WordPress 4.2.2
[autoinstalls/wordpress.git] / wp-includes / wp-db.php
index 4fc829fb6c56510ec81c82f32726018e12473d42..e749f517c43beac5f953c7bb8141c39a920d34c8 100644 (file)
@@ -17,7 +17,8 @@ define( 'EZSQL_VERSION', 'WP1.25' );
 /**
  * @since 0.71
  */
-define( 'OBJECT', 'OBJECT', true );
+define( 'OBJECT', 'OBJECT' );
+define( 'object', 'OBJECT' ); // Back compat.
 
 /**
  * @since 2.5.0
@@ -42,7 +43,7 @@ define( 'ARRAY_N', 'ARRAY_N' );
  * file to your class. The wpdb class will still be included,
  * so you can extend it or simply use your own.
  *
- * @link http://codex.wordpress.org/Function_Reference/wpdb_Class
+ * @link https://codex.wordpress.org/Function_Reference/wpdb_Class
  *
  * @package WordPress
  * @subpackage Database
@@ -51,7 +52,10 @@ define( 'ARRAY_N', 'ARRAY_N' );
 class wpdb {
 
        /**
-        * Whether to show SQL/DB errors
+        * Whether to show SQL/DB errors.
+        *
+        * Default behavior is to show errors if both WP_DEBUG and WP_DEBUG_DISPLAY
+        * evaluated to true.
         *
         * @since 0.71
         * @access private
@@ -74,7 +78,7 @@ class wpdb {
         * @since 2.5.0
         * @var string
         */
-       var $last_error = '';
+       public $last_error = '';
 
        /**
         * Amount of queries made
@@ -139,6 +143,43 @@ class wpdb {
         */
        protected $result;
 
+       /**
+        * Cached column info, for sanity checking data before inserting
+        *
+        * @since 4.2.0
+        * @access protected
+        * @var array
+        */
+       protected $col_meta = array();
+
+       /**
+        * Calculated character sets on tables
+        *
+        * @since 4.2.0
+        * @access protected
+        * @var array
+        */
+       protected $table_charset = array();
+
+       /**
+        * Whether text fields in the current query need to be sanity checked.
+        *
+        * @since 4.2.0
+        * @access protected
+        * @var bool
+        */
+       protected $check_current_query = true;
+
+       /**
+        * Flag to ensure we don't run into recursion problems when checking the collation.
+        *
+        * @since 4.2.0
+        * @access private
+        * @see wpdb::check_safe_collation()
+        * @var boolean
+        */
+       private $checking_collation = false;
+
        /**
         * Saved info on the table column
         *
@@ -157,6 +198,16 @@ class wpdb {
         */
        var $queries;
 
+       /**
+        * The number of times to retry reconnecting before dying.
+        *
+        * @since 3.9.0
+        * @access protected
+        * @see wpdb::check_connection()
+        * @var int
+        */
+       protected $reconnect_retries = 5;
+
        /**
         * WordPress table prefix
         *
@@ -170,6 +221,15 @@ class wpdb {
         */
        var $prefix = '';
 
+       /**
+        * WordPress base table prefix.
+        *
+        * @since 3.0.0
+        * @access public
+        * @var string
+        */
+        public $base_prefix;
+
        /**
         * Whether the database queries are ready to start executing.
         *
@@ -180,22 +240,22 @@ class wpdb {
        var $ready = false;
 
        /**
-        * {@internal Missing Description}}
+        * Blog ID.
         *
         * @since 3.0.0
         * @access public
         * @var int
         */
-       var $blogid = 0;
+       public $blogid = 0;
 
        /**
-        * {@internal Missing Description}}
+        * Site ID.
         *
         * @since 3.0.0
         * @access public
         * @var int
         */
-       var $siteid = 0;
+       public $siteid = 0;
 
        /**
         * List of WordPress per-blog tables
@@ -248,7 +308,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $comments;
+       public $comments;
 
        /**
         * WordPress Comment Metadata table
@@ -257,7 +317,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $commentmeta;
+       public $commentmeta;
 
        /**
         * WordPress Links table
@@ -266,7 +326,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $links;
+       public $links;
 
        /**
         * WordPress Options table
@@ -275,7 +335,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $options;
+       public $options;
 
        /**
         * WordPress Post Metadata table
@@ -284,7 +344,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $postmeta;
+       public $postmeta;
 
        /**
         * WordPress Posts table
@@ -293,7 +353,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $posts;
+       public $posts;
 
        /**
         * WordPress Terms table
@@ -302,7 +362,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $terms;
+       public $terms;
 
        /**
         * WordPress Term Relationships table
@@ -311,7 +371,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $term_relationships;
+       public $term_relationships;
 
        /**
         * WordPress Term Taxonomy table
@@ -320,7 +380,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $term_taxonomy;
+       public $term_taxonomy;
 
        /*
         * Global and Multisite tables
@@ -333,7 +393,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $usermeta;
+       public $usermeta;
 
        /**
         * WordPress Users table
@@ -342,7 +402,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $users;
+       public $users;
 
        /**
         * Multisite Blogs table
@@ -351,7 +411,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $blogs;
+       public $blogs;
 
        /**
         * Multisite Blog Versions table
@@ -360,7 +420,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $blog_versions;
+       public $blog_versions;
 
        /**
         * Multisite Registration Log table
@@ -369,7 +429,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $registration_log;
+       public $registration_log;
 
        /**
         * Multisite Signups table
@@ -378,7 +438,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $signups;
+       public $signups;
 
        /**
         * Multisite Sites table
@@ -387,7 +447,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $site;
+       public $site;
 
        /**
         * Multisite Sitewide Terms table
@@ -396,7 +456,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $sitecategories;
+       public $sitecategories;
 
        /**
         * Multisite Site Metadata table
@@ -405,7 +465,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $sitemeta;
+       public $sitemeta;
 
        /**
         * Format specifiers for DB columns. Columns not listed here default to %s. Initialized during WP load.
@@ -421,7 +481,7 @@ class wpdb {
         * @access public
         * @var array
         */
-       var $field_types = array();
+       public $field_types = array();
 
        /**
         * Database table columns charset
@@ -430,7 +490,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $charset;
+       public $charset;
 
        /**
         * Database table columns collate
@@ -439,16 +499,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $collate;
-
-       /**
-        * Whether to use mysql_real_escape_string
-        *
-        * @since 2.8.0
-        * @access public
-        * @var bool
-        */
-       var $real_escape = false;
+       public $collate;
 
        /**
         * Database Username
@@ -502,7 +553,7 @@ class wpdb {
         * @access public
         * @var string
         */
-       var $func_call;
+       public $func_call;
 
        /**
         * Whether MySQL is used as the database engine.
@@ -518,6 +569,34 @@ class wpdb {
         */
        public $is_mysql = null;
 
+       /**
+        * A list of incompatible SQL modes.
+        *
+        * @since 3.9.0
+        * @access protected
+        * @var array
+        */
+       protected $incompatible_modes = array( 'NO_ZERO_DATE', 'ONLY_FULL_GROUP_BY',
+               'STRICT_TRANS_TABLES', 'STRICT_ALL_TABLES', 'TRADITIONAL' );
+
+       /**
+        * Whether to use mysqli over mysql.
+        *
+        * @since 3.9.0
+        * @access private
+        * @var bool
+        */
+       private $use_mysqli = false;
+
+       /**
+        * Whether we've managed to successfully connect at some point
+        *
+        * @since 3.9.0
+        * @access private
+        * @var bool
+        */
+       private $has_connected = false;
+
        /**
         * Connects to the database server and selects a database
         *
@@ -525,7 +604,7 @@ class wpdb {
         * the actual setting up of the class properties and connection
         * to the database.
         *
-        * @link http://core.trac.wordpress.org/ticket/3354
+        * @link https://core.trac.wordpress.org/ticket/3354
         * @since 2.0.8
         *
         * @param string $dbuser MySQL database user
@@ -533,19 +612,38 @@ class wpdb {
         * @param string $dbname MySQL database name
         * @param string $dbhost MySQL database host
         */
-       function __construct( $dbuser, $dbpassword, $dbname, $dbhost ) {
+       public function __construct( $dbuser, $dbpassword, $dbname, $dbhost ) {
                register_shutdown_function( array( $this, '__destruct' ) );
 
-               if ( WP_DEBUG )
+               if ( WP_DEBUG && WP_DEBUG_DISPLAY )
                        $this->show_errors();
 
-               $this->init_charset();
+               /* Use ext/mysqli if it exists and:
+                *  - WP_USE_EXT_MYSQL is defined as false, or
+                *  - We are a development version of WordPress, or
+                *  - We are running PHP 5.5 or greater, or
+                *  - ext/mysql is not loaded.
+                */
+               if ( function_exists( 'mysqli_connect' ) ) {
+                       if ( defined( 'WP_USE_EXT_MYSQL' ) ) {
+                               $this->use_mysqli = ! WP_USE_EXT_MYSQL;
+                       } elseif ( version_compare( phpversion(), '5.5', '>=' ) || ! function_exists( 'mysql_connect' ) ) {
+                               $this->use_mysqli = true;
+                       } elseif ( false !== strpos( $GLOBALS['wp_version'], '-' ) ) {
+                               $this->use_mysqli = true;
+                       }
+               }
 
                $this->dbuser = $dbuser;
                $this->dbpassword = $dbpassword;
                $this->dbname = $dbname;
                $this->dbhost = $dbhost;
 
+               // wp-config.php creation will manually connect when ready.
+               if ( defined( 'WP_SETUP_CONFIG' ) ) {
+                       return;
+               }
+
                $this->db_connect();
        }
 
@@ -556,7 +654,7 @@ class wpdb {
         * @since 2.0.8
         * @return bool true
         */
-       function __destruct() {
+       public function __destruct() {
                return true;
        }
 
@@ -568,27 +666,35 @@ class wpdb {
         * @param string $name The private member to get, and optionally process
         * @return mixed The private member
         */
-       function __get( $name ) {
-               if ( 'col_info' == $name )
+       public function __get( $name ) {
+               if ( 'col_info' === $name )
                        $this->load_col_info();
 
                return $this->$name;
        }
 
        /**
-        * Magic function, for backwards compatibility
+        * Magic function, for backwards compatibility.
         *
         * @since 3.5.0
         *
         * @param string $name  The private member to set
         * @param mixed  $value The value to set
         */
-       function __set( $name, $value ) {
+       public function __set( $name, $value ) {
+               $protected_members = array(
+                       'col_meta',
+                       'table_charset',
+                       'check_current_query',
+               );
+               if (  in_array( $name, $protected_members, true ) ) {
+                       return;
+               }
                $this->$name = $value;
        }
 
        /**
-        * Magic function, for backwards compatibility
+        * Magic function, for backwards compatibility.
         *
         * @since 3.5.0
         *
@@ -596,18 +702,18 @@ class wpdb {
         *
         * @return bool If the member is set or not
         */
-       function __isset( $name ) {
+       public function __isset( $name ) {
                return isset( $this->$name );
        }
 
        /**
-        * Magic function, for backwards compatibility
+        * Magic function, for backwards compatibility.
         *
         * @since 3.5.0
         *
         * @param string $name  The private member to unset
         */
-       function __unset( $name ) {
+       public function __unset( $name ) {
                unset( $this->$name );
        }
 
