getnameinfo for IPv6 address on macOS

getnameinfo.c

/*
 * This shows somewhat special behaviour when getnameinfo on macOS converts
 * an IPv6 to a kind of IPv4-translated address.
 *
 * It turns IPv6 address "::ffff" into "::0.0.255.255"
 */
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>

int main() {
  struct sockaddr_in6 sin6 = {
    .sin6_len = 28,
    .sin6_family = AF_INET6,
    .sin6_port = 0,
    .sin6_flowinfo = 0,
    .sin6_addr = {
      .__u6_addr = {
        .__u6_addr16 = {
          0,
          0,
          0,
          0,
          0,
          0,
          0,
          0xffff,
        },
      },
    },
    .sin6_scope_id = 0,
  };

  char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
  int error;

  if ((error = getnameinfo((struct sockaddr *) &sin6, sin6.sin6_len,
                   hbuf, sizeof(hbuf),
                   sbuf, sizeof(sbuf),
                   NI_NUMERICHOST | NI_NUMERICSERV))) {
      printf("getnameinfo: %s\n", gai_strerror(error));
      return 1;
  }

  printf("host=%s, serv=%s\n", hbuf, sbuf);
  return 0;
}