Add Site Health test to verify that static assets are served with far-future expires

plugins/performance-lab/includes/site-health/far-future-headers/helper.php

@@ -0,0 +1,183 @@
+<?php
+/**
+ * Helper function to detect if static assets have far-future expiration headers.
+ *
+ * @package performance-lab
+ * @since n.e.x.t
+ */
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit; // Exit if accessed directly.
+}
+
+/**
+ * Callback for the far-future caching test.
+ *
+ * @since n.e.x.t
+ *
+ * @return array{label: string, status: string, badge: array{label: string, color: string}, description: string, actions: string, test: string} Result.
+ */
+function perflab_ffh_assets_test(): array {
+	$result = array(
+		'label'       => __( 'Your site serves static assets with far-future expiration headers', 'performance-lab' ),
+		'status'      => 'good',
+		'badge'       => array(
+			'label' => __( 'Performance', 'performance-lab' ),
+			'color' => 'blue',
+		),
+		'description' => sprintf(
+			'<p>%s</p>',
+			esc_html__(
+				'Serving static assets with far-future expiration headers improves performance by allowing browsers to cache files for a long time, reducing repeated requests.',
+				'performance-lab'
+			)
+		),
+		'actions'     => '',
+		'test'        => 'is_far_future_headers_enabled',
+	);
+
+	// List of assets to check.
+	$assets = array(
+		plugins_url( 'far-future-headers/assets/test.css', __DIR__ ),
+	);
+
+	// Check if far-future headers are enabled for all assets.
+	$status = perflab_ffh_check_assets( $assets );
+
+	if ( 'good' !== $status ) {
+		$result['status']  = $status;
+		$result['label']   = __( 'Your site does not serve static assets with recommended far-future expiration headers', 'performance-lab' );
+		$result['actions'] = sprintf(
+			'<p>%s</p>',
+			esc_html__( 'Far-future Cache-Control or Expires headers can be added or adjusted with a small configuration change by your hosting provider.', 'performance-lab' )
+		);
+	}
+
+	return $result;
+}
+
+/**
+ * Checks if far-future expiration headers are enabled for a list of assets.
+ *
+ * @since n.e.x.t
+ *
+ * @param  string[] $assets List of asset URLs to check.
+ * @return string 'good' if far-future headers are enabled for all assets, 'recommended' if some assets are missing headers.
+ */
+function perflab_ffh_check_assets( array $assets ): string {
+	$final_status = 'good';
+
+	foreach ( $assets as $asset ) {
+		$response = wp_remote_get( $asset, array( 'sslverify' => false ) );
+
+		if ( is_wp_error( $response ) ) {
+			continue;
+		}
+
+		$headers = wp_remote_retrieve_headers( $response );
+
+		if ( is_array( $headers ) ) {
+			continue;
+		}
+
+		if ( perflab_ffh_check_headers( $headers ) ) {
+			continue;
+		}
+
+		// If far-future headers are not enabled, attempt a conditional request.
+		if ( perflab_ffh_try_conditional_request( $asset, $headers ) ) {
+			$final_status = 'recommended';
+			continue;
+		}
+
+		$final_status = 'recommended';
+	}
+
+	return $final_status;
+}
+
+/**
+ * Checks if far-future expiration headers are enabled.
+ *
+ * @since n.e.x.t
+ *
+ * @param WpOrg\Requests\Utility\CaseInsensitiveDictionary $headers Response headers.
+ * @return bool True if far-future headers are enabled, false otherwise.
+ */
+function perflab_ffh_check_headers( WpOrg\Requests\Utility\CaseInsensitiveDictionary $headers ): bool {
+	/**
+	 * Filters the threshold for far-future headers.
+	 *
+	 * @since n.e.x.t
+	 *
+	 * @param int $threshold Threshold in seconds.
+	 */
+	$threshold = apply_filters( 'perflab_far_future_headers_threshold', YEAR_IN_SECONDS );
+
+	$cache_control = isset( $headers['cache-control'] ) ? $headers['cache-control'] : '';
+	$expires       = isset( $headers['expires'] ) ? $headers['expires'] : '';
+
+	// Check Cache-Control header for max-age.
+	$max_age = 0;
+	if ( '' !== $cache_control ) {
+		// Cache-Control can have multiple directives; we only care about max-age.
+		$controls = is_array( $cache_control ) ? $cache_control : array( $cache_control );
+		foreach ( $controls as $control ) {
+			if ( (bool) preg_match( '/max-age\s*=\s*(\d+)/', $control, $matches ) ) {
+				$max_age = (int) $matches[1];
+				break;
+			}
+		}
+	}
+
+	// If max-age meets or exceeds the threshold, we consider it good.
+	if ( $max_age >= $threshold ) {
+		return true;
+	}
+
+	// If max-age is not sufficient, check Expires.
+	// Expires is a date; we want to ensure it's far in the future.
+	if ( is_string( $expires ) && '' !== $expires ) {
+		$expires_time = strtotime( $expires );
+		if ( (bool) $expires_time && ( $expires_time - time() ) >= $threshold ) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/**
+ * Attempt a conditional request with ETag/Last-Modified.
+ *
+ * @param string                                           $url     The asset URL.
+ * @param WpOrg\Requests\Utility\CaseInsensitiveDictionary $headers The initial response headers.
+ * @return bool True if a 304 response was received.
+ */
+function perflab_ffh_try_conditional_request( string $url, WpOrg\Requests\Utility\CaseInsensitiveDictionary $headers ): bool {
+	$etag          = isset( $headers['etag'] ) ? $headers['etag'] : '';
+	$last_modified = isset( $headers['last-modified'] ) ? $headers['last-modified'] : '';
+
+	$conditional_headers = array();
+	if ( '' !== $etag ) {
+		$conditional_headers['If-None-Match'] = $etag;
+	}
+	if ( '' !== $last_modified ) {
+		$conditional_headers['If-Modified-Since'] = $last_modified;
+	}
+
+	$response = wp_remote_get(
+		$url,
+		array(
+			'sslverify' => false,
+			'headers'   => $conditional_headers,
+		)
+	);
+
+	if ( is_wp_error( $response ) ) {
+		return false;
+	}
+
+	$status_code = wp_remote_retrieve_response_code( $response );
+	return ( 304 === $status_code );
+}

plugins/performance-lab/includes/site-health/far-future-headers/hooks.php

@@ -0,0 +1,28 @@
+<?php
+/**
+ * Hook callbacks used for far-future headers.
+ *
+ * @package performance-lab
+ * @since n.e.x.t
+ */
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit; // Exit if accessed directly.
+}
+
+/**
+ * Adds tests to site health.
+ *
+ * @since n.e.x.t
+ *
+ * @param array{direct: array<string, array{label: string, test: string}>} $tests Site Health Tests.
+ * @return array{direct: array<string, array{label: string, test: string}>} Amended tests.
+ */
+function perflab_ffh_add_test( array $tests ): array {
+	$tests['direct']['far_future_headers'] = array(
+		'label' => __( 'Far-Future Caching Headers', 'performance-lab' ),
+		'test'  => 'perflab_ffh_assets_test',
+	);
+	return $tests;
+}
+add_filter( 'site_status_tests', 'perflab_ffh_add_test' );

plugins/performance-lab/includes/site-health/load.php

@@ -29,3 +29,7 @@
 // AVIF headers site health check.
 require_once __DIR__ . '/avif-headers/helper.php';
 require_once __DIR__ . '/avif-headers/hooks.php';
+
+// Far-Future Headers site health check.
+require_once __DIR__ . '/far-future-headers/helper.php';
+require_once __DIR__ . '/far-future-headers/hooks.php';