@@ -616,19 +722,34 @@ class wpdb {
         *
         * @since 3.1.0
         */
-       function init_charset() {
+       public function init_charset() {
                if ( function_exists('is_multisite') && is_multisite() ) {
                        $this->charset = 'utf8';
-                       if ( defined( 'DB_COLLATE' ) && DB_COLLATE )
+                       if ( defined( 'DB_COLLATE' ) && DB_COLLATE ) {
                                $this->collate = DB_COLLATE;
-                       else
+                       } else {
                                $this->collate = 'utf8_general_ci';
+                       }
                } elseif ( defined( 'DB_COLLATE' ) ) {
                        $this->collate = DB_COLLATE;
                }
 
-               if ( defined( 'DB_CHARSET' ) )
+               if ( defined( 'DB_CHARSET' ) ) {
                        $this->charset = DB_CHARSET;
+               }
+
+               if ( ( $this->use_mysqli && ! ( $this->dbh instanceof mysqli ) )
+                 || ( empty( $this->dbh ) || ! ( $this->dbh instanceof mysqli ) ) ) {
+                       return;
+               }
+
+               if ( 'utf8' === $this->charset && $this->has_cap( 'utf8mb4' ) ) {
+                       $this->charset = 'utf8mb4';
+               }
+
+               if ( 'utf8mb4' === $this->charset && ( ! $this->collate || stripos( $this->collate, 'utf8_' ) === 0 ) ) {
+                       $this->collate = 'utf8mb4_unicode_ci';
+               }
        }
 
        /**
@@ -637,25 +758,100 @@ class wpdb {
         * @since 3.1.0
         *
         * @param resource $dbh     The resource given by mysql_connect
-        * @param string   $charset The character set (optional)
-        * @param string   $collate The collation (optional)
+        * @param string   $charset Optional. The character set. Default null.
+        * @param string   $collate Optional. The collation. Default null.
         */
-       function set_charset($dbh, $charset = null, $collate = null) {
-               if ( !isset($charset) )
+       public function set_charset( $dbh, $charset = null, $collate = null ) {
+               if ( ! isset( $charset ) )
                        $charset = $this->charset;
-               if ( !isset($collate) )
+               if ( ! isset( $collate ) )
                        $collate = $this->collate;
-               if ( $this->has_cap( 'collation', $dbh ) && !empty( $charset ) ) {
-                       if ( function_exists( 'mysql_set_charset' ) && $this->has_cap( 'set_charset', $dbh ) ) {
-                               mysql_set_charset( $charset, $dbh );
-                               $this->real_escape = true;
+               if ( $this->has_cap( 'collation' ) && ! empty( $charset ) ) {
+                       if ( $this->use_mysqli ) {
+                               if ( function_exists( 'mysqli_set_charset' ) && $this->has_cap( 'set_charset' ) ) {
+                                       mysqli_set_charset( $dbh, $charset );
+                               } else {
+                                       $query = $this->prepare( 'SET NAMES %s', $charset );
+                                       if ( ! empty( $collate ) )
+                                               $query .= $this->prepare( ' COLLATE %s', $collate );
+                                       mysqli_query( $dbh, $query );
+                               }
+                       } else {
+                               if ( function_exists( 'mysql_set_charset' ) && $this->has_cap( 'set_charset' ) ) {
+                                       mysql_set_charset( $charset, $dbh );
+                               } else {
+                                       $query = $this->prepare( 'SET NAMES %s', $charset );
+                                       if ( ! empty( $collate ) )
+                                               $query .= $this->prepare( ' COLLATE %s', $collate );
+                                       mysql_query( $query, $dbh );
+                               }
+                       }
+               }
+       }
+
+       /**
+        * Change the current SQL mode, and ensure its WordPress compatibility.
+        *
+        * If no modes are passed, it will ensure the current MySQL server
+        * modes are compatible.
+        *
+        * @since 3.9.0
+        *
+        * @param array $modes Optional. A list of SQL modes to set.
+        */
+       public function set_sql_mode( $modes = array() ) {
+               if ( empty( $modes ) ) {
+                       if ( $this->use_mysqli ) {
+                               $res = mysqli_query( $this->dbh, 'SELECT @@SESSION.sql_mode' );
+                       } else {
+                               $res = mysql_query( 'SELECT @@SESSION.sql_mode', $this->dbh );
+                       }
+
+                       if ( empty( $res ) ) {
+                               return;
+                       }
+
+                       if ( $this->use_mysqli ) {
+                               $modes_array = mysqli_fetch_array( $res );
+                               if ( empty( $modes_array[0] ) ) {
+                                       return;
+                               }
+                               $modes_str = $modes_array[0];
                        } else {
-                               $query = $this->prepare( 'SET NAMES %s', $charset );
-                               if ( ! empty( $collate ) )
-                                       $query .= $this->prepare( ' COLLATE %s', $collate );
-                               mysql_query( $query, $dbh );
+                               $modes_str = mysql_result( $res, 0 );
+                       }
+
+                       if ( empty( $modes_str ) ) {
+                               return;
+                       }
+
+                       $modes = explode( ',', $modes_str );
+               }
+
+               $modes = array_change_key_case( $modes, CASE_UPPER );
+
+               /**
+                * Filter the list of incompatible SQL modes to exclude.
+                *
+                * @since 3.9.0
+                *
+                * @param array $incompatible_modes An array of incompatible modes.
+                */
+               $incompatible_modes = (array) apply_filters( 'incompatible_sql_modes', $this->incompatible_modes );
+
+               foreach( $modes as $i => $mode ) {
+                       if ( in_array( $mode, $incompatible_modes ) ) {
+                               unset( $modes[ $i ] );
                        }
                }
+
+               $modes_str = implode( ',', $modes );
+
+               if ( $this->use_mysqli ) {
+                       mysqli_query( $this->dbh, "SET SESSION sql_mode='$modes_str'" );
+               } else {
+                       mysql_query( "SET SESSION sql_mode='$modes_str'", $this->dbh );
+               }
        }
 
        /**
@@ -667,7 +863,7 @@ class wpdb {
         * @param bool $set_table_names Optional. Whether the table names, e.g. wpdb::$posts, should be updated or not.
         * @return string|WP_Error Old prefix or WP_Error on error
         */
-       function set_prefix( $prefix, $set_table_names = true ) {
+       public function set_prefix( $prefix, $set_table_names = true ) {
 
                if ( preg_match( '|[^a-z0-9_]|i', $prefix ) )
                        return new WP_Error('invalid_db_prefix', 'Invalid database prefix' );
@@ -704,9 +900,9 @@ class wpdb {
         * @access public
         * @param int $blog_id
         * @param int $site_id Optional.
-        * @return string previous blog id
+        * @return int previous blog id
         */
-       function set_blog_id( $blog_id, $site_id = 0 ) {
+       public function set_blog_id( $blog_id, $site_id = 0 ) {
                if ( ! empty( $site_id ) )
                        $this->siteid = $site_id;
 
@@ -727,12 +923,11 @@ class wpdb {
        /**
         * Gets blog prefix.
         *
-        * @uses is_multisite()
         * @since 3.0.0
         * @param int $blog_id Optional.
         * @return string Blog prefix.
         */
-       function get_blog_prefix( $blog_id = null ) {
+       public function get_blog_prefix( $blog_id = null ) {
                if ( is_multisite() ) {
                        if ( null === $blog_id )
                                $blog_id = $this->blogid;
@@ -766,7 +961,6 @@ class wpdb {
         * @uses wpdb::$old_tables
         * @uses wpdb::$global_tables
         * @uses wpdb::$ms_global_tables
-        * @uses is_multisite()
         *
         * @param string $scope Optional. Can be all, global, ms_global, blog, or old tables. Defaults to all.
         * @param bool $prefix Optional. Whether to include table prefixes. Default true. If blog
@@ -774,7 +968,7 @@ class wpdb {
         * @param int $blog_id Optional. The blog_id to prefix. Defaults to wpdb::$blogid. Used only when prefix is requested.
         * @return array Table names. When a prefix is requested, the key is the unprefixed table name.
         */
-       function tables( $scope = 'all', $prefix = true, $blog_id = 0 ) {
+       public function tables( $scope = 'all', $prefix = true, $blog_id = 0 ) {
                switch ( $scope ) {
                        case 'all' :
                                $tables = array_merge( $this->global_tables, $this->tables );
@@ -797,7 +991,6 @@ class wpdb {
                                break;
                        default :
                                return array();
-                               break;
                }
 
                if ( $prefix ) {
@@ -836,44 +1029,57 @@ class wpdb {
         * @param resource $dbh Optional link identifier.
         * @return null Always null.
         */
-       function select( $db, $dbh = null ) {
+       public function select( $db, $dbh = null ) {
                if ( is_null($dbh) )
                        $dbh = $this->dbh;
 
-               if ( !@mysql_select_db( $db, $dbh ) ) {
+               if ( $this->use_mysqli ) {
+                       $success = @mysqli_select_db( $dbh, $db );
+               } else {
+                       $success = @mysql_select_db( $db, $dbh );
+               }
+               if ( ! $success ) {
                        $this->ready = false;
-                       wp_load_translations_early();
-                       $this->bail( sprintf( __( '<h1>Can&#8217;t select database</h1>
+                       if ( ! did_action( 'template_redirect' ) ) {
+                               wp_load_translations_early();
+                               $this->bail( sprintf( __( '<h1>Can&#8217;t select database</h1>
 <p>We were able to connect to the database server (which means your username and password is okay) but not able to select the <code>%1$s</code> database.</p>
 <ul>
 <li>Are you sure it exists?</li>
 <li>Does the user <code>%2$s</code> have permission to use the <code>%1$s</code> database?</li>
 <li>On some systems the name of your database is prefixed with your username, so it would be like <code>username_%1$s</code>. Could that be the problem?</li>
 </ul>
-<p>If you don\'t know how to set up a database you should <strong>contact your host</strong>. If all else fails you may find help at the <a href="http://wordpress.org/support/">WordPress Support Forums</a>.</p>' ), htmlspecialchars( $db, ENT_QUOTES ), htmlspecialchars( $this->dbuser, ENT_QUOTES ) ), 'db_select_fail' );
+<p>If you don\'t know how to set up a database you should <strong>contact your host</strong>. If all else fails you may find help at the <a href="https://wordpress.org/support/">WordPress Support Forums</a>.</p>' ), htmlspecialchars( $db, ENT_QUOTES ), htmlspecialchars( $this->dbuser, ENT_QUOTES ) ), 'db_select_fail' );
+                       }
                        return;
                }
        }
 
        /**
-        * Weak escape, using addslashes()
+        * Do not use, deprecated.
+        *
+        * Use esc_sql() or wpdb::prepare() instead.
         *
-        * @see addslashes()
         * @since 2.8.0
+        * @deprecated 3.6.0
+        * @see wpdb::prepare
+        * @see esc_sql()
         * @access private
         *
         * @param string $string
         * @return string
         */
        function _weak_escape( $string ) {
+               if ( func_num_args() === 1 && function_exists( '_deprecated_function' ) )
+                       _deprecated_function( __METHOD__, '3.6', 'wpdb::prepare() or esc_sql()' );
                return addslashes( $string );
        }
 
