Add output buffering checkbox to Server-Timing screen

admin/server-timing.php

@@ -43,6 +43,13 @@ function perflab_add_server_timing_page() {
  * @since n.e.x.t
  */
 function perflab_load_server_timing_page() {
+	add_settings_section(
+		'output-buffering',
+		__( 'Output Buffering', 'performance-lab' ),
+		'perflab_render_server_timing_page_output_buffer_checkbox',
+		PERFLAB_SERVER_TIMING_SCREEN
+	);
+
 	add_settings_section(
 		'benchmarking',
 		__( 'Benchmarking', 'performance-lab' ),
@@ -71,12 +78,16 @@ static function() {
 					<?php
 					echo wp_kses(
 						sprintf(
-							/* translators: 1: Server-Timing, 2: template_include */
-							__( 'Since the %1$s header is sent before the template is loaded, only hooks before the %2$s filter can be measured.', 'performance-lab' ),
+							/* translators: 1: Server-Timing, 2: template_include, 3: anchor link */
+							__( 'Since the %1$s header is sent before the template is loaded, only hooks before the %2$s filter can be measured. Enable <a href="%3$s">Output Buffering</a> to measure hooks during template rendering.', 'performance-lab' ),
 							'<code>Server-Timing</code>',
-							'<code>template_include</code>'
+							'<code>template_include</code>',
+							esc_url( '#server_timing_output_buffering' )
 						),
-						array( 'code' => array() )
+						array(
+							'code' => array(),
+							'a'    => array( 'href' => true ),
+						)
 					);
 				}
 				?>
@@ -95,7 +106,7 @@ static function() {
 		'benchmarking_actions',
 		__( 'Actions', 'performance-lab' ),
 		static function() {
-			perflab_render_server_timing_page_field( 'benchmarking_actions' );
+			perflab_render_server_timing_page_hooks_field( 'benchmarking_actions' );
 		},
 		PERFLAB_SERVER_TIMING_SCREEN,
 		'benchmarking',
@@ -105,7 +116,7 @@ static function() {
 		'benchmarking_filters',
 		__( 'Filters', 'performance-lab' ),
 		static function() {
-			perflab_render_server_timing_page_field( 'benchmarking_filters' );
+			perflab_render_server_timing_page_hooks_field( 'benchmarking_filters' );
 		},
 		PERFLAB_SERVER_TIMING_SCREEN,
 		'benchmarking',
@@ -136,13 +147,13 @@ function perflab_render_server_timing_page() {
 }
 
 /**
- * Renders a field for the given Server-Timing option.
+ * Renders a hooks field for the given Server-Timing option.
  *
  * @since n.e.x.t
  *
  * @param string $slug Slug of the field and sub-key in the Server-Timing option.
  */
-function perflab_render_server_timing_page_field( $slug ) {
+function perflab_render_server_timing_page_hooks_field( $slug ) {
 	$options = (array) get_option( PERFLAB_SERVER_TIMING_SETTING, array() );
 
