getaddrinfo.c

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
    struct addrinfo hints, *res, *p;
    int status;
    char ipstr[INET6_ADDRSTRLEN];

    if (argc != 2) {
        fprintf(stderr,"usage: getaddrinfo <hostname>\n");
        return 1;
    }

    printf("IP addresses for %s:\n\n", argv[1]);

    int AI_FLAGS_TO_CHECK[5] = { AI_V4MAPPED, AI_V4MAPPED | AI_ALL, AI_ADDRCONFIG, AI_V4MAPPED | AI_ADDRCONFIG, AI_V4MAPPED | AI_ALL | AI_ADDRCONFIG };
    int AI_FAMILY_TO_CHECK[3] = { AF_INET, AF_INET6, AF_UNSPEC };
    int ai_flags, flag_no, ai_family, family_no;

    for (family_no = 0; family_no < sizeof(AI_FAMILY_TO_CHECK) / sizeof(int); family_no++) {
        for (flag_no = 0; flag_no < sizeof(AI_FLAGS_TO_CHECK) / sizeof(int); flag_no++) {
            ai_family = AI_FAMILY_TO_CHECK[family_no];
            if (ai_family == AF_INET) {
                printf("[AF_INET] ");
            } else if (ai_family == AF_INET6) {
                printf("[AF_INET6] ");
            } else if (ai_family == AF_UNSPEC) {
                printf("[AF_UNSPEC] ");
            } else {
                fprintf(stderr, "Unknown family\n");
                return 2;
            }
            ai_flags = AI_FLAGS_TO_CHECK[flag_no];
            if (ai_flags & AI_V4MAPPED) {
                printf("AI_V4MAPPED ");
            }

            if (ai_flags & AI_ALL) {
                printf("AI_ALL ");
            }

            if (ai_flags & AI_ADDRCONFIG) {
                printf("AI_ADDRCONFIG ");
            }

            printf("\n");

            memset(&hints, 0, sizeof hints);
            hints.ai_flags = ai_flags;
            hints.ai_family = ai_family;
            hints.ai_socktype = SOCK_STREAM;

            if ((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0) {
                fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
                continue;
                //return 3;
            }

            for (p = res; p != NULL; p = p->ai_next) {
                void *addr;
                char *ipver;

                if (p->ai_family == AF_INET) {
                    struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
                    addr = &(ipv4->sin_addr);
                    ipver = "IPv4";
                } else if (p->ai_family == AF_INET6) {
                    struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
                    addr = &(ipv6->sin6_addr);
                    ipver = "IPv6";
                } else {
                    continue;
                }

                inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);
                printf("  %s: %s\n", ipver, ipstr);
            }

            freeaddrinfo(res);
        }

        printf("--------------\n\n");
            }
    return 0;
}