        /**
-        * Real escape, using mysql_real_escape_string() or addslashes()
+        * Real escape, using mysqli_real_escape_string() or mysql_real_escape_string()
         *
+        * @see mysqli_real_escape_string()
         * @see mysql_real_escape_string()
-        * @see addslashes()
         * @since 2.8.0
         * @access private
         *
@@ -881,16 +1087,26 @@ class wpdb {
         * @return string escaped
         */
        function _real_escape( $string ) {
-               if ( $this->dbh && $this->real_escape )
-                       return mysql_real_escape_string( $string, $this->dbh );
-               else
-                       return addslashes( $string );
+               if ( $this->dbh ) {
+                       if ( $this->use_mysqli ) {
+                               return mysqli_real_escape_string( $this->dbh, $string );
+                       } else {
+                               return mysql_real_escape_string( $string, $this->dbh );
+                       }
+               }
+
+               $class = get_class( $this );
+               if ( function_exists( '__' ) ) {
+                       _doing_it_wrong( $class, sprintf( __( '%s must set a database connection for use with escaping.' ), $class ), E_USER_NOTICE );
+               } else {
+                       _doing_it_wrong( $class, sprintf( '%s must set a database connection for use with escaping.', $class ), E_USER_NOTICE );
+               }
+               return addslashes( $string );
        }
 
        /**
         * Escape data. Works on arrays.
         *
-        * @uses wpdb::_escape()
         * @uses wpdb::_real_escape()
         * @since  2.8.0
         * @access private
@@ -900,7 +1116,7 @@ class wpdb {
         */
        function _escape( $data ) {
                if ( is_array( $data ) ) {
-                       foreach ( (array) $data as $k => $v ) {
+                       foreach ( $data as $k => $v ) {
                                if ( is_array($v) )
                                        $data[$k] = $this->_escape( $v );
                                else
@@ -914,24 +1130,30 @@ class wpdb {
        }
 
        /**
-        * Escapes content for insertion into the database using addslashes(), for security.
+        * Do not use, deprecated.
         *
-        * Works on arrays.
+        * Use esc_sql() or wpdb::prepare() instead.
         *
         * @since 0.71
-        * @param string|array $data to escape
-        * @return string|array escaped as query safe string
+        * @deprecated 3.6.0
+        * @see wpdb::prepare()
+        * @see esc_sql()
+        *
+        * @param mixed $data
+        * @return mixed
         */
-       function escape( $data ) {
+       public function escape( $data ) {
+               if ( func_num_args() === 1 && function_exists( '_deprecated_function' ) )
+                       _deprecated_function( __METHOD__, '3.6', 'wpdb::prepare() or esc_sql()' );
                if ( is_array( $data ) ) {
-                       foreach ( (array) $data as $k => $v ) {
+                       foreach ( $data as $k => $v ) {
                                if ( is_array( $v ) )
-                                       $data[$k] = $this->escape( $v );
+                                       $data[$k] = $this->escape( $v, 'recursive' );
                                else
-                                       $data[$k] = $this->_weak_escape( $v );
+                                       $data[$k] = $this->_weak_escape( $v, 'internal' );
                        }
                } else {
-                       $data = $this->_weak_escape( $data );
+                       $data = $this->_weak_escape( $data, 'internal' );
                }
 
                return $data;
@@ -945,7 +1167,7 @@ class wpdb {
         * @param string $string to escape
         * @return void
         */
-       function escape_by_ref( &$string ) {
+       public function escape_by_ref( &$string ) {
                if ( ! is_float( $string ) )
                        $string = $this->_real_escape( $string );
        }
@@ -970,10 +1192,8 @@ class wpdb {
         *
         * Both %d and %s should be left unquoted in the query string.
         *
-        * <code>
-        * wpdb::prepare( "SELECT * FROM `table` WHERE `column` = %s AND `field` = %d", 'foo', 1337 )
-        * wpdb::prepare( "SELECT DATE_FORMAT(`field`, '%%c') FROM `table` WHERE `column` = %s", 'foo' );
-        * </code>
+        *     wpdb::prepare( "SELECT * FROM `table` WHERE `column` = %s AND `field` = %d", 'foo', 1337 )
+        *     wpdb::prepare( "SELECT DATE_FORMAT(`field`, '%%c') FROM `table` WHERE `column` = %s", 'foo' );
         *
         * @link http://php.net/sprintf Description of syntax.
         * @since 2.3.0
@@ -987,12 +1207,14 @@ class wpdb {
         * @return null|false|string Sanitized query string, null if there is no query, false if there is an error and string
         *      if there was something to prepare
         */
-       function prepare( $query, $args = null ) {
+       public function prepare( $query, $args ) {
                if ( is_null( $query ) )
                        return;
 
-               if ( func_num_args() < 2 )
-                       _doing_it_wrong( 'wpdb::prepare', 'wpdb::prepare() requires at least two arguments.', '3.5' );
+               // This is not meant to be foolproof -- but it will catch obviously incorrect usage.
+               if ( strpos( $query, '%' ) === false ) {
+                       _doing_it_wrong( 'wpdb::prepare', sprintf( __( 'The query argument of %s must have a placeholder.' ), 'wpdb::prepare()' ), '3.9' );
+               }
 
                $args = func_get_args();
                array_shift( $args );
@@ -1007,6 +1229,32 @@ class wpdb {
                return @vsprintf( $query, $args );
        }
 
+       /**
+        * First half of escaping for LIKE special characters % and _ before preparing for MySQL.
+        *
+        * Use this only before wpdb::prepare() or esc_sql().  Reversing the order is very bad for security.
+        *
+        * Example Prepared Statement:
+        *  $wild = '%';
+        *  $find = 'only 43% of planets';
+        *  $like = $wild . $wpdb->esc_like( $find ) . $wild;
+        *  $sql  = $wpdb->prepare( "SELECT * FROM $wpdb->posts WHERE post_content LIKE %s", $like );
+        *
+        * Example Escape Chain:
+        *  $sql  = esc_sql( $wpdb->esc_like( $input ) );
+        *
+        * @since 4.0.0
+        * @access public
+        *
+        * @param string $text The raw text to be escaped. The input typed by the user should have no
+        *                     extra or deleted slashes.
+        * @return string Text in the form of a LIKE phrase. The output is not SQL safe. Call $wpdb::prepare()
+        *                or real_escape next.
+        */
+       public function esc_like( $text ) {
+               return addcslashes( $text, '_%\\' );
+       }
+
        /**
         * Print SQL/DB error.
         *
@@ -1014,13 +1262,18 @@ class wpdb {
         * @global array $EZSQL_ERROR Stores error information of query and error string
         *
         * @param string $str The error to display
-        * @return bool False if the showing of errors is disabled.
+        * @return false|null False if the showing of errors is disabled.
         */
-       function print_error( $str = '' ) {
+       public function print_error( $str = '' ) {
                global $EZSQL_ERROR;
 
-               if ( !$str )
-                       $str = mysql_error( $this->dbh );
+               if ( !$str ) {
+                       if ( $this->use_mysqli ) {
+                               $str = mysqli_error( $this->dbh );
+                       } else {
+                               $str = mysql_error( $this->dbh );
+                       }
+               }
                $EZSQL_ERROR[] = array( 'query' => $this->last_query, 'error_str' => $str );
 
                if ( $this->suppress_errors )
@@ -1071,7 +1324,7 @@ class wpdb {
         * @param bool $show Whether to show or hide errors
         * @return bool Old value for showing errors.
         */
-       function show_errors( $show = true ) {
+       public function show_errors( $show = true ) {
                $errors = $this->show_errors;
                $this->show_errors = $show;
                return $errors;
@@ -1087,7 +1340,7 @@ class wpdb {
         *
         * @return bool Whether showing of errors was active
         */
-       function hide_errors() {
+       public function hide_errors() {
                $show = $this->show_errors;
                $this->show_errors = false;
                return $show;
@@ -1104,7 +1357,7 @@ class wpdb {
         * @param bool $suppress Optional. New value. Defaults to true.
         * @return bool Old value
         */
-       function suppress_errors( $suppress = true ) {
+       public function suppress_errors( $suppress = true ) {
                $errors = $this->suppress_errors;
                $this->suppress_errors = (bool) $suppress;
                return $errors;
@@ -1116,37 +1369,123 @@ class wpdb {
         * @since 0.71
         * @return void
         */
-       function flush() {
+       public function flush() {
                $this->last_result = array();
                $this->col_info    = null;
                $this->last_query  = null;
                $this->rows_affected = $this->num_rows = 0;
                $this->last_error  = '';
 
-               if ( is_resource( $this->result ) )
+               if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
+                       mysqli_free_result( $this->result );
+                       $this->result = null;
+
+                       // Sanity check before using the handle
+                       if ( empty( $this->dbh ) || !( $this->dbh instanceof mysqli ) ) {
+                               return;
+                       }
+
+                       // Clear out any results from a multi-query
+                       while ( mysqli_more_results( $this->dbh ) ) {
+                               mysqli_next_result( $this->dbh );
+                       }
+               } elseif ( is_resource( $this->result ) ) {
                        mysql_free_result( $this->result );
+               }
        }
 
        /**
-        * Connect to and select database
+        * Connect to and select database.
+        *
+        * If $allow_bail is false, the lack of database connection will need
+        * to be handled manually.
         *
         * @since 3.0.0
+        * @since 3.9.0 $allow_bail parameter added.
+        *
+        * @param bool $allow_bail Optional. Allows the function to bail. Default true.
+        * @return null|bool True with a successful connection, false on failure.
         */
-       function db_connect() {
+       public function db_connect( $allow_bail = true ) {
 
                $this->is_mysql = true;
 
+               /*
+                * Deprecated in 3.9+ when using MySQLi. No equivalent
+                * $new_link parameter exists for mysqli_* functions.
+                */
                $new_link = defined( 'MYSQL_NEW_LINK' ) ? MYSQL_NEW_LINK : true;
                $client_flags = defined( 'MYSQL_CLIENT_FLAGS' ) ? MYSQL_CLIENT_FLAGS : 0;
 
-               if ( WP_DEBUG ) {
-                       $this->dbh = mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
+               if ( $this->use_mysqli ) {
+                       $this->dbh = mysqli_init();
+
+                       // mysqli_real_connect doesn't support the host param including a port or socket
+                       // like mysql_connect does. This duplicates how mysql_connect detects a port and/or socket file.
+                       $port = null;
+                       $socket = null;
+                       $host = $this->dbhost;
+                       $port_or_socket = strstr( $host, ':' );
+                       if ( ! empty( $port_or_socket ) ) {
+                               $host = substr( $host, 0, strpos( $host, ':' ) );
+                               $port_or_socket = substr( $port_or_socket, 1 );
+                               if ( 0 !== strpos( $port_or_socket, '/' ) ) {
+                                       $port = intval( $port_or_socket );
+                                       $maybe_socket = strstr( $port_or_socket, ':' );
+                                       if ( ! empty( $maybe_socket ) ) {
+                                               $socket = substr( $maybe_socket, 1 );
+                                       }
+                               } else {
+                                       $socket = $port_or_socket;
+                               }
+                       }
+
+                       if ( WP_DEBUG ) {
+                               mysqli_real_connect( $this->dbh, $host, $this->dbuser, $this->dbpassword, null, $port, $socket, $client_flags );
+                       } else {
+                               @mysqli_real_connect( $this->dbh, $host, $this->dbuser, $this->dbpassword, null, $port, $socket, $client_flags );
+                       }
+
+                       if ( $this->dbh->connect_errno ) {
+                               $this->dbh = null;
+
+                               /* It's possible ext/mysqli is misconfigured. Fall back to ext/mysql if:
+                                *  - We haven't previously connected, and
+                                *  - WP_USE_EXT_MYSQL isn't set to false, and
+                                *  - ext/mysql is loaded.
+                                */
+                               $attempt_fallback = true;
+
+                               if ( $this->has_connected ) {
+                                       $attempt_fallback = false;
+                               } elseif ( defined( 'WP_USE_EXT_MYSQL' ) && ! WP_USE_EXT_MYSQL ) {
+                                       $attempt_fallback = false;
+                               } elseif ( ! function_exists( 'mysql_connect' ) ) {
+                                       $attempt_fallback = false;
+                               }
+
+                               if ( $attempt_fallback ) {
+                                       $this->use_mysqli = false;
+                                       $this->db_connect();
+                               }
+                       }
                } else {
-                       $this->dbh = @mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
+                       if ( WP_DEBUG ) {
+                               $this->dbh = mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
+                       } else {
+                               $this->dbh = @mysql_connect( $this->dbhost, $this->dbuser, $this->dbpassword, $new_link, $client_flags );
+                       }
                }
 
