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<?php |
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/** |
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* Lazy_Loader — rewrites img / iframe / video tags in rendered HTML to |
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* add native `loading="lazy"` (or "eager" for above-the-fold) plus |
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* `decoding="async"` on images. Also auto-adds missing width/height |
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* attributes to prevent CLS. |
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* |
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* Why regex instead of DOMDocument: |
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* - DOMDocument forces a full HTML5 parse round trip per filter call; |
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* on a content-heavy post that's measurably slow. Regex over the |
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* specific tags is ~10× faster. |
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* - We don't need full DOM understanding — every rewrite is a tag- |
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* local attribute injection. Regex is sufficient + predictable. |
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* - Edge cases (img inside HTML comments, img in <script>) are rare |
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* in real post content; we leave those alone with a pre-pass that |
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* stubs out script / style / pre blocks before rewriting. |
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* |
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* @package XSpeed |
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*/ |
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|
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declare(strict_types=1); |
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|
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namespace XSpeed; |
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|
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defined( 'ABSPATH' ) || exit; |
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|
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final class Lazy_Loader { |
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|
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/** |
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* In-process counter for above-the-fold skipping. Reset by |
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* process_html on every call so a fresh post starts at 0. |
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* |
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* @var int |
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*/ |
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private static $image_counter = 0; |
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|
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/** |
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* Settings cache (one read per request). |
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* |
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* @var array|null |
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*/ |
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private static $opts = null; |
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|
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/** |
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* Main entry point: take rendered HTML, return rewritten HTML. |
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* Pure function aside from the static counters. |
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*/ |
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public static function process_html( string $html ): string { |
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if ( '' === $html ) { |
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return $html; |
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} |
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$opts = self::opts(); |
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|
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// NOTE: the eager-load budget counter is NOT reset here. process_html |
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// runs once per filter pass — the_content, post_thumbnail_html, and |
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// once per get_avatar — so resetting per call let the featured image, |
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// the first content image, AND every comment avatar each claim an |
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// "eager" slot, defeating the budget. The counter is reset once per |
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// page render via reset_state() on template_redirect, so it now |
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// accumulates across all passes as intended. (FBS-82172 Bug 1) |
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|
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// Stub out <script>, <style>, <noscript>, <pre>, <code> blocks |
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// so img tags embedded in them as text examples aren't |
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// rewritten. Restore after pass. |
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[ $work, $stubs ] = self::stub_safe_blocks( $html ); |
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|
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// Tag matcher that respects quoted attribute values, so a ">" inside |
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// an attribute (e.g. alt="a > b") doesn't end the match early and |
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// corrupt the tag. Matches: double-quoted runs, single-quoted runs, |
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// or any non-> char — repeated up to the real closing >. |
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// (FBS-82172 Bug 3) |
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$tag_re = static function ( string $name ): string { |
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return '#<' . $name . '\b(?:"[^"]*"|\'[^\']*\'|[^>"\'])*>#i'; |
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}; |
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|
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if ( ! empty( $opts['lazy_images'] ) || ! empty( $opts['add_missing_dimensions'] ) ) { |
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$work = preg_replace_callback( |
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$tag_re( 'img' ), |
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array( __CLASS__, 'rewrite_img' ), |
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$work |
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); |
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} |
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if ( ! empty( $opts['lazy_iframes'] ) ) { |
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$work = preg_replace_callback( |
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$tag_re( 'iframe' ), |
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array( __CLASS__, 'rewrite_iframe' ), |
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$work |
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); |
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} |
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if ( ! empty( $opts['lazy_videos'] ) ) { |
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$work = preg_replace_callback( |
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$tag_re( 'video' ), |
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array( __CLASS__, 'rewrite_video' ), |
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$work |
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); |
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} |
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|
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return self::restore_safe_blocks( $work, $stubs ); |
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} |
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|
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private static function rewrite_img( array $m ): string { |
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$tag = $m[0]; |
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$opts = self::opts(); |
