README

Sends Link headers to bring HTTP/2 Server Push for scripts and styles to WordPress. Falls back to <link> element if headers are already sent.
Provides filters to customize and extend the resources to push.

Installation

Install the latest version with

composer require wearerequired/h2push

The plugin requires at least PHP 7.4 and WordPress 5.6.

Hooks reference

h2push.as_header

By default the plugin will use the Link header if no headers are sent yet and falls back to the <link> element. To change this behavior you can use the h2push.as_header filter. Example:

// Force H2 Push to always use the `<link>` element.
add_filter( 'h2push.as_header', '__return_false' );

This filter is also useful if the server doesn't support HTTP/2 yet and you still want to benefit from preloading.

h2push.push_resources

By default the plugin collects all enqueued scripts and styles which are have been registered before or at the wp_enqueue_scripts hook. The h2push.push_resources filters allows to customize the list of resources. Example:

/**
 * Add web font and hero image to the list of resources to push/preload.
 *
 * @param array $resources List of resources.
 * @return array List of resources.
 */
function my_theme_push_resources( array $resources ): array {
	$relative_template_directory_uri = wp_parse_url( get_template_directory_uri(), PHP_URL_PATH );

	// Push web font.
	$resources[] = [
		'href' => $relative_template_directory_uri . '/assets/fonts/fancy.woff2',
		'as'   => 'font',
		'type' => 'font/woff2',
		'crossorigin',
	];

	if ( is_front_page() && ! is_paged() ) {
		// Push hero image.
		$resources[] = [
			'href' => $relative_template_directory_uri . '/assets/images/hero.webp',
			'as'   => 'image',
			'type' => 'image/webp',
		];
	}

	return $resources;
}
add_filter( 'h2push.push_resources', 'my_theme_push_resources' );

h2push.is_allowed_push_host

By default the plugin only sends push requests for local resources where the asset URL matches the home URL. To change this behavior you can use the h2push.is_allowed_push_host filter. Example:

/**
 * Allow resources from example.org to be pushed/preloaded too.
 *
 * @param bool   $is_allowed Whether the host should be allowed. Default true for local resources.
 * @param string $host       The host name of the resource.
 * @return bool Whether the host should be allowed.
 */
function my_theme_is_allowed_push_host( $is_allowed, $host ) {
	return $is_allowed || 'example.org' === $host;
}
add_filter( 'h2push.is_allowed_push_host', 'my_theme_is_allowed_push_host' );