 	// Value for the sub-key is an array of hook names.
@@ -168,3 +179,77 @@ class="large-text code"
 	</p>
 	<?php
 }
+
+/**
+ * Renders a checkbox for enabling output buffering for Server-Timing.
+ *
+ * @since n.e.x.t
+ */
+function perflab_render_server_timing_page_output_buffer_checkbox() {
+	$slug           = 'output_buffering';
+	$field_id       = "server_timing_{$slug}";
+	$field_name     = PERFLAB_SERVER_TIMING_SETTING . '[' . $slug . ']';
+	$description_id = "{$field_id}_description";
+	$has_filter     = has_filter( 'perflab_server_timing_use_output_buffer' );
+	$is_enabled     = perflab_server_timing_use_output_buffer();
+
+	?>
+	<style>
+	/* The following styles are copied from core where they normally include `.form-table td` in the selectors. */
+	fieldset.output-buffering {
+		margin-bottom: 9px;
+		padding: 15px 10px 15px 0;
+		line-height: 1.3;
+		vertical-align: middle;
+		font-size: 14px;
+	}
+	fieldset.output-buffering label,
+	fieldset.output-buffering p {
+		line-height: 1.4;
+	}
+	fieldset.output-buffering label {
+		margin: 0.35em 0 0.5em !important;
+		display: inline-block;
+	}
+	fieldset.output-buffering p {
+		font-size: 14px;
+	}
+	</style>
+	<fieldset class="output-buffering">
+		<legend class="screen-reader-text">
+			<?php esc_html_e( 'Output Buffering', 'performance-lab' ); ?>
+		</legend>
+		<input
+			type="checkbox"
+			id="<?php echo esc_attr( $field_id ); ?>"
+			name="<?php echo esc_attr( $field_name ); ?>"
+			aria-describedby="<?php echo esc_attr( $description_id ); ?>"
+			<?php disabled( $has_filter ); ?>
+			<?php checked( $is_enabled ); ?>
+		>
+		<label for="<?php echo esc_attr( $field_id ); ?>">
+			<?php esc_html_e( 'Enable output buffering of template rendering.', 'performance-lab' ); ?>
+		</label>
+		<p id="<?php echo esc_attr( $description_id ); ?>" class="description">
+			<?php if ( $has_filter ) : ?>
+				<?php if ( $is_enabled ) : ?>
+					<?php
+					echo wp_kses(
+						__( 'Output buffering has been forcibly enabled via the <code>perflab_server_timing_use_output_buffer</code> filter.', 'performance-lab' ),
+						array( 'code' => array() )
+					);
+					?>
+				<?php else : ?>
+					<?php
+					echo wp_kses(
+						__( 'Output buffering has been forcibly disabled via the <code>perflab_server_timing_use_output_buffer</code> filter.', 'performance-lab' ),
+						array( 'code' => array() )
+					);
+					?>
+				<?php endif; ?>
+			<?php endif; ?>
+			<?php esc_html_e( 'This is needed to capture metrics after headers have been sent and while the template is being rendered. Note that output buffering may possibly cause an increase in TTFB if the response would be flushed multiple times.', 'performance-lab' ); ?>
+		</p>
+	</fieldset>
+	<?php
+}

server-timing/class-perflab-server-timing.php

@@ -195,6 +195,10 @@ static function( $value ) {
 	 * @return bool True if an output buffer should be used, false otherwise.
 	 */
 	public function use_output_buffer() {
+		$slug    = 'output_buffering';
+		$options = (array) get_option( PERFLAB_SERVER_TIMING_SETTING, array() );
+		$enabled = ! empty( $options[ $slug ] );
+
 		/**
 		 * Filters whether an output buffer should be used to be able to gather additional Server-Timing metrics.
 		 *
@@ -206,7 +210,7 @@ public function use_output_buffer() {
 		 *
 		 * @param bool $use_output_buffer Whether to use an output buffer.
 		 */
-		return apply_filters( 'perflab_server_timing_use_output_buffer', false );
+		return (bool) apply_filters( 'perflab_server_timing_use_output_buffer', $enabled );
 	}
 
 	/**

server-timing/load.php

@@ -163,6 +163,7 @@ function perflab_sanitize_server_timing_setting( $value ) {
 	static $allowed_keys = array(
 		'benchmarking_actions' => true,
 		'benchmarking_filters' => true,
+		'output_buffering'     => true,
 	);
 
 	if ( ! is_array( $value ) ) {
@@ -175,7 +176,7 @@ function perflab_sanitize_server_timing_setting( $value ) {
 	 * Ensure that every element is an indexed array of hook names.
 	 * Any duplicates across a group of hooks are removed.
 	 */
-	foreach ( $value as $key => $hooks ) {
+	foreach ( wp_array_slice_assoc( $value, array( 'benchmarking_actions', 'benchmarking_filters' ) ) as $key => $hooks ) {
 		if ( ! is_array( $hooks ) ) {
 			$hooks = explode( "\n", $hooks );
 		}
@@ -203,5 +204,7 @@ static function( $hookname ) {
 		);
 	}
 
