WordPress · felixarntz · Mar 13, 2024 · Mar 11, 2024 · Mar 11, 2024 · Mar 12, 2024
diff --git a/load.php b/load.php
@@ -29,6 +29,7 @@
 if ( ! defined( 'PERFLAB_OBJECT_CACHE_DROPIN_VERSION' ) ) {
 	define( 'PERFLAB_OBJECT_CACHE_DROPIN_VERSION', false );
 }
+define( 'PERFLAB_OBJECT_CACHE_DROPIN_LATEST_VERSION', 3 );
 
 // Load server-timing API.
 require_once PERFLAB_PLUGIN_DIR_PATH . 'includes/server-timing/class-perflab-server-timing-metric.php';
@@ -371,11 +372,6 @@ function perflab_maybe_set_object_cache_dropin() {
 		return;
 	}
 
-	// Bail if already placed.
-	if ( PERFLAB_OBJECT_CACHE_DROPIN_VERSION ) {
-		return;
-	}
-
 	/**
 	 * Filters whether the Perflab server timing drop-in should be set.
 	 *
@@ -387,6 +383,24 @@ function perflab_maybe_set_object_cache_dropin() {
 		return;
 	}
 
+	/**
+	 * Filters the value of the `object-cache.php` drop-in constant.
+	 *
+	 * This filter should not be used outside of tests.
+	 *
+	 * @since n.e.x.t
+	 * @internal
+	 *
+	 * @param int|bool $current_dropin_version The drop-in version as defined by the
+	 *                                         `PERFLAB_OBJECT_CACHE_DROPIN_VERSION` constant.
+	 */
+	$current_dropin_version = apply_filters( 'perflab_object_cache_dropin_version', PERFLAB_OBJECT_CACHE_DROPIN_VERSION );
+
+	// Bail if already placed in the latest version or newer.
+	if ( $current_dropin_version && $current_dropin_version >= PERFLAB_OBJECT_CACHE_DROPIN_LATEST_VERSION ) {
+		return;
+	}
+
 	// Bail if already attempted before timeout has been completed.
 	// This is present in case placing the file fails for some reason, to avoid
 	// excessively retrying to place it on every request.
@@ -398,8 +412,11 @@ function perflab_maybe_set_object_cache_dropin() {
 	if ( $wp_filesystem || WP_Filesystem() ) {
 		$dropin_path = WP_CONTENT_DIR . '/object-cache.php';
 
-		/**
-		 * If there is an actual object-cache.php file, do not replace it.
+		/*
+		 * If there is an actual object-cache.php file, it is most likely from
+		 * a third party, or it may be an older version of the Performance Lab
+		 * object-cache.php. If it's from a third party, do not replace it.
+		 *
 		 * Previous versions of the Performance Lab plugin were renaming the
 		 * original object-cache.php file and then loading both. However, due
 		 * to other plugins eagerly checking file headers, this caused too many
@@ -408,9 +425,27 @@ function perflab_maybe_set_object_cache_dropin() {
 		 * safest solution.
 		 */
 		if ( $wp_filesystem->exists( $dropin_path ) ) {
-			// Set timeout of 1 day before retrying again (only in case the file already exists).
-			set_transient( 'perflab_set_object_cache_dropin', true, DAY_IN_SECONDS );
-			return;
+			// If this constant evaluates to `false`, the existing file is for sure from a third party.
+			if ( ! $current_dropin_version ) {
+				// Set timeout of 1 day before retrying again (only in case the file already exists).
+				set_transient( 'perflab_set_object_cache_dropin', true, DAY_IN_SECONDS );
+				return;
+			}
+
+			// Otherwise, verify that it's actually the Performance Lab drop-in.
+			$test_content = "<?php\n/**\n * Plugin Name: Performance Lab Server Timing Object Cache Drop-In\n";
+			if ( ! str_starts_with( $wp_filesystem->get_contents( $dropin_path ), $test_content ) ) {
+				// Set timeout of 1 day before retrying again (only in case the file already exists).
+				set_transient( 'perflab_set_object_cache_dropin', true, DAY_IN_SECONDS );
+				return;
+			}
+
+			/*
+			 * If this logic is reached, the existing file is an older version
+			 * of the Performance Lab drop-in, so it can be safely deleted, and
+			 * then be replaced below.
+			 */
+			$wp_filesystem->delete( $dropin_path );
 		}
 
 		$wp_filesystem->copy( PERFLAB_PLUGIN_DIR_PATH . 'includes/server-timing/object-cache.copy.php', $dropin_path );

diff --git a/tests/load-tests.php b/tests/load-tests.php
@@ -214,6 +214,62 @@ public function test_perflab_maybe_set_object_cache_dropin_with_conflict() {
 		$this->assertSame( $dummy_file_content, $wp_filesystem->get_contents( WP_CONTENT_DIR . '/object-cache.php' ) );
 	}
 
