/* IP Address Of
 * Copyright 2019 Tj <hacker@iam.tj>
 * Licensed on the terms of the GNU General Public Licence version 3.
 *
 * Build using: gcc -o ipaddrof ipaddrof.c
 * 
 * Call with name to be resolved. This is a multicall binary; it will change its
 * behaviour based on the name it is called with.
 *
 * Create symlinks to the binary:
 * ln -s ipaddrof ipaddrof4
 * ln -s ipaddrof ipaddrof6
 *
 * ./ipaddrof mail.google.com  # returns first IPv4 or IPv6 address found
 * ./ipaddrof4 mail.google.com # returns first IPv4 address found
 * ./ipaddrof6 mail.google.com # returns first IPv6 address found
 *
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <libgen.h>

static const char const *ipv6 = "ipaddrof6";
static const char const *ipv4 = "ipaddrof4";

int main(int argc, char **argv, char **env)
{
  struct addrinfo hints;
  struct addrinfo *results, *rp;
  int family = AF_UNSPEC; // any
  char *multicall = basename(argv[0]);

  if ( strncmp(multicall, ipv4, strlen(ipv4)) == 0) {
    family = AF_INET;
   }else if ( strncmp(multicall, ipv6, strlen(ipv6)) == 0 ) {
    family = AF_INET6;
  }

  memset(&hints, 0, sizeof(struct addrinfo));
  hints.ai_family = family;
  hints.ai_protocol = 0;

  if (argc > 1) {
    if (getaddrinfo(argv[1], NULL, &hints, &results) == 0) {
      char answer[INET6_ADDRSTRLEN];
      void *addr;
      for (rp = results; rp != NULL; rp = rp->ai_next) {
        if (rp->ai_family == family || family == AF_UNSPEC) {
          if (rp->ai_family == AF_INET) {
            struct sockaddr_in *ipv4 = (struct sockaddr_in *)rp->ai_addr;
            addr = &(ipv4->sin_addr);
          } else {
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)rp->ai_addr;
            addr = &(ipv6->sin6_addr);
          }
          inet_ntop(rp->ai_family, addr, answer, sizeof(answer));
          printf("%s\n", answer);
		  break;
        }
      }
      freeaddrinfo(results);
    }
  }
  return 0;
}