-               if ( !$this->dbh ) {
+               if ( ! $this->dbh && $allow_bail ) {
                        wp_load_translations_early();
+
+                       // Load custom DB error template, if present.
+                       if ( file_exists( WP_CONTENT_DIR . '/db-error.php' ) ) {
+                               require_once( WP_CONTENT_DIR . '/db-error.php' );
+                               die();
+                       }
+
                        $this->bail( sprintf( __( "
 <h1>Error establishing a database connection</h1>
 <p>This either means that the username and password information in your <code>wp-config.php</code> file is incorrect or we can't contact the database server at <code>%s</code>. This could mean your host's database server is down.</p>
@@ -1155,17 +1494,103 @@ class wpdb {
        <li>Are you sure that you have typed the correct hostname?</li>
        <li>Are you sure that the database server is running?</li>
 </ul>
-<p>If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href='http://wordpress.org/support/'>WordPress Support Forums</a>.</p>
+<p>If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href='https://wordpress.org/support/'>WordPress Support Forums</a>.</p>
 " ), htmlspecialchars( $this->dbhost, ENT_QUOTES ) ), 'db_connect_fail' );
 
-                       return;
+                       return false;
+               } elseif ( $this->dbh ) {
+                       if ( ! $this->has_connected ) {
+                               $this->init_charset();
+                       }
+
+                       $this->has_connected = true;
+
+                       $this->set_charset( $this->dbh );
+
+                       $this->ready = true;
+                       $this->set_sql_mode();
+                       $this->select( $this->dbname, $this->dbh );
+
+                       return true;
+               }
+
+               return false;
+       }
+
+       /**
+        * Check that the connection to the database is still up. If not, try to reconnect.
+        *
+        * If this function is unable to reconnect, it will forcibly die, or if after the
+        * the template_redirect hook has been fired, return false instead.
+        *
+        * If $allow_bail is false, the lack of database connection will need
+        * to be handled manually.
+        *
+        * @since 3.9.0
+        *
+        * @param bool $allow_bail Optional. Allows the function to bail. Default true.
+        * @return bool|null True if the connection is up.
+        */
+       public function check_connection( $allow_bail = true ) {
+               if ( $this->use_mysqli ) {
+                       if ( @mysqli_ping( $this->dbh ) ) {
+                               return true;
+                       }
+               } else {
+                       if ( @mysql_ping( $this->dbh ) ) {
+                               return true;
+                       }
+               }
+
+               $error_reporting = false;
+
+               // Disable warnings, as we don't want to see a multitude of "unable to connect" messages
+               if ( WP_DEBUG ) {
+                       $error_reporting = error_reporting();
+                       error_reporting( $error_reporting & ~E_WARNING );
+               }
+
+               for ( $tries = 1; $tries <= $this->reconnect_retries; $tries++ ) {
+                       // On the last try, re-enable warnings. We want to see a single instance of the
+                       // "unable to connect" message on the bail() screen, if it appears.
+                       if ( $this->reconnect_retries === $tries && WP_DEBUG ) {
+                               error_reporting( $error_reporting );
+                       }
+
+                       if ( $this->db_connect( false ) ) {
+                               if ( $error_reporting ) {
+                                       error_reporting( $error_reporting );
+                               }
+
+                               return true;
+                       }
+
+                       sleep( 1 );
+               }
+
+               // If template_redirect has already happened, it's too late for wp_die()/dead_db().
+               // Let's just return and hope for the best.
+               if ( did_action( 'template_redirect' ) ) {
+                       return false;
                }
 
-               $this->set_charset( $this->dbh );
+               if ( ! $allow_bail ) {
+                       return false;
+               }
 
-               $this->ready = true;
+               // We weren't able to reconnect, so we better bail.
+               $this->bail( sprintf( ( "
+<h1>Error reconnecting to the database</h1>
+<p>This means that we lost contact with the database server at <code>%s</code>. This could mean your host's database server is down.</p>
+<ul>
+       <li>Are you sure that the database server is running?</li>
+       <li>Are you sure that the database server is not under particularly heavy load?</li>
+</ul>
+<p>If you're unsure what these terms mean you should probably contact your host. If you still need help you can always visit the <a href='https://wordpress.org/support/'>WordPress Support Forums</a>.</p>
+" ), htmlspecialchars( $this->dbhost, ENT_QUOTES ) ), 'db_connect_fail' );
 
-               $this->select( $this->dbname, $this->dbh );
+               // Call dead_db() if bail didn't die, because this database is no more. It has ceased to be (at least temporarily).
+               dead_db();
        }
 
        /**
@@ -1178,33 +1603,79 @@ class wpdb {
         * @param string $query Database query
         * @return int|false Number of rows affected/selected or false on error
         */
-       function query( $query ) {
-               if ( ! $this->ready )
+       public function query( $query ) {
+               if ( ! $this->ready ) {
+                       $this->check_current_query = true;
                        return false;
+               }
 
-               // some queries are made before the plugins have been loaded, and thus cannot be filtered with this method
+               /**
+                * Filter the database query.
+                *
+                * Some queries are made before the plugins have been loaded,
+                * and thus cannot be filtered with this method.
+                *
+                * @since 2.1.0
+                *
+                * @param string $query Database query.
+                */
                $query = apply_filters( 'query', $query );
 
-               $return_val = 0;
                $this->flush();
 
                // Log how the function was called
                $this->func_call = "\$db->query(\"$query\")";
 
+               // If we're writing to the database, make sure the query will write safely.
+               if ( $this->check_current_query && ! $this->check_ascii( $query ) ) {
+                       $stripped_query = $this->strip_invalid_text_from_query( $query );
+                       // strip_invalid_text_from_query() can perform queries, so we need
+                       // to flush again, just to make sure everything is clear.
+                       $this->flush();
+                       if ( $stripped_query !== $query ) {
+                               $this->insert_id = 0;
+                               return false;
+                       }
+               }
+
+               $this->check_current_query = true;
+
                // Keep track of the last query for debug..
                $this->last_query = $query;
 
-               if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
-                       $this->timer_start();
+               $this->_do_query( $query );
 
-               $this->result = @mysql_query( $query, $this->dbh );
-               $this->num_queries++;
+               // MySQL server has gone away, try to reconnect
+               $mysql_errno = 0;
+               if ( ! empty( $this->dbh ) ) {
+                       if ( $this->use_mysqli ) {
+                               $mysql_errno = mysqli_errno( $this->dbh );
+                       } else {
+                               $mysql_errno = mysql_errno( $this->dbh );
+                       }
+               }
 
-               if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
-                       $this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );
+               if ( empty( $this->dbh ) || 2006 == $mysql_errno ) {
+                       if ( $this->check_connection() ) {
+                               $this->_do_query( $query );
+                       } else {
+                               $this->insert_id = 0;
+                               return false;
+                       }
+               }
 
                // If there is an error then take note of it..
-               if ( $this->last_error = mysql_error( $this->dbh ) ) {
+               if ( $this->use_mysqli ) {
+                       $this->last_error = mysqli_error( $this->dbh );
+               } else {
+                       $this->last_error = mysql_error( $this->dbh );
+               }
+
+               if ( $this->last_error ) {
+                       // Clear insert_id on a subsequent failed insert.
+                       if ( $this->insert_id && preg_match( '/^\s*(insert|replace)\s/i', $query ) )
+                               $this->insert_id = 0;
+
                        $this->print_error();
                        return false;
                }
@@ -1212,18 +1683,33 @@ class wpdb {
                if ( preg_match( '/^\s*(create|alter|truncate|drop)\s/i', $query ) ) {
                        $return_val = $this->result;
                } elseif ( preg_match( '/^\s*(insert|delete|update|replace)\s/i', $query ) ) {
-                       $this->rows_affected = mysql_affected_rows( $this->dbh );
+                       if ( $this->use_mysqli ) {
+                               $this->rows_affected = mysqli_affected_rows( $this->dbh );
+                       } else {
+                               $this->rows_affected = mysql_affected_rows( $this->dbh );
+                       }
                        // Take note of the insert_id
                        if ( preg_match( '/^\s*(insert|replace)\s/i', $query ) ) {
-                               $this->insert_id = mysql_insert_id($this->dbh);
+                               if ( $this->use_mysqli ) {
+                                       $this->insert_id = mysqli_insert_id( $this->dbh );
+                               } else {
+                                       $this->insert_id = mysql_insert_id( $this->dbh );
+                               }
                        }
                        // Return number of rows affected
                        $return_val = $this->rows_affected;
                } else {
                        $num_rows = 0;
-                       while ( $row = @mysql_fetch_object( $this->result ) ) {
-                               $this->last_result[$num_rows] = $row;
-                               $num_rows++;
+                       if ( $this->use_mysqli && $this->result instanceof mysqli_result ) {
+                               while ( $row = @mysqli_fetch_object( $this->result ) ) {
+                                       $this->last_result[$num_rows] = $row;
+                                       $num_rows++;
+                               }
+                       } elseif ( is_resource( $this->result ) ) {
+                               while ( $row = @mysql_fetch_object( $this->result ) ) {
+                                       $this->last_result[$num_rows] = $row;
+                                       $num_rows++;
+                               }
                        }
 
                        // Log number of rows the query returned
@@ -1235,13 +1721,38 @@ class wpdb {
                return $return_val;
        }
 
+       /**
+        * Internal function to perform the mysql_query() call.
+        *
+        * @since 3.9.0
+        *
+        * @access private
+        * @see wpdb::query()
+        *
+        * @param string $query The query to run.
+        */
+       private function _do_query( $query ) {
+               if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES ) {
+                       $this->timer_start();
+               }
+
+               if ( $this->use_mysqli ) {
+                       $this->result = @mysqli_query( $this->dbh, $query );
+               } else {
+                       $this->result = @mysql_query( $query, $this->dbh );
+               }
+               $this->num_queries++;
+
+               if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES ) {
+                       $this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );
+               }
+       }
+
        /**
         * Insert a row into a table.
         *
-        * <code>
-        * wpdb::insert( 'table', array( 'column' => 'foo', 'field' => 'bar' ) )
-        * wpdb::insert( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( '%s', '%d' ) )
-        * </code>
+        *     wpdb::insert( 'table', array( 'column' => 'foo', 'field' => 'bar' ) )
+        *     wpdb::insert( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( '%s', '%d' ) )
         *
         * @since 2.5.0
         * @see wpdb::prepare()
@@ -1254,17 +1765,15 @@ class wpdb {
         *      A format is one of '%d', '%f', '%s' (integer, float, string). If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @return int|false The number of rows inserted, or false on error.
         */
-       function insert( $table, $data, $format = null ) {
+       public function insert( $table, $data, $format = null ) {
                return $this->_insert_replace_helper( $table, $data, $format, 'INSERT' );
        }
 