+	public function test_perflab_maybe_set_object_cache_dropin_with_older_version() {
+		global $wp_filesystem;
+
+		$this->set_up_mock_filesystem();
+
+		$latest_file_content = file_get_contents( PERFLAB_PLUGIN_DIR_PATH . 'includes/server-timing/object-cache.copy.php' );
+		$older_file_content  = preg_replace( '/define\( \'PERFLAB_OBJECT_CACHE_DROPIN_VERSION\', (\d+) \)\;/', "define( 'PERFLAB_OBJECT_CACHE_DROPIN_VERSION', 1 );", $latest_file_content );
+		$wp_filesystem->put_contents( WP_CONTENT_DIR . '/object-cache.php', $older_file_content );
+
+		// Simulate PL constant is set to the value from the older file.
+		add_filter(
+			'perflab_object_cache_dropin_version',
+			static function () {
+				return 1;
+			}
+		);
+
+		// Ensure older object-cache.php drop-in is present.
+		$this->assertTrue( $wp_filesystem->exists( WP_CONTENT_DIR . '/object-cache.php' ) );
+		$this->assertSame( $older_file_content, $wp_filesystem->get_contents( WP_CONTENT_DIR . '/object-cache.php' ) );
+
+		// Run function to place drop-in and ensure it overrides the existing drop-in with the latest version.
+		perflab_maybe_set_object_cache_dropin();
+		$this->assertTrue( $wp_filesystem->exists( WP_CONTENT_DIR . '/object-cache.php' ) );
+		$this->assertSame( $latest_file_content, $wp_filesystem->get_contents( WP_CONTENT_DIR . '/object-cache.php' ) );
+	}
+
+	public function test_perflab_maybe_set_object_cache_dropin_with_latest_version() {
+		global $wp_filesystem;
+
+		$this->set_up_mock_filesystem();
+
+		$latest_file_content = file_get_contents( PERFLAB_PLUGIN_DIR_PATH . 'includes/server-timing/object-cache.copy.php' );
+		$wp_filesystem->put_contents( WP_CONTENT_DIR . '/object-cache.php', $latest_file_content );
+
+		// Simulate PL constant is set to the value from the current file.
+		$this->assertTrue( (bool) preg_match( '/define\( \'PERFLAB_OBJECT_CACHE_DROPIN_VERSION\', (\d+) \)\;/', $latest_file_content, $matches ) );
+		$latest_version = (int) $matches[1];
+		add_filter(
+			'perflab_object_cache_dropin_version',
+			static function () use ( $latest_version ) {
+				return $latest_version;
+			}
+		);
+
+		// Ensure latest object-cache.php drop-in is present.
+		$this->assertTrue( $wp_filesystem->exists( WP_CONTENT_DIR . '/object-cache.php' ) );
+		$this->assertSame( $latest_file_content, $wp_filesystem->get_contents( WP_CONTENT_DIR . '/object-cache.php' ) );
+
+		// Run function to place drop-in and ensure it doesn't attempt to replace the file.
+		perflab_maybe_set_object_cache_dropin();
+		$this->assertTrue( $wp_filesystem->exists( WP_CONTENT_DIR . '/object-cache.php' ) );
+		$this->assertSame( $latest_file_content, $wp_filesystem->get_contents( WP_CONTENT_DIR . '/object-cache.php' ) );
+		$this->assertFalse( get_transient( 'perflab_set_object_cache_dropin' ) );
+	}
+
 	public function test_perflab_object_cache_dropin_may_be_disabled_via_filter() {
 		global $wp_filesystem;
 
@@ -231,6 +287,20 @@ public function test_perflab_object_cache_dropin_may_be_disabled_via_filter() {
 		$this->assertFalse( $wp_filesystem->exists( WP_CONTENT_DIR . '/object-cache.php' ) );
 	}
 
+	public function test_perflab_object_cache_dropin_version_matches_latest() {
+		$file_content = file_get_contents( PERFLAB_PLUGIN_DIR_PATH . 'includes/server-timing/object-cache.copy.php' );
+
+		// Get the version from the file header and the constant.
+		$this->assertTrue( (bool) preg_match( '/^ \* Version: (\d+)$/m', $file_content, $matches ) );
+		$file_header_version = (int) $matches[1];
+		$this->assertTrue( (bool) preg_match( '/define\( \'PERFLAB_OBJECT_CACHE_DROPIN_VERSION\', (\d+) \)\;/', $file_content, $matches ) );
+		$file_constant_version = (int) $matches[1];
+
+		// Assert the versions are in sync.
+		$this->assertSame( PERFLAB_OBJECT_CACHE_DROPIN_LATEST_VERSION, $file_header_version );
+		$this->assertSame( PERFLAB_OBJECT_CACHE_DROPIN_LATEST_VERSION, $file_constant_version );
+	}
+
 	private function set_up_mock_filesystem() {
 		global $wp_filesystem;