wordpress-mask-media-file-url.php

<?php

add_action( 'get_header', function() {

	if ( !is_attachment() ) return;

	$file_url  = wp_get_attachment_url( get_the_ID() );
	$file_name = basename( $file_url );

	header( sprintf('Content-type: %s', get_post_mime_type() ) );
	header( sprintf('Content-Disposition: attachment; filename="%s"', $file_name ) );
	readfile( get_attached_file( get_the_ID() ) );

	exit;
	
});