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<?php
/**
* Implements the system to avoid render blocking JS execution.
*
* @link https://automattic.com
* @since 0.2
* @package automattic/jetpack-boost
*/
namespace Automattic\Jetpack_Boost\Modules\Optimizations\Render_Blocking_JS;
use Automattic\Jetpack_Boost\Contracts\Changes_Output_On_Activation;
use Automattic\Jetpack_Boost\Contracts\Feature;
use Automattic\Jetpack_Boost\Contracts\Optimization;
use Automattic\Jetpack_Boost\Lib\Output_Filter;
/**
* Class Render_Blocking_JS
*/
class Render_Blocking_JS implements Feature, Changes_Output_On_Activation, Optimization {
/**
* Holds the script tags removed from the output buffer.
*
* @var array
*/
protected $buffered_script_tags = array();
/**
* HTML attribute name to be added to <script> tag to make it
* ignored by this class.
*
* @var string|null
*/
private $ignore_attribute;
/**
* HTML attribute value to be added to <script> tag to make it
* ignored by this class.
*
* @var string
*/
private $ignore_value = 'ignore';
/**
* Utility class that supports output filtering.
*
* @var Output_Filter
*/
private $output_filter = null;
/**
* Flag indicating an opened <script> tag in output.
*
* @var string
*/
private $is_opened_script = false;
public function setup() {
$this->output_filter = new Output_Filter();
/**
* Filters the ignore attribute
*
* @param $string $ignore_attribute The string used to ignore elements of the page.
*
* @since 1.0.0
*/
$this->ignore_attribute = apply_filters( 'jetpack_boost_render_blocking_js_ignore_attribute', 'data-jetpack-boost' );
add_action( 'template_redirect', array( $this, 'start_output_filtering' ), -999999 );
/**
* Shortcodes can sometimes output script to embed widget. It's safer to ignore them.
*/
add_filter( 'do_shortcode_tag', array( $this, 'add_ignore_attribute' ) );
}
public static function is_available() {
return true;
}
/**
* Set up an output filtering callback.
*
* @return void
*/
public function start_output_filtering() {
/**
* We're doing heavy output filtering in this module
* by using output buffering.
*
* Here are a few scenarios when we shouldn't do it:
*/
/**
* Filter to disable defer blocking JS
*
* @param bool $defer return false to disable defer blocking
*
* @since 1.0.0
*/
if ( false === apply_filters( 'jetpack_boost_should_defer_js', '__return_true' ) ) {
return;
}
// Disable in robots.txt.
if ( isset( $_SERVER['REQUEST_URI'] ) && strpos( home_url( wp_unslash( $_SERVER['REQUEST_URI'] ) ), 'robots.txt' ) !== false ) { // phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized -- This is validating.
return;
}
// Disable in other possible AJAX requests setting cors related header.
if ( isset( $_SERVER['HTTP_SEC_FETCH_MODE'] ) && 'cors' === strtolower( $_SERVER['HTTP_SEC_FETCH_MODE'] ) ) { // phpcs:ignore WordPress.Security.ValidatedSanitizedInput -- This is validating.
return;
}
// Disable in other possible AJAX requests setting XHR related header.
if ( isset( $_SERVER['HTTP_X_REQUESTED_WITH'] ) && 'xmlhttprequest' === strtolower( $_SERVER['HTTP_X_REQUESTED_WITH'] ) ) { // phpcs:ignore WordPress.Security.ValidatedSanitizedInput -- This is validating.
return;
}
// Disable in all XLS (see the WP_Sitemaps_Renderer class which is responsible for rendering Sitemaps data to XML
// in accordance with sitemap protocol).
if ( isset( $_SERVER['REQUEST_URI'] ) &&
(
// phpcs:disable WordPress.Security.ValidatedSanitizedInput -- This is validating.
str_contains( $_SERVER['REQUEST_URI'], '.xsl' ) ||
str_contains( $_SERVER['REQUEST_URI'], 'sitemap-stylesheet=index' ) ||
str_contains( $_SERVER['REQUEST_URI'], 'sitemap-stylesheet=sitemap' )
// phpcs:enable WordPress.Security.ValidatedSanitizedInput
) ) {
return;
}
// Disable in all POST Requests.
