<?php
/**
* Class and methods to add DNS prefetch hints to your page.
*
* @link https://ewww.io/swis/
* @package SWIS_Performance
*/
namespace SWIS;
if ( ! defined( 'ABSPATH' ) ) {
exit;
}
/**
* Searches the page for linked domains and adds prefetch headers for the top 5 non-local domains.
*/
final class Prefetch extends Base {
/**
* The local domain.
*
* @access protected
* @var string $local_domain
*/
protected $local_domain = '';
/**
* Existing prefetch hints.
*
* @access protected
* @var array $hints
*/
protected $hints = array(
'dns-prefetch' => array(),
'preconnect' => array(),
);
/**
* Register actions and filters for DNS Prefetch.
*/
function __construct() {
parent::__construct();
$this->debug_message( '<b>' . __METHOD__ . '()</b>' );
if ( ! is_admin() ) {
$this->local_domain = $this->parse_url( get_home_url(), PHP_URL_HOST );
// Start an output buffer before any output starts.
add_filter( $this->prefix . 'filter_page_output', array( $this, 'filter_page_output' ) );
// Get a list of existing prefetch hints.
add_filter( 'wp_resource_hints', array( $this, 'get_resource_hints' ), PHP_INT_MAX, 2 );
// Apply internal exclusions.
add_filter( 'swis_skip_prefetch', array( $this, 'skip_prefetch' ), 10, 2 );
add_filter( 'swis_skip_preconnect', array( $this, 'skip_prefetch' ), 10, 3 );
add_filter( 'swis_preconnect_domains', array( $this, 'add_domains' ) );
add_filter( 'swis_prefetch_domains', array( $this, 'add_domains' ) );
}
}
/**
* Add domains specified by the user.
*
* @param array $domains A list of third-party domains found in the content.
* @return array The list of domains, possibly with more added.
*/
function add_domains( $domains ) {
$this->debug_message( '<b>' . __METHOD__ . '()</b>' );
$user_domains = $this->get_option( 'pre_hint_domains' );
if ( $this->is_iterable( $user_domains ) ) {
$this->debug_message( 'have domains to add' );
foreach ( $user_domains as $domain ) {
$domain = filter_var( $domain, FILTER_VALIDATE_DOMAIN );
$this->debug_message( "attempting to add $domain" );
if ( $domain && ! isset( $domains[ $domain ] ) ) {
$this->debug_message( 'adding domain that did not exist' );
$domains = array_merge( array( $domain => 9999 ), $domains );
} elseif ( $domain && isset( $domains[ $domain ] ) && count( $domains ) > 5 ) {
$this->debug_message( 're-prioritizing user-defined domain' );
unset( $domains[ $domain ] );
$domains = array_merge( array( $domain => 9999 ), $domains );
}
}
}
return $domains;
}
/**
* Exclude domain from being prefetched.
*
* @param bool $skip Whether SWIS should skip processing.
* @param string $domain The domain name to prefetch.
* @param string $relationship_type The type of hint being filtered: dns-prefetch, preconnect, etc. Defaults to 'dns-prefetch'.
* @return bool True to skip the domain, unchanged otherwise.
*/
function skip_prefetch( $skip, $domain, $relationship_type = 'dns-prefetch' ) {
$skip_domains = apply_filters( 'swis_' . $relationship_type . '_skip_domains', array( $this->local_domain, 'gmpg.org', 'www.w3.org', 'api.w.org' ) );
foreach ( $skip_domains as $skip_domain ) {
if ( $skip_domain === $domain ) {
return true;
}
}
foreach ( $this->hints[ $relationship_type ] as $dns_hint ) {
if ( false !== strpos( $dns_hint, $domain ) ) {
return true;
}
}
return $skip;
}
/**
* Checks existing DNS prefetch hints and stores the list for later.
*
* @param array $hints A list of hints for a particular relationship type.
* @param string $relationship_type The type of hint being filtered: dns-prefetch, preconnect, etc.
* @return array The list of hints, unaltered.
*/
function get_resource_hints( $hints, $relationship_type ) {
if ( is_array( $hints ) && ( 'dns-prefetch' === $relationship_type || 'preconnect' === $relationship_type ) ) {
$this->debug_message( '<b>' . __METHOD__ . '()</b>' );
foreach ( $hints as $key => $hint ) {
if ( $this->get_option( 'optimize_fonts_css' ) && is_string( $hint ) && false !== strpos( $hint, 'fonts.googleapis.com' ) ) {
unset( $hints[ $key ] );
continue;
}
if ( is_string( $hint ) ) {
$this->debug_message( "$relationship_type hint: $hint" );
$this->hints[ $relationship_type ][] = $hint;
} elseif ( is_array( $hint ) && isset( $hint['href'] ) ) {
$hint = $hint['href'];
$this->debug_message( "$relationship_type hint: $hint" );
$this->hints[ $relationship_type ][] = $hint;
} elseif ( $this->function_exists( 'print_r' ) ) {
$this->debug_message( print_r( $hint, true ) );
}
}
}
return $hints;
}
/**
* Get linked/resource domains from content.
*
* @param string $content The HTML content through which to search.
* @return array A list of domains found in the HTML content.