        /**
         * Replace a row into a table.
         *
-        * <code>
-        * wpdb::replace( 'table', array( 'column' => 'foo', 'field' => 'bar' ) )
-        * wpdb::replace( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( '%s', '%d' ) )
-        * </code>
+        *     wpdb::replace( 'table', array( 'column' => 'foo', 'field' => 'bar' ) )
+        *     wpdb::replace( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( '%s', '%d' ) )
         *
         * @since 3.0.0
         * @see wpdb::prepare()
@@ -1277,7 +1786,7 @@ class wpdb {
         *      A format is one of '%d', '%f', '%s' (integer, float, string). If omitted, all values in $data will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @return int|false The number of rows affected, or false on error.
         */
-       function replace( $table, $data, $format = null ) {
+       public function replace( $table, $data, $format = null ) {
                return $this->_insert_replace_helper( $table, $data, $format, 'REPLACE' );
        }
 
@@ -1300,34 +1809,39 @@ class wpdb {
         * @return int|false The number of rows affected, or false on error.
         */
        function _insert_replace_helper( $table, $data, $format = null, $type = 'INSERT' ) {
-               if ( ! in_array( strtoupper( $type ), array( 'REPLACE', 'INSERT' ) ) )
-                       return false;
                $this->insert_id = 0;
-               $formats = $format = (array) $format;
-               $fields = array_keys( $data );
-               $formatted_fields = array();
-               foreach ( $fields as $field ) {
-                       if ( !empty( $format ) )
-                               $form = ( $form = array_shift( $formats ) ) ? $form : $format[0];
-                       elseif ( isset( $this->field_types[$field] ) )
-                               $form = $this->field_types[$field];
-                       else
-                               $form = '%s';
-                       $formatted_fields[] = $form;
+
+               if ( ! in_array( strtoupper( $type ), array( 'REPLACE', 'INSERT' ) ) ) {
+                       return false;
                }
-               $sql = "{$type} INTO `$table` (`" . implode( '`,`', $fields ) . "`) VALUES (" . implode( ",", $formatted_fields ) . ")";
-               return $this->query( $this->prepare( $sql, $data ) );
-       }
 
-       /**
-        * Update a row in the table
-        *
-        * <code>
-        * wpdb::update( 'table', array( 'column' => 'foo', 'field' => 'bar' ), array( 'ID' => 1 ) )
-        * wpdb::update( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( 'ID' => 1 ), array( '%s', '%d' ), array( '%d' ) )
-        * </code>
-        *
-        * @since 2.5.0
+               $data = $this->process_fields( $table, $data, $format );
+               if ( false === $data ) {
+                       return false;
+               }
+
+               $formats = $values = array();
+               foreach ( $data as $value ) {
+                       $formats[] = $value['format'];
+                       $values[]  = $value['value'];
+               }
+
+               $fields  = '`' . implode( '`, `', array_keys( $data ) ) . '`';
+               $formats = implode( ', ', $formats );
+
+               $sql = "$type INTO `$table` ($fields) VALUES ($formats)";
+
+               $this->check_current_query = false;
+               return $this->query( $this->prepare( $sql, $values ) );
+       }
+
+       /**
+        * Update a row in the table
+        *
+        *     wpdb::update( 'table', array( 'column' => 'foo', 'field' => 'bar' ), array( 'ID' => 1 ) )
+        *     wpdb::update( 'table', array( 'column' => 'foo', 'field' => 1337 ), array( 'ID' => 1 ), array( '%s', '%d' ), array( '%d' ) )
+        *
+        * @since 2.5.0
         * @see wpdb::prepare()
         * @see wpdb::$field_types
         * @see wp_set_wpdb_vars()
@@ -1340,44 +1854,44 @@ class wpdb {
         * @param array|string $where_format Optional. An array of formats to be mapped to each of the values in $where. If string, that format will be used for all of the items in $where. A format is one of '%d', '%f', '%s' (integer, float, string). If omitted, all values in $where will be treated as strings.
         * @return int|false The number of rows updated, or false on error.
         */
-       function update( $table, $data, $where, $format = null, $where_format = null ) {
-               if ( ! is_array( $data ) || ! is_array( $where ) )
+       public function update( $table, $data, $where, $format = null, $where_format = null ) {
+               if ( ! is_array( $data ) || ! is_array( $where ) ) {
                        return false;
+               }
 
-               $formats = $format = (array) $format;
-               $bits = $wheres = array();
-               foreach ( (array) array_keys( $data ) as $field ) {
-                       if ( !empty( $format ) )
-                               $form = ( $form = array_shift( $formats ) ) ? $form : $format[0];
-                       elseif ( isset($this->field_types[$field]) )
-                               $form = $this->field_types[$field];
-                       else
-                               $form = '%s';
-                       $bits[] = "`$field` = {$form}";
+               $data = $this->process_fields( $table, $data, $format );
+               if ( false === $data ) {
+                       return false;
+               }
+               $where = $this->process_fields( $table, $where, $where_format );
+               if ( false === $where ) {
+                       return false;
                }
 
-               $where_formats = $where_format = (array) $where_format;
-               foreach ( (array) array_keys( $where ) as $field ) {
-                       if ( !empty( $where_format ) )
-                               $form = ( $form = array_shift( $where_formats ) ) ? $form : $where_format[0];
-                       elseif ( isset( $this->field_types[$field] ) )
-                               $form = $this->field_types[$field];
-                       else
-                               $form = '%s';
-                       $wheres[] = "`$field` = {$form}";
+               $fields = $conditions = $values = array();
+               foreach ( $data as $field => $value ) {
+                       $fields[] = "`$field` = " . $value['format'];
+                       $values[] = $value['value'];
                }
+               foreach ( $where as $field => $value ) {
+                       $conditions[] = "`$field` = " . $value['format'];
+                       $values[] = $value['value'];
+               }
+
+               $fields = implode( ', ', $fields );
+               $conditions = implode( ' AND ', $conditions );
 
-               $sql = "UPDATE `$table` SET " . implode( ', ', $bits ) . ' WHERE ' . implode( ' AND ', $wheres );
-               return $this->query( $this->prepare( $sql, array_merge( array_values( $data ), array_values( $where ) ) ) );
+               $sql = "UPDATE `$table` SET $fields WHERE $conditions";
+
+               $this->check_current_query = false;
+               return $this->query( $this->prepare( $sql, $values ) );
        }
 
        /**
         * Delete a row in the table
         *
-        * <code>
-        * wpdb::delete( 'table', array( 'ID' => 1 ) )
-        * wpdb::delete( 'table', array( 'ID' => 1 ), array( '%d' ) )
-        * </code>
+        *     wpdb::delete( 'table', array( 'ID' => 1 ) )
+        *     wpdb::delete( 'table', array( 'ID' => 1 ), array( '%d' ) )
         *
         * @since 3.4.0
         * @see wpdb::prepare()
@@ -1389,30 +1903,167 @@ class wpdb {
         * @param array|string $where_format Optional. An array of formats to be mapped to each of the values in $where. If string, that format will be used for all of the items in $where. A format is one of '%d', '%f', '%s' (integer, float, string). If omitted, all values in $where will be treated as strings unless otherwise specified in wpdb::$field_types.
         * @return int|false The number of rows updated, or false on error.
         */
-       function delete( $table, $where, $where_format = null ) {
-               if ( ! is_array( $where ) )
+       public function delete( $table, $where, $where_format = null ) {
+               if ( ! is_array( $where ) ) {
+                       return false;
+               }
+
+               $where = $this->process_fields( $table, $where, $where_format );
+               if ( false === $where ) {
+                       return false;
+               }
+
+               $conditions = $values = array();
+               foreach ( $where as $field => $value ) {
+                       $conditions[] = "`$field` = " . $value['format'];
+                       $values[] = $value['value'];
+               }
+
+               $conditions = implode( ' AND ', $conditions );
+
+               $sql = "DELETE FROM `$table` WHERE $conditions";
+
+               $this->check_current_query = false;
+               return $this->query( $this->prepare( $sql, $values ) );
+       }
+
+       /**
+        * Processes arrays of field/value pairs and field formats.
+        *
+        * This is a helper method for wpdb's CRUD methods, which take field/value
+        * pairs for inserts, updates, and where clauses. This method first pairs
+        * each value with a format. Then it determines the charset of that field,
+        * using that to determine if any invalid text would be stripped. If text is
+        * stripped, then field processing is rejected and the query fails.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param string $table  Table name.
+        * @param array  $data   Field/value pair.
+        * @param mixed  $format Format for each field.
+        * @return array|bool Returns an array of fields that contain paired values
+        *                    and formats. Returns false for invalid values.
+        */
+       protected function process_fields( $table, $data, $format ) {
+               $data = $this->process_field_formats( $data, $format );
+               if ( false === $data ) {
+                       return false;
+               }
+
+               $data = $this->process_field_charsets( $data, $table );
+               if ( false === $data ) {
+                       return false;
+               }
+
+               $data = $this->process_field_lengths( $data, $table );
+               if ( false === $data ) {
                        return false;
+               }
+
+               $converted_data = $this->strip_invalid_text( $data );
+
+               if ( $data !== $converted_data ) {
+                       return false;
+               }
+
+               return $data;
+       }
 
-               $bits = $wheres = array();
+       /**
+        * Prepares arrays of value/format pairs as passed to wpdb CRUD methods.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param array $data   Array of fields to values.
+        * @param mixed $format Formats to be mapped to the values in $data.
+        * @return array Array, keyed by field names with values being an array
+        *               of 'value' and 'format' keys.
+        */
+       protected function process_field_formats( $data, $format ) {
+               $formats = $original_formats = (array) $format;
 
-               $where_formats = $where_format = (array) $where_format;
+               foreach ( $data as $field => $value ) {
+                       $value = array(
+                               'value'  => $value,
+                               'format' => '%s',
+                       );
 
-               foreach ( array_keys( $where ) as $field ) {
-                       if ( !empty( $where_format ) ) {
-                               $form = ( $form = array_shift( $where_formats ) ) ? $form : $where_format[0];
+                       if ( ! empty( $format ) ) {
+                               $value['format'] = array_shift( $formats );
+                               if ( ! $value['format'] ) {
+                                       $value['format'] = reset( $original_formats );
+                               }
                        } elseif ( isset( $this->field_types[ $field ] ) ) {
-                               $form = $this->field_types[ $field ];
+                               $value['format'] = $this->field_types[ $field ];
+                       }
+
+                       $data[ $field ] = $value;
+               }
+
+               return $data;
+       }
+
+       /**
+        * Adds field charsets to field/value/format arrays generated by
+        * the wpdb::process_field_formats() method.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param array  $data  As it comes from the wpdb::process_field_formats() method.
+        * @param string $table Table name.
+        * @return The same array as $data with additional 'charset' keys.
+        */
+       protected function process_field_charsets( $data, $table ) {
+               foreach ( $data as $field => $value ) {
+                       if ( '%d' === $value['format'] || '%f' === $value['format'] ) {
+                               // We can skip this field if we know it isn't a string.
+                               // This checks %d/%f versus ! %s because it's sprintf() could take more.
+                               $value['charset'] = false;
                        } else {
-                               $form = '%s';
+                               $value['charset'] = $this->get_col_charset( $table, $field );
+                               if ( is_wp_error( $value['charset'] ) ) {
+                                       return false;
+                               }
                        }
 