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|
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// Explicit skip flag, or matches an exclusion pattern: opt OUT of |
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// LAZY-LOADING only. Dimension injection (CLS protection) still |
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// applies — excluding an above-the-fold hero/logo from lazy-load is |
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// exactly when you most want its width/height kept. Previously both |
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// of these returned early, silently stripping dimensions too. |
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// (FBS-82172 Bug 2) |
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$skip_lazy = false !== stripos( $tag, 'data-skip-lazy' ) |
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|| false !== stripos( $tag, 'data-no-lazy' ) |
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|| self::is_excluded( $tag, $opts ); |
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|
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if ( $skip_lazy && ! empty( $opts['lazy_images'] ) ) { |
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// An EXCLUDED image is one the user marked as above-the-fold (a |
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// hero/logo) — the opposite of lazy. WordPress core adds |
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// `loading="lazy"` to images by default (since 5.5), so merely |
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// *skipping* our lazy pass would leave core's lazy attribute on |
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// the LCP hero and tank LCP. Actively make it eager + |
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// high-priority so an excluded hero loads immediately. |
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$tag = self::set_attr( $tag, 'loading', 'eager' ); |
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$tag = self::set_attr( $tag, 'fetchpriority', 'high', true ); |
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$tag = self::set_attr( $tag, 'decoding', 'async', true ); |
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} elseif ( ! empty( $opts['lazy_images'] ) ) { |
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// Above-the-fold skip: first N images get loading="eager" |
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// instead of "lazy" so the LCP image isn't deferred. Only |
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// non-excluded images consume the budget. |
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self::$image_counter++; |
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$is_above_fold = self::$image_counter <= max( 0, (int) ( $opts['eager_first_n'] ?? 1 ) ); |
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$tag = self::set_attr( $tag, 'loading', $is_above_fold ? 'eager' : 'lazy' ); |
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$tag = self::set_attr( $tag, 'decoding', 'async', true ); |
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// The eager hero should also drop any core `loading="lazy"`; the |
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// set_attr above already overrode it. Give the first eager image |
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// high fetch priority so it wins the LCP race. |
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if ( $is_above_fold ) { |
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$tag = self::set_attr( $tag, 'fetchpriority', 'high', true ); |
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} |
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} |
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|
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if ( ! empty( $opts['add_missing_dimensions'] ) ) { |
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$tag = self::ensure_dimensions( $tag ); |
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} |
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|
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return $tag; |
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} |
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|
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private static function rewrite_iframe( array $m ): string { |
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$tag = $m[0]; |
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if ( false !== stripos( $tag, 'data-skip-lazy' ) ) { |
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return $tag; |
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} |
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if ( self::is_excluded( $tag, self::opts() ) ) { |
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return $tag; |
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} |
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return self::set_attr( $tag, 'loading', 'lazy' ); |
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} |
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|
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private static function rewrite_video( array $m ): string { |
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$tag = $m[0]; |
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if ( false !== stripos( $tag, 'data-skip-lazy' ) ) { |
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return $tag; |
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} |
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// HTML5 `<video>` doesn't support loading=lazy yet (Chromium |
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// won't add it before there's broad support). What we CAN do |
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// is set preload="none" so the browser doesn't pre-fetch the |
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// video bytes until play is requested — that's the actual win |
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// users want from "lazy-load videos". |
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if ( false === stripos( $tag, 'preload=' ) ) { |
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$tag = self::set_attr( $tag, 'preload', 'none' ); |
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} |
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return $tag; |
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} |
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|
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/** |
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* Add an attribute to an opening tag if it isn't already present. |
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* Pass $only_if_missing=false to override an existing value (e.g. |
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* flipping loading="lazy" → "eager" on the first image). |
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*/ |
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private static function set_attr( string $tag, string $name, string $value, bool $only_if_missing = false ): string { |
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$pattern = '#\b' . preg_quote( $name, '#' ) . '\s*=\s*(["\'][^"\']*["\']|\S+)#i'; |
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if ( preg_match( $pattern, $tag ) ) { |
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if ( $only_if_missing ) { |
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return $tag; |
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} |
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return (string) preg_replace( $pattern, $name . '="' . $value . '"', $tag, 1 ); |
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} |
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// Inject before the closing > (preserving self-closing `/>` if present). |
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if ( preg_match( '#(/?>)$#', $tag, $m ) ) { |
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$close = $m[1]; |
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return substr( $tag, 0, -strlen( $close ) ) . ' ' . $name . '="' . $value . '"' . $close; |
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} |
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return $tag; |
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} |
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|
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/** |
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* Attempt to fill in missing width / height from either an attached |
