string_vis
printf("%s", string_vis(str, len));
printf(" %s\n", string_vis(str, l));
static const char *string_vis(const char *, size_t);
printf("\"%s\"\n", string_vis(str, len));
printf(" %s\n", string_vis(str, l));
printf("\"%s\"\n", string_vis(url, len));