-                       $wheres[] = "$field = $form";
+                       $data[ $field ] = $value;
                }
 
-               $sql = "DELETE FROM $table WHERE " . implode( ' AND ', $wheres );
-               return $this->query( $this->prepare( $sql, $where ) );
+               return $data;
        }
 
+       /**
+        * For string fields, record the maximum string length that field can safely save.
+        *
+        * @since 4.2.1
+        * @access protected
+        *
+        * @param array  $data  As it comes from the wpdb::process_field_charsets() method.
+        * @param string $table Table name.
+        * @return array|False The same array as $data with additional 'length' keys, or false if
+        *                     any of the values were too long for their corresponding field.
+        */
+       protected function process_field_lengths( $data, $table ) {
+               foreach ( $data as $field => $value ) {
+                       if ( '%d' === $value['format'] || '%f' === $value['format'] ) {
+                               // We can skip this field if we know it isn't a string.
+                               // This checks %d/%f versus ! %s because it's sprintf() could take more.
+                               $value['length'] = false;
+                       } else {
+                               $value['length'] = $this->get_col_length( $table, $field );
+                               if ( is_wp_error( $value['length'] ) ) {
+                                       return false;
+                               }
+                       }
+
+                       $data[ $field ] = $value;
+               }
+
+               return $data;
+       }
 
        /**
         * Retrieve one variable from the database.
@@ -1428,10 +2079,16 @@ class wpdb {
         * @param int $y Optional. Row of value to return. Indexed from 0.
         * @return string|null Database query result (as string), or null on failure
         */
-       function get_var( $query = null, $x = 0, $y = 0 ) {
+       public function get_var( $query = null, $x = 0, $y = 0 ) {
                $this->func_call = "\$db->get_var(\"$query\", $x, $y)";
-               if ( $query )
+
+               if ( $this->check_safe_collation( $query ) ) {
+                       $this->check_current_query = false;
+               }
+
+               if ( $query ) {
                        $this->query( $query );
+               }
 
                // Extract var out of cached results based x,y vals
                if ( !empty( $this->last_result[$y] ) ) {
@@ -1455,12 +2112,18 @@ class wpdb {
         * @param int $y Optional. Row to return. Indexed from 0.
         * @return mixed Database query result in format specified by $output or null on failure
         */
-       function get_row( $query = null, $output = OBJECT, $y = 0 ) {
+       public function get_row( $query = null, $output = OBJECT, $y = 0 ) {
                $this->func_call = "\$db->get_row(\"$query\",$output,$y)";
-               if ( $query )
+
+               if ( $this->check_safe_collation( $query ) ) {
+                       $this->check_current_query = false;
+               }
+
+               if ( $query ) {
                        $this->query( $query );
-               else
+               } else {
                        return null;
+               }
 
                if ( !isset( $this->last_result[$y] ) )
                        return null;
@@ -1471,6 +2134,9 @@ class wpdb {
                        return $this->last_result[$y] ? get_object_vars( $this->last_result[$y] ) : null;
                } elseif ( $output == ARRAY_N ) {
                        return $this->last_result[$y] ? array_values( get_object_vars( $this->last_result[$y] ) ) : null;
+               } elseif ( strtoupper( $output ) === OBJECT ) {
+                       // Back compat for OBJECT being previously case insensitive.
+                       return $this->last_result[$y] ? $this->last_result[$y] : null;
                } else {
                        $this->print_error( " \$db->get_row(string query, output type, int offset) -- Output type must be one of: OBJECT, ARRAY_A, ARRAY_N" );
                }
@@ -1489,9 +2155,14 @@ class wpdb {
         * @param int $x Optional. Column to return. Indexed from 0.
         * @return array Database query result. Array indexed from 0 by SQL result row number.
         */
-       function get_col( $query = null , $x = 0 ) {
-               if ( $query )
+       public function get_col( $query = null , $x = 0 ) {
+               if ( $this->check_safe_collation( $query ) ) {
+                       $this->check_current_query = false;
+               }
+
+               if ( $query ) {
                        $this->query( $query );
+               }
 
                $new_array = array();
                // Extract the column values
@@ -1514,13 +2185,18 @@ class wpdb {
         *      With OBJECT_K, return an associative array of row objects keyed by the value of each row's first column's value. Duplicate keys are discarded.
         * @return mixed Database query results
         */
-       function get_results( $query = null, $output = OBJECT ) {
+       public function get_results( $query = null, $output = OBJECT ) {
                $this->func_call = "\$db->get_results(\"$query\", $output)";
 
-               if ( $query )
+               if ( $this->check_safe_collation( $query ) ) {
+                       $this->check_current_query = false;
+               }
+
+               if ( $query ) {
                        $this->query( $query );
-               else
+               } else {
                        return null;
+               }
 
                $new_array = array();
                if ( $output == OBJECT ) {
@@ -1550,10 +2226,661 @@ class wpdb {
                                }
                        }
                        return $new_array;
+               } elseif ( strtoupper( $output ) === OBJECT ) {
+                       // Back compat for OBJECT being previously case insensitive.
+                       return $this->last_result;
                }
                return null;
        }
 
