From 2bbd21f543aee73edd0b55bd23623eb1dd6199e9 Mon Sep 17 00:00:00 2001
From: Gary Pendergast <gary@pento.net>
Date: Mon, 20 Apr 2015 04:46:25 +0000
Subject: [PATCH] WPDB: When sanity checking read queries, there are some
 collations we can skip, for improved performance.

Props pento, nacin.

See #21212.


Built from https://develop.svn.wordpress.org/trunk@32162


git-svn-id: http://core.svn.wordpress.org/trunk@32137 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/version.php |  2 +-
 wp-includes/wp-db.php   | 68 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/wp-includes/version.php b/wp-includes/version.php
index db7eb70880..b4ea6adb5c 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.2-RC1-32161';
+$wp_version = '4.2-RC1-32162';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/wp-db.php b/wp-includes/wp-db.php
index 08fc3e5565..cdb9eda8c8 100644
--- a/wp-includes/wp-db.php
+++ b/wp-includes/wp-db.php
@@ -170,6 +170,16 @@ class wpdb {
 	 */
 	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
 	 *
@@ -2038,6 +2048,10 @@ class wpdb {
 	public function get_var( $query = null, $x = 0, $y = 0 ) {
 		$this->func_call = "\$db->get_var(\"$query\", $x, $y)";
 
+		if ( $this->check_safe_collation( $query ) ) {
+			$this->check_current_query = false;
+		}
+
 		if ( $query ) {
 			$this->query( $query );
 		}
@@ -2066,6 +2080,11 @@ class wpdb {
 	 */
 	public function get_row( $query = null, $output = OBJECT, $y = 0 ) {
 		$this->func_call = "\$db->get_row(\"$query\",$output,$y)";
+
+		if ( $this->check_safe_collation( $query ) ) {
+			$this->check_current_query = false;
+		}
+
 		if ( $query ) {
 			$this->query( $query );
 		} else {
@@ -2103,6 +2122,10 @@ class wpdb {
 	 * @return array Database query result. Array indexed from 0 by SQL result row number.
 	 */
 	public function get_col( $query = null , $x = 0 ) {
+		if ( $this->check_safe_collation( $query ) ) {
+			$this->check_current_query = false;
+		}
+
 		if ( $query ) {
 			$this->query( $query );
 		}
@@ -2131,6 +2154,10 @@ class wpdb {
 	public function get_results( $query = null, $output = OBJECT ) {
 		$this->func_call = "\$db->get_results(\"$query\", $output)";
 
+		if ( $this->check_safe_collation( $query ) ) {
+			$this->check_current_query = false;
+		}
+
 		if ( $query ) {
 			$this->query( $query );
 		} else {
@@ -2358,6 +2385,47 @@ class wpdb {
 		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;
+		}
+
+		$table = $this->get_table_from_query( $query );
+		if ( ! $table ) {
+			return false;
+		}
+
+		$this->checking_collation = true;
+		$this->get_table_charset( $table );
+		$this->checking_collation = false;
+
+		$table = strtolower( $table );
+		if ( empty( $this->col_meta[ $table ] ) ) {
+			return false;
+		}
+
+		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.
 	 *