// phpcs:disable WordPress.Security.NonceVerification.Missing
if ( ! empty( $_POST ) ) {
return;
}
// Disable in customizer previews
if ( is_customize_preview() ) {
return;
}
// Disable in feeds, AJAX, Cron, XML.
if ( is_feed() || wp_doing_ajax() || wp_doing_cron() || wp_is_xml_request() ) {
return;
}
// Disable in sitemaps.
if ( ! empty( get_query_var( 'sitemap' ) ) ) {
return;
}
// Disable in AMP pages.
if ( function_exists( 'amp_is_request' ) && amp_is_request() ) {
return;
}
// Print the filtered script tags to the very end of the page.
add_filter( 'jetpack_boost_output_filtering_last_buffer', array( $this, 'append_script_tags' ), 10, 1 );
// Handle exclusions.
add_filter( 'script_loader_tag', array( $this, 'handle_exclusions' ), 10, 2 );
$this->output_filter->add_callback( array( $this, 'handle_output_stream' ) );
}
/**
* Remove all inline and external <script> tags from the default output.
*
* @param string $buffer_start First part of the buffer.
* @param string $buffer_end Second part of the buffer.
*
* For explanation on why there are two parts of a buffer here, see
* the comments and examples in the Output_Filter class.
*
* @return array Parts of the buffer.
*/
public function handle_output_stream( $buffer_start, $buffer_end ) {
$joint_buffer = $this->ignore_exclusion_scripts( $buffer_start . $buffer_end );
$script_tags = $this->get_script_tags( $joint_buffer );
if ( ! $script_tags ) {
if ( $this->is_opened_script ) {
// We have an opened script tag, move everything to the second buffer to avoid printing it to the page.
// We will do this until the </script> closing tag is encountered.
return array( '', $joint_buffer );
}
// No script tags detected, return both chunks unaltered.
return array( $buffer_start, $buffer_end );
}
// Makes sure all whole <script>...</script> tags are in $buffer_start.
list( $buffer_start, $buffer_end ) = $this->recalculate_buffer_split( $joint_buffer, $script_tags );
foreach ( $script_tags as $script_tag ) {
$this->buffered_script_tags[] = $script_tag[0];
$buffer_start = str_replace( $script_tag[0], '', $buffer_start );
}
// Detect a lingering opened script.
$this->is_opened_script = $this->is_opened_script( $buffer_start . $buffer_end );
return array( $buffer_start, $buffer_end );
}
/**
* Matches <script> tags with their content in a string buffer.
*
* @param string $buffer Captured piece of output buffer.
*
* @return array
*/
protected function get_script_tags( $buffer ) {
$regex = sprintf( '~<script(?![^>]*%s=(?<q>["\']*)%s\k<q>)([^>]*)>[\s\S]*?<\/script>~si', preg_quote( $this->ignore_attribute, '~' ), preg_quote( $this->ignore_value, '~' ) );
preg_match_all( $regex, $buffer, $script_tags, PREG_OFFSET_CAPTURE );
// No script_tags in the joint buffer.
if ( empty( $script_tags[0] ) ) {
return array();
}
/**
* Filter to remove any scripts that should not be moved to the end of the document.
*
* @param array $script_tags array of script tags. Remove any scripts that should not be moved to the end of the documents.
*
* @since 1.0.0
*/
return apply_filters( 'jetpack_boost_render_blocking_js_exclude_scripts', $script_tags[0] );
}
/**
* Adds the ignore attribute to scripts in the exclusion list.
*
* @param string $buffer Captured piece of output buffer.
