presto-main/src/main/java/io/prestosql/operator/HttpPageBufferClient.java/PageResponseHandler/getNextToken
class PageResponseHandler:        private static long getNextToken(Response response)
        {
            String nextTokenHeader = response.getHeader(PRESTO_PAGE_NEXT_TOKEN);
            if (nextTokenHeader == null) {
                throw new PageTransportErrorException(format("Expected %s header", PRESTO_PAGE_NEXT_TOKEN));
            }
            return Long.parseLong(nextTokenHeader);
        }