+       /**
+        * Retrieves the character set for the given table.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param string $table Table name.
+        * @return string|WP_Error Table character set, WP_Error object if it couldn't be found.
+        */
+       protected function get_table_charset( $table ) {
+               $tablekey = strtolower( $table );
+
+               /**
+                * Filter the table charset value before the DB is checked.
+                *
+                * Passing a non-null value to the filter will effectively short-circuit
+                * checking the DB for the charset, returning that value instead.
+                *
+                * @since 4.2.0
+                *
+                * @param string $charset The character set to use. Default null.
+                * @param string $table   The name of the table being checked.
+                */
+               $charset = apply_filters( 'pre_get_table_charset', null, $table );
+               if ( null !== $charset ) {
+                       return $charset;
+               }
+
+               if ( isset( $this->table_charset[ $tablekey ] ) ) {
+                       return $this->table_charset[ $tablekey ];
+               }
+
+               $charsets = $columns = array();
+
+               $table_parts = explode( '.', $table );
+               $table = '`' . implode( '`.`', $table_parts ) . '`';
+               $results = $this->get_results( "SHOW FULL COLUMNS FROM $table" );
+               if ( ! $results ) {
+                       return new WP_Error( 'wpdb_get_table_charset_failure' );
+               }
+
+               foreach ( $results as $column ) {
+                       $columns[ strtolower( $column->Field ) ] = $column;
+               }
+
+               $this->col_meta[ $tablekey ] = $columns;
+
+               foreach ( $columns as $column ) {
+                       if ( ! empty( $column->Collation ) ) {
+                               list( $charset ) = explode( '_', $column->Collation );
+
+                               // If the current connection can't support utf8mb4 characters, let's only send 3-byte utf8 characters.
+                               if ( 'utf8mb4' === $charset && ! $this->has_cap( 'utf8mb4' ) ) {
+                                       $charset = 'utf8';
+                               }
+
+                               $charsets[ strtolower( $charset ) ] = true;
+                       }
+
+                       list( $type ) = explode( '(', $column->Type );
+
+                       // A binary/blob means the whole query gets treated like this.
+                       if ( in_array( strtoupper( $type ), array( 'BINARY', 'VARBINARY', 'TINYBLOB', 'MEDIUMBLOB', 'BLOB', 'LONGBLOB' ) ) ) {
+                               $this->table_charset[ $tablekey ] = 'binary';
+                               return 'binary';
+                       }
+               }
+
+               // utf8mb3 is an alias for utf8.
+               if ( isset( $charsets['utf8mb3'] ) ) {
+                       $charsets['utf8'] = true;
+                       unset( $charsets['utf8mb3'] );
+               }
+
+               // Check if we have more than one charset in play.
+               $count = count( $charsets );
+               if ( 1 === $count ) {
+                       $charset = key( $charsets );
+               } elseif ( 0 === $count ) {
+                       // No charsets, assume this table can store whatever.
+                       $charset = false;
+               } else {
+                       // More than one charset. Remove latin1 if present and recalculate.
+                       unset( $charsets['latin1'] );
+                       $count = count( $charsets );
+                       if ( 1 === $count ) {
+                               // Only one charset (besides latin1).
+                               $charset = key( $charsets );
+                       } elseif ( 2 === $count && isset( $charsets['utf8'], $charsets['utf8mb4'] ) ) {
+                               // Two charsets, but they're utf8 and utf8mb4, use utf8.
+                               $charset = 'utf8';
+                       } else {
+                               // Two mixed character sets. ascii.
+                               $charset = 'ascii';
+                       }
+               }
+
+               $this->table_charset[ $tablekey ] = $charset;
+               return $charset;
+       }
+
+       /**
+        * Retrieves the character set for the given column.
+        *
+        * @since 4.2.0
+        * @access public
+        *
+        * @param string $table  Table name.
+        * @param string $column Column name.
+        * @return mixed Column character set as a string. False if the column has no
+        *               character set. WP_Error object if there was an error.
+        */
+       public function get_col_charset( $table, $column ) {
+               $tablekey = strtolower( $table );
+               $columnkey = strtolower( $column );
+
+               /**
+                * Filter the column charset value before the DB is checked.
+                *
+                * Passing a non-null value to the filter will short-circuit
+                * checking the DB for the charset, returning that value instead.
+                *
+                * @since 4.2.0
+                *
+                * @param string $charset The character set to use. Default null.
+                * @param string $table   The name of the table being checked.
+                * @param string $column  The name of the column being checked.
+                */
+               $charset = apply_filters( 'pre_get_col_charset', null, $table, $column );
+               if ( null !== $charset ) {
+                       return $charset;
+               }
+
+               // Skip this entirely if this isn't a MySQL database.
+               if ( false === $this->is_mysql ) {
+                       return false;
+               }
+
+               if ( empty( $this->table_charset[ $tablekey ] ) ) {
+                       // This primes column information for us.
+                       $table_charset = $this->get_table_charset( $table );
+                       if ( is_wp_error( $table_charset ) ) {
+                               return $table_charset;
+                       }
+               }
+
+               // If still no column information, return the table charset.
+               if ( empty( $this->col_meta[ $tablekey ] ) ) {
+                       return $this->table_charset[ $tablekey ];
+               }
+
+               // If this column doesn't exist, return the table charset.
+               if ( empty( $this->col_meta[ $tablekey ][ $columnkey ] ) ) {
+                       return $this->table_charset[ $tablekey ];
+               }
+
+               // Return false when it's not a string column.
+               if ( empty( $this->col_meta[ $tablekey ][ $columnkey ]->Collation ) ) {
+                       return false;
+               }
+
+               list( $charset ) = explode( '_', $this->col_meta[ $tablekey ][ $columnkey ]->Collation );
+               return $charset;
+       }
+
+       /**
+        * Retrieve the maximum string length allowed in a given column.
+        * The length may either be specified as a byte length or a character length.
+        *
+        * @since 4.2.1
+        * @access public
+        *
+        * @param string $table  Table name.
+        * @param string $column Column name.
+        * @return mixed array( 'length' => (int), 'type' => 'byte' | 'char' )
+        *               false if the column has no length (for example, numeric column)
+        *               WP_Error object if there was an error.
+        */
+       public function get_col_length( $table, $column ) {
+               $tablekey = strtolower( $table );
+               $columnkey = strtolower( $column );
+
+               // Skip this entirely if this isn't a MySQL database.
+               if ( false === $this->is_mysql ) {
+                       return false;
+               }
+
+               if ( empty( $this->col_meta[ $tablekey ] ) ) {
+                       // This primes column information for us.
+                       $table_charset = $this->get_table_charset( $table );
+                       if ( is_wp_error( $table_charset ) ) {
+                               return $table_charset;
+                       }
+               }
+
+               if ( empty( $this->col_meta[ $tablekey ][ $columnkey ] ) ) {
+                       return false;
+               }
+
+               $typeinfo = explode( '(', $this->col_meta[ $tablekey ][ $columnkey ]->Type );
+
+               $type = strtolower( $typeinfo[0] );
+               if ( ! empty( $typeinfo[1] ) ) {
+                       $length = trim( $typeinfo[1], ')' );
+               } else {
+                       $length = false;
+               }
+
+               switch( $type ) {
+                       case 'char':
+                       case 'varchar':
+                               return array(
+                                       'type'   => 'char',
+                                       'length' => (int) $length,
+                               );
+                               break;
+                       case 'binary':
+                       case 'varbinary':
+                               return array(
+                                       'type'   => 'byte',
+                                       'length' => (int) $length,
+                               );
+                               break;
+                       case 'tinyblob':
+                       case 'tinytext':
+                               return array(
+                                       'type'   => 'byte',
+                                       'length' => 255,        // 2^8 - 1
+                               );
+                               break;
+                       case 'blob':
+                       case 'text':
+                               return array(
+                                       'type'   => 'byte',
+                                       'length' => 65535,      // 2^16 - 1
+                               );
+                               break;
+                       case 'mediumblob':
+                       case 'mediumtext':
+                               return array(
+                                       'type'   => 'byte',
+                                       'length' => 16777215,   // 2^24 - 1
+                               );
+                               break;
+                       case 'longblob':
+                       case 'longtext':
+                               return array(
+                                       'type'   => 'byte',
+                                       'length' => 4294967295, // 2^32 - 1
+                               );
+                               break;
+                       default:
+                               return false;
+               }
+
+               return false;
+       }
+
+       /**
+        * Check if a string is ASCII.
+        *
+        * The negative regex is faster for non-ASCII strings, as it allows
+        * the search to finish as soon as it encounters a non-ASCII character.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param string $string String to check.
+        * @return bool True if ASCII, false if not.
+        */
+       protected function check_ascii( $string ) {
+               if ( function_exists( 'mb_check_encoding' ) ) {
+                       if ( mb_check_encoding( $string, 'ASCII' ) ) {
+                               return true;
+                       }
+               } elseif ( ! preg_match( '/[^\x00-\x7F]/', $string ) ) {
+                       return true;
+               }
+
+               return false;
+       }
+
+       /**
+        * Check if the query is accessing a collation considered safe on the current version of MySQL.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param string $query The query to check.
+        * @return bool True if the collation is safe, false if it isn't.
+        */
+       protected function check_safe_collation( $query ) {
+               if ( $this->checking_collation ) {
+                       return true;
+               }
+
+               // We don't need to check the collation for queries that don't read data.
+               $query = ltrim( $query, "\r\n\t (" );
+               if ( preg_match( '/^(?:SHOW|DESCRIBE|DESC|EXPLAIN|CREATE)\s/i', $query ) ) {
+                       return true;
+               }
+
+               // All-ASCII queries don't need extra checking.
+               if ( $this->check_ascii( $query ) ) {
+                       return true;
+               }
+
+               $table = $this->get_table_from_query( $query );
+               if ( ! $table ) {
+                       return false;
+               }
+
+               $this->checking_collation = true;
+               $collation = $this->get_table_charset( $table );
+               $this->checking_collation = false;
+
+               // Tables with no collation, or latin1 only, don't need extra checking.
+               if ( false === $collation || 'latin1' === $collation ) {
+                       return true;
+               }
+
+               $table = strtolower( $table );
+               if ( empty( $this->col_meta[ $table ] ) ) {
+                       return false;
+               }
+
+               // If any of the columns don't have one of these collations, it needs more sanity checking.
+               foreach( $this->col_meta[ $table ] as $col ) {
+                       if ( empty( $col->Collation ) ) {
+                               continue;
+                       }
+
+                       if ( ! in_array( $col->Collation, array( 'utf8_general_ci', 'utf8_bin', 'utf8mb4_general_ci', 'utf8mb4_bin' ), true ) ) {
+                               return false;
+                       }
+               }
+
+               return true;
+       }
+
+       /**
+        * Strips any invalid characters based on value/charset pairs.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param array $data Array of value arrays. Each value array has the keys
+        *                    'value' and 'charset'. An optional 'ascii' key can be
+        *                    set to false to avoid redundant ASCII checks.
+        * @return array|WP_Error The $data parameter, with invalid characters removed from
+        *                        each value. This works as a passthrough: any additional keys
+        *                        such as 'field' are retained in each value array. If we cannot
+        *                        remove invalid characters, a WP_Error object is returned.
+        */
+       protected function strip_invalid_text( $data ) {
+               $db_check_string = false;
+
+               foreach ( $data as &$value ) {
+                       $charset = $value['charset'];
+
+                       if ( is_array( $value['length'] ) ) {
+                               $length = $value['length']['length'];
+                       } else {
+                               $length = false;
+                       }
+
+                       // There's no charset to work with.
+                       if ( false === $charset ) {
+                               continue;
+                       }
+
+                       // Column isn't a string.
+                       if ( ! is_string( $value['value'] ) ) {
+                               continue;
+                       }
+
+                       $truncate_by_byte_length = 'byte' === $value['length']['type'];
+
+                       $needs_validation = true;
+                       if (
+                               // latin1 can store any byte sequence
+                               'latin1' === $charset
+                       ||
+                               // ASCII is always OK.
+                               ( ! isset( $value['ascii'] ) && $this->check_ascii( $value['value'] ) )
+                       ) {
+                               $truncate_by_byte_length = true;
+                               $needs_validation = false;
+                       }
+
+                       if ( $truncate_by_byte_length ) {
+                               mbstring_binary_safe_encoding();
+                               if ( false !== $length && strlen( $value['value'] ) > $length ) {
+                                       $value['value'] = substr( $value['value'], 0, $length );
+                               }
+                               reset_mbstring_encoding();
+
+                               if ( ! $needs_validation ) {
+                                       continue;
+                               }
+                       }
+
+                       // utf8 can be handled by regex, which is a bunch faster than a DB lookup.
+                       if ( ( 'utf8' === $charset || 'utf8mb3' === $charset || 'utf8mb4' === $charset ) && function_exists( 'mb_strlen' ) ) {
+                               $regex = '/
+                                       (
+                                               (?: [\x00-\x7F]                  # single-byte sequences   0xxxxxxx
+                                               |   [\xC2-\xDF][\x80-\xBF]       # double-byte sequences   110xxxxx 10xxxxxx
+                                               |   \xE0[\xA0-\xBF][\x80-\xBF]   # triple-byte sequences   1110xxxx 10xxxxxx * 2
+                                               |   [\xE1-\xEC][\x80-\xBF]{2}
+                                               |   \xED[\x80-\x9F][\x80-\xBF]
+                                               |   [\xEE-\xEF][\x80-\xBF]{2}';
+
+                               if ( 'utf8mb4' === $charset ) {
+                                       $regex .= '
+                                               |    \xF0[\x90-\xBF][\x80-\xBF]{2} # four-byte sequences   11110xxx 10xxxxxx * 3
+                                               |    [\xF1-\xF3][\x80-\xBF]{3}
+                                               |    \xF4[\x80-\x8F][\x80-\xBF]{2}
+                                       ';
+                               }
+
+                               $regex .= '){1,40}                          # ...one or more times
+                                       )
+                                       | .                                  # anything else
+                                       /x';
+                               $value['value'] = preg_replace( $regex, '$1', $value['value'] );
+
+
+                               if ( false !== $length && mb_strlen( $value['value'], 'UTF-8' ) > $length ) {
+                                       $value['value'] = mb_substr( $value['value'], 0, $length, 'UTF-8' );
+                               }
+                               continue;
+                       }
+
+                       // We couldn't use any local conversions, send it to the DB.
+                       $value['db'] = $db_check_string = true;
+               }
+               unset( $value ); // Remove by reference.
+
+               if ( $db_check_string ) {
+                       $queries = array();
+                       foreach ( $data as $col => $value ) {
+                               if ( ! empty( $value['db'] ) ) {
+                                       if ( ! isset( $queries[ $value['charset'] ] ) ) {
+                                               $queries[ $value['charset'] ] = array();
+                                       }
+
+                                       // We're going to need to truncate by characters or bytes, depending on the length value we have.
+                                       if ( 'byte' === $value['length']['type'] ) {
+                                               // Split the CONVERT() calls by charset, so we can make sure the connection is right
+                                               $queries[ $value['charset'] ][ $col ] = $this->prepare( "CONVERT( LEFT( CONVERT( %s USING binary ), %d ) USING {$value['charset']} )", $value['value'], $value['length']['length'] );
+                                       } else {
+                                               $queries[ $value['charset'] ][ $col ] = $this->prepare( "LEFT( CONVERT( %s USING {$value['charset']} ), %d )", $value['value'], $value['length']['length'] );
+                                       }
+
+                                       unset( $data[ $col ]['db'] );
+                               }
+                       }
+
+                       $connection_charset = $this->charset;
+                       foreach ( $queries as $charset => $query ) {
+                               if ( ! $query ) {
+                                       continue;
+                               }
+
+                               // Change the charset to match the string(s) we're converting
+                               if ( $charset !== $connection_charset ) {
+                                       $connection_charset = $charset;
+                                       $this->set_charset( $this->dbh, $charset );
+                               }
+
+                               $this->check_current_query = false;
+
+                               $sql = array();
+                               foreach ( $query as $column => $column_query ) {
+                                       $sql[] = $column_query . " AS x_$column";
+                               }
+
+                               $row = $this->get_row( "SELECT " . implode( ', ', $sql ), ARRAY_A );
+                               if ( ! $row ) {
+                                       $this->set_charset( $this->dbh, $connection_charset );
+                                       return new WP_Error( 'wpdb_strip_invalid_text_failure' );
+                               }
+
+                               foreach ( array_keys( $query ) as $column ) {
+                                       $data[ $column ]['value'] = $row["x_$column"];
+                               }
+                       }
+
+                       // Don't forget to change the charset back!
+                       if ( $connection_charset !== $this->charset ) {
+                               $this->set_charset( $this->dbh );
+                       }
+               }
+
+               return $data;
+       }
+
+       /**
+        * Strips any invalid characters from the query.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param string $query Query to convert.
+        * @return string|WP_Error The converted query, or a WP_Error object if the conversion fails.
+        */
+       protected function strip_invalid_text_from_query( $query ) {
+               // We don't need to check the collation for queries that don't read data.
+               $trimmed_query = ltrim( $query, "\r\n\t (" );
+               if ( preg_match( '/^(?:SHOW|DESCRIBE|DESC|EXPLAIN|CREATE)\s/i', $trimmed_query ) ) {
+                       return $query;
+               }
+
+               $table = $this->get_table_from_query( $query );
+               if ( $table ) {
+                       $charset = $this->get_table_charset( $table );
+                       if ( is_wp_error( $charset ) ) {
+                               return $charset;
+                       }
+
+                       // We can't reliably strip text from tables containing binary/blob columns
+                       if ( 'binary' === $charset ) {
+                               return $query;
+                       }
+               } else {
+                       $charset = $this->charset;
+               }
+
+               $data = array(
+                       'value'   => $query,
+                       'charset' => $charset,
+                       'ascii'   => false,
+                       'length'  => false,
+               );
+
+               $data = $this->strip_invalid_text( array( $data ) );
+               if ( is_wp_error( $data ) ) {
+                       return $data;
+               }
+
+               return $data[0]['value'];
+       }
+
+       /**
+        * Strips any invalid characters from the string for a given table and column.
+        *
+        * @since 4.2.0
+        * @access public
+        *
+        * @param string $table  Table name.
+        * @param string $column Column name.
+        * @param string $value  The text to check.
+        * @return string|WP_Error The converted string, or a WP_Error object if the conversion fails.
+        */
+       public function strip_invalid_text_for_column( $table, $column, $value ) {
+               if ( ! is_string( $value ) ) {
+                       return $value;
+               }
+
+               $charset = $this->get_col_charset( $table, $column );
+               if ( ! $charset ) {
+                       // Not a string column.
+                       return $value;
+               } elseif ( is_wp_error( $charset ) ) {
+                       // Bail on real errors.
+                       return $charset;
+               }
+
+               $data = array(
+                       $column => array(
+                               'value'   => $value,
+                               'charset' => $charset,
+                               'length'  => $this->get_col_length( $table, $column ),
+                       )
+               );
+
+               $data = $this->strip_invalid_text( $data );
+               if ( is_wp_error( $data ) ) {
+                       return $data;
+               }
+
+               return $data[ $column ]['value'];
+       }
+
+       /**
+        * Find the first table name referenced in a query.
+        *
+        * @since 4.2.0
+        * @access protected
+        *
+        * @param string $query The query to search.
+        * @return string|false $table The table name found, or false if a table couldn't be found.
+        */
+       protected function get_table_from_query( $query ) {
+               // Remove characters that can legally trail the table name.
+               $query = rtrim( $query, ';/-#' );
+
+               // Allow (select...) union [...] style queries. Use the first query's table name.
+               $query = ltrim( $query, "\r\n\t (" );
+
+               /*
+                * Strip everything between parentheses except nested selects and use only 1,000
+                * chars of the query.
+                */
+               $query = preg_replace( '/\((?!\s*select)[^(]*?\)/is', '()', substr( $query, 0, 1000 ) );
+
+               // Quickly match most common queries.
+               if ( preg_match( '/^\s*(?:'
+                               . 'SELECT.*?\s+FROM'
+                               . '|INSERT(?:\s+LOW_PRIORITY|\s+DELAYED|\s+HIGH_PRIORITY)?(?:\s+IGNORE)?(?:\s+INTO)?'
+                               . '|REPLACE(?:\s+LOW_PRIORITY|\s+DELAYED)?(?:\s+INTO)?'
+                               . '|UPDATE(?:\s+LOW_PRIORITY)?(?:\s+IGNORE)?'
+                               . '|DELETE(?:\s+LOW_PRIORITY|\s+QUICK|\s+IGNORE)*(?:\s+FROM)?'
+                               . ')\s+((?:[0-9a-zA-Z$_.`]|[\xC2-\xDF][\x80-\xBF])+)/is', $query, $maybe ) ) {
+                       return str_replace( '`', '', $maybe[1] );
+               }
+
+               // SHOW TABLE STATUS and SHOW TABLES
+               if ( preg_match( '/^\s*(?:'
+                               . 'SHOW\s+TABLE\s+STATUS.+(?:LIKE\s+|WHERE\s+Name\s*=\s*)'
+                               . '|SHOW\s+(?:FULL\s+)?TABLES.+(?:LIKE\s+|WHERE\s+Name\s*=\s*)'
+                               . ')\W((?:[0-9a-zA-Z$_.`]|[\xC2-\xDF][\x80-\xBF])+)\W/is', $query, $maybe ) ) {
+                       return str_replace( '`', '', $maybe[1] );
+               }
+
+               // Big pattern for the rest of the table-related queries.
+               if ( preg_match( '/^\s*(?:'
+                               . '(?:EXPLAIN\s+(?:EXTENDED\s+)?)?SELECT.*?\s+FROM'
+                               . '|DESCRIBE|DESC|EXPLAIN|HANDLER'
+                               . '|(?:LOCK|UNLOCK)\s+TABLE(?:S)?'
+                               . '|(?:RENAME|OPTIMIZE|BACKUP|RESTORE|CHECK|CHECKSUM|ANALYZE|REPAIR).*\s+TABLE'
+                               . '|TRUNCATE(?:\s+TABLE)?'
+                               . '|CREATE(?:\s+TEMPORARY)?\s+TABLE(?:\s+IF\s+NOT\s+EXISTS)?'
+                               . '|ALTER(?:\s+IGNORE)?\s+TABLE'
+                               . '|DROP\s+TABLE(?:\s+IF\s+EXISTS)?'
+                               . '|CREATE(?:\s+\w+)?\s+INDEX.*\s+ON'
+                               . '|DROP\s+INDEX.*\s+ON'
+                               . '|LOAD\s+DATA.*INFILE.*INTO\s+TABLE'
+                               . '|(?:GRANT|REVOKE).*ON\s+TABLE'
+                               . '|SHOW\s+(?:.*FROM|.*TABLE)'
+                               . ')\s+\(*\s*((?:[0-9a-zA-Z$_.`]|[\xC2-\xDF][\x80-\xBF])+)\s*\)*/is', $query, $maybe ) ) {
+                       return str_replace( '`', '', $maybe[1] );
+               }
+
+               return false;
+       }
+
        /**
         * Load the column metadata from the last query.
         *
@@ -1565,8 +2892,14 @@ class wpdb {
                if ( $this->col_info )
                        return;
 
