Testing DNS stub resolver (getaddrinfo(3))

getaddrinfo-name2addr.c

#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <errno.h>

int main(int argc, char **argv)
{
  struct addrinfo hints, *ai, *ai_p;
  const char *name;
  char addr[NI_MAXHOST];
  int err;

  if (argc != 2) {
    printf("Usage: %s NAME\n", argv[0]);
    return 1;
  }

  name = argv[1];
  memset(&hints, 0, sizeof(hints));
  hints.ai_family = AF_UNSPEC;
  hints.ai_socktype = SOCK_STREAM;
  err = getaddrinfo(name, NULL, &hints, &ai);
  if (err) {
    fprintf(stderr, "%s: ERROR: %s\n", argv[0], gai_strerror(err));
    return 1;
  }

  for (ai_p = ai; ai_p; ai_p = ai_p->ai_next){
    void *ia;

    switch (ai_p->ai_family) {
    case AF_INET:
      ia = &((struct sockaddr_in *)(ai_p->ai_addr))->sin_addr.s_addr;
      break;
    case AF_INET6:
      ia = &((struct sockaddr_in6 *)(ai_p->ai_addr))->sin6_addr;
      break;
    default:
      fprintf(stderr, "%s: ERROR: Unknown address family: %d\n", argv[0], ai_p->ai_family);
      continue;
    }

    if (inet_ntop(ai_p->ai_family, ia, addr, sizeof(addr)) == NULL) {
      fprintf(stderr, "%s: ERROR: inet_ntop() failed: %s\n", argv[0], strerror(errno));
      continue;
    }

    printf("%s\n", addr);
  }

  freeaddrinfo(ai);

  return 0;
}