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✏️ Editing: dns-prefetch.php

<?php
defined( 'ABSPATH' ) or	die( 'Cheatin&#8217; uh?' );

/**
 * Launch DNS Prefetching process
 *
 * @since 2.8.9 Use the wp_resource_hints filter introduced in WP 4.6 if possible, fallback to rocket_buffer hook for previous versions
 * @since 2.5 Don't add CNAMES if CDN is disabled HTTPS pages or on specific posts
 * @since 2.1 Adding CNAMES fo CDN automatically in DNS Prefetch process
 * @since 2.0
 */
if ( function_exists( 'wp_resource_hints' ) ) {
	add_filter( 'wp_resource_hints', 'rocket_dns_prefetch', 10, 2 );
} else {
	add_filter( 'rocket_buffer', 'rocket_dns_prefetch_buffer', 12 );
}

/**
 * Adds domain names to the list of DNS Prefetch printed by wp_resource_hints
 *
 * @since 2.8.9
 * @author Remy Perona
 *
 * @param Array  $hints URLs to print for resource hints.
 * @param String $relation_type The relation type the URL are printed for.
 * @return Array URLs to print
 */
function rocket_dns_prefetch( $hints, $relation_type ) {
	$domains = rocket_get_dns_prefetch_domains();

if ( (bool) $domains ) {
		foreach ( $domains as $domain ) {
			if ( 'dns-prefetch' === $relation_type ) {
				$hints[] = $domain;
			}
		}
	}

return $hints;
}

/**
 * Inserts html code for domain names to DNS prefetch in the buffer before creating the cache file
 *
 * @since 2.0
 * @author Jonathan Buttigieg
 *
 * @param String $buffer HTML content.
 * @return String Updated buffer
 */
function rocket_dns_prefetch_buffer( $buffer ) {
	$dns_link_tags = '';
	$domains       = rocket_get_dns_prefetch_domains();

if ( (bool) $domains ) {
		foreach ( $domains as $domain ) {
			$dns_link_tags .= '<link rel="dns-prefetch" href="' . esc_url( $domain ) . '" />';
		}
	}

$old_ie_conditional_tag = '';

/**
	 * Allow to print an empty IE conditional tag to speed up old IE versions to load CSS & JS files
	 *
	 * @since 2.6.5
	 *
	 * @param bool true will print the IE conditional tag
	 */
	if ( apply_filters( 'do_rocket_old_ie_prefetch_conditional_tag', true ) ) {
		$old_ie_conditional_tag = '';
	}

// Insert all DNS prefecth tags in head.
	$buffer = preg_replace( '/<head(.*)>/', '<head$1>' . $old_ie_conditional_tag . $dns_link_tags, $buffer, 1 );

return $buffer;
}

MR SKB