show getaddrinfo(3) results

showaddrinfo.c

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

int main(int argc, char **argv) {
    const char *hostname = NULL;
    const char *servname = NULL;

    struct addrinfo hints, *res;
    memset(&hints, 0, sizeof(hints));

    for (char ch; (ch = getopt(argc, argv, "46f:h:s:tu")) != -1;) {
        // clang-format off
        switch (ch) {
        case '4': hints.ai_family = AF_INET; break;
        case '6': hints.ai_family = AF_INET6; break;
        case 'f':
#define AI_(f) if (!strcmp(#f, optarg)) hints.ai_flags |= AI_##f; else
        AI_(ALL)
        AI_(CANONNAME)
        AI_(DEFAULT)
        AI_(NUMERICHOST)
        AI_(NUMERICSERV)
        AI_(PASSIVE)
        AI_(V4MAPPED)
#undef AI_
            fprintf(stderr, "%s: unknown flag -- %s\n", argv[0], optarg);
        break;
        case 'h': hostname = optarg; break;
        case 's': servname = optarg; break;
        case 't': hints.ai_socktype = SOCK_STREAM; hints.ai_protocol = IPPROTO_TCP; break;
        case 'u': hints.ai_socktype = SOCK_DGRAM; hints.ai_protocol = IPPROTO_UDP; break;
        case '?':
        default:
            fprintf(stderr, "usage: %s [-46tu] [-f ALL|CANONNAME|DEFAULT|NUMERICHOST|NUMERICSERV|PASSIVE|V4MAPPED] [-h hostname] [-s servname]\n", argv[0]);
            exit(EXIT_FAILURE);
        }
        // clang-format on
    }

    int error = getaddrinfo(hostname, servname, &hints, &res);
    if (error) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(error));
        exit(EXIT_FAILURE);
    }

    for (struct addrinfo *p = res; p != NULL; p = p->ai_next) {
        char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
        if (getnameinfo(p->ai_addr, p->ai_addrlen, hbuf, sizeof(hbuf), sbuf, sizeof(sbuf), NI_NUMERICHOST | NI_NUMERICSERV)) {
            fprintf(stderr, "could not get numeric hostname");
            exit(EXIT_FAILURE);
        }
        printf("%s%s\t%s\t%s\n",
               p->ai_protocol == IPPROTO_TCP ? "tcp" : "udp",
               p->ai_family == AF_INET ? "4" : "6",
               hbuf, sbuf);
    }

    freeaddrinfo(res);

    return 0;
}