         *   - persistent: Set this to true to allow connections to persist across
         *     multiple web requests. False by default.
         *
         *   - password: The authentication password, will be sent to Redis in
         *     clear text. Optional, if it is unspecified, no AUTH command will be
         *     sent.
         *
         *   - automaticFailover: If this is false, then each key will be mapped to
         *     a single server, and if that server is down, any requests for that key
         *     will fail. If this is true, a connection failure will cause the client
         *     to immediately try the next server in the list (as determined by a
         *     consistent hashing algorithm). True by default. This has the
         *     potential to create consistency issues if a server is slow enough to
         *     flap, for example if it is in swap death.
         * @param array $params
         */
        function __construct( $params ) {
                parent::__construct( $params );
                $redisConf = array( 'serializer' => 'none' ); // manage that in this class
                foreach ( array( 'connectTimeout', 'persistent', 'password' ) as $opt ) {
                        if ( isset( $params[$opt] ) ) {
                                $redisConf[$opt] = $params[$opt];
                        }
                }
                $this->redisPool = RedisConnectionPool::singleton( $redisConf );

                $this->servers = $params['servers'];
                foreach ( $this->servers as $key => $server ) {
                        $this->serverTagMap[is_int( $key ) ? $server : $key] = $server;
                }

                if ( isset( $params['automaticFailover'] ) ) {
                        $this->automaticFailover = $params['automaticFailover'];
                } else {
                        $this->automaticFailover = true;
                }
        }

        protected function doGet( $key, $flags = 0 ) {
                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                try {
                        $value = $conn->get( $key );
                        $result = $this->unserialize( $value );
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $conn, $e );
                }

                $this->logRequest( 'get', $key, $server, $result );
                return $result;
        }

        public function set( $key, $value, $expiry = 0, $flags = 0 ) {
                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                $expiry = $this->convertToRelative( $expiry );
                try {
                        if ( $expiry ) {
                                $result = $conn->setex( $key, $expiry, $this->serialize( $value ) );
                        } else {
                                // No expiry, that is very different from zero expiry in Redis
                                $result = $conn->set( $key, $this->serialize( $value ) );
                        }
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $conn, $e );
                }

                $this->logRequest( 'set', $key, $server, $result );
                return $result;
        }

        public function delete( $key ) {
                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                try {
                        $conn->delete( $key );
                        // Return true even if the key didn't exist
                        $result = true;
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $conn, $e );
                }

                $this->logRequest( 'delete', $key, $server, $result );
                return $result;
        }

        public function getMulti( array $keys, $flags = 0 ) {
                $batches = array();
                $conns = array();
                foreach ( $keys as $key ) {
                        list( $server, $conn ) = $this->getConnection( $key );
                        if ( !$conn ) {
                                continue;
                        }
                        $conns[$server] = $conn;
                        $batches[$server][] = $key;
                }
                $result = array();
                foreach ( $batches as $server => $batchKeys ) {
                        $conn = $conns[$server];
                        try {
                                $conn->multi( Redis::PIPELINE );
                                foreach ( $batchKeys as $key ) {
                                        $conn->get( $key );
                                }
                                $batchResult = $conn->exec();
                                if ( $batchResult === false ) {
                                        $this->debug( "multi request to $server failed" );
                                        continue;
                                }
                                foreach ( $batchResult as $i => $value ) {
                                        if ( $value !== false ) {
                                                $result[$batchKeys[$i]] = $this->unserialize( $value );
                                        }
                                }
                        } catch ( RedisException $e ) {
                                $this->handleException( $conn, $e );
                        }
                }

                $this->debug( "getMulti for " . count( $keys ) . " keys " .
                        "returned " . count( $result ) . " results" );
                return $result;
        }

        /**
         * @param array $data
         * @param int $expiry
         * @return bool
         */
        public function setMulti( array $data, $expiry = 0 ) {
                $batches = array();
                $conns = array();
                foreach ( $data as $key => $value ) {
                        list( $server, $conn ) = $this->getConnection( $key );
                        if ( !$conn ) {
                                continue;
                        }
                        $conns[$server] = $conn;
                        $batches[$server][] = $key;
                }

                $expiry = $this->convertToRelative( $expiry );
                $result = true;
                foreach ( $batches as $server => $batchKeys ) {
                        $conn = $conns[$server];
                        try {
                                $conn->multi( Redis::PIPELINE );
                                foreach ( $batchKeys as $key ) {
                                        if ( $expiry ) {
                                                $conn->setex( $key, $expiry, $this->serialize( $data[$key] ) );
                                        } else {
                                                $conn->set( $key, $this->serialize( $data[$key] ) );
                                        }
                                }
                                $batchResult = $conn->exec();
                                if ( $batchResult === false ) {
                                        $this->debug( "setMulti request to $server failed" );
                                        continue;
                                }
                                foreach ( $batchResult as $value ) {
                                        if ( $value === false ) {
                                                $result = false;
                                        }
                                }
                        } catch ( RedisException $e ) {
                                $this->handleException( $server, $conn, $e );
                                $result = false;
                        }
                }

                return $result;
        }

        public function add( $key, $value, $expiry = 0 ) {
                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                $expiry = $this->convertToRelative( $expiry );
                try {
                        if ( $expiry ) {
                                $result = $conn->set(
                                        $key,
                                        $this->serialize( $value ),
                                        array( 'nx', 'ex' => $expiry )
                                );
                        } else {
                                $result = $conn->setnx( $key, $this->serialize( $value ) );
                        }
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $conn, $e );
                }