*
* @return string
*/
protected function ignore_exclusion_scripts( $buffer ) {
$exclusions = array(
// Scripts inside HTML comments.
'~<!--.*?-->~si',
// Scripts with types that do not execute complex code. Moving them down can be dangerous
// and does not benefit performance. Includes types: application/json, application/ld+json and importmap.
'~<script\s+[^\>]*type=(?<q>["\']*)(application\/(ld\+)?json|importmap)\k<q>.*?>.*?<\/script>~si',
);
return preg_replace_callback(
$exclusions,
function ( $script_match ) {
return $this->add_ignore_attribute( $script_match[0] );
},
$buffer
);
}
/**
* Splits the buffer into two parts.
*
* First part contains all whole <script> tags, the second part
* contains the rest of the buffer.
*
* @param string $buffer Captured piece of output buffer.
* @param array $script_tags Matched <script> tags.
*
* @return array
*/
protected function recalculate_buffer_split( $buffer, $script_tags ) {
$last_script_tag_index = count( $script_tags ) - 1;
$last_script_tag_end_position = strrpos( $buffer, $script_tags[ $last_script_tag_index ][0] ) + strlen( $script_tags[ $last_script_tag_index ][0] );
// Bundle all script tags into the first buffer.
$buffer_start = substr( $buffer, 0, $last_script_tag_end_position );
// Leave the rest of the data in the second buffer.
$buffer_end = substr( $buffer, $last_script_tag_end_position );
return array( $buffer_start, $buffer_end );
}
/**
* Insert the buffered script tags just before the body tag if possible in the last buffer
* otherwise at append it at the end.
*
* @param string $buffer String buffer.
*
* @return string
*/
public function append_script_tags( $buffer ) {
if ( str_contains( $buffer, '</body>' ) ) {
return str_replace( '</body>', implode( '', $this->buffered_script_tags ) . '</body>', $buffer );
}
return $buffer . implode( '', $this->buffered_script_tags );
}
/**
* Exclude certain scripts from being processed by this class.
*
* @param string $tag <script> opening tag.
* @param string $handle Script handle from register_ or enqueue_ methods.
*
* @return string
*/
public function handle_exclusions( $tag, $handle ) {
/**
* Filter to provide an array of registered script handles that should not be moved to the end of the document.
*
* @param array $script_handles array of script handles. Remove any scripts that should not be moved to the end of the documents.
*
* @since 1.0.0
*/
$exclude_handles = apply_filters( 'jetpack_boost_render_blocking_js_exclude_handles', array() );
if ( ! in_array( $handle, $exclude_handles, true ) ) {
return $tag;
}
return $this->add_ignore_attribute( $tag );
}
/**
* Add the ignore attribute to the script tags
*
* @param string $html HTML code possibly containing a <script> opening tag.
*
* @return string
*/
public function add_ignore_attribute( $html ) {
return str_replace( '<script', sprintf( '<script %s="%s"', esc_html( $this->ignore_attribute ), esc_attr( $this->ignore_value ) ), $html );
}
/**
* Detects an unclosed script tag in a buffer.
*
* @param string $buffer Joint buffer.
*
* @return bool
*/
public function is_opened_script( $buffer ) {
$opening_tags_count = preg_match_all( '~<\s*script(?![^>]*%s="%s")([^>]*)>~', $buffer );
$closing_tags_count = preg_match_all( '~<\s*/script[^>]*>~', $buffer );
/**
* This works, because the logic in `handle_output_stream` will never
* allow an unpaired closing </script> tag to appear in the buffer.
*
* Open script tags are always kept in the buffer until their closing
* tags eventually arrive as well. That means it's only possible to
* encounter an unpaired opening <script> in a buffer, which is why
* a simple comparison works.
*
* @todo What if there is a <!-- </script> --> comment?
* @todo What happens when script tags are unclosed?
*/
return $opening_tags_count > $closing_tags_count;
}
public static function get_slug() {
return 'render_blocking_js';
}
}