+	$value['output_buffering'] = ! empty( $value['output_buffering'] );
+
 	return $value;
 }

tests/admin/server-timing-tests.php

@@ -57,7 +57,7 @@ public function test_perflab_load_server_timing_page() {
 			array_keys( $wp_settings_fields[ PERFLAB_SERVER_TIMING_SCREEN ] )
 		);
 		$this->assertEqualSets(
-			array( 'benchmarking_actions', 'benchmarking_filters' ),
+			array( 'benchmarking_actions', 'benchmarking_filters', 'output_buffering' ),
 			array_keys( $wp_settings_fields[ PERFLAB_SERVER_TIMING_SCREEN ]['benchmarking'] )
 		);
 	}
@@ -75,7 +75,7 @@ public function test_perflab_render_server_timing_page_field() {
 		$slug = 'benchmarking_actions';
 
 		ob_start();
-		perflab_render_server_timing_page_field( $slug );
+		perflab_render_server_timing_page_hooks_field( $slug );
 		$output = ob_get_clean();
 
 		$this->assertStringContainsString( '<textarea', $output );
@@ -87,7 +87,7 @@ public function test_perflab_render_server_timing_page_field_empty_option() {
 		delete_option( PERFLAB_SERVER_TIMING_SETTING );
 
 		ob_start();
-		perflab_render_server_timing_page_field( 'benchmarking_actions' );
+		perflab_render_server_timing_page_hooks_field( 'benchmarking_actions' );
 		$output = ob_get_clean();
 
 		$this->assertStringContainsString( '></textarea>', $output );
@@ -100,7 +100,7 @@ public function test_perflab_render_server_timing_page_field_populated_option()
 		);
 
 		ob_start();
-		perflab_render_server_timing_page_field( 'benchmarking_actions' );
+		perflab_render_server_timing_page_hooks_field( 'benchmarking_actions' );
 		$output = ob_get_clean();
 
 		// Array is formatted/imploded as strings, one per line.

tests/server-timing/load-tests.php

@@ -103,39 +103,43 @@ public function data_perflab_sanitize_server_timing_setting() {
 			),
 			'empty list, array'                           => array(
 				array( 'benchmarking_actions' => array() ),
-				array( 'benchmarking_actions' => array() ),
+				array( 'benchmarking_actions' => array(), 'output_buffering' => false ),
 			),
 			'empty list, string'                          => array(
 				array( 'benchmarking_actions' => '' ),
-				array( 'benchmarking_actions' => array() ),
+				array( 'benchmarking_actions' => array(), 'output_buffering' => false ),
 			),
 			'empty list, string with whitespace'          => array(
 				array( 'benchmarking_actions' => ' ' ),
-				array( 'benchmarking_actions' => array() ),
+				array( 'benchmarking_actions' => array(), 'output_buffering' => false ),
 			),
 			'regular list, array'                         => array(
 				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ) ),
-				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ) ),
+				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ), 'output_buffering' => false ),
 			),
 			'regular list, string'                        => array(
 				array( 'benchmarking_actions' => "after_setup_theme\ninit\nwp_loaded" ),
-				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ) ),
+				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ), 'output_buffering' => false ),
 			),
 			'regular list, string with whitespace'        => array(
 				array( 'benchmarking_actions' => "after_setup_  theme \ninit \n\nwp_loaded\n" ),
-				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ) ),
+				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ), 'output_buffering' => false ),
 			),
 			'regular list, array with duplicates'         => array(
 				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded', 'init' ) ),
-				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ) ),
+				array( 'benchmarking_actions' => array( 'after_setup_theme', 'init', 'wp_loaded' ), 'output_buffering' => false ),
 			),
 			'regular list, array with special hook chars' => array(
 				array( 'benchmarking_actions' => array( 'namespace/hookname', 'namespace.hookname' ) ),
-				array( 'benchmarking_actions' => array( 'namespace/hookname', 'namespace.hookname' ) ),
+				array( 'benchmarking_actions' => array( 'namespace/hookname', 'namespace.hookname' ), 'output_buffering' => false ),
+			),
+			'output buffering enabled' => array(
+				array( 'output_buffering' => 'on' ),
+				array( 'output_buffering' => true ),
 			),
 			'regular list, disallowed key'                => array(
 				array( 'not_allowed' => array( 'after_setup_theme', 'init', 'wp_loaded' ) ),
-				array(),
+				array( 'output_buffering' => false ),
 			),
 		);
 	}