BP_Activity_Feed::http_headers()

	protected function http_headers() {
		// Set up some additional headers if not on a directory page
		// this is done b/c BP uses pseudo-pages.
		if ( ! bp_is_directory() ) {
			global $wp_query;

			$wp_query->is_404 = false;
			status_header( 200 );
		}

		// Set content-type.
		@header( 'Content-Type: text/xml; charset=' . get_option( 'blog_charset' ), true );
		send_nosniff_header();

		// Cache-related variables.
		$last_modified      = mysql2date( 'D, d M Y H:i:s O', bp_activity_get_last_updated(), false );
		$modified_timestamp = strtotime( $last_modified );
		$etag               = md5( $last_modified );

		// Set cache-related headers.
		@header( 'Last-Modified: ' . $last_modified );
		@header( 'Pragma: no-cache' );
		@header( 'ETag: ' . '"' . $etag . '"' );

		// First commit of BuddyPress! (Easter egg).
		@header( 'Expires: Tue, 25 Mar 2008 17:13:55 GMT');

		// Get ETag from supported user agents.
		if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ) {
			$client_etag = wp_unslash( $_SERVER['HTTP_IF_NONE_MATCH'] );

			// Remove quotes from ETag.
			$client_etag = trim( $client_etag, '"' );

			// Strip suffixes from ETag if they exist (eg. "-gzip").
			$etag_suffix_pos = strpos( $client_etag, '-' );
			if ( ! empty( $etag_suffix_pos ) ) {
				$client_etag = substr( $client_etag, 0, $etag_suffix_pos );
			}

		// No ETag found.
		} else {
			$client_etag = false;
		}

		// Get client last modified timestamp from supported user agents.
		$client_last_modified      = empty( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) ? '' : trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
		$client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;

		// Set 304 status if feed hasn't been updated since last fetch.
		if ( ( $client_last_modified && $client_etag ) ?
				 ( ( $client_modified_timestamp >= $modified_timestamp ) && ( $client_etag == $etag ) ) :
				 ( ( $client_modified_timestamp >= $modified_timestamp ) || ( $client_etag == $etag ) ) ) {
			$status = 304;
		} else {
			$status = false;
		}

		// If feed hasn't changed as reported by the user agent, set 304 status header.
		if ( ! empty( $status ) ) {
			status_header( $status );

			// Cached response, so stop now!
			if ( $status == 304 ) {
				exit();
			}
		}
	}