private static Iterable < String > extend ( final Iterable < String > head , final String header ) { if ( ! RsWithHeader . HEADER . matcher ( header ) . matches ( ) ) { throw new IllegalArgumentException ( String . format ( // @checkstyle LineLength (1 line) "header line of HTTP response \"%s\" doesn't match \"%s\" regular expression, but it should, according to RFC 7230" , header , RsWithHeader . HEADER ) ) ; } return new Concat <> ( head , Collections . singleton ( header ) ) ; }
Add to head additional header .