*/
function get_domains( $content ) {
if ( empty( $content ) || ! is_string( $content ) ) {
return array();
}
$domains = array();
$links = array();
preg_match_all( '#\s(?>rel|src)\s*=\s*["\']https?:\/\/([^\/?\'"]{4,256})[/?\'"]#is', $content, $links );
if ( $this->is_iterable( $links[1] ) ) {
foreach ( $links[1] as $domain ) {
$domains[] = $domain;
}
}
$links = array();
preg_match_all( '#[^a-zA-Z0-9]url\s*?\(\s*["\']?\s*?https?:\/\/([^\/?\'"]{4,256})[/?\'"]#is', $content, $links );
if ( $this->is_iterable( $links[1] ) ) {
foreach ( $links[1] as $domain ) {
$domains[] = $domain;
}
}
return $domains;
}
/**
* Parse page content looking for jQuery script tag to rewrite.
*
* @param string $content The HTML content to parse.
* @return string The filtered HTML content.
*/
function filter_page_output( $content ) {
$this->debug_message( '<b>' . __METHOD__ . '()</b>' );
if ( $this->is_json( $content ) ) {
return $content;
}
if ( ! defined( 'SWIS_NO_PREFETCH' ) || ! SWIS_NO_PREFETCH ) {
$preconnect_html = '';
$prefetch_html = '';
$preconnect_domains = array();
$prefetch_domains = array();
$font_domains = array(
'use.fontawesome.com',
'fonts.gstatic.com',
'use.typekit.com',
'use.typekit.net',
'cloud.webtype.com',
);
$domains = $this->get_domains( $content );
foreach ( $domains as $domain ) {
if ( ! apply_filters( 'swis_skip_preconnect', false, $domain ) ) {
if ( isset( $preconnect_domains[ $domain ] ) ) {
$preconnect_domains[ $domain ]++;
} else {
$preconnect_domains[ $domain ] = 1;
}
}
if ( ! apply_filters( 'swis_skip_prefetch', false, $domain ) ) {
if ( isset( $prefetch_domains[ $domain ] ) ) {
$prefetch_domains[ $domain ]++;
} else {
$prefetch_domains[ $domain ] = 1;
}
}
}
if ( strpos( $content, '//fonts.gstatic.com/' ) || strpos( $content, '//fonts.googleapis.com/' ) ) {
$preconnect_domains['fonts.gstatic.com'] = 999;
$prefetch_domains['fonts.gstatic.com'] = 999;
}
arsort( $preconnect_domains, SORT_NUMERIC );
arsort( $prefetch_domains, SORT_NUMERIC );
/**
* Allow adding or removing preconnect domains (or altering the priority).
* Increase the array value for a given domain to increase the priority.
*
* @param array $preconnect_domains Single-dimensional associative array.
* The array keys are the domains found within the page.
* Array values indicate how many times a domain occurred within the page.
*/
$preconnect_domains = apply_filters( 'swis_preconnect_domains', $preconnect_domains );
/**
* Allow adding or removing dns-prefetch domains (or altering the priority).
* Increase the array value for a given domain to increase the priority.
*
* @param array $prefetch_domains Single-dimensional associative array.
* The array keys are the domains found within the page.
* Array values indicate how many times a domain occurred within the page.
*/
$prefetch_domains = apply_filters( 'swis_prefetch_domains', $prefetch_domains );
/**
* Adjust how many DNS records may be prefetched.
*
* @param int 5 How many records will be prefetched, prioritized by the # of references within any given page.
*/
$max_prefetch_hints = apply_filters( 'swis_prefetch_max_domains', 5 );
/**
* Adjust how many preconnect hints are allowed.
*
* @param int $max_prefetch_hints How many preconnect hints are allowed, defaults to the same # as the dns-prefetch hints.
*/
$max_preconnect_hints = apply_filters( 'swis_preconnect_max_domains', $max_prefetch_hints );
$max_prefetch_hints -= count( $this->hints['dns-prefetch'] );
$max_preconnect_hints -= count( $this->hints['preconnect'] );
foreach ( $prefetch_domains as $domain => $count ) {
if ( $max_prefetch_hints > 0 ) {
$this->debug_message( "prefetching $domain" );
$prefetch_html .= "<link rel='dns-prefetch' href='//$domain' />\n";
} else {
$this->debug_message( "not prefetching $domain" );
}
$max_prefetch_hints--;
}
foreach ( $preconnect_domains as $domain => $count ) {
if ( $max_preconnect_hints > 0 ) {
$this->debug_message( "preconnecting $domain" );
if ( in_array( $domain, $font_domains, true ) ) {
$preconnect_html .= "<link rel='preconnect' href='//$domain' crossorigin />\n";
} else {
$preconnect_html .= "<link rel='preconnect' href='//$domain' />\n";
}
} else {
$this->debug_message( "not preconnecting $domain" );
}
$max_preconnect_hints--;
}
// 'preconnect' hints go first.
if ( $prefetch_html || $preconnect_html ) {
$pos = strpos( $content, '</title>' );
if ( false !== $pos ) {
$content = substr_replace( $content, "</title>\n$preconnect_html" . $prefetch_html, $pos, strlen( '</title>' ) );
}
}
}
return $content;
}
}