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* media library record (when class="wp-image-N") or from the local |
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* filesystem when src points at the uploads dir. Skip when we can't |
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* resolve cheaply — never block the request on a remote getimagesize. |
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*/ |
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private static function ensure_dimensions( string $tag ): string { |
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$has_w = (bool) preg_match( '#\bwidth\s*=#i', $tag ); |
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$has_h = (bool) preg_match( '#\bheight\s*=#i', $tag ); |
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if ( $has_w && $has_h ) { |
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return $tag; |
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} |
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|
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// Try wp-image-<id> class first (cheapest path; one DB-cached |
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// get_post_meta call). |
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if ( preg_match( '#\bclass\s*=\s*["\']([^"\']*)["\']#i', $tag, $cm ) && preg_match( '#wp-image-(\d+)#i', $cm[1], $idm ) ) { |
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$dims = self::dimensions_for_attachment( (int) $idm[1] ); |
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if ( $dims ) { |
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if ( ! $has_w ) { |
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$tag = self::set_attr( $tag, 'width', (string) $dims[0] ); |
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} |
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if ( ! $has_h ) { |
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$tag = self::set_attr( $tag, 'height', (string) $dims[1] ); |
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} |
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return $tag; |
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} |
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} |
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|
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// Couldn't resolve. Leave the tag alone — better no dimensions |
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// than wrong ones. |
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return $tag; |
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} |
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|
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/** |
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* @return int[]|null [width, height] or null |
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*/ |
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private static function dimensions_for_attachment( int $attachment_id ): ?array { |
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if ( ! function_exists( 'wp_get_attachment_metadata' ) ) { |
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return null; |
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} |
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$meta = wp_get_attachment_metadata( $attachment_id ); |
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if ( ! is_array( $meta ) || empty( $meta['width'] ) || empty( $meta['height'] ) ) { |
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return null; |
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} |
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return array( (int) $meta['width'], (int) $meta['height'] ); |
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} |
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|
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private static function is_excluded( string $tag, array $opts ): bool { |
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$excluded = $opts['excluded_images'] ?? array(); |
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if ( ! is_array( $excluded ) || empty( $excluded ) ) { |
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return false; |
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} |
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foreach ( $excluded as $pattern ) { |
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$pattern = (string) $pattern; |
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if ( '' === $pattern ) { |
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continue; |
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} |
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if ( false !== stripos( $tag, $pattern ) ) { |
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return true; |
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} |
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} |
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return false; |
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} |
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|
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/** |
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* Replace <script>, <style>, <noscript>, <pre>, <code> blocks with |
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* placeholder tokens before tag rewriting. Returns [stubbed_html, |
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* stubs_map]. Restore via restore_safe_blocks(). |
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* |
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* @return array{0: string, 1: array<string,string>} |
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*/ |
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private static function stub_safe_blocks( string $html ): array { |
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$stubs = array(); |
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$re = '#<(script|style|noscript|pre|code)\b[^>]*>.*?</\1>#is'; |
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$out = preg_replace_callback( |
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$re, |
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static function ( $m ) use ( &$stubs ) { |
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$key = '<!--XSPEED_LAZY_STUB_' . count( $stubs ) . '-->'; |
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$stubs[ $key ] = $m[0]; |
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return $key; |
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}, |
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$html |
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); |
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return array( (string) $out, $stubs ); |
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} |
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|
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private static function restore_safe_blocks( string $html, array $stubs ): string { |
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if ( empty( $stubs ) ) { |
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return $html; |
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} |
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return strtr( $html, $stubs ); |
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} |
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|
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private static function opts(): array { |
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if ( null === self::$opts ) { |
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self::$opts = Settings_Manager::get( 'lazy' ); |
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} |
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return self::$opts; |
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} |
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|
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/** |
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* Test-only: clear cached opts + counter between assertions. |
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*/ |
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public static function reset_state(): void { |
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self::$opts = null; |
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self::$image_counter = 0; |
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} |
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} |
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|
