// Experiment 7: DNS lookup - display IP address of a given domain name
// Compile: gcc 07_dns_lookup.c -o dnslookup
// Run    : ./dnslookup www.google.com

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

int main(int argc, char *argv[]) {
    if (argc != 2) {
        printf("Usage: %s <domain-name>\n", argv[0]);
        return 1;
    }

    struct addrinfo hints, *res, *p;
    int status;
    char ipstr[INET6_ADDRSTRLEN];

    memset(&hints, 0, sizeof(hints));
    hints.ai_family   = AF_UNSPEC;     // IPv4 or IPv6
    hints.ai_socktype = SOCK_STREAM;

    if ((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
        return 2;
    }

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

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

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

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

    freeaddrinfo(res);
    return 0;
}