test.c

#include <re.h>


/*
      Prefix        Precedence Label
      ::1/128               50     0
      ::/0                  40     1
      ::ffff:0:0/96         35     4
      2002::/16             30     2
      2001::/32              5     5
      fc00::/7               3    13
      ::/96                  1     3
      fec0::/10              1    11
      3ffe::/16              1    12

 */
static const struct policy {
	const char *addr;
	unsigned prefix_len;
	unsigned precedence;
} policy_table[] = {
	{ "::1",        128,   50 },
	{ "::",           0,   40 },
	{ "::ffff:0:0",  96,   35 },
	{ "2002::",      16,   30 },
	{ "2001::",      32,    5 },
	{ "fc00::",       7,    3 },
	{ "::",          96,    1 },
	{ "fec0::",      10,    1 },
	{ "3ffe::",      16,    1 },
};


static void sa_init_netmask(struct sa *netmask, unsigned prefix_len)
{
	long i, j;

	if (!netmask)
		return;

	sa_init(netmask, AF_INET6);

	for (i = prefix_len, j = 0; i > 0; i -= 8, ++j) {
		uint8_t b;

		b = i >= 8 ? 0xff : (unsigned)((0xffu << ( 8 - i ) ) & 0xffu);

		netmask->u.in6.sin6_addr.s6_addr[j] = b;
	}
}


static void sa_apply_mask(struct sa *dst, const struct sa *src,
			  const struct sa *netmask)
{
	unsigned i;

	if (!dst || !src || !netmask)
		return;

	*dst = *src;

	for (i = 0; i < 16; i++) {
		dst->u.in6.sin6_addr.s6_addr[i] =
			src->u.in6.sin6_addr.s6_addr[i] &
			netmask->u.in6.sin6_addr.s6_addr[i];
	}
}


/*
 * The policy table is a longest-matching-prefix lookup table
 */
static int ipv6_calc_precedence(const struct sa *sa)
{
	const struct policy *policy_best = NULL;
	unsigned prefix_longest = 0;
	unsigned i;

	if (AF_INET6 != sa_af(sa)) {
		re_printf("not an ipv6 address\n");
		return 0;
	}

	for (i=0; i<ARRAY_SIZE(policy_table); i++) {

		const struct policy *policy = &policy_table[i];
		struct sa netmask;
		struct sa addr;
		struct sa addr_input;
		bool match;

		sa_set_str(&addr, policy->addr, 0);

		sa_init_netmask(&netmask, policy->prefix_len);

		sa_apply_mask(&addr, &addr, &netmask);
		sa_apply_mask(&addr_input, sa, &netmask);

		match = sa_cmp(&addr, &addr_input, SA_ADDR);

		if (match && policy->prefix_len >= prefix_longest) {
			policy_best = policy;
			prefix_longest = policy->prefix_len;
		}
	}

	if (policy_best) {
		return policy_best->precedence;
	}
	else {
		re_printf("no matches in policy table\n");
		return 0;
	}

	return 0;
}


static bool net_ifaddr_handler(const char *ifname, const struct sa *sa,
			       void *arg)
{
	unsigned precedence;
	(void)arg;

	if (AF_INET6 != sa_af(sa))
		return false;

	precedence = ipv6_calc_precedence(sa);

	re_printf("ifaddr:   %10s   %32j   precedence=%u\n",
		  ifname, sa, precedence);

	return false;
}


int main(void)
{
	re_printf("List of IPv6 addresses:\n");
	net_getifaddrs(net_ifaddr_handler, 0);
}