/*
 * Find suitable IPv6/IPv4 address to bind to based on a numeric port number
 */
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>
#include <arpa/inet.h>

/*
int getaddrinfo(const char *node, const char *service,
               const struct addrinfo *hints,
               struct addrinfo **res);

void freeaddrinfo(struct addrinfo *res);

struct addrinfo {
   int     ai_flags;
   int     ai_family;
   int     ai_socktype;
   int     ai_protocol;
   size_t  ai_addrlen;
   struct sockaddr *ai_addr;
   char   *ai_canonname;
   struct addrinfo *ai_next;
};
*/


int
main(int ac, char *av[])
{
    struct addrinfo *info, *pinfo;
    struct addrinfo hint;
    memset(&hint, 0, sizeof hint);
    if (ac < 2) printf("Usage: %s <port>\n", av[0]), exit(0);

    hint.ai_flags = AI_PASSIVE | AI_NUMERICSERV;
    int rc = getaddrinfo(NULL, av[1], &hint, &info);
    if (rc != 0)
        gai_strerror(rc), exit(-1);

    char printed_addr[1024];
    for (pinfo = info; pinfo; pinfo = pinfo->ai_next) {
        if (pinfo->ai_protocol != IPPROTO_TCP)
            continue;

        switch (pinfo->ai_family) {
        case AF_INET:
            {
                struct sockaddr_in *sa; 
                sa = (struct sockaddr_in *)pinfo->ai_addr;
                inet_ntop(pinfo->ai_family, (const void *)&sa->sin_addr,
                    printed_addr, sizeof printed_addr);
                printf("AF_INET: %s\n", printed_addr);
                break;
            }
        case AF_INET6:
            {
                struct sockaddr_in6 *sa; 
                sa = (struct sockaddr_in6 *)pinfo->ai_addr;
                inet_ntop(pinfo->ai_family, (const void *)&sa->sin6_addr,
                    printed_addr, sizeof printed_addr);
                printf("AF_INET6: %s\n", printed_addr);
                break;
            }
        default:
            printf("Unknown address family\n");
            break;
        }
    }
    freeaddrinfo(info);
    return 0;
}