                $this->logRequest( 'add', $key, $server, $result );
                return $result;
        }

        /**
         * Non-atomic implementation of incr().
         *
         * Probably all callers actually want incr() to atomically initialise
         * values to zero if they don't exist, as provided by the Redis INCR
         * command. But we are constrained by the memcached-like interface to
         * return null in that case. Once the key exists, further increments are
         * atomic.
         * @param string $key Key to increase
         * @param int $value Value to add to $key (Default 1)
         * @return int|bool New value or false on failure
         */
        public function incr( $key, $value = 1 ) {
                list( $server, $conn ) = $this->getConnection( $key );
                if ( !$conn ) {
                        return false;
                }
                if ( !$conn->exists( $key ) ) {
                        return null;
                }
                try {
                        // @FIXME: on races, the key may have a 0 TTL
                        $result = $conn->incrBy( $key, $value );
                } catch ( RedisException $e ) {
                        $result = false;
                        $this->handleException( $conn, $e );
                }

                $this->logRequest( 'incr', $key, $server, $result );
                return $result;
        }

        public function modifySimpleRelayEvent( array $event ) {
                if ( array_key_exists( 'val', $event ) ) {
                        $event['val'] = serialize( $event['val'] ); // this class uses PHP serialization
                }

                return $event;
        }

        /**
         * @param mixed $data
         * @return string
         */
        protected function serialize( $data ) {
                // Serialize anything but integers so INCR/DECR work
                // Do not store integer-like strings as integers to avoid type confusion (bug 60563)
                return is_int( $data ) ? $data : serialize( $data );
        }

        /**
         * @param string $data
         * @return mixed
         */
        protected function unserialize( $data ) {
                return ctype_digit( $data ) ? intval( $data ) : unserialize( $data );
        }

        /**
         * Get a Redis object with a connection suitable for fetching the specified key
         * @param string $key
         * @return array (server, RedisConnRef) or (false, false)
         */
        protected function getConnection( $key ) {
                $candidates = array_keys( $this->serverTagMap );

                if ( count( $this->servers ) > 1 ) {
                        ArrayUtils::consistentHashSort( $candidates, $key, '/' );
                        if ( !$this->automaticFailover ) {
                                $candidates = array_slice( $candidates, 0, 1 );
                        }
                }

                while ( ( $tag = array_shift( $candidates ) ) !== null ) {
                        $server = $this->serverTagMap[$tag];
                        $conn = $this->redisPool->getConnection( $server );
                        if ( !$conn ) {
                                continue;
                        }

                        // If automatic failover is enabled, check that the server's link
                        // to its master (if any) is up -- but only if there are other
                        // viable candidates left to consider. Also, getMasterLinkStatus()
                        // does not work with twemproxy, though $candidates will be empty
                        // by now in such cases.
                        if ( $this->automaticFailover && $candidates ) {
                                try {
                                        if ( $this->getMasterLinkStatus( $conn ) === 'down' ) {
                                                // If the master cannot be reached, fail-over to the next server.
                                                // If masters are in data-center A, and slaves in data-center B,
                                                // this helps avoid the case were fail-over happens in A but not
                                                // to the corresponding server in B (e.g. read/write mismatch).
                                                continue;
                                        }
                                } catch ( RedisException $e ) {
                                        // Server is not accepting commands
                                        $this->handleException( $conn, $e );
                                        continue;
                                }
                        }

                        return array( $server, $conn );
                }

                $this->setLastError( BagOStuff::ERR_UNREACHABLE );

                return array( false, false );
        }

        /**
         * Check the master link status of a Redis server that is configured as a slave.
         * @param RedisConnRef $conn
         * @return string|null Master link status (either 'up' or 'down'), or null
         *  if the server is not a slave.
         */
        protected function getMasterLinkStatus( RedisConnRef $conn ) {
                $info = $conn->info();
                return isset( $info['master_link_status'] )
                        ? $info['master_link_status']
                        : null;
        }

        /**
         * Log a fatal error
         * @param string $msg
         */
        protected function logError( $msg ) {
                $this->logger->error( "Redis error: $msg" );
        }

        /**
         * The redis extension throws an exception in response to various read, write
         * and protocol errors. Sometimes it also closes the connection, sometimes
         * not. The safest response for us is to explicitly destroy the connection
         * object and let it be reopened during the next request.
         * @param RedisConnRef $conn
         * @param Exception $e
         */
        protected function handleException( RedisConnRef $conn, $e ) {
                $this->setLastError( BagOStuff::ERR_UNEXPECTED );
                $this->redisPool->handleError( $conn, $e );
        }

        /**
         * Send information about a single request to the debug log
         * @param string $method
         * @param string $key
         * @param string $server
         * @param bool $result
         */
        public function logRequest( $method, $key, $server, $result ) {
                $this->debug( "$method $key on $server: " .
                        ( $result === false ? "failure" : "success" ) );
        }
}