wp_headers │ filter-hook │ WP 2.8.0

Allows you to change HTTP headers before they are sent to the browser.

Usage

add_filter( 'wp_headers', 'wp_kama_headers_filter', 10, 2 );

/**
 * Function for `wp_headers` filter-hook.
 * 
 * @param string[] $headers Associative array of headers to be sent.
 * @param WP       $wp      Current WordPress environment instance.
 *
 * @return string[]
 */
function wp_kama_headers_filter( $headers, $wp ){

	// filter...
	return $headers;
}

$headers(string[])

An associative array of headers to send.

$wp(WP)

The current WP{} instance.

Examples

#1 Headers passed through the filter

Add the following code to functions.php and visit the site's home page:

add_filter( 'wp_headers', 'wp_kama_headers_filter_test', 10, 2 )

function wp_kama_headers_filter_test( $headers, $wp ){
	error_log( print_r( $headers, true ) );

	return $headers;
}

The debug log will contain the following.

Logged-in user:

Array
(
	[Expires] => Wed, 11 Jan 1984 05:00:00 GMT
	[Cache-Control] => no-cache, must-revalidate, max-age=0
	[Last-Modified] =>
	[Content-Type] => text/html; charset=UTF-8
)

Guest:

Array
(
	[Content-Type] => text/html; charset=UTF-8
)

#2 Prevent site indexing during development

Developers often demonstrate work on a DEV version of a site. To prevent this duplicate site from being indexed, use the following code to tell search engines “do not index me”:

if ( 'development' === wp_get_environment_type() ){

	add_filter( 'wp_headers', 'disable_indexing_site' );

	/**
	 * Prevents site indexing during development.
	 */
	function disable_indexing_site( $headers ) {
		$headers['X-Robots-Tag'] = 'noindex, nofollow';

		return $headers;
	}

}

See also: Prevent search engines from indexing a DEV version of a site.