Source

File: wp-includes/formatting.php

function url_shorten( $url, $length = 35 ) {
	$stripped  = str_replace( array( 'https://', 'http://', 'www.' ), '', $url );
	$short_url = untrailingslashit( $stripped );

	if ( strlen( $short_url ) > $length ) {
		$short_url = substr( $short_url, 0, $length - 3 ) . '…';
	}
	return $short_url;
}