-               for ( $i = 0; $i < @mysql_num_fields( $this->result ); $i++ ) {
-                       $this->col_info[ $i ] = @mysql_fetch_field( $this->result, $i );
+               if ( $this->use_mysqli ) {
+                       for ( $i = 0; $i < @mysqli_num_fields( $this->result ); $i++ ) {
+                               $this->col_info[ $i ] = @mysqli_fetch_field( $this->result );
+                       }
+               } else {
+                       for ( $i = 0; $i < @mysql_num_fields( $this->result ); $i++ ) {
+                               $this->col_info[ $i ] = @mysql_fetch_field( $this->result, $i );
+                       }
                }
        }
 
@@ -1579,7 +2912,7 @@ class wpdb {
         * @param int $col_offset Optional. 0: col name. 1: which table the col's in. 2: col's max length. 3: if the col is numeric. 4: col's type
         * @return mixed Column Results
         */
-       function get_col_info( $info_type = 'name', $col_offset = -1 ) {
+       public function get_col_info( $info_type = 'name', $col_offset = -1 ) {
                $this->load_col_info();
 
                if ( $this->col_info ) {
@@ -1602,9 +2935,9 @@ class wpdb {
         *
         * @since 1.5.0
         *
-        * @return true
+        * @return bool
         */
-       function timer_start() {
+       public function timer_start() {
                $this->time_start = microtime( true );
                return true;
        }
@@ -1616,7 +2949,7 @@ class wpdb {
         *
         * @return float Total time spent on the query, in seconds
         */
-       function timer_stop() {
+       public function timer_stop() {
                return ( microtime( true ) - $this->time_start );
        }
 
@@ -1631,7 +2964,7 @@ class wpdb {
         * @param string $error_code Optional. A Computer readable string to identify the error.
         * @return false|void
         */
-       function bail( $message, $error_code = '500' ) {
+       public function bail( $message, $error_code = '500' ) {
                if ( !$this->show_errors ) {
                        if ( class_exists( 'WP_Error' ) )
                                $this->error = new WP_Error($error_code, $message);
@@ -1651,7 +2984,7 @@ class wpdb {
         *
         * @return WP_Error
         */
-       function check_database_version() {
+       public function check_database_version() {
                global $wp_version, $required_mysql_version;
                // Make sure the server has the required MySQL version
                if ( version_compare($this->db_version(), $required_mysql_version, '<') )
@@ -1669,7 +3002,7 @@ class wpdb {
         *
         * @return bool True if collation is supported, false if version does not
         */
-       function supports_collation() {
+       public function supports_collation() {
                _deprecated_function( __FUNCTION__, '3.5', 'wpdb::has_cap( \'collation\' )' );
                return $this->has_cap( 'collation' );
        }
@@ -1693,25 +3026,49 @@ class wpdb {
        }
 
        /**
-        * Determine if a database supports a particular feature
+        * Determine if a database supports a particular feature.
         *
         * @since 2.7.0
-        * @see   wpdb::db_version()
+        * @since 4.1.0 Support was added for the 'utf8mb4' feature.
         *
-        * @param string $db_cap the feature
-        * @return bool
+        * @see wpdb::db_version()
+        *
+        * @param string $db_cap The feature to check for. Accepts 'collation',
+        *                       'group_concat', 'subqueries', 'set_charset',
+        *                       or 'utf8mb4'.
+        * @return bool Whether the database feature is supported, false otherwise.
         */
-       function has_cap( $db_cap ) {
+       public function has_cap( $db_cap ) {
                $version = $this->db_version();
 
                switch ( strtolower( $db_cap ) ) {
                        case 'collation' :    // @since 2.5.0
-                       case 'group_concat' : // @since 2.7
-                       case 'subqueries' :   // @since 2.7
+                       case 'group_concat' : // @since 2.7.0
+                       case 'subqueries' :   // @since 2.7.0
                                return version_compare( $version, '4.1', '>=' );
                        case 'set_charset' :
-                               return version_compare($version, '5.0.7', '>=');
-               };
+                               return version_compare( $version, '5.0.7', '>=' );
+                       case 'utf8mb4' :      // @since 4.1.0
+                               if ( version_compare( $version, '5.5.3', '<' ) ) {
+                                       return false;
+                               }
+                               if ( $this->use_mysqli ) {
+                                       $client_version = mysqli_get_client_info();
+                               } else {
+                                       $client_version = mysql_get_client_info();
+                               }
+
+                               /*
+                                * libmysql has supported utf8mb4 since 5.5.3, same as the MySQL server.
+                                * mysqlnd has supported utf8mb4 since 5.0.9.
+                                */
+                               if ( false !== strpos( $client_version, 'mysqlnd' ) ) {
+                                       $client_version = preg_replace( '/^\D+([\d.]+).*/', '$1', $client_version );
+                                       return version_compare( $client_version, '5.0.9', '>=' );
+                               } else {
+                                       return version_compare( $client_version, '5.5.3', '>=' );
+                               }
+               }
 
                return false;
        }
@@ -1726,7 +3083,7 @@ class wpdb {
         *
         * @return string The name of the calling function
         */
-       function get_caller() {
+       public function get_caller() {
                return wp_debug_backtrace_summary( __CLASS__ );
        }
 
@@ -1735,9 +3092,14 @@ class wpdb {
         *
         * @since 2.7.0
         *
-        * @return false|string false on failure, version number on success
+        * @return null|string Null on failure, version number on success.
         */
-       function db_version() {
-               return preg_replace( '/[^0-9.].*/', '', mysql_get_server_info( $this->dbh ) );
+       public function db_version() {
+               if ( $this->use_mysqli ) {
+                       $server_info = mysqli_get_server_info( $this->dbh );
+               } else {
+                       $server_info = mysql_get_server_info( $this->dbh );
+               }
+               return preg_replace( '/[^0-9.].*/', '', $server_info );
        }
 }